Internet Engineering Task Force (IETF) C. Bormann
Request for Comments: 8990 Universität Bremen TZI
Category: Standards Track B. Carpenter, Ed.
ISSN: 2070-1721 Univ. of Auckland
B. Liu, Ed.
Huawei Technologies Co., Ltd
May 2021
GeneRic Autonomic Signaling Protocol (GRASP)
Abstract
This document specifies the GeneRic Autonomic Signaling Protocol
(GRASP), which enables autonomic nodes and Autonomic Service Agents
to dynamically discover peers, to synchronize state with each other,
and to negotiate parameter settings with each other. GRASP depends
on an external security environment that is described elsewhere. The
technical objectives and parameters for specific application
scenarios are to be described in separate documents. Appendices
briefly discuss requirements for the protocol and existing protocols
with comparable features.
Status of This Memo
This is an Internet Standards Track document.
This document is a product of the Internet Engineering Task Force
(IETF). It represents the consensus of the IETF community. It has
received public review and has been approved for publication by the
Internet Engineering Steering Group (IESG). Further information on
Internet Standards is available in Section 2 of RFC 7841.
Information about the current status of this document, any errata,
and how to provide feedback on it may be obtained at
https://www.rfc-editor.org/info/rfc8990.
Copyright Notice
Copyright (c) 2021 IETF Trust and the persons identified as the
document authors. All rights reserved.
This document is subject to BCP 78 and the IETF Trust's Legal
Provisions Relating to IETF Documents
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described in the Simplified BSD License.
Table of Contents
1. Introduction
2. Protocol Overview
2.1. Terminology
2.2. High-Level Deployment Model
2.3. High-Level Design
2.4. Quick Operating Overview
2.5. GRASP Basic Properties and Mechanisms
2.5.1. Required External Security Mechanism
2.5.2. Discovery Unsolicited Link-Local (DULL) GRASP
2.5.3. Transport Layer Usage
2.5.4. Discovery Mechanism and Procedures
2.5.5. Negotiation Procedures
2.5.6. Synchronization and Flooding Procedures
2.6. GRASP Constants
2.7. Session Identifier (Session ID)
2.8. GRASP Messages
2.8.1. Message Overview
2.8.2. GRASP Message Format
2.8.3. Message Size
2.8.4. Discovery Message
2.8.5. Discovery Response Message
2.8.6. Request Messages
2.8.7. Negotiation Message
2.8.8. Negotiation End Message
2.8.9. Confirm Waiting Message
2.8.10. Synchronization Message
2.8.11. Flood Synchronization Message
2.8.12. Invalid Message
2.8.13. No Operation Message
2.9. GRASP Options
2.9.1. Format of GRASP Options
2.9.2. Divert Option
2.9.3. Accept Option
2.9.4. Decline Option
2.9.5. Locator Options
2.10. Objective Options
2.10.1. Format of Objective Options
2.10.2. Objective Flags
2.10.3. General Considerations for Objective Options
2.10.4. Organizing of Objective Options
2.10.5. Experimental and Example Objective Options
3. Security Considerations
4. CDDL Specification of GRASP
5. IANA Considerations
6. References
6.1. Normative References
6.2. Informative References
Appendix A. Example Message Formats
A.1. Discovery Example
A.2. Flood Example
A.3. Synchronization Example
A.4. Simple Negotiation Example
A.5. Complete Negotiation Example
Appendix B. Requirement Analysis of Discovery, Synchronization,
and Negotiation
B.1. Requirements for Discovery
B.2. Requirements for Synchronization and Negotiation Capability
B.3. Specific Technical Requirements
Appendix C. Capability Analysis of Current Protocols
Acknowledgments
Authors' Addresses
1. Introduction
The success of the Internet has made IP-based networks bigger and
more complicated. Large-scale ISP and enterprise networks have
become more and more problematic for human-based management. Also,
operational costs are growing quickly. Consequently, there are
increased requirements for autonomic behavior in the networks.
General aspects of Autonomic Networks are discussed in [RFC7575] and
[RFC7576].
One approach is to largely decentralize the logic of network
management by migrating it into network elements. A reference model
for Autonomic Networking on this basis is given in [RFC8993]. The
reader should consult this document to understand how various
autonomic components fit together. In order to achieve autonomy,
devices that embody Autonomic Service Agents (ASAs, [RFC7575]) have
specific signaling requirements. In particular, they need to
discover each other, to synchronize state with each other, and to
negotiate parameters and resources directly with each other. There
is no limitation on the types of parameters and resources concerned,
which can include very basic information needed for addressing and
routing, as well as anything else that might be configured in a
conventional non-autonomic network. The atomic unit of discovery,
synchronization, or negotiation is referred to as a technical
objective, i.e., a configurable parameter or set of parameters
(defined more precisely in Section 2.1).
Negotiation is an iterative process, requiring multiple message
exchanges forming a closed loop between the negotiating entities. In
fact, these entities are ASAs, normally but not necessarily in
different network devices. State synchronization, when needed, can
be regarded as a special case of negotiation without iteration. Both
negotiation and synchronization must logically follow discovery.
More details of the requirements are found in Appendix B.
Section 2.3 describes a behavior model for a protocol intended to
support discovery, synchronization, and negotiation. The design of
GeneRic Autonomic Signaling Protocol (GRASP) in Section 2 is based on
this behavior model. The relevant capabilities of various existing
protocols are reviewed in Appendix C.
The proposed discovery mechanism is oriented towards synchronization
and negotiation objectives. It is based on a neighbor discovery
process on the local link, but it also supports diversion to peers on
other links. There is no assumption of any particular form of
network topology. When a device starts up with no preconfiguration,
it has no knowledge of the topology. The protocol itself is capable
of being used in a small and/or flat network structure such as a
small office or home network as well as in a large, professionally
managed network. Therefore, the discovery mechanism needs to be able
to allow a device to bootstrap itself without making any prior
assumptions about network structure.
Because GRASP can be used as part of a decision process among
distributed devices or between networks, it must run in a secure and
strongly authenticated environment.
In realistic deployments, not all devices will support GRASP.
Therefore, some Autonomic Service Agents will directly manage a group
of non-autonomic nodes, and other non-autonomic nodes will be managed
traditionally. Such mixed scenarios are not discussed in this
specification.
2. Protocol Overview
2.1. Terminology
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and
"OPTIONAL" in this document are to be interpreted as described in
BCP 14 [RFC2119] [RFC8174] when, and only when, they appear in all
capitals, as shown here.
This document uses terminology defined in [RFC7575].
The following additional terms are used throughout this document:
Discovery:
A process by which an ASA discovers peers according to a specific
discovery objective. The discovery results may be different
according to the different discovery objectives. The discovered
peers may later be used as negotiation counterparts or as sources
of synchronization data.
Negotiation:
A process by which two ASAs interact iteratively to agree on
parameter settings that best satisfy the objectives of both ASAs.
State Synchronization:
A process by which ASAs interact to receive the current state of
parameter values stored in other ASAs. This is a special case of
negotiation in which information is sent, but the ASAs do not
request their peers to change parameter settings. All other
definitions apply to both negotiation and synchronization.
Technical Objective (usually abbreviated as Objective):
A technical objective is a data structure whose main contents are
a name and a value. The value consists of a single configurable
parameter or a set of parameters of some kind. The exact format
of an objective is defined in Section 2.10.1. An objective occurs
in three contexts: discovery, negotiation, and synchronization.
Normally, a given objective will not occur in negotiation and
synchronization contexts simultaneously.
One ASA may support multiple independent objectives.
The parameter(s) in the value of a given objective apply to a
specific service or function or action. They may in principle
be anything that can be set to a specific logical, numerical,
or string value, or a more complex data structure, by a network
node. Each node is expected to contain one or more ASAs which
may each manage subsidiary non-autonomic nodes.
Discovery Objective: an objective in the process of discovery.
Its value may be undefined.
Synchronization Objective: an objective whose specific
technical content needs to be synchronized among two or more
ASAs. Thus, each ASA will maintain its own copy of the
objective.
Negotiation Objective: an objective whose specific technical
content needs to be decided in coordination with another
ASA. Again, each ASA will maintain its own copy of the
objective.
A detailed discussion of objectives, including their format, is
found in Section 2.10.
Discovery Initiator:
An ASA that starts discovery by sending a Discovery message
referring to a specific discovery objective.
Discovery Responder:
A peer that either contains an ASA supporting the discovery
objective indicated by the discovery initiator or caches the
locator(s) of the ASA(s) supporting the objective. It sends a
Discovery Response, as described later.
Synchronization Initiator:
An ASA that starts synchronization by sending a request message
referring to a specific synchronization objective.
Synchronization Responder:
A peer ASA that responds with the value of a synchronization
objective.
Negotiation Initiator:
An ASA that starts negotiation by sending a request message
referring to a specific negotiation objective.
Negotiation Counterpart:
A peer with which the negotiation initiator negotiates a specific
negotiation objective.
GRASP Instance:
This refers to an instantiation of a GRASP protocol engine, likely
including multiple threads or processes as well as dynamic data
structures such as a discovery cache, running in a given security
environment on a single device.
GRASP Core:
This refers to the code and shared data structures of a GRASP
instance, which will communicate with individual ASAs via a
suitable Application Programming Interface (API).
Interface or GRASP Interface:
Unless otherwise stated, this refers to a network interface, which
might be physical or virtual, that a specific instance of GRASP is
currently using. A device might have other interfaces that are
not used by GRASP and which are outside the scope of the Autonomic
Network.
2.2. High-Level Deployment Model
A GRASP implementation will be part of the Autonomic Networking
Infrastructure (ANI) in an autonomic node, which must also provide an
appropriate security environment. In accordance with [RFC8993], this
SHOULD be the Autonomic Control Plane (ACP) [RFC8994]. As a result,
all autonomic nodes in the ACP are able to trust each other. It is
expected that GRASP will access the ACP by using a typical socket
programming interface, and the ACP will make available only network
interfaces within the Autonomic Network. If there is no ACP, the
considerations described in Section 2.5.1 apply.
There will also be one or more Autonomic Service Agents (ASAs). In
the minimal case of a single-purpose device, these components might
be fully integrated with GRASP and the ACP. A more common model is
expected to be a multipurpose device capable of containing several
ASAs, such as a router or large switch. In this case it is expected
that the ACP, GRASP and the ASAs will be implemented as separate
processes, which are able to support asynchronous and simultaneous
operations, for example by multithreading.
In some scenarios, a limited negotiation model might be deployed
based on a limited trust relationship such as that between two
administrative domains. ASAs might then exchange limited information
and negotiate some particular configurations.
GRASP is explicitly designed to operate within a single addressing
realm. Its discovery and flooding mechanisms do not support
autonomic operations that cross any form of address translator or
upper-layer proxy.
A suitable Application Programming Interface (API) will be needed
between GRASP and the ASAs. In some implementations, ASAs would run
in user space with a GRASP library providing the API, and this
library would in turn communicate via system calls with core GRASP
functions. Details of the API are out of scope for the present
document. For further details of possible deployment models, see
[RFC8993].
An instance of GRASP must be aware of the network interfaces it will
use, and of the appropriate global-scope and link-local addresses.
In the presence of the ACP, such information will be available from
the adjacency table discussed in [RFC8993]. In other cases, GRASP
must determine such information for itself. Details depend on the
device and operating system. In the rest of this document, the terms
'interfaces' or 'GRASP interfaces' refers only to the set of network
interfaces that a specific instance of GRASP is currently using.
Because GRASP needs to work with very high reliability, especially
during bootstrapping and during fault conditions, it is essential
that every implementation continues to operate in adverse conditions.
For example, discovery failures, or any kind of socket exception at
any time, must not cause irrecoverable failures in GRASP itself, and
must return suitable error codes through the API so that ASAs can
also recover.
GRASP must not depend upon nonvolatile data storage. All runtime
error conditions, and events such as address renumbering, network
interface failures, and CPU sleep/wake cycles, must be handled in
such a way that GRASP will still operate correctly and securely
afterwards (Section 2.5.1).
An autonomic node will normally run a single instance of GRASP, which
is used by multiple ASAs. Possible exceptions are mentioned below.
2.3. High-Level Design
This section describes the behavior model and general design of
GRASP, supporting discovery, synchronization, and negotiation, to act
as a platform for different technical objectives.
A generic platform:
The protocol design is generic and independent of the
synchronization or negotiation contents. The technical contents
will vary according to the various technical objectives and the
different pairs of counterparts.
Multiple instances:
Normally, a single main instance of the GRASP protocol engine will
exist in an autonomic node, and each ASA will run as an
independent asynchronous process. However, scenarios where
multiple instances of GRASP run in a single node, perhaps with
different security properties, are possible (Section 2.5.2). In
this case, each instance MUST listen independently for GRASP link-
local multicasts, and all instances MUST be woken by each such
multicast in order for discovery and flooding to work correctly.
Security infrastructure:
As noted above, the protocol itself has no built-in security
functionality and relies on a separate secure infrastructure.
Discovery, synchronization, and negotiation are designed together:
The discovery method and the synchronization and negotiation
methods are designed in the same way and can be combined when this
is useful, allowing a rapid mode of operation described in
Section 2.5.4. These processes can also be performed
independently when appropriate.
Thus, for some objectives, especially those concerned with
application-layer services, another discovery mechanism such as
DNS-based Service Discovery [RFC7558] MAY be used. The choice
is left to the designers of individual ASAs.
A uniform pattern for technical objectives:
The synchronization and negotiation objectives are defined
according to a uniform pattern. The values that they contain
could be carried either in a simple binary format or in a complex
object format. The basic protocol design uses the Concise Binary
Object Representation (CBOR) [RFC8949], which is readily
extensible for unknown, future requirements.
A flexible model for synchronization:
GRASP supports synchronization between two nodes, which could be
used repeatedly to perform synchronization among a small number of
nodes. It also supports an unsolicited flooding mode when large
groups of nodes, possibly including all autonomic nodes, need data
for the same technical objective.
There may be some network parameters for which a more
traditional flooding mechanism such as the Distributed Node
Consensus Protocol (DNCP) [RFC7787] is considered more
appropriate. GRASP can coexist with DNCP.
A simple initiator/responder model for negotiation:
Multiparty negotiations are very complicated to model and cannot
readily be guaranteed to converge. GRASP uses a simple bilateral
model and can support multiparty negotiations by indirect steps.
Organizing of synchronization or negotiation content:
The technical content transmitted by GRASP will be organized
according to the relevant function or service. The objectives for
different functions or services are kept separate because they may
be negotiated or synchronized with different counterparts or have
different response times. Thus a normal arrangement is a single
ASA managing a small set of closely related objectives, with a
version of that ASA in each relevant autonomic node. Further
discussion of this aspect is out of scope for the current
document.
Requests and responses in negotiation procedures:
The initiator can negotiate a specific negotiation objective with
relevant counterpart ASAs. It can request relevant information
from a counterpart so that it can coordinate its local
configuration. It can request the counterpart to make a matching
configuration. It can request simulation or forecast results by
sending some dry-run conditions.
Beyond the traditional yes/no answer, the responder can reply with
a suggested alternative value for the objective concerned. This
would start a bidirectional negotiation ending in a compromise
between the two ASAs.
Convergence of negotiation procedures:
To enable convergence when a responder suggests a new value or
condition in a negotiation step reply, it should be as close as
possible to the original request or previous suggestion. The
suggested value of later negotiation steps should be chosen
between the suggested values from the previous two steps. GRASP
provides mechanisms to guarantee convergence (or failure) in a
small number of steps, namely a timeout and a maximum number of
iterations.
Extensibility:
GRASP intentionally does not have a version number, and it can be
extended by adding new message types and options. The Invalid
message (M_INVALID) will be used to signal that an implementation
does not recognize a message or option sent by another
implementation. In normal use, new semantics will be added by
defining new synchronization or negotiation objectives.
2.4. Quick Operating Overview
An instance of GRASP is expected to run as a separate core module,
providing an API (such as [RFC8991]) to interface to various ASAs.
These ASAs may operate without special privilege, unless they need it
for other reasons (such as configuring IP addresses or manipulating
routing tables).
The GRASP mechanisms used by the ASA are built around GRASP
objectives defined as data structures containing administrative
information such as the objective's unique name and its current
value. The format and size of the value is not restricted by the
protocol, except that it must be possible to serialize it for
transmission in CBOR, which is no restriction at all in practice.
GRASP provides the following mechanisms:
* A discovery mechanism (M_DISCOVERY, M_RESPONSE) by which an ASA
can discover other ASAs supporting a given objective.
* A negotiation request mechanism (M_REQ_NEG) by which an ASA can
start negotiation of an objective with a counterpart ASA. Once a
negotiation has started, the process is symmetrical, and there is
a negotiation step message (M_NEGOTIATE) for each ASA to use in
turn. Two other functions support negotiating steps (M_WAIT,
M_END).
* A synchronization mechanism (M_REQ_SYN) by which an ASA can
request the current value of an objective from a counterpart ASA.
With this, there is a corresponding response function (M_SYNCH)
for an ASA that wishes to respond to synchronization requests.
* A flood mechanism (M_FLOOD) by which an ASA can cause the current
value of an objective to be flooded throughout the Autonomic
Network so that any ASA can receive it. One application of this
is to act as an announcement, avoiding the need for discovery of a
widely applicable objective.
Some example messages and simple message flows are provided in
Appendix A.
2.5. GRASP Basic Properties and Mechanisms
2.5.1. Required External Security Mechanism
GRASP does not specify transport security because it is meant to be
adapted to different environments. Every solution adopting GRASP
MUST specify a security and transport substrate used by GRASP in that
solution.
The substrate MUST enforce sending and receiving GRASP messages only
between members of a mutually trusted group running GRASP. Each
group member is an instance of GRASP. The group members are nodes of
a connected graph. The group and graph are created by the security
and transport substrate and are called the GRASP domain. The
substrate must support unicast messages between any group members and
(link-local) multicast messages between adjacent group members. It
must deny messages between group members and non-group members. With
this model, security is provided by enforcing group membership, but
any member of the trusted group can attack the entire network until
revoked.
Substrates MUST use cryptographic member authentication and message
integrity for GRASP messages. This can be end to end or hop by hop
across the domain. The security and transport substrate MUST provide
mechanisms to remove untrusted members from the group.
If the substrate does not mandate and enforce GRASP message
encryption, then any service using GRASP in such a solution MUST
provide protection and encryption for message elements whose exposure
could constitute an attack vector.
The security and transport substrate for GRASP in the ANI is the ACP.
Unless otherwise noted, we assume this security and transport
substrate in the remainder of this document. The ACP does mandate
the use of encryption; therefore, GRASP in the ANI can rely on GRASP
messages being encrypted. The GRASP domain is the ACP: all nodes in
an autonomic domain connected by encrypted virtual links formed by
the ACP. The ACP uses hop-by-hop security (authentication and
encryption) of messages. Removal of nodes relies on standard PKI
certificate revocation or expiry of sufficiently short-lived
certificates. Refer to [RFC8994] for more details.
As mentioned in Section 2.3, some GRASP operations might be performed
across an administrative domain boundary by mutual agreement, without
the benefit of an ACP. Such operations MUST be confined to a
separate instance of GRASP with its own copy of all GRASP data
structures running across a separate GRASP domain with a security and
transport substrate. In the most simple case, each point-to-point
interdomain GRASP peering could be a separate domain, and the
security and transport substrate could be built using transport or
network-layer security protocols. This is subject to future
specifications.
An exception to the requirements for the security and transport
substrate exists for highly constrained subsets of GRASP meant to
support the establishment of a security and transport substrate,
described in the following section.
2.5.2. Discovery Unsolicited Link-Local (DULL) GRASP
Some services may need to use insecure GRASP discovery, response, and
flood messages without being able to use preexisting security
associations, for example, as part of discovery for establishing
security associations such as a security substrate for GRASP.
Such operations being intrinsically insecure, they need to be
confined to link-local use to minimize the risk of malicious actions.
Possible examples include discovery of candidate ACP neighbors
[RFC8994], discovery of bootstrap proxies [RFC8995], or perhaps
initialization services in networks using GRASP without being fully
autonomic (e.g., no ACP). Such usage MUST be limited to link-local
operations on a single interface and MUST be confined to a separate
insecure instance of GRASP with its own copy of all GRASP data
structures. This instance is nicknamed DULL -- Discovery Unsolicited
Link-Local.
The detailed rules for the DULL instance of GRASP are as follows:
* An initiator MAY send Discovery or Flood Synchronization link-
local multicast messages that MUST have a loop count of 1, to
prevent off-link operations. Other unsolicited GRASP message
types MUST NOT be sent.
* A responder MUST silently discard any message whose loop count is
not 1.
* A responder MUST silently discard any message referring to a GRASP
objective that is not directly part of a service that requires
this insecure mode.
* A responder MUST NOT relay any multicast messages.
* A Discovery Response MUST indicate a link-local address.
* A Discovery Response MUST NOT include a Divert option.
* A node MUST silently discard any message whose source address is
not link-local.
To minimize traffic possibly observed by third parties, GRASP traffic
SHOULD be minimized by using only Flood Synchronization to announce
objectives and their associated locators, rather than by using
Discovery and Discovery Response messages. Further details are out
of scope for this document.
2.5.3. Transport Layer Usage
All GRASP messages, after they are serialized as a CBOR byte string,
are transmitted as such directly over the transport protocol in use.
The transport protocol(s) for a GRASP domain are specified by the
security and transport substrate as introduced in Section 2.5.1.
GRASP discovery and flooding messages are designed for GRASP domain-
wide flooding through hop-by-hop link-local multicast forwarding
between adjacent GRASP nodes. The GRASP security and transport
substrate needs to specify how these link-local multicasts are
transported. This can be unreliable transport (UDP) but it SHOULD be
reliable transport (e.g., TCP).
If the substrate specifies an unreliable transport such as UDP for
discovery and flooding messages, then it MUST NOT use IP
fragmentation because of its loss characteristic, especially in
multi-hop flooding. GRASP MUST then enforce at the user API level a
limit to the size of discovery and flooding messages, so that no
fragmentation can occur. For IPv6 transport, this means that the
size of those messages' IPv6 packets must be at most 1280 bytes
(unless there is a known larger minimum link MTU across the whole
GRASP domain).
All other GRASP messages are unicast between group members of the
GRASP domain. These MUST use a reliable transport protocol because
GRASP itself does not provide for error detection, retransmission, or
flow control. Unless otherwise specified by the security and
transport substrate, TCP MUST be used.
The security and transport substrate for GRASP in the ANI is the ACP.
Unless otherwise noted, we assume this security and transport
substrate in the remainder of this document when describing GRASP's
message transport. In the ACP, TCP is used for GRASP unicast
messages. GRASP discovery and flooding messages also use TCP: these
link-local messages are forwarded by replicating them to all adjacent
GRASP nodes on the link via TCP connections to those adjacent GRASP
nodes. Because of this, GRASP in the ANI has no limitations on the
size of discovery and flooding messages with respect to fragmentation
issues. While the ACP is being built using a DULL instance of GRASP,
native UDP multicast is used to discover ACP/GRASP neighbors on
links.
For link-local UDP multicast, GRASP listens to the well-known GRASP
Listen Port (Section 2.6). Transport connections for discovery and
flooding on relay nodes must terminate in GRASP instances (e.g.,
GRASP ASAs) so that link-local multicast, hop-by-hop flooding of
M_DISCOVERY and M_FLOOD messages and hop-by-hop forwarding of
M_RESPONSE responses and caching of those responses along the path
work correctly.
Unicast transport connections used for synchronization and
negotiation can terminate directly in ASAs that implement objectives;
therefore, this traffic does not need to pass through GRASP
instances. For this, the ASA listens on its own dynamically assigned
ports, which are communicated to its peers during discovery.
Alternatively, the GRASP instance can also terminate the unicast
transport connections and pass the traffic from/to the ASA if that is
preferable in some implementations (e.g., to better decouple ASAs
from network connections).
2.5.4. Discovery Mechanism and Procedures
2.5.4.1. Separated Discovery and Negotiation Mechanisms
Although discovery and negotiation or synchronization are defined
together in GRASP, they are separate mechanisms. The discovery
process could run independently from the negotiation or
synchronization process. Upon receiving a Discovery message
(Section 2.8.4), the recipient node should return a Discovery
Response message in which it either indicates itself as a discovery
responder or diverts the initiator towards another more suitable ASA.
However, this response may be delayed if the recipient needs to relay
the Discovery message onward, as described in Section 2.5.4.4.
The discovery action (M_DISCOVERY) will normally be followed by a
negotiation (M_REQ_NEG) or synchronization (M_REQ_SYN) action. The
discovery results could be utilized by the negotiation protocol to
decide which ASA the initiator will negotiate with.
The initiator of a discovery action for a given objective need not be
capable of responding to that objective as a negotiation counterpart,
as a synchronization responder, or as source for flooding. For
example, an ASA might perform discovery even if it only wishes to act
as a synchronization initiator or negotiation initiator. Such an ASA
does not itself need to respond to Discovery messages.
It is also entirely possible to use GRASP discovery without any
subsequent negotiation or synchronization action. In this case, the
discovered objective is simply used as a name during the discovery
process, and any subsequent operations between the peers are outside
the scope of GRASP.
2.5.4.2. Discovery Overview
A complete discovery process will start with a multicast Discovery
message (M_DISCOVERY) on the local link. On-link neighbors
supporting the discovery objective will respond directly with
Discovery Response (M_RESPONSE) messages. A neighbor with multiple
interfaces may respond with a cached Discovery Response. If it has
no cached response, it will relay the Discovery message on its other
GRASP interfaces. If a node receiving the relayed Discovery message
supports the discovery objective, it will respond to the relayed
Discovery message. If it has a cached response, it will respond with
that. If not, it will repeat the discovery process, which thereby
becomes iterative. The loop count and timeout will ensure that the
process ends. Further details are given in Section 2.5.4.4.
A Discovery message MAY be sent unicast to a peer node, which SHOULD
then proceed exactly as if the message had been multicast, except
that when TCP is used, the response will be on the same socket as the
query. However, this mode does not guarantee successful discovery in
the general case.
2.5.4.3. Discovery Procedures
Discovery starts as an on-link operation. The Divert option can tell
the discovery initiator to contact an off-link ASA for that discovery
objective. If the security and transport substrate of the GRASP
domain (see Section 2.5.3) uses UDP link-local multicast, then the
discovery initiator sends these to the ALL_GRASP_NEIGHBORS link-local
multicast address (Section 2.6), and all GRASP nodes need to listen
to this address to act as discovery responders. Because this port is
unique in a device, this is a function of the GRASP instance and not
of an individual ASA. As a result, each ASA will need to register
the objectives that it supports with the local GRASP instance.
If an ASA in a neighbor device supports the requested discovery
objective, the device SHOULD respond to the link-local multicast with
a unicast Discovery Response message (Section 2.8.5) with locator
option(s) (Section 2.9.5) unless it is temporarily unavailable.
Otherwise, if the neighbor has cached information about an ASA that
supports the requested discovery objective (usually because it
discovered the same objective before), it SHOULD respond with a
Discovery Response message with a Divert option pointing to the
appropriate discovery responder. However, it SHOULD NOT respond with
a cached response on an interface if it learned that information from
the same interface because the peer in question will answer directly
if still operational.
If a device has no information about the requested discovery
objective and is not acting as a discovery relay (see
Section 2.5.4.4), it MUST silently discard the Discovery message.
The discovery initiator MUST set a reasonable timeout on the
discovery process. A suggested value is 100 milliseconds multiplied
by the loop count embedded in the objective.
If no Discovery Response is received within the timeout, the
Discovery message MAY be repeated with a newly generated Session ID
(Section 2.7). An exponential backoff SHOULD be used for subsequent
repetitions to limit the load during busy periods. The details of
the backoff algorithm will depend on the use case for the objective
concerned but MUST be consistent with the recommendations in
[RFC8085] for low data-volume multicast. Frequent repetition might
be symptomatic of a denial-of-service attack.
After a GRASP device successfully discovers a locator for a discovery
responder supporting a specific objective, it SHOULD cache this
information, including the interface index [RFC3493] via which it was
discovered. This cache record MAY be used for future negotiation or
synchronization, and the locator SHOULD be passed on when appropriate
as a Divert option to another discovery initiator.
The cache mechanism MUST include a lifetime for each entry. The
lifetime is derived from a time-to-live (ttl) parameter in each
Discovery Response message. Cached entries MUST be ignored or
deleted after their lifetime expires. In some environments,
unplanned address renumbering might occur. In such cases, the
lifetime SHOULD be short compared to the typical address lifetime.
The discovery mechanism needs to track the node's current address to
ensure that Discovery Responses always indicate the correct address.
If multiple discovery responders are found for the same objective,
they SHOULD all be cached unless this creates a resource shortage.
The method of choosing between multiple responders is an
implementation choice. This choice MUST be available to each ASA,
but the GRASP implementation SHOULD provide a default choice.
Because discovery responders will be cached in a finite cache, they
might be deleted at any time. In this case, discovery will need to
be repeated. If an ASA exits for any reason, its locator might still
be cached for some time, and attempts to connect to it will fail.
ASAs need to be robust in these circumstances.
2.5.4.4. Discovery Relaying
A GRASP instance with multiple link-layer interfaces (typically
running in a router) MUST support discovery on all GRASP interfaces.
We refer to this as a 'relaying instance'.
DULL instances (Section 2.5.2) are always single-interface instances
and therefore MUST NOT perform discovery relaying.
If a relaying instance receives a Discovery message on a given
interface for a specific objective that it does not support and for
which it has not previously cached a discovery responder, it MUST
relay the query by reissuing a new Discovery message as a link-local
multicast on its other GRASP interfaces.
The relayed Discovery message MUST have the same Session ID and
'initiator' field as the incoming message (see Section 2.8.4). The
IP address in the 'initiator' field is only used to disambiguate the
Session ID and is never used to address Response packets. Response
packets are sent back to the relaying instance, not the original
initiator.
The M_DISCOVERY message does not encode the transport address of the
originator or relay. Response packets must therefore be sent to the
transport-layer address of the connection on which the M_DISCOVERY
message was received. If the M_DISCOVERY was relayed via a reliable
hop-by-hop transport connection, the response is simply sent back via
the same connection.
If the M_DISCOVERY was relayed via link-local (e.g., UDP) multicast,
the response is sent back via a reliable hop-by-hop transport
connection with the same port number as the source port of the link-
local multicast. Therefore, if link-local multicast is used and
M_RESPONSE messages are required (which is the case in almost all
GRASP instances except for the limited use of DULL instances in the
ANI), GRASP needs to be able to bind to one port number on UDP from
which to originate the link-local multicast M_DISCOVERY messages and
the same port number on the reliable hop-by-hop transport (e.g., TCP
by default) to be able to respond to transport connections from
responders that want to send M_RESPONSE messages back. Note that
this port does not need to be the GRASP_LISTEN_PORT.
The relaying instance MUST decrement the loop count within the
objective, and MUST NOT relay the Discovery message if the result is
zero. Also, it MUST limit the total rate at which it relays
Discovery messages to a reasonable value in order to mitigate
possible denial-of-service attacks. For example, the rate limit
could be set to a small multiple of the observed rate of Discovery
messages during normal operation. The relaying instance MUST cache
the Session ID value and initiator address of each relayed Discovery
message until any Discovery Responses have arrived or the discovery
process has timed out. To prevent loops, it MUST NOT relay a
Discovery message that carries a given cached Session ID and
initiator address more than once. These precautions avoid discovery
loops and mitigate potential overload.
Since the relay device is unaware of the timeout set by the original
initiator, it SHOULD set a suitable timeout for the relayed Discovery
message. A suggested value is 100 milliseconds multiplied by the
remaining loop count.
The discovery results received by the relaying instance MUST in turn
be sent as a Discovery Response message to the Discovery message that
caused the relay action.
2.5.4.5. Rapid Mode (Discovery with Negotiation or Synchronization)
A Discovery message MAY include an objective option. This allows a
rapid mode of negotiation (Section 2.5.5.1) or synchronization
(Section 2.5.6.3). Rapid mode is currently limited to a single
objective for simplicity of design and implementation. A possible
future extension is to allow multiple objectives in rapid mode for
greater efficiency.
2.5.5. Negotiation Procedures
A negotiation initiator opens a transport connection to a counterpart
ASA using the address, protocol, and port obtained during discovery.
It then sends a negotiation request (using M_REQ_NEG) to the
counterpart, including a specific negotiation objective. It may
request the negotiation counterpart to make a specific configuration.
Alternatively, it may request a certain simulation or forecast result
by sending a dry-run configuration. The details, including the
distinction between a dry run and a live configuration change, will
be defined separately for each type of negotiation objective. Any
state associated with a dry-run operation, such as temporarily
reserving a resource for subsequent use in a live run, is entirely a
matter for the designer of the ASA concerned.
Each negotiation session as a whole is subject to a timeout (default
GRASP_DEF_TIMEOUT milliseconds, Section 2.6), initialized when the
request is sent (see Section 2.8.6). If no reply message of any kind
is received within the timeout, the negotiation request MAY be
repeated with a newly generated Session ID (Section 2.7). An
exponential backoff SHOULD be used for subsequent repetitions. The
details of the backoff algorithm will depend on the use case for the
objective concerned.
If the counterpart can immediately apply the requested configuration,
it will give an immediate positive (O_ACCEPT) answer using the
Negotiation End (M_END) message. This will end the negotiation phase
immediately. Otherwise, it will negotiate (using M_NEGOTIATE). It
will reply with a proposed alternative configuration that it can
apply (typically, a configuration that uses fewer resources than
requested by the negotiation initiator). This will start a
bidirectional negotiation using the Negotiate (M_NEGOTIATE) message
to reach a compromise between the two ASAs.
The negotiation procedure is ended when one of the negotiation peers
sends a Negotiation End (M_END) message, which contains an Accept
(O_ACCEPT) or Decline (O_DECLINE) option and does not need a response
from the negotiation peer. Negotiation may also end in failure
(equivalent to a decline) if a timeout is exceeded or a loop count is
exceeded. When the procedure ends for whatever reason, the transport
connection SHOULD be closed. A transport session failure is treated
as a negotiation failure.
A negotiation procedure concerns one objective and one counterpart.
Both the initiator and the counterpart may take part in simultaneous
negotiations with various other ASAs or in simultaneous negotiations
about different objectives. Thus, GRASP is expected to be used in a
multithreaded mode or its logical equivalent. Certain negotiation
objectives may have restrictions on multithreading, for example to
avoid over-allocating resources.
Some configuration actions, for example, wavelength switching in
optical networks, might take considerable time to execute. The ASA
concerned needs to allow for this by design, but GRASP does allow for
a peer to insert latency in a negotiation process if necessary
(Section 2.8.9, M_WAIT).
2.5.5.1. Rapid Mode (Discovery/Negotiation Linkage)
A Discovery message MAY include a Negotiation Objective option. In
this case, it is as if the initiator sent the sequence M_DISCOVERY
immediately followed by M_REQ_NEG. This has implications for the
construction of the GRASP core, as it must carefully pass the
contents of the Negotiation Objective option to the ASA so that it
may evaluate the objective directly. When a Negotiation Objective
option is present, the ASA replies with an M_NEGOTIATE message (or
M_END with O_ACCEPT if it is immediately satisfied with the proposal)
rather than with an M_RESPONSE. However, if the recipient node does
not support rapid mode, discovery will continue normally.
It is possible that a Discovery Response will arrive from a responder
that does not support rapid mode before such a Negotiation message
arrives. In this case, rapid mode will not occur.
This rapid mode could reduce the interactions between nodes so that a
higher efficiency could be achieved. However, a network in which
some nodes support rapid mode and others do not will have complex
timing-dependent behaviors. Therefore, the rapid negotiation
function SHOULD be disabled by default.
2.5.6. Synchronization and Flooding Procedures
2.5.6.1. Unicast Synchronization
A synchronization initiator opens a transport connection to a
counterpart ASA using the address, protocol, and port obtained during
discovery. It then sends a Request Synchronization message
(M_REQ_SYN, Section 2.8.6) to the counterpart, including a specific
synchronization objective. The counterpart responds with a
Synchronization message (M_SYNCH, Section 2.8.10) containing the
current value of the requested synchronization objective. No further
messages are needed, and the transport connection SHOULD be closed.
A transport session failure is treated as a synchronization failure.
If no reply message of any kind is received within a given timeout
(default GRASP_DEF_TIMEOUT milliseconds, Section 2.6), the
synchronization request MAY be repeated with a newly generated
Session ID (Section 2.7). An exponential backoff SHOULD be used for
subsequent repetitions. The details of the backoff algorithm will
depend on the use case for the objective concerned.
2.5.6.2. Flooding
In the case just described, the message exchange is unicast and
concerns only one synchronization objective. For large groups of
nodes requiring the same data, synchronization flooding is available.
For this, a flooding initiator MAY send an unsolicited Flood
Synchronization message (Section 2.8.11) containing one or more
Synchronization Objective option(s), if and only if the specification
of those objectives permits it. This is sent as a multicast message
to the ALL_GRASP_NEIGHBORS multicast address (Section 2.6).
Receiving flood multicasts is a function of the GRASP core, as in the
case of discovery multicasts (Section 2.5.4.3).
To ensure that flooding does not result in a loop, the originator of
the Flood Synchronization message MUST set the loop count in the
objectives to a suitable value (the default is GRASP_DEF_LOOPCT).
Also, a suitable mechanism is needed to avoid excessive multicast
traffic. This mechanism MUST be defined as part of the specification
of the synchronization objective(s) concerned. It might be a simple
rate limit or a more complex mechanism such as the Trickle algorithm
[RFC6206].
A GRASP device with multiple link-layer interfaces (typically a
router) MUST support synchronization flooding on all GRASP
interfaces. If it receives a multicast Flood Synchronization message
on a given interface, it MUST relay it by reissuing a Flood
Synchronization message as a link-local multicast on its other GRASP
interfaces. The relayed message MUST have the same Session ID as the
incoming message and MUST be tagged with the IP address of its
original initiator.
Link-layer flooding is supported by GRASP by setting the loop count
to 1 and sending with a link-local source address. Floods with link-
local source addresses and a loop count other than 1 are invalid, and
such messages MUST be discarded.
The relaying device MUST decrement the loop count within the first
objective and MUST NOT relay the Flood Synchronization message if the
result is zero. Also, it MUST limit the total rate at which it
relays Flood Synchronization messages to a reasonable value, in order
to mitigate possible denial-of-service attacks. For example, the
rate limit could be set to a small multiple of the observed rate of
flood messages during normal operation. The relaying device MUST
cache the Session ID value and initiator address of each relayed
Flood Synchronization message for a time not less than twice
GRASP_DEF_TIMEOUT milliseconds. To prevent loops, it MUST NOT relay
a Flood Synchronization message that carries a given cached Session
ID and initiator address more than once. These precautions avoid
synchronization loops and mitigate potential overload.
Note that this mechanism is unreliable in the case of sleeping nodes,
or new nodes that join the network, or nodes that rejoin the network
after a fault. An ASA that initiates a flood SHOULD repeat the flood
at a suitable frequency, which MUST be consistent with the
recommendations in [RFC8085] for low data-volume multicast. The ASA
SHOULD also act as a synchronization responder for the objective(s)
concerned. Thus nodes that require an objective subject to flooding
can either wait for the next flood or request unicast synchronization
for that objective.
The multicast messages for synchronization flooding are subject to
the security rules in Section 2.5.1. In practice, this means that
they MUST NOT be transmitted and MUST be ignored on receipt unless
there is an operational ACP or equivalent strong security in place.
However, because of the security weakness of link-local multicast
(Section 3), synchronization objectives that are flooded SHOULD NOT
contain unencrypted private information and SHOULD be validated by
the recipient ASA.
2.5.6.3. Rapid Mode (Discovery/Synchronization Linkage)
A Discovery message MAY include a Synchronization Objective option.
In this case, the Discovery message also acts as a Request
Synchronization message to indicate to the discovery responder that
it could directly reply to the discovery initiator with a
Synchronization message (Section 2.8.10) with synchronization data
for rapid processing, if the discovery target supports the
corresponding synchronization objective. The design implications are
similar to those discussed in Section 2.5.5.1.
It is possible that a Discovery Response will arrive from a responder
that does not support rapid mode before such a Synchronization
message arrives. In this case, rapid mode will not occur.
This rapid mode could reduce the interactions between nodes so that a
higher efficiency could be achieved. However, a network in which
some nodes support rapid mode and others do not will have complex
timing-dependent behaviors. Therefore, the rapid synchronization
function SHOULD be configured off by default and MAY be configured on
or off by Intent.
2.6. GRASP Constants
ALL_GRASP_NEIGHBORS
A link-local scope multicast address used by a GRASP-enabled
device to discover GRASP-enabled neighbor (i.e., on-link) devices.
All devices that support GRASP are members of this multicast
group.
* IPv6 multicast address: ff02::13
* IPv4 multicast address: 224.0.0.119
GRASP_LISTEN_PORT (7017)
A well-known UDP user port that every GRASP-enabled network device
MUST listen to for link-local multicasts when UDP is used for
M_DISCOVERY or M_FLOOD messages in the GRASP instance. This user
port MAY also be used to listen for TCP or UDP unicast messages in
a simple implementation of GRASP (Section 2.5.3).
GRASP_DEF_TIMEOUT (60000 milliseconds)
The default timeout used to determine that an operation has failed
to complete.
GRASP_DEF_LOOPCT (6)
The default loop count used to determine that a negotiation has
failed to complete and to avoid looping messages.
GRASP_DEF_MAX_SIZE (2048)
The default maximum message size in bytes.
2.7. Session Identifier (Session ID)
This is an up to 32-bit opaque value used to distinguish multiple
sessions between the same two devices. A new Session ID MUST be
generated by the initiator for every new Discovery, Flood
Synchronization, or Request message. All responses and follow-up
messages in the same discovery, synchronization, or negotiation
procedure MUST carry the same Session ID.
The Session ID SHOULD have a very low collision rate locally. It
MUST be generated by a pseudorandom number generator (PRNG) using a
locally generated seed that is unlikely to be used by any other
device in the same network. The PRNG SHOULD be cryptographically
strong [RFC4086]. When allocating a new Session ID, GRASP MUST check
that the value is not already in use and SHOULD check that it has not
been used recently by consulting a cache of current and recent
sessions. In the unlikely event of a clash, GRASP MUST generate a
new value.
However, there is a finite probability that two nodes might generate
the same Session ID value. For that reason, when a Session ID is
communicated via GRASP, the receiving node MUST tag it with the
initiator's IP address to allow disambiguation. In the highly
unlikely event of two peers opening sessions with the same Session ID
value, this tag will allow the two sessions to be distinguished.
Multicast GRASP messages and their responses, which may be relayed
between links, therefore include a field that carries the initiator's
global IP address.
There is a highly unlikely race condition in which two peers start
simultaneous negotiation sessions with each other using the same
Session ID value. Depending on various implementation choices, this
might lead to the two sessions being confused. See Section 2.8.6 for
details of how to avoid this.
2.8. GRASP Messages
2.8.1. Message Overview
This section defines the GRASP message format and message types.
Message types not listed here are reserved for future use.
The messages currently defined are:
Discovery and Discovery Response (M_DISCOVERY, M_RESPONSE).
Request Negotiation, Negotiation, Confirm Waiting, and Negotiation
End (M_REQ_NEG, M_NEGOTIATE, M_WAIT, M_END).
Request Synchronization, Synchronization, and Flood
Synchronization (M_REQ_SYN, M_SYNCH, M_FLOOD).
No Operation and Invalid (M_NOOP, M_INVALID).
2.8.2. GRASP Message Format
GRASP messages share an identical header format and a variable format
area for options. GRASP message headers and options are transmitted
in Concise Binary Object Representation (CBOR) [RFC8949]. In this
specification, they are described using Concise Data Definition
Language (CDDL) [RFC8610]. Fragmentary CDDL is used to describe each
item in this section. A complete and normative CDDL specification of
GRASP is given in Section 4, including constants such as message
types.
Every GRASP message, except the No Operation message, carries a
Session ID (Section 2.7). Options are then presented serially.
In fragmentary CDDL, every GRASP message follows the pattern:
grasp-message = (message .within message-structure) / noop-message
message-structure = [MESSAGE_TYPE, session-id, ?initiator,
*grasp-option]
MESSAGE_TYPE = 0..255
session-id = 0..4294967295 ; up to 32 bits
grasp-option = any
The MESSAGE_TYPE indicates the type of the message and thus defines
the expected options. Any options received that are not consistent
with the MESSAGE_TYPE SHOULD be silently discarded.
The No Operation (noop) message is described in Section 2.8.13.
The various MESSAGE_TYPE values are defined in Section 4.
All other message elements are described below and formally defined
in Section 4.
If an unrecognized MESSAGE_TYPE is received in a unicast message, an
Invalid message (Section 2.8.12) MAY be returned. Otherwise, the
message MAY be logged and MUST be discarded. If an unrecognized
MESSAGE_TYPE is received in a multicast message, it MAY be logged and
MUST be silently discarded.
2.8.3. Message Size
GRASP nodes MUST be able to receive unicast messages of at least
GRASP_DEF_MAX_SIZE bytes. GRASP nodes MUST NOT send unicast messages
longer than GRASP_DEF_MAX_SIZE bytes unless a longer size is
explicitly allowed for the objective concerned. For example, GRASP
negotiation itself could be used to agree on a longer message size.
The message parser used by GRASP should be configured to know about
the GRASP_DEF_MAX_SIZE, or any larger negotiated message size, so
that it may defend against overly long messages.
The maximum size of multicast messages (M_DISCOVERY and M_FLOOD)
depends on the link-layer technology or the link-adaptation layer in
use.
2.8.4. Discovery Message
In fragmentary CDDL, a Discovery message follows the pattern:
discovery-message = [M_DISCOVERY, session-id, initiator, objective]
A discovery initiator sends a Discovery message to initiate a
discovery process for a particular objective option.
The discovery initiator sends all Discovery messages via UDP to port
GRASP_LISTEN_PORT at the link-local ALL_GRASP_NEIGHBORS multicast
address on each link-layer interface in use by GRASP. It then
listens for unicast TCP responses on a given port and stores the
discovery results, including responding discovery objectives and
corresponding unicast locators.
The listening port used for TCP MUST be the same port as used for
sending the Discovery UDP multicast, on a given interface. In an
implementation with a single GRASP instance in a node, this MAY be
GRASP_LISTEN_PORT. To support multiple instances in the same node,
the GRASP discovery mechanism in each instance needs to find, for
each interface, a dynamic port that it can bind to for both sending
UDP link-local multicast and listening for TCP before initiating any
discovery.
The 'initiator' field in the message is a globally unique IP address
of the initiator for the sole purpose of disambiguating the Session
ID in other nodes. If for some reason the initiator does not have a
globally unique IP address, it MUST use a link-local address that is
highly likely to be unique for this purpose, for example, using
[RFC7217]. Determination of a node's globally unique IP address is
implementation dependent.
A Discovery message MUST include exactly one of the following:
* A Discovery Objective option (Section 2.10.1). Its loop count
MUST be set to a suitable value to prevent discovery loops
(default value is GRASP_DEF_LOOPCT). If the discovery initiator
requires only on-link responses, the loop count MUST be set to 1.
* A Negotiation Objective option (Section 2.10.1). This is used
both for the purpose of discovery and to indicate to the discovery
target that it MAY directly reply to the discovery initiator with
a Negotiation message for rapid processing, if it could act as the
corresponding negotiation counterpart. The sender of such a
Discovery message MUST initialize a negotiation timer and loop
count in the same way as a Request Negotiation message
(Section 2.8.6).
* A Synchronization Objective option (Section 2.10.1). This is used
both for the purpose of discovery and to indicate to the discovery
target that it MAY directly reply to the discovery initiator with
a Synchronization message for rapid processing, if it could act as
the corresponding synchronization counterpart. Its loop count
MUST be set to a suitable value to prevent discovery loops
(default value is GRASP_DEF_LOOPCT).
As mentioned in Section 2.5.4.2, a Discovery message MAY be sent
unicast to a peer node, which SHOULD then proceed exactly as if the
message had been multicast.
2.8.5. Discovery Response Message
In fragmentary CDDL, a Discovery Response message follows the
pattern:
response-message = [M_RESPONSE, session-id, initiator, ttl,
(+locator-option // divert-option), ?objective]
ttl = 0..4294967295 ; in milliseconds
A node that receives a Discovery message SHOULD send a Discovery
Response message if and only if it can respond to the discovery.
It MUST contain the same Session ID and initiator as the Discovery
message.
It MUST contain a time-to-live (ttl) for the validity of the
response, given as a positive integer value in milliseconds. Zero
implies a value significantly greater than GRASP_DEF_TIMEOUT
milliseconds (Section 2.6). A suggested value is ten times that
amount.
It MAY include a copy of the discovery objective from the
Discovery message.
It is sent to the sender of the Discovery message via TCP at the port
used to send the Discovery message (as explained in Section 2.8.4).
In the case of a relayed Discovery message, the Discovery Response is
thus sent to the relay, not the original initiator.
In all cases, the transport session SHOULD be closed after sending
the Discovery Response. A transport session failure is treated as no
response.
If the responding node supports the discovery objective of the
discovery, it MUST include at least one kind of locator option
(Section 2.9.5) to indicate its own location. A sequence of multiple
kinds of locator options (e.g., IP address option and FQDN option) is
also valid.
If the responding node itself does not support the discovery
objective, but it knows the locator of the discovery objective, then
it SHOULD respond to the Discovery message with a Divert option
(Section 2.9.2) embedding a locator option or a combination of
multiple kinds of locator options that indicate the locator(s) of the
discovery objective.
More details on the processing of Discovery Responses are given in
Section 2.5.4.
2.8.6. Request Messages
In fragmentary CDDL, Request Negotiation and Request Synchronization
messages follow the patterns:
request-negotiation-message = [M_REQ_NEG, session-id, objective]
request-synchronization-message = [M_REQ_SYN, session-id, objective]
A negotiation or synchronization requesting node sends the
appropriate Request message to the unicast address of the negotiation
or synchronization counterpart, using the appropriate protocol and
port numbers (selected from the discovery result). If the discovery
result is an FQDN, it will be resolved first.
A Request message MUST include the relevant objective option. In the
case of Request Negotiation, the objective option MUST include the
requested value.
When an initiator sends a Request Negotiation message, it MUST
initialize a negotiation timer for the new negotiation thread. The
default is GRASP_DEF_TIMEOUT milliseconds. Unless this timeout is
modified by a Confirm Waiting message (Section 2.8.9), the initiator
will consider that the negotiation has failed when the timer expires.
Similarly, when an initiator sends a Request Synchronization, it
SHOULD initialize a synchronization timer. The default is
GRASP_DEF_TIMEOUT milliseconds. The initiator will consider that
synchronization has failed if there is no response before the timer
expires.
When an initiator sends a Request message, it MUST initialize the
loop count of the objective option with a value defined in the
specification of the option or, if no such value is specified, with
GRASP_DEF_LOOPCT.
If a node receives a Request message for an objective for which no
ASA is currently listening, it MUST immediately close the relevant
socket to indicate this to the initiator. This is to avoid
unnecessary timeouts if, for example, an ASA exits prematurely but
the GRASP core is listening on its behalf.
To avoid the highly unlikely race condition in which two nodes
simultaneously request sessions with each other using the same
Session ID (Section 2.7), a node MUST verify that the received
Session ID is not already locally active when it receives a Request
message. In case of a clash, it MUST discard the Request message, in
which case the initiator will detect a timeout.
2.8.7. Negotiation Message
In fragmentary CDDL, a Negotiation message follows the pattern:
negotiation-message = [M_NEGOTIATE, session-id, objective]
A negotiation counterpart sends a Negotiation message in response to
a Request Negotiation message, a Negotiation message, or a Discovery
message in rapid mode. A negotiation process MAY include multiple
steps.
The Negotiation message MUST include the relevant Negotiation
Objective option, with its value updated according to progress in the
negotiation. The sender MUST decrement the loop count by 1. If the
loop count becomes zero, the message MUST NOT be sent. In this case,
the negotiation session has failed and will time out.
2.8.8. Negotiation End Message
In fragmentary CDDL, a Negotiation End message follows the pattern:
end-message = [M_END, session-id, accept-option / decline-option]
A negotiation counterpart sends a Negotiation End message to close
the negotiation. It MUST contain either an Accept option or a
Decline option, defined in Section 2.9.3 and Section 2.9.4. It could
be sent either by the requesting node or the responding node.
2.8.9. Confirm Waiting Message
In fragmentary CDDL, a Confirm Waiting message follows the pattern:
wait-message = [M_WAIT, session-id, waiting-time]
waiting-time = 0..4294967295 ; in milliseconds
A responding node sends a Confirm Waiting message to ask the
requesting node to wait for a further negotiation response. It might
be that the local process needs more time or that the negotiation
depends on another triggered negotiation. This message MUST NOT
include any other options. When received, the waiting time value
overwrites and restarts the current negotiation timer
(Section 2.8.6).
The responding node SHOULD send a Negotiation, Negotiation End, or
another Confirm Waiting message before the negotiation timer expires.
If not, when the initiator's timer expires, the initiator MUST treat
the negotiation procedure as failed.
2.8.10. Synchronization Message
In fragmentary CDDL, a Synchronization message follows the pattern:
synch-message = [M_SYNCH, session-id, objective]
A node that receives a Request Synchronization, or a Discovery
message in rapid mode, sends back a unicast Synchronization message
with the synchronization data, in the form of a GRASP option for the
specific synchronization objective present in the Request
Synchronization.
2.8.11. Flood Synchronization Message
In fragmentary CDDL, a Flood Synchronization message follows the
pattern:
flood-message = [M_FLOOD, session-id, initiator, ttl,
+[objective, (locator-option / [])]]
ttl = 0..4294967295 ; in milliseconds
A node MAY initiate flooding by sending an unsolicited Flood
Synchronization message with synchronization data. This MAY be sent
to port GRASP_LISTEN_PORT at the link-local ALL_GRASP_NEIGHBORS
multicast address, in accordance with the rules in Section 2.5.6.
The initiator address is provided, as described for Discovery
messages (Section 2.8.4), only to disambiguate the Session ID.
The message MUST contain a time-to-live (ttl) for the validity of
the contents, given as a positive integer value in milliseconds.
There is no default; zero indicates an indefinite lifetime.
The synchronization data are in the form of GRASP option(s) for
specific synchronization objective(s). The loop count(s) MUST be
set to a suitable value to prevent flood loops (default value is
GRASP_DEF_LOOPCT).
Each objective option MAY be followed by a locator option
(Section 2.9.5) associated with the flooded objective. In its
absence, an empty option MUST be included to indicate a null
locator.
A node that receives a Flood Synchronization message MUST cache the
received objectives for use by local ASAs. Each cached objective
MUST be tagged with the locator option sent with it, or with a null
tag if an empty locator option was sent. If a subsequent Flood
Synchronization message carries an objective with the same name and
the same tag, the corresponding cached copy of the objective MUST be
overwritten. If a subsequent Flood Synchronization message carrying
an objective with same name arrives with a different tag, a new
cached entry MUST be created.
Note: the purpose of this mechanism is to allow the recipient of
flooded values to distinguish between different senders of the same
objective, and if necessary communicate with them using the locator,
protocol, and port included in the locator option. Many objectives
will not need this mechanism, so they will be flooded with a null
locator.
Cached entries MUST be ignored or deleted after their lifetime
expires.
2.8.12. Invalid Message
In fragmentary CDDL, an Invalid message follows the pattern:
invalid-message = [M_INVALID, session-id, ?any]
This message MAY be sent by an implementation in response to an
incoming unicast message that it considers invalid. The Session ID
value MUST be copied from the incoming message. The content SHOULD
be diagnostic information such as a partial copy of the invalid
message up to the maximum message size. An M_INVALID message MAY be
silently ignored by a recipient. However, it could be used in
support of extensibility, since it indicates that the remote node
does not support a new or obsolete message or option.
An M_INVALID message MUST NOT be sent in response to an M_INVALID
message.
2.8.13. No Operation Message
In fragmentary CDDL, a No Operation message follows the pattern:
noop-message = [M_NOOP]
This message MAY be sent by an implementation that for practical
reasons needs to initialize a socket. It MUST be silently ignored by
a recipient.
2.9. GRASP Options
This section defines the GRASP options for the negotiation and
synchronization protocol signaling. Additional options may be
defined in the future.
2.9.1. Format of GRASP Options
GRASP options SHOULD be CBOR arrays that MUST start with an unsigned
integer identifying the specific option type carried in this option.
These option types are formally defined in Section 4.
GRASP options may be defined to include encapsulated GRASP options.
2.9.2. Divert Option
The Divert option is used to redirect a GRASP request to another
node, which may be more appropriate for the intended negotiation or
synchronization. It may redirect to an entity that is known as a
specific negotiation or synchronization counterpart (on-link or off-
link) or a default gateway. The Divert option MUST only be
encapsulated in Discovery Response messages. If found elsewhere, it
SHOULD be silently ignored.
A discovery initiator MAY ignore a Divert option if it only requires
direct Discovery Responses.
In fragmentary CDDL, the Divert option follows the pattern:
divert-option = [O_DIVERT, +locator-option]
The embedded locator option(s) (Section 2.9.5) point to diverted
destination target(s) in response to a Discovery message.
2.9.3. Accept Option
The Accept option is used to indicate to the negotiation counterpart
that the proposed negotiation content is accepted.
The Accept option MUST only be encapsulated in Negotiation End
messages. If found elsewhere, it SHOULD be silently ignored.
In fragmentary CDDL, the Accept option follows the pattern:
accept-option = [O_ACCEPT]
2.9.4. Decline Option
The Decline option is used to indicate to the negotiation counterpart
the proposed negotiation content is declined and to end the
negotiation process.
The Decline option MUST only be encapsulated in Negotiation End
messages. If found elsewhere, it SHOULD be silently ignored.
In fragmentary CDDL, the Decline option follows the pattern:
decline-option = [O_DECLINE, ?reason]
reason = text ; optional UTF-8 error message
Note: there might be scenarios where an ASA wants to decline the
proposed value and restart the negotiation process. In this case, it
is an implementation choice whether to send a Decline option or to
continue with a Negotiation message, with an objective option that
contains a null value or one that contains a new value that might
achieve convergence.
2.9.5. Locator Options
These locator options are used to present reachability information
for an ASA, a device, or an interface. They are Locator IPv6 Address
option, Locator IPv4 Address option, Locator FQDN option, and Locator
URI option.
Since ASAs will normally run as independent user programs, locator
options need to indicate the network-layer locator plus the transport
protocol and port number for reaching the target. For this reason,
the locator options for IP addresses and FQDNs include this
information explicitly. In the case of the Locator URI option, this
information can be encoded in the URI itself.
Note: It is assumed that all locators used in locator options are in
scope throughout the GRASP domain. As stated in Section 2.2, GRASP
is not intended to work across disjoint addressing or naming realms.
2.9.5.1. Locator IPv6 Address Option
In fragmentary CDDL, the Locator IPv6 Address option follows the
pattern:
ipv6-locator-option = [O_IPv6_LOCATOR, ipv6-address,
transport-proto, port-number]
ipv6-address = bytes .size 16
transport-proto = IPPROTO_TCP / IPPROTO_UDP
IPPROTO_TCP = 6
IPPROTO_UDP = 17
port-number = 0..65535
The content of this option is a binary IPv6 address followed by the
protocol number and port number to be used.
Note 1: The IPv6 address MUST normally have global scope. However,
during initialization, a link-local address MAY be used for specific
objectives only (Section 2.5.2). In this case, the corresponding
Discovery Response message MUST be sent via the interface to which
the link-local address applies.
Note 2: A link-local IPv6 address MUST NOT be used when this option
is included in a Divert option.
Note 3: The IPPROTO values are taken from the existing IANA Protocol
Numbers registry in order to specify TCP or UDP. If GRASP requires
future values that are not in that registry, a new registry for
values outside the range 0..255 will be needed.
2.9.5.2. Locator IPv4 Address Option
In fragmentary CDDL, the Locator IPv4 Address option follows the
pattern:
ipv4-locator-option = [O_IPv4_LOCATOR, ipv4-address,
transport-proto, port-number]
ipv4-address = bytes .size 4
The content of this option is a binary IPv4 address followed by the
protocol number and port number to be used.
Note: If an operator has internal network address translation for
IPv4, this option MUST NOT be used within the Divert option.
2.9.5.3. Locator FQDN Option
In fragmentary CDDL, the Locator FQDN option follows the pattern:
fqdn-locator-option = [O_FQDN_LOCATOR, text,
transport-proto, port-number]
The content of this option is the FQDN of the target followed by the
protocol number and port number to be used.
Note 1: Any FQDN that might not be valid throughout the network in
question, such as a Multicast DNS name [RFC6762], MUST NOT be used
when this option is used within the Divert option.
Note 2: Normal GRASP operations are not expected to use this option.
It is intended for special purposes such as discovering external
services.
2.9.5.4. Locator URI Option
In fragmentary CDDL, the Locator URI option follows the pattern:
uri-locator-option = [O_URI_LOCATOR, text,
transport-proto / null, port-number / null]
The content of this option is the URI of the target followed by the
protocol number and port number to be used (or by null values if not
required) [RFC3986].
Note 1: Any URI which might not be valid throughout the network in
question, such as one based on a Multicast DNS name [RFC6762], MUST
NOT be used when this option is used within the Divert option.
Note 2: Normal GRASP operations are not expected to use this option.
It is intended for special purposes such as discovering external
services. Therefore, its use is not further described in this
specification.
2.10. Objective Options
2.10.1. Format of Objective Options
An objective option is used to identify objectives for the purposes
of discovery, negotiation, or synchronization. All objectives MUST
be in the following format, described in fragmentary CDDL:
objective = [objective-name, objective-flags,
loop-count, ?objective-value]
objective-name = text
objective-value = any
loop-count = 0..255
All objectives are identified by a unique name that is a UTF-8 string
[RFC3629], to be compared byte by byte.
The names of generic objectives MUST NOT include a colon (":") and
MUST be registered with IANA (Section 5).
The names of privately defined objectives MUST include at least one
colon (":"). The string preceding the last colon in the name MUST be
globally unique and in some way identify the entity or person
defining the objective. The following three methods MAY be used to
create such a globally unique string:
1. The unique string is a decimal number representing a registered
32-bit Private Enterprise Number (PEN) [RFC5612] that uniquely
identifies the enterprise defining the objective.
2. The unique string is a FQDN that uniquely identifies the entity
or person defining the objective.
3. The unique string is an email address that uniquely identifies
the entity or person defining the objective.
GRASP treats the objective name as an opaque string. For example,
"EX1", "32473:EX1", "example.com:EX1", "example.org:EX1", and
"user@example.org:EX1" are five different objectives.
The 'objective-flags' field is described in Section 2.10.2.
The 'loop-count' field is used for terminating negotiation as
described in Section 2.8.7. It is also used for terminating
discovery as described in Section 2.5.4 and for terminating flooding
as described in Section 2.5.6.2. It is placed in the objective
rather than in the GRASP message format because, as far as the ASA is
concerned, it is a property of the objective itself.
The 'objective-value' field expresses the actual value of a
negotiation or synchronization objective. Its format is defined in
the specification of the objective and may be a simple value or a
data structure of any kind, as long as it can be represented in CBOR.
It is optional only in a Discovery or Discovery Response message.
2.10.2. Objective Flags
An objective may be relevant for discovery only, for discovery and
negotiation, or for discovery and synchronization. This is expressed
in the objective by logical flag bits:
objective-flags = uint .bits objective-flag
objective-flag = &(
F_DISC: 0 ; valid for discovery
F_NEG: 1 ; valid for negotiation
F_SYNCH: 2 ; valid for synchronization
F_NEG_DRY: 3 ; negotiation is a dry run
)
These bits are independent and may be combined appropriately, e.g.,
(F_DISC and F_SYNCH) or (F_DISC and F_NEG) or (F_DISC and F_NEG and
F_NEG_DRY).
Note that for a given negotiation session, an objective must be used
either for negotiation or for dry-run negotiation. Mixing the two
modes in a single negotiation is not possible.
2.10.3. General Considerations for Objective Options
As mentioned above, objective options MUST be assigned a unique name.
As long as privately defined objective options obey the rules above,
this document does not restrict their choice of name, but the entity
or person concerned SHOULD publish the names in use.
Names are expressed as UTF-8 strings for convenience in designing
objective options for localized use. For generic usage, names
expressed in the ASCII subset of UTF-8 are RECOMMENDED. Designers
planning to use non-ASCII names are strongly advised to consult
[RFC8264] or its successor to understand the complexities involved.
Since GRASP compares names byte by byte, all issues of Unicode
profiling and canonicalization MUST be specified in the design of the
objective option.
All objective options MUST respect the CBOR patterns defined above as
"objective" and MUST replace the 'any' field with a valid CBOR data
definition for the relevant use case and application.
An objective option that contains no additional fields beyond its
'loop-count' can only be a discovery objective and MUST only be used
in Discovery and Discovery Response messages.
The Negotiation Objective options contain negotiation objectives,
which vary according to different functions and/or services. They
MUST be carried by Discovery, Request Negotiation, or Negotiation
messages only. The negotiation initiator MUST set the initial 'loop-
count' to a value specified in the specification of the objective or,
if no such value is specified, to GRASP_DEF_LOOPCT.
For most scenarios, there should be initial values in the negotiation
requests. Consequently, the Negotiation Objective options MUST
always be completely presented in a Request Negotiation message, or
in a Discovery message in rapid mode. If there is no initial value,
the 'value' field SHOULD be set to the 'null' value defined by CBOR.
Synchronization Objective options are similar, but MUST be carried by
Discovery, Discovery Response, Request Synchronization, or Flood
Synchronization messages only. They include 'value' fields only in
Synchronization or Flood Synchronization messages.
The design of an objective interacts in various ways with the design
of the ASAs that will use it. ASA design considerations are
discussed in [ASA-GUIDELINES].
2.10.4. Organizing of Objective Options
Generic objective options MUST be specified in documents available to
the public and SHOULD be designed to use either the negotiation or
the synchronization mechanism described above.
As noted earlier, one negotiation objective is handled by each GRASP
negotiation thread. Therefore, a negotiation objective, which is
based on a specific function or action, SHOULD be organized as a
single GRASP option. It is NOT RECOMMENDED to organize multiple
negotiation objectives into a single option nor to split a single
function or action into multiple negotiation objectives.
It is important to understand that GRASP negotiation does not support
transactional integrity. If transactional integrity is needed for a
specific objective, this must be ensured by the ASA. For example, an
ASA might need to ensure that it only participates in one negotiation
thread at the same time. Such an ASA would need to stop listening
for incoming negotiation requests before generating an outgoing
negotiation request.
A synchronization objective SHOULD be organized as a single GRASP
option.
Some objectives will support more than one operational mode. An
example is a negotiation objective with both a dry-run mode (where
the negotiation is to determine whether the other end can, in fact,
make the requested change without problems) and a live mode, as
explained in Section 2.5.5. The semantics of such modes will be
defined in the specification of the objectives. These objectives
SHOULD include flags indicating the applicable mode(s).
An issue requiring particular attention is that GRASP itself is not a
transactionally safe protocol. Any state associated with a dry-run
operation, such as temporarily reserving a resource for subsequent
use in a live run, is entirely a matter for the designer of the ASA
concerned.
As indicated in Section 2.1, an objective's value may include
multiple parameters. Parameters might be categorized into two
classes: the obligatory ones presented as fixed fields and the
optional ones presented in some other form of data structure embedded
in CBOR. The format might be inherited from an existing management
or configuration protocol, with the objective option acting as a
carrier for that format. The data structure might be defined in a
formal language, but that is a matter for the specifications of
individual objectives. There are many candidates, according to the
context, such as ABNF, RBNF, XML Schema, YANG, etc. GRASP itself is
agnostic on these questions. The only restriction is that the format
can be mapped into CBOR.
It is NOT RECOMMENDED to mix parameters that have significantly
different response-time characteristics in a single objective.
Separate objectives are more suitable for such a scenario.
All objectives MUST support GRASP discovery. However, as mentioned
in Section 2.3, it is acceptable for an ASA to use an alternative
method of discovery.
Normally, a GRASP objective will refer to specific technical
parameters as explained in Section 2.1. However, it is acceptable to
define an abstract objective for the purpose of managing or
coordinating ASAs. It is also acceptable to define a special-purpose
objective for purposes such as trust bootstrapping or formation of
the ACP.
To guarantee convergence, a limited number of rounds or a timeout is
needed for each negotiation objective. Therefore, the definition of
each negotiation objective SHOULD clearly specify this, for example,
a default loop count and timeout, so that the negotiation can always
be terminated properly. If not, the GRASP defaults will apply.
There must be a well-defined procedure for concluding that a
negotiation cannot succeed, and if so, deciding what happens next
(e.g., deadlock resolution, tie-breaking, or reversion to best-effort
service). This MUST be specified for individual negotiation
objectives.
2.10.5. Experimental and Example Objective Options
The names "EX0" through "EX9" have been reserved for experimental
options. Multiple names have been assigned because a single
experiment may use multiple options simultaneously. These
experimental options are highly likely to have different meanings
when used for different experiments. Therefore, they SHOULD NOT be
used without an explicit human decision and MUST NOT be used in
unmanaged networks such as home networks.
These names are also RECOMMENDED for use in documentation examples.
3. Security Considerations
A successful attack on negotiation-enabled nodes would be extremely
harmful, as such nodes might end up with a completely undesirable
configuration that would also adversely affect their peers. GRASP
nodes and messages therefore require full protection. As explained
in Section 2.5.1, GRASP MUST run within a secure environment such as
the ACP [RFC8994], except for the constrained instances described in
Section 2.5.2.
Authentication
A cryptographically authenticated identity for each device is
needed in an Autonomic Network. It is not safe to assume that a
large network is physically secured against interference or that
all personnel are trustworthy. Each autonomic node MUST be
capable of proving its identity and authenticating its messages.
GRASP relies on a separate, external certificate-based security
mechanism to support authentication, data integrity protection,
and anti-replay protection.
Since GRASP must be deployed in an existing secure environment,
the protocol itself specifies nothing concerning the trust anchor
and certification authority. For example, in the ACP [RFC8994],
all nodes can trust each other and the ASAs installed in them.
If GRASP is used temporarily without an external security
mechanism, for example, during system bootstrap (Section 2.5.1),
the Session ID (Section 2.7) will act as a nonce to provide
limited protection against the injecting of responses by third
parties. A full analysis of the secure bootstrap process is in
[RFC8995].
Authorization and roles
GRASP is agnostic about the roles and capabilities of individual
ASAs and about which objectives a particular ASA is authorized to
support. An implementation might support precautions such as
allowing only one ASA in a given node to modify a given objective,
but this may not be appropriate in all cases. For example, it
might be operationally useful to allow an old and a new version of
the same ASA to run simultaneously during an overlap period.
These questions are out of scope for the present specification.
Privacy and confidentiality
GRASP is intended for network-management purposes involving
network elements, not end hosts. Therefore, no personal
information is expected to be involved in the signaling protocol,
so there should be no direct impact on personal privacy.
Nevertheless, applications that do convey personal information
cannot be excluded. Also, traffic flow paths, VPNs, etc., could
be negotiated, which could be of interest for traffic analysis.
Operators generally want to conceal details of their network
topology and traffic density from outsiders. Therefore, since
insider attacks cannot be excluded in a large network, the
security mechanism for the protocol MUST provide message
confidentiality. This is why Section 2.5.1 requires either an ACP
or an alternative security mechanism.
Link-local multicast security
GRASP has no reasonable alternative to using link-local multicast
for Discovery or Flood Synchronization messages, and these
messages are sent in the clear and with no authentication. They
are only sent on interfaces within the Autonomic Network (see
Section 2.1 and Section 2.5.1). They are, however, available to
on-link eavesdroppers and could be forged by on-link attackers.
In the case of discovery, the Discovery Responses are unicast and
will therefore be protected (Section 2.5.1), and an untrusted
forger will not be able to receive responses. In the case of
flood synchronization, an on-link eavesdropper will be able to
receive the flooded objectives, but there is no response message
to consider. Some precautions for Flood Synchronization messages
are suggested in Section 2.5.6.2.
DoS attack protection
GRASP discovery partly relies on insecure link-local multicast.
Since routers participating in GRASP sometimes relay Discovery
messages from one link to another, this could be a vector for
denial-of-service attacks. Some mitigations are specified in
Section 2.5.4. However, malicious code installed inside the ACP
could always launch DoS attacks consisting of either spurious
Discovery messages or spurious Discovery Responses. It is
important that firewalls prevent any GRASP messages from entering
the domain from an unknown source.
Security during bootstrap and discovery
A node cannot trust GRASP traffic from other nodes until the
security environment (such as the ACP) has identified the trust
anchor and can authenticate traffic by validating certificates for
other nodes. Also, until it has successfully enrolled [RFC8995],
a node cannot assume that other nodes are able to authenticate its
own traffic. Therefore, GRASP discovery during the bootstrap
phase for a new device will inevitably be insecure. Secure
synchronization and negotiation will be impossible until
enrollment is complete. Further details are given in
Section 2.5.2.
Security of discovered locators
When GRASP discovery returns an IP address, it MUST be that of a
node within the secure environment (Section 2.5.1). If it returns
an FQDN or a URI, the ASA that receives it MUST NOT assume that
the target of the locator is within the secure environment.
4. CDDL Specification of GRASP
<CODE BEGINS> file "grasp.cddl"
grasp-message = (message .within message-structure) / noop-message
message-structure = [MESSAGE_TYPE, session-id, ?initiator,
*grasp-option]
MESSAGE_TYPE = 0..255
session-id = 0..4294967295 ; up to 32 bits
grasp-option = any
message /= discovery-message
discovery-message = [M_DISCOVERY, session-id, initiator, objective]
message /= response-message ; response to Discovery
response-message = [M_RESPONSE, session-id, initiator, ttl,
(+locator-option // divert-option), ?objective]
message /= synch-message ; response to Synchronization request
synch-message = [M_SYNCH, session-id, objective]
message /= flood-message
flood-message = [M_FLOOD, session-id, initiator, ttl,
+[objective, (locator-option / [])]]
message /= request-negotiation-message
request-negotiation-message = [M_REQ_NEG, session-id, objective]
message /= request-synchronization-message
request-synchronization-message = [M_REQ_SYN, session-id, objective]
message /= negotiation-message
negotiation-message = [M_NEGOTIATE, session-id, objective]
message /= end-message
end-message = [M_END, session-id, accept-option / decline-option]
message /= wait-message
wait-message = [M_WAIT, session-id, waiting-time]
message /= invalid-message
invalid-message = [M_INVALID, session-id, ?any]
noop-message = [M_NOOP]
divert-option = [O_DIVERT, +locator-option]
accept-option = [O_ACCEPT]
decline-option = [O_DECLINE, ?reason]
reason = text ; optional UTF-8 error message
waiting-time = 0..4294967295 ; in milliseconds
ttl = 0..4294967295 ; in milliseconds
locator-option /= [O_IPv4_LOCATOR, ipv4-address,
transport-proto, port-number]
ipv4-address = bytes .size 4
locator-option /= [O_IPv6_LOCATOR, ipv6-address,
transport-proto, port-number]
ipv6-address = bytes .size 16
locator-option /= [O_FQDN_LOCATOR, text, transport-proto,
port-number]
locator-option /= [O_URI_LOCATOR, text,
transport-proto / null, port-number / null]
transport-proto = IPPROTO_TCP / IPPROTO_UDP
IPPROTO_TCP = 6
IPPROTO_UDP = 17
port-number = 0..65535
initiator = ipv4-address / ipv6-address
objective-flags = uint .bits objective-flag
objective-flag = &(
F_DISC: 0 ; valid for discovery
F_NEG: 1 ; valid for negotiation
F_SYNCH: 2 ; valid for synchronization
F_NEG_DRY: 3 ; negotiation is a dry run
)
objective = [objective-name, objective-flags,
loop-count, ?objective-value]
objective-name = text ; see section "Format of Objective Options"
objective-value = any
loop-count = 0..255
; Constants for message types and option types
M_NOOP = 0
M_DISCOVERY = 1
M_RESPONSE = 2
M_REQ_NEG = 3
M_REQ_SYN = 4
M_NEGOTIATE = 5
M_END = 6
M_WAIT = 7
M_SYNCH = 8
M_FLOOD = 9
M_INVALID = 99
O_DIVERT = 100
O_ACCEPT = 101
O_DECLINE = 102
O_IPv6_LOCATOR = 103
O_IPv4_LOCATOR = 104
O_FQDN_LOCATOR = 105
O_URI_LOCATOR = 106
<CODE ENDS>
5. IANA Considerations
This document defines the GeneRic Autonomic Signaling Protocol
(GRASP).
Section 2.6 explains the following link-local multicast addresses
that IANA has assigned for use by GRASP.
Assigned in the "Link-Local Scope Multicast Addresses" subregistry of
the "IPv6 Multicast Address Space Registry":
Address(es): ff02::13
Description: ALL_GRASP_NEIGHBORS
Reference: RFC 8990
Assigned in the "Local Network Control Block (224.0.0.0 - 224.0.0.255
(224.0.0/24))" subregistry of the "IPv4 Multicast Address Space
Registry":
Address(es): 224.0.0.119
Description: ALL_GRASP_NEIGHBORS
Reference: RFC 8990
Section 2.6 explains the following User Port (GRASP_LISTEN_PORT),
which IANA has assigned for use by GRASP for both UDP and TCP:
Service Name: grasp
Port Number: 7017
Transport Protocol: udp, tcp
Description GeneRic Autonomic Signaling Protocol
Assignee: IESG <iesg@ietf.org>
Contact: IETF Chair <chair@ietf.org>
Reference: RFC 8990
The IANA has created the "GeneRic Autonomic Signaling Protocol
(GRASP) Parameters" registry, which includes two subregistries:
"GRASP Messages and Options" and "GRASP Objective Names".
The values in the "GRASP Messages and Options" subregistry are names
paired with decimal integers. Future values MUST be assigned using
the Standards Action policy defined by [RFC8126]. The following
initial values are assigned by this document:
+=======+================+
| Value | Message/Option |
+=======+================+
| 0 | M_NOOP |
+-------+----------------+
| 1 | M_DISCOVERY |
+-------+----------------+
| 2 | M_RESPONSE |
+-------+----------------+
| 3 | M_REQ_NEG |
+-------+----------------+
| 4 | M_REQ_SYN |
+-------+----------------+
| 5 | M_NEGOTIATE |
+-------+----------------+
| 6 | M_END |
+-------+----------------+
| 7 | M_WAIT |
+-------+----------------+
| 8 | M_SYNCH |
+-------+----------------+
| 9 | M_FLOOD |
+-------+----------------+
| 99 | M_INVALID |
+-------+----------------+
| 100 | O_DIVERT |
+-------+----------------+
| 101 | O_ACCEPT |
+-------+----------------+
| 102 | O_DECLINE |
+-------+----------------+
| 103 | O_IPv6_LOCATOR |
+-------+----------------+
| 104 | O_IPv4_LOCATOR |
+-------+----------------+
| 105 | O_FQDN_LOCATOR |
+-------+----------------+
| 106 | O_URI_LOCATOR |
+-------+----------------+
Table 1: Initial
Values of the "GRASP
Messages and Options"
Subregistry
The values in the "GRASP Objective Names" subregistry are UTF-8
strings that MUST NOT include a colon (":"), according to
Section 2.10.1. Future values MUST be assigned using the
Specification Required policy defined by [RFC8126].
To assist expert review of a new objective, the specification should
include a precise description of the format of the new objective,
with sufficient explanation of its semantics to allow independent
implementations. See Section 2.10.3 for more details. If the new
objective is similar in name or purpose to a previously registered
objective, the specification should explain why a new objective is
justified.
The following initial values are assigned by this document:
+================+===========+
| Objective Name | Reference |
+================+===========+
| EX0 | RFC 8990 |
+----------------+-----------+
| EX1 | RFC 8990 |
+----------------+-----------+
| EX2 | RFC 8990 |
+----------------+-----------+
| EX3 | RFC 8990 |
+----------------+-----------+
| EX4 | RFC 8990 |
+----------------+-----------+
| EX5 | RFC 8990 |
+----------------+-----------+
| EX6 | RFC 8990 |
+----------------+-----------+
| EX7 | RFC 8990 |
+----------------+-----------+
| EX8 | RFC 8990 |
+----------------+-----------+
| EX9 | RFC 8990 |
+----------------+-----------+
Table 2: Initial Values of
the "GRASP Objective
Names" Subregistry
6. References
6.1. Normative References
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119,
DOI 10.17487/RFC2119, March 1997,
<https://www.rfc-editor.org/info/rfc2119>.
[RFC3629] Yergeau, F., "UTF-8, a transformation format of ISO
10646", STD 63, RFC 3629, DOI 10.17487/RFC3629, November
2003, <https://www.rfc-editor.org/info/rfc3629>.
[RFC3986] Berners-Lee, T., Fielding, R., and L. Masinter, "Uniform
Resource Identifier (URI): Generic Syntax", STD 66,
RFC 3986, DOI 10.17487/RFC3986, January 2005,
<https://www.rfc-editor.org/info/rfc3986>.
[RFC4086] Eastlake 3rd, D., Schiller, J., and S. Crocker,
"Randomness Requirements for Security", BCP 106, RFC 4086,
DOI 10.17487/RFC4086, June 2005,
<https://www.rfc-editor.org/info/rfc4086>.
[RFC7217] Gont, F., "A Method for Generating Semantically Opaque
Interface Identifiers with IPv6 Stateless Address
Autoconfiguration (SLAAC)", RFC 7217,
DOI 10.17487/RFC7217, April 2014,
<https://www.rfc-editor.org/info/rfc7217>.
[RFC8085] Eggert, L., Fairhurst, G., and G. Shepherd, "UDP Usage
Guidelines", BCP 145, RFC 8085, DOI 10.17487/RFC8085,
March 2017, <https://www.rfc-editor.org/info/rfc8085>.
[RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC
2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174,
May 2017, <https://www.rfc-editor.org/info/rfc8174>.
[RFC8610] Birkholz, H., Vigano, C., and C. Bormann, "Concise Data
Definition Language (CDDL): A Notational Convention to
Express Concise Binary Object Representation (CBOR) and
JSON Data Structures", RFC 8610, DOI 10.17487/RFC8610,
June 2019, <https://www.rfc-editor.org/info/rfc8610>.
[RFC8949] Bormann, C. and P. Hoffman, "Concise Binary Object
Representation (CBOR)", STD 94, RFC 8949,
DOI 10.17487/RFC8949, December 2020,
<https://www.rfc-editor.org/info/rfc8949>.
[RFC8994] Eckert, T., Ed., Behringer, M., Ed., and S. Bjarnason, "An
Autonomic Control Plane (ACP)", RFC 8994,
DOI 10.17487/RFC8994, May 2021,
<https://www.rfc-editor.org/info/rfc8994>.
6.2. Informative References
[ADNCP] Stenberg, M., "Autonomic Distributed Node Consensus
Protocol", Work in Progress, Internet-Draft, draft-
stenberg-anima-adncp-00, 5 March 2015,
<https://tools.ietf.org/html/draft-stenberg-anima-adncp-
00>.
[ASA-GUIDELINES]
Carpenter, B., Ciavaglia, L., Jiang, S., and P. Peloso,
"Guidelines for Autonomic Service Agents", Work in
Progress, Internet-Draft, draft-ietf-anima-asa-guidelines-
00, 14 November 2020, <https://tools.ietf.org/html/draft-
ietf-anima-asa-guidelines-00>.
[IGCP] Behringer, M. H., Chaparadza, R., Xin, L., Mahkonen, H.,
and R. Petre, "IP based Generic Control Protocol (IGCP)",
Work in Progress, Internet-Draft, draft-chaparadza-
intarea-igcp-00, 25 July 2011,
<https://tools.ietf.org/html/draft-chaparadza-intarea-
igcp-00>.
[RFC2205] Braden, R., Ed., Zhang, L., Berson, S., Herzog, S., and S.
Jamin, "Resource ReSerVation Protocol (RSVP) -- Version 1
Functional Specification", RFC 2205, DOI 10.17487/RFC2205,
September 1997, <https://www.rfc-editor.org/info/rfc2205>.
[RFC2334] Luciani, J., Armitage, G., Halpern, J., and N. Doraswamy,
"Server Cache Synchronization Protocol (SCSP)", RFC 2334,
DOI 10.17487/RFC2334, April 1998,
<https://www.rfc-editor.org/info/rfc2334>.
[RFC2608] Guttman, E., Perkins, C., Veizades, J., and M. Day,
"Service Location Protocol, Version 2", RFC 2608,
DOI 10.17487/RFC2608, June 1999,
<https://www.rfc-editor.org/info/rfc2608>.
[RFC2865] Rigney, C., Willens, S., Rubens, A., and W. Simpson,
"Remote Authentication Dial In User Service (RADIUS)",
RFC 2865, DOI 10.17487/RFC2865, June 2000,
<https://www.rfc-editor.org/info/rfc2865>.
[RFC3416] Presuhn, R., Ed., "Version 2 of the Protocol Operations
for the Simple Network Management Protocol (SNMP)",
STD 62, RFC 3416, DOI 10.17487/RFC3416, December 2002,
<https://www.rfc-editor.org/info/rfc3416>.
[RFC3493] Gilligan, R., Thomson, S., Bound, J., McCann, J., and W.
Stevens, "Basic Socket Interface Extensions for IPv6",
RFC 3493, DOI 10.17487/RFC3493, February 2003,
<https://www.rfc-editor.org/info/rfc3493>.
[RFC4861] Narten, T., Nordmark, E., Simpson, W., and H. Soliman,
"Neighbor Discovery for IP version 6 (IPv6)", RFC 4861,
DOI 10.17487/RFC4861, September 2007,
<https://www.rfc-editor.org/info/rfc4861>.
[RFC5612] Eronen, P. and D. Harrington, "Enterprise Number for
Documentation Use", RFC 5612, DOI 10.17487/RFC5612, August
2009, <https://www.rfc-editor.org/info/rfc5612>.
[RFC5971] Schulzrinne, H. and R. Hancock, "GIST: General Internet
Signalling Transport", RFC 5971, DOI 10.17487/RFC5971,
October 2010, <https://www.rfc-editor.org/info/rfc5971>.
[RFC6206] Levis, P., Clausen, T., Hui, J., Gnawali, O., and J. Ko,
"The Trickle Algorithm", RFC 6206, DOI 10.17487/RFC6206,
March 2011, <https://www.rfc-editor.org/info/rfc6206>.
[RFC6241] Enns, R., Ed., Bjorklund, M., Ed., Schoenwaelder, J., Ed.,
and A. Bierman, Ed., "Network Configuration Protocol
(NETCONF)", RFC 6241, DOI 10.17487/RFC6241, June 2011,
<https://www.rfc-editor.org/info/rfc6241>.
[RFC6733] Fajardo, V., Ed., Arkko, J., Loughney, J., and G. Zorn,
Ed., "Diameter Base Protocol", RFC 6733,
DOI 10.17487/RFC6733, October 2012,
<https://www.rfc-editor.org/info/rfc6733>.
[RFC6762] Cheshire, S. and M. Krochmal, "Multicast DNS", RFC 6762,
DOI 10.17487/RFC6762, February 2013,
<https://www.rfc-editor.org/info/rfc6762>.
[RFC6763] Cheshire, S. and M. Krochmal, "DNS-Based Service
Discovery", RFC 6763, DOI 10.17487/RFC6763, February 2013,
<https://www.rfc-editor.org/info/rfc6763>.
[RFC6887] Wing, D., Ed., Cheshire, S., Boucadair, M., Penno, R., and
P. Selkirk, "Port Control Protocol (PCP)", RFC 6887,
DOI 10.17487/RFC6887, April 2013,
<https://www.rfc-editor.org/info/rfc6887>.
[RFC7558] Lynn, K., Cheshire, S., Blanchet, M., and D. Migault,
"Requirements for Scalable DNS-Based Service Discovery
(DNS-SD) / Multicast DNS (mDNS) Extensions", RFC 7558,
DOI 10.17487/RFC7558, July 2015,
<https://www.rfc-editor.org/info/rfc7558>.
[RFC7575] Behringer, M., Pritikin, M., Bjarnason, S., Clemm, A.,
Carpenter, B., Jiang, S., and L. Ciavaglia, "Autonomic
Networking: Definitions and Design Goals", RFC 7575,
DOI 10.17487/RFC7575, June 2015,
<https://www.rfc-editor.org/info/rfc7575>.
[RFC7576] Jiang, S., Carpenter, B., and M. Behringer, "General Gap
Analysis for Autonomic Networking", RFC 7576,
DOI 10.17487/RFC7576, June 2015,
<https://www.rfc-editor.org/info/rfc7576>.
[RFC7787] Stenberg, M. and S. Barth, "Distributed Node Consensus
Protocol", RFC 7787, DOI 10.17487/RFC7787, April 2016,
<https://www.rfc-editor.org/info/rfc7787>.
[RFC7788] Stenberg, M., Barth, S., and P. Pfister, "Home Networking
Control Protocol", RFC 7788, DOI 10.17487/RFC7788, April
2016, <https://www.rfc-editor.org/info/rfc7788>.
[RFC8040] Bierman, A., Bjorklund, M., and K. Watsen, "RESTCONF
Protocol", RFC 8040, DOI 10.17487/RFC8040, January 2017,
<https://www.rfc-editor.org/info/rfc8040>.
[RFC8126] Cotton, M., Leiba, B., and T. Narten, "Guidelines for
Writing an IANA Considerations Section in RFCs", BCP 26,
RFC 8126, DOI 10.17487/RFC8126, June 2017,
<https://www.rfc-editor.org/info/rfc8126>.
[RFC8264] Saint-Andre, P. and M. Blanchet, "PRECIS Framework:
Preparation, Enforcement, and Comparison of
Internationalized Strings in Application Protocols",
RFC 8264, DOI 10.17487/RFC8264, October 2017,
<https://www.rfc-editor.org/info/rfc8264>.
[RFC8368] Eckert, T., Ed. and M. Behringer, "Using an Autonomic
Control Plane for Stable Connectivity of Network
Operations, Administration, and Maintenance (OAM)",
RFC 8368, DOI 10.17487/RFC8368, May 2018,
<https://www.rfc-editor.org/info/rfc8368>.
[RFC8415] Mrugalski, T., Siodelski, M., Volz, B., Yourtchenko, A.,
Richardson, M., Jiang, S., Lemon, T., and T. Winters,
"Dynamic Host Configuration Protocol for IPv6 (DHCPv6)",
RFC 8415, DOI 10.17487/RFC8415, November 2018,
<https://www.rfc-editor.org/info/rfc8415>.
[RFC8991] Carpenter, B., Liu, B., Ed., Wang, W., and X. Gong,
"GeneRic Autonomic Signaling Protocol Application Program
Interface (GRASP API)", RFC 8991, DOI 10.17487/RFC8991,
May 2021, <https://www.rfc-editor.org/info/rfc8991>.
[RFC8993] Behringer, M., Ed., Carpenter, B., Eckert, T., Ciavaglia,
L., and J. Nobre, "A Reference Model for Autonomic
Networking", RFC 8993, DOI 10.17487/RFC8993, May 2021,
<https://www.rfc-editor.org/info/rfc8993>.
[RFC8995] Pritikin, M., Richardson, M., Eckert, T., Behringer, M.,
and K. Watsen, "Bootstrapping Remote Secure Key
Infrastructure (BRSKI)", RFC 8995, DOI 10.17487/RFC8995,
May 2021, <https://www.rfc-editor.org/info/rfc8995>.
Appendix A. Example Message Formats
For readers unfamiliar with CBOR, this appendix shows a number of
example GRASP messages conforming to the CDDL syntax given in
Section 4. Each message is shown three times in the following
formats:
1. CBOR diagnostic notation.
2. Similar, but showing the names of the constants. (Details of the
flag bit encoding are omitted.)
3. Hexadecimal version of the CBOR wire format.
Long lines are split for display purposes only.
A.1. Discovery Example
The initiator (2001:db8:f000:baaa:28cc:dc4c:9703:6781) multicasts a
Discovery message looking for objective EX1:
[1, 13948744, h'20010db8f000baaa28ccdc4c97036781', ["EX1", 5, 2, 0]]
[M_DISCOVERY, 13948744, h'20010db8f000baaa28ccdc4c97036781',
["EX1", F_SYNCH_bits, 2, 0]]
h'84011a00d4d7485020010db8f000baaa28ccdc4c970367818463455831050200'
A peer (2001:0db8:f000:baaa:f000:baaa:f000:baaa) responds with a
locator:
[2, 13948744, h'20010db8f000baaa28ccdc4c97036781', 60000,
[103, h'20010db8f000baaaf000baaaf000baaa', 6, 49443]]
[M_RESPONSE, 13948744, h'20010db8f000baaa28ccdc4c97036781', 60000,
[O_IPv6_LOCATOR, h'20010db8f000baaaf000baaaf000baaa',
IPPROTO_TCP, 49443]]
h'85021a00d4d7485020010db8f000baaa28ccdc4c9703678119ea6084186750
20010db8f000baaaf000baaaf000baaa0619c123'
A.2. Flood Example
The initiator multicasts a Flood Synchronization message. The single
objective has a null locator. There is no response:
[9, 3504974, h'20010db8f000baaa28ccdc4c97036781', 10000,
[["EX1", 5, 2, ["Example 1 value=", 100]],[] ] ]
[M_FLOOD, 3504974, h'20010db8f000baaa28ccdc4c97036781', 10000,
[["EX1", F_SYNCH_bits, 2, ["Example 1 value=", 100]],[] ] ]
h'85091a00357b4e5020010db8f000baaa28ccdc4c97036781192710
828463455831050282704578616d706c6520312076616c75653d186480'
A.3. Synchronization Example
Following successful discovery of objective EX2, the initiator
unicasts a Request Synchronization message:
[4, 4038926, ["EX2", 5, 5, 0]]
[M_REQ_SYN, 4038926, ["EX2", F_SYNCH_bits, 5, 0]]
h'83041a003da10e8463455832050500'
The peer responds with a value:
[8, 4038926, ["EX2", 5, 5, ["Example 2 value=", 200]]]
[M_SYNCH, 4038926, ["EX2", F_SYNCH_bits, 5, ["Example 2 value=", 200]]]
h'83081a003da10e8463455832050582704578616d706c6520322076616c75653d18c8'
A.4. Simple Negotiation Example
Following successful discovery of objective EX3, the initiator
unicasts a Request Negotiation message:
[3, 802813, ["EX3", 3, 6, ["NZD", 47]]]
[M_REQ_NEG, 802813, ["EX3", F_NEG_bits, 6, ["NZD", 47]]]
h'83031a000c3ffd8463455833030682634e5a44182f'
The peer responds with immediate acceptance. Note that no objective
is needed because the initiator's request was accepted without
change:
[6, 802813, [101]]
[M_END , 802813, [O_ACCEPT]]
h'83061a000c3ffd811865'
A.5. Complete Negotiation Example
Again the initiator unicasts a Request Negotiation message:
[3, 13767778, ["EX3", 3, 6, ["NZD", 410]]]
[M_REQ_NEG, 13767778, ["EX3", F_NEG_bits, 6, ["NZD", 410]]]
h'83031a00d214628463455833030682634e5a4419019a'
The responder starts to negotiate (making an offer):
[5, 13767778, ["EX3", 3, 6, ["NZD", 80]]]
[M_NEGOTIATE, 13767778, ["EX3", F_NEG_bits, 6, ["NZD", 80]]]
h'83051a00d214628463455833030682634e5a441850'
The initiator continues to negotiate (reducing its request, and note
that the loop count is decremented):
[5, 13767778, ["EX3", 3, 5, ["NZD", 307]]]
[M_NEGOTIATE, 13767778, ["EX3", F_NEG_bits, 5, ["NZD", 307]]]
h'83051a00d214628463455833030582634e5a44190133'
The responder asks for more time:
[7, 13767778, 34965]
[M_WAIT, 13767778, 34965]
h'83071a00d21462198895'
The responder continues to negotiate (increasing its offer):
[5, 13767778, ["EX3", 3, 4, ["NZD", 120]]]
[M_NEGOTIATE, 13767778, ["EX3", F_NEG_bits, 4, ["NZD", 120]]]
h'83051a00d214628463455833030482634e5a441878'
The initiator continues to negotiate (reducing its request):
[5, 13767778, ["EX3", 3, 3, ["NZD", 246]]]
[M_NEGOTIATE, 13767778, ["EX3", F_NEG_bits, 3, ["NZD", 246]]]
h'83051a00d214628463455833030382634e5a4418f6'
The responder refuses to negotiate further:
[6, 13767778, [102, "Insufficient funds"]]
[M_END , 13767778, [O_DECLINE, "Insufficient funds"]]
h'83061a00d2146282186672496e73756666696369656e742066756e6473'
This negotiation has failed. If either side had sent [M_END,
13767778, [O_ACCEPT]] it would have succeeded, converging on the
objective value in the preceding M_NEGOTIATE. Note that apart from
the initial M_REQ_NEG, the process is symmetrical.
Appendix B. Requirement Analysis of Discovery, Synchronization, and
Negotiation
This section discusses the requirements for discovery, negotiation,
and synchronization capabilities. The primary user of the protocol
is an Autonomic Service Agent (ASA), so the requirements are mainly
expressed as the features needed by an ASA. A single physical device
might contain several ASAs, and a single ASA might manage several
technical objectives. If a technical objective is managed by several
ASAs, any necessary coordination is outside the scope of GRASP.
Furthermore, requirements for ASAs themselves, such as the processing
of Intent [RFC7575], are out of scope for the present document.
B.1. Requirements for Discovery
D1. ASAs may be designed to manage any type of configurable device
or software, as required in Appendix B.2. A basic requirement
is therefore that the protocol can represent and discover any
kind of technical objective (as defined in Section 2.1) among
arbitrary subsets of participating nodes.
In an Autonomic Network, we must assume that when a device
starts up, it has no information about any peer devices, the
network structure, or the specific role it must play. The
ASA(s) inside the device are in the same situation. In some
cases, when a new application session starts within a device,
the device or ASA may again lack information about relevant
peers. For example, it might be necessary to set up resources
on multiple other devices, coordinated and matched to each
other so that there is no wasted resource. Security settings
might also need updating to allow for the new device or user.
The relevant peers may be different for different technical
objectives. Therefore discovery needs to be repeated as often
as necessary to find peers capable of acting as counterparts
for each objective that a discovery initiator needs to handle.
From this background we derive the next three requirements:
D2. When an ASA first starts up, it may have no knowledge of the
specific network to which it is attached. Therefore the
discovery process must be able to support any network scenario,
assuming only that the device concerned is bootstrapped from
factory condition.
D3. When an ASA starts up, it must require no configured location
information about any peers in order to discover them.
D4. If an ASA supports multiple technical objectives, relevant
peers may be different for different discovery objectives, so
discovery needs to be performed separately to find counterparts
for each objective. Thus, there must be a mechanism by which
an ASA can separately discover peer ASAs for each of the
technical objectives that it needs to manage, whenever
necessary.
D5. Following discovery, an ASA will normally perform negotiation
or synchronization for the corresponding objectives. The
design should allow for this by conveniently linking discovery
to negotiation and synchronization. It may provide an optional
mechanism to combine discovery and negotiation/synchronization
in a single protocol exchange.
D6. Some objectives may only be significant on the local link, but
others may be significant across the routed network and require
off-link operations. Thus, the relevant peers might be
immediate neighbors on the same layer 2 link, or they might be
more distant and only accessible via layer 3. The mechanism
must therefore provide both on-link and off-link discovery of
ASAs supporting specific technical objectives.
D7. The discovery process should be flexible enough to allow for
special cases, such as the following:
* During initialization, a device must be able to establish
mutual trust with autonomic nodes elsewhere in the network
and participate in an authentication mechanism. Although
this will inevitably start with a discovery action, it is a
special case precisely because trust is not yet established.
This topic is the subject of [RFC8995]. We require that
once trust has been established for a device, all ASAs
within the device inherit the device's credentials and are
also trusted. This does not preclude the device having
multiple credentials.
* Depending on the type of network involved, discovery of
other central functions might be needed, such as the Network
Operations Center (NOC) [RFC8368]. The protocol must be
capable of supporting such discovery during initialization,
as well as discovery during ongoing operation.
D8. The discovery process must not generate excessive traffic and
must take account of sleeping nodes.
D9. There must be a mechanism for handling stale discovery results.
B.2. Requirements for Synchronization and Negotiation Capability
Autonomic Networks need to be able to manage many different types of
parameters and consider many dimensions, such as latency, load,
unused or limited resources, conflicting resource requests, security
settings, power saving, load balancing, etc. Status information and
resource metrics need to be shared between nodes for dynamic
adjustment of resources and for monitoring purposes. While this
might be achieved by existing protocols when they are available, the
new protocol needs to be able to support parameter exchange,
including mutual synchronization, even when no negotiation as such is
required. In general, these parameters do not apply to all
participating nodes, but only to a subset.
SN1. A basic requirement for the protocol is therefore the ability
to represent, discover, synchronize, and negotiate almost any
kind of network parameter among selected subsets of
participating nodes.
SN2. Negotiation is an iterative request/response process that must
be guaranteed to terminate (with success or failure). While
tie-breaking rules must be defined specifically for each use
case, the protocol should have some general mechanisms in
support of loop and deadlock prevention, such as hop-count
limits or timeouts.
SN3. Synchronization must be possible for groups of nodes ranging
from small to very large.
SN4. To avoid "reinventing the wheel", the protocol should be able
to encapsulate the data formats used by existing configuration
protocols (such as Network Configuration Protocol (NETCONF) and
YANG) in cases where that is convenient.
SN5. Human intervention in complex situations is costly and error
prone. Therefore, synchronization or negotiation of parameters
without human intervention is desirable whenever the
coordination of multiple devices can improve overall network
performance. It follows that the protocol's resource
requirements must be small enough to fit in any device that
would otherwise need human intervention. The issue of running
in constrained nodes is discussed in [RFC8993].
SN6. Human intervention in large networks is often replaced by use
of a top-down network management system (NMS). It therefore
follows that the protocol, as part of the Autonomic Networking
Infrastructure, should be capable of running in any device that
would otherwise be managed by an NMS, and that it can coexist
with an NMS and with protocols such as SNMP and NETCONF.
SN7. Specific autonomic features are expected to be implemented by
individual ASAs, but the protocol must be general enough to
allow them. Some examples follow:
* Dependencies and conflicts: In order to decide upon a
configuration for a given device, the device may need
information from neighbors. This can be established through
the negotiation procedure, or through synchronization if
that is sufficient. However, a given item in a neighbor may
depend on other information from its own neighbors, which
may need another negotiation or synchronization procedure to
obtain or decide. Therefore, there are potential
dependencies and conflicts among negotiation or
synchronization procedures. Resolving dependencies and
conflicts is a matter for the individual ASAs involved. To
allow this, there need to be clear boundaries and
convergence mechanisms for negotiations. Also some
mechanisms are needed to avoid loop dependencies or
uncontrolled growth in a tree of dependencies. It is the
ASA designer's responsibility to avoid or detect looping
dependencies or excessive growth of dependency trees. The
protocol's role is limited to bilateral signaling between
ASAs and the avoidance of loops during bilateral signaling.
* Recovery from faults and identification of faulty devices
should be as automatic as possible. The protocol's role is
limited to discovery, synchronization, and negotiation.
These processes can occur at any time, and an ASA may need
to repeat any of these steps when the ASA detects an event
such as a negotiation counterpart failing.
* Since a major goal is to minimize human intervention, it is
necessary that the network can in effect "think ahead"
before changing its parameters. One aspect of this is an
ASA that relies on a knowledge base to predict network
behavior. This is out of scope for the signaling protocol.
However, another aspect is forecasting the effect of a
change by a "dry run" negotiation before actually installing
the change. Signaling a dry run is therefore a desirable
feature of the protocol.
Note that management logging, monitoring, alerts, and tools for
intervention are required. However, these can only be features
of individual ASAs, not of the protocol itself. Another
document [RFC8368] discusses how such agents may be linked into
conventional Operations, Administration, and Maintenance (OAM)
systems via an Autonomic Control Plane [RFC8994].
SN8. The protocol will be able to deal with a wide variety of
technical objectives, covering any type of network parameter.
Therefore the protocol will need a flexible and easily
extensible format for describing objectives. At a later stage,
it may be desirable to adopt an explicit information model.
One consideration is whether to adopt an existing information
model or to design a new one.
B.3. Specific Technical Requirements
T1. It should be convenient for ASA designers to define new
technical objectives and for programmers to express them,
without excessive impact on runtime efficiency and footprint.
In particular, it should be convenient for ASAs to be
implemented independently of each other as user-space programs
rather than as kernel code, where such a programming model is
possible. The classes of device in which the protocol might
run is discussed in [RFC8993].
T2. The protocol should be easily extensible in case the initially
defined discovery, synchronization, and negotiation mechanisms
prove to be insufficient.
T3. To be a generic platform, the protocol payload format should be
independent of the transport protocol or IP version. In
particular, it should be able to run over IPv6 or IPv4.
However, some functions, such as multicasting on a link, might
need to be IP version dependent. By default, IPv6 should be
preferred.
T4. The protocol must be able to access off-link counterparts via
routable addresses, i.e., must not be restricted to link-local
operation.
T5. It must also be possible for an external discovery mechanism to
be used, if appropriate for a given technical objective. In
other words, GRASP discovery must not be a prerequisite for
GRASP negotiation or synchronization.
T6. The protocol must be capable of distinguishing multiple
simultaneous operations with one or more peers, especially when
wait states occur.
T7. Intent: Although the distribution of Intent is out of scope for
this document, the protocol must not by design exclude its use
for Intent distribution.
T8. Management monitoring, alerts, and intervention: Devices should
be able to report to a monitoring system. Some events must be
able to generate operator alerts, and some provision for
emergency intervention must be possible (e.g., to freeze
synchronization or negotiation in a misbehaving device). These
features might not use the signaling protocol itself, but its
design should not exclude such use.
T9. Because this protocol may directly cause changes to device
configurations and have significant impacts on a running
network, all protocol exchanges need to be fully secured
against forged messages and man-in-the-middle attacks, and
secured as much as reasonably possible against denial-of-
service attacks. There must also be an encryption mechanism to
resist unwanted monitoring. However, it is not required that
the protocol itself provides these security features; it may
depend on an existing secure environment.
Appendix C. Capability Analysis of Current Protocols
This appendix discusses various existing protocols with properties
related to the requirements described in Appendix B. The purpose is
to evaluate whether any existing protocol, or a simple combination of
existing protocols, can meet those requirements.
Numerous protocols include some form of discovery, but these all
appear to be very specific in their applicability. Service Location
Protocol (SLP) [RFC2608] provides service discovery for managed
networks, but it requires configuration of its own servers. DNS-
Based Service Discovery (DNS-SD) [RFC6763] combined with Multicast
DNS (mDNS) [RFC6762] provides service discovery for small networks
with a single link layer. [RFC7558] aims to extend this to larger
autonomous networks, but this is not yet standardized. However, both
SLP and DNS-SD appear to target primarily application-layer services,
not the layer 2 and 3 objectives relevant to basic network
configuration. Both SLP and DNS-SD are text-based protocols.
Simple Network Management Protocol (SNMP) [RFC3416] uses a command/
response model not well suited for peer negotiation. NETCONF
[RFC6241] uses an RPC model that does allow positive or negative
responses from the target system, but this is still not adequate for
negotiation.
There are various existing protocols that have elementary negotiation
abilities, such as Dynamic Host Configuration Protocol for IPv6
(DHCPv6) [RFC8415], Neighbor Discovery (ND) [RFC4861], Port Control
Protocol (PCP) [RFC6887], Remote Authentication Dial-In User Service
(RADIUS) [RFC2865], Diameter [RFC6733], etc. Most of them are
configuration or management protocols. However, they either provide
only a simple request/response model in a master/slave context or
very limited negotiation abilities.
There are some signaling protocols with an element of negotiation.
For example, Resource ReSerVation Protocol (RSVP) [RFC2205] was
designed for negotiating quality-of-service parameters along the path
of a unicast or multicast flow. RSVP is a very specialized protocol
aimed at end-to-end flows. A more generic design is General Internet
Signalling Transport (GIST) [RFC5971]; however, it tries to solve
many problems, making it complex, and is also aimed at per-flow
signaling across many hops rather than at device-to-device signaling.
However, we cannot completely exclude extended RSVP or GIST as a
synchronization and negotiation protocol. They do not appear to be
directly usable for peer discovery.
RESTCONF [RFC8040] is a protocol intended to convey NETCONF
information expressed in the YANG language via HTTP, including the
ability to transit HTML intermediaries. While this is a powerful
approach in the context of centralized configuration of a complex
network, it is not well adapted to efficient interactive negotiation
between peer devices, especially simple ones that might not include
YANG processing already.
The Distributed Node Consensus Protocol (DNCP) [RFC7787] is defined
as a generic form of a state synchronization protocol, with a
proposed usage profile being the Home Networking Control Protocol
(HNCP) [RFC7788] for configuring Homenet routers. A specific
application of DNCP for Autonomic Networking was proposed in [ADNCP].
According to [RFC7787]:
| DNCP is designed to provide a way for each participating node to
| publish a set of TLV (Type-Length-Value) tuples (at most 64 KB)
| and to provide a shared and common view about the data
| published...
|
| DNCP is most suitable for data that changes only infrequently...
|
| If constant rapid state changes are needed, the preferable choice
| is to use an additional point-to-point channel...
Specific features of DNCP include:
* Every participating node has a unique node identifier.
* DNCP messages are encoded as a sequence of TLV objects and sent
over unicast UDP or TCP, with or without (D)TLS security.
* Multicast is used only for discovery of DNCP neighbors when lower
security is acceptable.
* Synchronization of state is maintained by a flooding process using
the Trickle algorithm. There is no bilateral synchronization or
negotiation capability.
* The HNCP profile of DNCP is designed to operate between directly
connected neighbors on a shared link using UDP and link-local IPv6
addresses.
DNCP does not meet the needs of a general negotiation protocol
because it is designed specifically for flooding synchronization.
Also, in its HNCP profile, it is limited to link-local messages and
to IPv6. However, at the minimum, it is a very interesting test case
for this style of interaction between devices without needing a
central authority, and it is a proven method of network-wide state
synchronization by flooding.
The Server Cache Synchronization Protocol (SCSP) [RFC2334] also
describes a method for cache synchronization and cache replication
among a group of nodes.
A proposal was made some years ago for an IP based Generic Control
Protocol (IGCP) [IGCP]. This was aimed at information exchange and
negotiation but not directly at peer discovery. However, it has many
points in common with the present work.
None of the above solutions appears to completely meet the needs of
generic discovery, state synchronization, and negotiation in a single
solution. Many of the protocols assume that they are working in a
traditional top-down or north-south scenario, rather than a fluid
peer-to-peer scenario. Most of them are specialized in one way or
another. As a result, we have not identified a combination of
existing protocols that meets the requirements in Appendix B. Also,
we have not identified a path by which one of the existing protocols
could be extended to meet the requirements.
Acknowledgments
A major contribution to the original draft version of this document
was made by Sheng Jiang, and significant contributions were made by
Toerless Eckert. Significant early review inputs were received from
Joel Halpern, Barry Leiba, Charles E. Perkins, and Michael
Richardson. William Atwood provided important assistance in
debugging a prototype implementation.
Valuable comments were received from Michael Behringer, Jéferson
Campos Nobre, Laurent Ciavaglia, Zongpeng Du, Yu Fu, Joel Jaeggli,
Zhenbin Li, Dimitri Papadimitriou, Pierre Peloso, Reshad Rahman,
Markus Stenberg, Martin Stiemerling, Rene Struik, Martin Thomson,
Dacheng Zhang, and participants in the Network Management Research
Group, the ANIMA Working Group, and the IESG.
Authors' Addresses
Carsten Bormann
Universität Bremen TZI
Postfach 330440
D-28359 Bremen
Germany
Email: cabo@tzi.org
Brian Carpenter (editor)
School of Computer Science
University of Auckland
PB 92019
Auckland 1142
New Zealand
Email: brian.e.carpenter@gmail.com
Bing Liu (editor)
Huawei Technologies Co., Ltd
Q14, Huawei Campus
Hai-Dian District
No.156 Beiqing Road
Beijing
100095
China