| Rfc | 6411 |
|---|
| Title | Applicability of Keying Methods for RSVP Security |
|---|
| Author | M. Behringer, F.
Le Faucheur, B. Weis |
|---|
| Date | October 2011 |
|---|
| Format: | TXT, HTML |
|---|
| Status: | INFORMATIONAL |
|---|
|
Internet Engineering Task Force (IETF) M. Behringer
Request for Comments: 6411 F. Le Faucheur
Category: Informational B. Weis
ISSN: 2070-1721 Cisco Systems
October 2011
Applicability of Keying Methods for RSVP Security
Abstract
The Resource reSerVation Protocol (RSVP) allows hop-by-hop integrity
protection of RSVP neighbors. This requires messages to be
cryptographically protected using a shared secret between
participating nodes. This document compares group keying for RSVP
with per-neighbor or per-interface keying, and discusses the
associated key provisioning methods as well as applicability and
limitations of these approaches. This document also discusses
applicability of encrypting RSVP messages.
Status of This Memo
This document is not an Internet Standards Track specification; it is
published for informational purposes.
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). Not all documents
approved by the IESG are a candidate for any level of Internet
Standard; see Section 2 of RFC 5741.
Information about the current status of this document, any errata,
and how to provide feedback on it may be obtained at
http://www.rfc-editor.org/info/rfc6411.
Copyright Notice
Copyright (c) 2011 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
(http://trustee.ietf.org/license-info) in effect on the date of
publication of this document. Please review these documents
carefully, as they describe your rights and restrictions with respect
to this document. Code Components extracted from this document must
include Simplified BSD License text as described in Section 4.e of
the Trust Legal Provisions and are provided without warranty as
described in the Simplified BSD License.
Table of Contents
1. Introduction and Problem Statement . . . . . . . . . . . . . . 3
1.1. Terminology . . . . . . . . . . . . . . . . . . . . . . . 3
2. The RSVP Hop-by-Hop Trust Model . . . . . . . . . . . . . . . 4
3. Applicability of Key Types for RSVP . . . . . . . . . . . . . 5
3.1. Per-Interface and Per-Neighbor Keys . . . . . . . . . . . 5
3.2. Group Keys . . . . . . . . . . . . . . . . . . . . . . . . 6
4. Key Provisioning Methods for RSVP . . . . . . . . . . . . . . 8
4.1. Static Key Provisioning . . . . . . . . . . . . . . . . . 8
4.2. Dynamic Keying . . . . . . . . . . . . . . . . . . . . . . 8
4.2.1. Per-Neighbor and Per-Interface Key Negotiation . . . . 8
4.2.2. Dynamic Group Key Distribution . . . . . . . . . . . . 8
5. Specific Cases Supporting Use of Group Keying . . . . . . . . 9
5.1. RSVP Notify Messages . . . . . . . . . . . . . . . . . . . 9
5.2. RSVP-TE and GMPLS . . . . . . . . . . . . . . . . . . . . 9
6. Applicability of IPsec for RSVP . . . . . . . . . . . . . . . 10
6.1. General Considerations Using IPsec . . . . . . . . . . . . 10
6.2. Comparing AH and the INTEGRITY Object . . . . . . . . . . 11
6.3. Applicability of Tunnel Mode . . . . . . . . . . . . . . . 11
6.4. Non-Applicability of Transport Mode . . . . . . . . . . . 12
6.5. Applicability of Tunnel Mode with Address Preservation . . 12
7. End-Host Considerations . . . . . . . . . . . . . . . . . . . 13
8. Applicability to Other Architectures and Protocols . . . . . . 14
9. Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . 15
10. Security Considerations . . . . . . . . . . . . . . . . . . . 16
10.1. Subverted Nodes . . . . . . . . . . . . . . . . . . . . . 16
11. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 16
12. Informative References . . . . . . . . . . . . . . . . . . . . 16
1. Introduction and Problem Statement
The Resource reSerVation Protocol [RFC2205] allows hop-by-hop
authentication of RSVP neighbors, as specified in [RFC2747]. In this
mode, an integrity object is attached to each RSVP message to
transmit a keyed message digest. This message digest allows the
recipient to verify the identity of the RSVP node that sent the
message and to validate the integrity of the message. Through the
inclusion of a sequence number in the scope of the digest, the digest
also offers replay protection.
[RFC2747] does not dictate how the key for the integrity operation is
derived. Currently, most implementations of RSVP use a statically
configured key, per interface or per neighbor. However, to manually
configure a key per router pair across an entire network is
operationally hard, especially when key changes are to be performed
on a regular basis. Effectively, many users of RSVP therefore resort
to using the same key throughout their RSVP network, and they change
it rarely, if ever, because of the operational burden. However, it
is often necessary to change keys due to network operational
requirements (e.g., change of operational staff).
This document discusses a variety of keying methods and their
applicability to different RSVP deployment environments, for both
message integrity and encryption. It is meant as a comparative guide
to understand where each RSVP keying method is best deployed and the
limitations of each method. Furthermore, it discusses how RSVP hop-
by-hop authentication is impacted in the presence of non-RSVP nodes,
or subverted nodes, in the reservation path.
"RSVP Security Properties" ([RFC4230]) provides an overview of RSVP
security, including RSVP Cryptographic Authentication [RFC2747], but
does not discuss key management. It states that "RFC 2205 assumes
that security associations are already available". The present
document focuses specifically on key management with different key
types, including group keys. Therefore, this document complements
[RFC4230].
1.1. Terminology
A security domain is defined in this document as two or more nodes
that share a common RSVP security policy.
When a key is mentioned in this document, it is a symmetric key. A
symmetric key best meets the operational requirements of RSVP
deployments and is the only type of key currently explicitly
supported for protecting RSVP messages.
2. The RSVP Hop-by-Hop Trust Model
Many protocol security mechanisms used in networks require and use
per-peer authentication. Each hop authenticates messages from its
neighbor with a shared key or certificate. This is also the model
used for RSVP. Trust in this model is transitive. Each RSVP node
trusts explicitly only its RSVP next-hop peers, through the message
digest contained in the INTEGRITY object. The next-hop RSVP speaker
in turn trusts its own peers and so on. See also "RSVP Security
Properties" [RFC4230] for more background.
The keys used for protecting RSVP messages can, in particular, be
group keys (for example, distributed via the Group Domain of
Interpretation (GDOI) [RFC6407], as discussed in [GDOI-MAC]). If a
group key is used, the authentication granularity becomes group
membership of devices, not (individual) peer authentication between
devices.
The trust an RSVP node has to another RSVP node within a common
security domain has an explicit and an implicit component.
Explicitly, the node trusts the other node to maintain the RSVP
messages intact or confidential, depending on whether authentication
or encryption (or both) is used. This means only that the message
has not been altered or seen by another, non-trusted node.
Implicitly, each node trusts the other node to maintain the level of
protection specified within that security domain. In any group-
keying scheme like GDOI, a node trusts all the other members of the
group (because the authentication is now based on group membership,
as noted above).
The RSVP protocol can operate in the presence of a non-RSVP router in
the path from the sender to the receiver. The non-RSVP hop will
ignore the RSVP message and just pass it along. The next RSVP node
can then process the RSVP message. For RSVP authentication or
encryption to work in this case, the key used for computing the RSVP
message digest needs to be shared by the two RSVP neighbors, even if
they are not IP neighbors. In the presence of non-RSVP hops, while
an RSVP node always knows the next IP hop before forwarding an RSVP
message, it does not always know the RSVP next hop. In fact, part of
the role of a Path message is precisely to discover the RSVP next hop
(and to dynamically re-discover it when it changes, for example,
because of a routing change). Thus, the presence of non-RSVP hops
impacts operation of RSVP authentication or encryption and may
influence the selection of keying approaches.
Figure 1 illustrates this scenario. R2 in this picture does not
participate in RSVP; the other nodes do. In this case, R2 will pass
on any RSVP messages unchanged and will ignore them.
----R3---
/ \
sender----R1---R2(*) R4----receiver
\ /
----R5---
(*) Non-RSVP hop
Figure 1: A Non-RSVP Node in the Path
This creates a challenge for RSVP authentication and encryption. In
the presence of a non-RSVP hop, with some RSVP messages such as a
PATH message, an RSVP router does not know the RSVP next hop for that
message at the time of forwarding it. For example, in Figure 1, R1
knows that the next IP hop for a Path message addressed to the
receiver is R2, but it does not necessarily know if the RSVP next hop
is R3 or R5. This means that per-interface and per-neighbor keys
cannot easily be used in the presence of non-RSVP routers on the path
between senders and receivers.
Section 4.3 of [RFC2747] states that "... the receiver MAY initiate
an integrity handshake with the sender". If this handshake is taking
place, it can be used to determine the identity of the next RSVP hop.
In this case, non-RSVP hops can be traversed also using per-interface
or per-neighbor keys.
Group keying will naturally work in the presence of non-RSVP routers.
Referring back to Figure 1, with group keying, R1 would use the group
key to protect a Path message addressed to the receiver and forwards
it to R2. Being a non-RSVP node, R2 will ignore and forward the Path
message to R3 or R5 depending on the current shortest path as
determined by routing. Whether it is R3 or R5, the RSVP router that
receives the Path message will be able to authenticate the message
successfully using the group key.
3. Applicability of Key Types for RSVP
3.1. Per-Interface and Per-Neighbor Keys
Most current RSVP authentication implementations support per-
interface RSVP keys. When the interface is point-to-point (and
therefore an RSVP router has only a single RSVP neighbor on each
interface), this is equivalent to per-neighbor keys in the sense that
a different key is used for each neighbor. In the point-to-point
case, the security domain is simply between the router and its
neighbor. However, when the interface is multipoint, all RSVP
speakers on a given subnet have to belong to the same security domain
and share the same key in this model. This makes it unsuitable for
deployment scenarios where nodes from different security domains are
present on a subnet, for example, Internet exchange points. In such
cases, per-neighbor keys are required, and the security domain is
between the router and its neighbor.
With per-neighbor keys, each RSVP key is bound to an interface plus a
neighbor on that interface. It allows for the existence of different
security domains on a single interface and subnet.
Per-interface and per-neighbor keys can be used within a single
security domain.
These key types can also be used between security domains, since they
are specific to a particular interface or neighbor.
Both monotonically increasing sequence number (e.g., the INTEGRITY
object simple sequence numbers [RFC2747], or the Encapsulating
Security Payload (ESP) and Authentication Header (AH) anti-replay
service [RFC4301] sequence numbers) and time-based anti-replay
methods (e.g., the INTEGRITY sequence numbers based on a clock
[RFC2747]) can be used with per-neighbor and per-interface keys.
As discussed in the previous section, per-neighbor and per-interface
keys can not be used in the presence of non-RSVP hops.
3.2. Group Keys
In the case of group keys, all members of a group of RSVP nodes share
the same key. This implies that a node uses the same key regardless
of the next RSVP hop that will process the message (within the group
of nodes sharing the particular key). It also implies that a node
will use the same key on the receiving as on the sending side (when
exchanging RSVP messages within the group).
Group keys apply naturally to intra-domain RSVP authentication, where
all RSVP nodes are part of the same security domain and implicitly
trust each other. The nodes also extended trust to a group key
server (GKS), which administers group membership and provides group
keys. This is represented in Figure 2.
......GKS1.............
: : : : :
: : : : :
source--R1--R2--R3-----destination
| |
|<-----domain 1----------------->|
Figure 2: A Group Key Server within a Single Security Domain
A single group key cannot normally be used to cover multiple security
domains because, by definition, the different domains do not trust
each other. They would therefore not be willing to trust the same
group key server. For a single group key to be used in several
security domains, there is a need for a single group key server,
which is trusted by both sides. While this is theoretically
possible, in practice it is unlikely that there is a single such
entity trusted by both domains. Figure 3 illustrates this setup.
...............GKS1....................
: : : : : : : :
: : : : : : : :
source--R1--R2--R3--------R4--R5--R6--destination
| | | |
|<-----domain 1--->| |<-------domain 2----->|
Figure 3: A Single Group Key Server across Security Domains
A more practical approach for RSVP operation across security domains,
is to use a separate group key server for each security domain, and
to use per-interface or per-neighbor keys between the two domains
(thus comprising a third security domain). Figure 4 shows this
setup.
....GKS1...... ....GKS2.........
: : : : : : : :
: : : : : : : :
source--R1--R2--R3--------R4--R5--R6--destination
| | | |
|<-----domain 1--->| |<-------domain 2----->|
|<-->|
domain 3
Figure 4: A Group Key Server per Security Domain
As discussed in Section 2, group keying can be used in the presence
of non-RSVP hops.
Because a group key may be used to verify messages from different
peers, monotonically increasing sequence number methods are not
appropriate. Time-based anti-replay methods (e.g., the INTEGRITY
sequence numbers based on a clock [RFC2747]) can be used with group
keys.
4. Key Provisioning Methods for RSVP
4.1. Static Key Provisioning
Static keys are preconfigured, either manually or through a network
management system. The simplest way to implement RSVP authentication
is to use static keys. Static keying can be used with per-interface
keys, per-neighbor keys, or group keys.
The provisioning of static keys requires either manual operator
intervention on each node or a network management system performing
the same task. Time synchronization of static key provisioning and
changes is critical in order to avoid inconsistent keys within a
security domain.
Static key provisioning is therefore not an ideal model in a large
network.
Often, the number of interconnection points across two domains where
RSVP is allowed to transit is relatively small and well controlled.
Also, the different domains may not be in a position to use an
infrastructure trusted by both domains to update keys on both sides.
Thus, statically provisioned keys may be applicable to inter-domain
RSVP authentication.
Since it is not feasible to carry out a key change at the exact same
time in communicating RSVP nodes, some grace period needs to be
implemented during which an RSVP node will accept both the old and
the new key. Otherwise, RSVP operation would suffer interruptions.
(Also with dynamic keying approaches, there can be a grace period
where two keys are valid at the same time; however, the grace period
in manual keying tends to be significantly longer than with dynamic
key rollover schemes.)
4.2. Dynamic Keying
4.2.1. Per-Neighbor and Per-Interface Key Negotiation
To avoid the problem of manual key provisioning and updates in static
key deployments, key negotiation between RSVP neighbors could be used
to derive either per-interface or per-neighbor keys.
4.2.2. Dynamic Group Key Distribution
With this approach, group keys are dynamically distributed among a
set of RSVP routers. For example, [GDOI-MAC] describes a mechanism
to distribute group keys to a group of RSVP speakers, using GDOI
[RFC6407]. In this solution, each RSVP node requests a group key
from a key server as part of an encrypted and integrity-protected key
agreement protocol. Once the key server has authenticated and
authorized the RSVP nodes, it distributes a group key to the group
member. The authentication in this model can be based on public key
mechanisms, thereby avoiding the need for static key provisioning.
5. Specific Cases Supporting Use of Group Keying
5.1. RSVP Notify Messages
[RFC3473] introduces the Notify message and allows such messages to
be sent in a non-hop-by-hop fashion. As discussed in the Security
Considerations section of [RFC3473], this can interfere with RSVP's
hop-by-hop integrity and authentication model. [RFC3473] describes
how standard IPsec-based integrity and authentication can be used to
protect Notify messages.
Group keying may allow use of regular RSVP authentication [RFC2747]
for protection of non-hop-by-hop Notify messages. For example, RSVP
Notify messages commonly used for traffic engineering in MPLS
networks are non-hop-by-hop messages. Such messages may be sent from
an ingress node directly to an egress node. Group keying in such a
case avoids the establishment of node-to-node keying when node-to-
node keying is not otherwise used.
5.2. RSVP-TE and GMPLS
Use of RSVP authentication for RSVP-TE [RFC3209] and for RSVP-TE Fast
Reroute [RFC4090] deserves additional considerations.
With the facility backup method of Fast Reroute, a backup tunnel from
the Point of Local Repair (PLR) to the Merge Point (MP) is used to
protect Label Switched Paths (protected LSPs) against the failure of
a facility (e.g., a router) located between the PLR and the MP.
During the failure of the facility, the PLR redirects a protected LSP
inside the backup tunnel and as a result, the PLR and MP then need to
exchange RSVP control messages between each other (e.g., for the
maintenance of the protected LSP). Some of the RSVP messages between
the PLR and MP are sent over the backup tunnel (e.g., a Path message
from PLR to MP), while some are directly addressed to the RSVP node
(e.g., a Resv message from MP to PLR). During the rerouted period,
the PLR and the MP effectively become RSVP neighbors, while they may
not be directly connected to each other and thus do not behave as
RSVP neighbors in the absence of failure. This point is raised in
the Security Considerations section of [RFC4090] that says: "Note
that the facility backup method requires that a PLR and its selected
merge point trust RSVP messages received from each other". Such
environments may benefit from group keying. A group key can be used
among a set of routers enabled for Fast Reroute, thereby easily
ensuring that PLR and MP authenticate messages from each other,
without requiring prior specific configuration of keys, or activation
of key update mechanism, for every possible pair of PLR and MP.
Where RSVP-TE or RSVP-TE Fast Reroute is deployed across AS
boundaries (see [RFC4216]), the considerations presented above in
Sections 3.1 and 3.2 apply, such that per-interface or per-neighbor
keys can be used between two RSVP neighbors in different ASes
(independently of the keying method used by the RSVP router to talk
to the RSVP routers in the same AS).
[RFC4875] specifies protocol extensions for support of Point-to-
Multipoint (P2MP) RSVP-TE. RSVP message integrity mechanisms for
hop-by-hop RSVP signaling apply to the hop-by-hop P2MP RSVP-TE
signaling (see the Security Considerations in [RFC4875]).
[RFC4206] defines LSP Hierarchy with GMPLS TE and uses non-hop-by-hop
signaling. Because it reuses LSP Hierarchy procedures for some of
its operations, P2MP RSVP-TE also uses non-hop-by-hop signaling.
Both LSP hierarchy and P2MP RSVP-TE rely on the security mechanisms
defined in [RFC3473] and [RFC4206] for non hop-by-hop RSVP-TE
signaling. Group keying can simplify protection of non-hop-by-hop
signaling for LSP Hierarchy and P2MP RSVP-TE.
6. Applicability of IPsec for RSVP
6.1. General Considerations Using IPsec
The discussions about the various keying methods in this document are
also applicable when using IPsec [RFC4301] to protect RSVP. Section
1.2 of [RFC2747] states that IPsec is not an optimal choice to
protect RSVP. The key argument is that an IPsec security association
(SA) and an RSVP SA are not based on the same parameters.
Nevertheless, IPsec can be used to protect RSVP. The Security Policy
Database (SPD) traffic selectors for related RSVP flows will not be
constant. In some cases, the source and destination addresses are
end hosts, and sometimes they are RSVP routers. Therefore, traffic
selectors in the SPD are expected to specify ANY for the source
address and destination addresses, and to specify IP protocol 46
(RSVP).
"The Multicast Group Security Architecture" [RFC3740] defines in
detail a "Group Security Association" (GSA). This definition is also
applicable in the context discussed here, and allows the use of IPsec
for RSVP. The existing GDOI specification [RFC6407] manages group
security associations, which can be used by IPsec. An example GDOI
policy would be to encrypt or authenticate all packets of the RSVP
protocol itself (IP protocol 46). A router implementing GDOI and the
AH and/or ESP protocols is therefore able to implement this policy.
Because the traffic selectors for an SA cannot be predicted, SA
lookup is expected to use only the Security Parameters Index (SPI)
(or SPI plus protocol).
6.2. Comparing AH and the INTEGRITY Object
The INTEGRITY object defined by [RFC2747] provides integrity
protection for RSVP also in a group-keying context, as discussed
above. AH [RFC4302] is an alternative method to provide integrity
protection for RSVP packets.
The RSVP INTEGRITY object protects the entire RSVP message, but does
not protect the IP header of the packet nor the IP options (in IPv4)
or extension headers (in IPv6).
AH tunnel mode (transport mode is not applicable; see Section 6.4)
protects the entire original IP packet, including the IP header of
the original IP packet ("inner header"), IP options or extension
headers, plus the entire RSVP packet. It also protects the immutable
fields of the outer header.
The difference between the two schemes in terms of covered fields is
therefore whether the IPv4 header and IP options, or the IPv6 header
and extension headers, of the original IP packet are protected (as is
the case with AH) or not (as is the case with the INTEGRITY object).
Also, AH covers the immutable fields of the outer header.
As described in the next section, IPsec tunnel mode cannot be applied
for RSVP traffic in the presence of non-RSVP nodes; therefore, the
security associations in both cases, AH and INTEGRITY object, are
between the same RSVP neighbors. From a keying point of view, both
approaches are therefore comparable.
6.3. Applicability of Tunnel Mode
IPsec tunnel mode encapsulates the original packet, prepending a new
IP header plus an ESP or AH sub-header. The entire original packet
plus the ESP/AH sub-header is secured. However, in the case of ESP,
the new, outer IP header is not cryptographically secured in this
process.
Protecting RSVP packets with IPsec tunnel mode works with any of the
keying methods described above (per-interface, per-neighbor, or group
keying), as long as there are no non-RSVP nodes on the path (however,
see the group-keying considerations below). For RSVP messages to be
visible and considered at each hop, such a tunnel would not cross
routers, but each RSVP node would establish a tunnel with each of its
peers, effectively leading to link protection.
In the presence of a non-RSVP hop, tunnel mode cannot be applied
because a router upstream from a non-RSVP hop does not know the next
RSVP hop, and thus cannot apply the correct tunnel header. The same
situation applies to a host attached to the network by a non-RSVP-
enabled first hop. This is independent of the key type used.
The use of group keying with ESP tunnel mode where a security gateway
places a peer security gateway address as the destination of the ESP
packet has consequences. In particular, if a man-in-the-middle
attacker redirects the ESP-protected reservation to a different
security gateway, the receiving security gateway cannot detect that
the destination address was changed. However, it has received and
will act upon an RSVP reservation that will be routed along an
unintended path. Because RSVP routers encountering the RSVP packet
path will not be aware that this is an unintended path, they will act
upon it, and the resulting RSVP state along both the intended path
and unintended path will be incorrect. Therefore, using group keying
with ESP tunnel mode is not recommended, unless address preservation
is used (see Section 6.5).
6.4. Non-Applicability of Transport Mode
IPsec transport mode, as defined in [RFC4303] is not suitable for
securing RSVP Path messages, since those messages preserve the
original source and destination. [RFC4301] states explicitly that
"the use of transport mode by an intermediate system (e.g., a
security gateway) is permitted only when applied to packets whose
source address (for outbound packets) or destination address (for
inbound packets) is an address belonging to the intermediate system
itself". This would not be the case for RSVP Path messages.
6.5. Applicability of Tunnel Mode with Address Preservation
When the identity of the next-hop RSVP peer is not known, it is not
possible to use a tunnel-endpoint destination address in the tunnel
mode outer IP header. Section 3.1 of "Multicast Extensions to the
Security Architecture for the Internet Protocol" [RFC5374] defines a
new tunnel mode: tunnel mode with address preservation. This mode
copies the destination and optionally the source address from the
inner header to the outer header. Therefore, the encapsulated packet
will have the same destination address as the original packet, and
will be normally subject to the same routing decisions. While
[RFC5374] is focusing on multicast environments, tunnel mode with
address preservation can be used also to protect unicast traffic in
conjunction with group keying. In this tunnel mode, the RSVP
speakers act as security gateways because they maintain the original
end-system addresses of the RSVP packets in the tunnel mode outer IP
header. This addressing scheme is used by RSVP to ensure that the
packets continue along the routed path toward the destination end
host.
Tunnel mode with address preservation, in conjunction with group
keying, allows the use of AH or ESP for protection of RSVP even in
cases where non-RSVP nodes have to be traversed. This is because it
allows routing of the IPsec-protected packet through the non-RSVP
nodes in the same way as if it were not IPsec protected.
When used with group keying, tunnel mode with address preservation
can be used to mitigate redirection attacks where a man-in-the-middle
modifies the destination of the outer IP header of the tunnel mode
packet. The inbound processing rules for tunnel mode with address
preservation (Section 5.2 of [RFC5374]) require that the receiver
verify that the addresses in the outer IP header and the inner IP
header are consistent. Therefore, the attack can be detected, and
RSVP reservations will not proceed along an unintended path.
7. End-Host Considerations
Unless RSVP Proxy entities [RFC5945] are used, RSVP signaling is
controlled by end systems and not routers. As discussed in
[RFC4230], RSVP allows both user-based security and host-based
security. User-based authentication aims at "providing policy based
admission control mechanism based on user identities or application"
[RFC3182]. To identify the user or the application, a policy element
called AUTH_DATA, which is contained in the POLICY_DATA object, is
created by the RSVP daemon at the user's host and transmitted inside
the RSVP message. This way, a user may authenticate to the Policy
Decision Point (or directly to the first-hop router). Host-based
security relies on the same mechanisms as between routers (i.e., the
INTEGRITY object) as specified in [RFC2747]. For host-based
security, per-interface or per-neighbor keys may be used; however,
key management with statically provisioned keys can be difficult in a
large-scale deployment, as described in Section 4. In principle, an
end host can also be part of a group key scheme, such as GDOI. If
the end systems are part of the same security domain as the RSVP hops
in the network, group keying can be extended to include the end
systems. If the end systems and the network are in different zones
of trust, group keying cannot be used.
8. Applicability to Other Architectures and Protocols
While, so far, this document discusses only RSVP security assuming
the traditional RSVP model as defined by [RFC2205] and [RFC2747], the
analysis is also applicable to other RSVP deployment models as well
as to similar protocols. These include the following:
o "Aggregation of RSVP for IPv4 and IPv6 Reservations" [RFC3175]:
This scheme defines aggregation of individual RSVP reservations,
and discusses use of RSVP authentication for the signaling
messages. Group keying is applicable to this scheme, particularly
when automatic Deaggregator discovery is used, since in that case,
the Aggregator does not know ahead of time which Deaggregator will
intercept the initial end-to-end RSVP Path message.
o "Generic Aggregate Resource ReSerVation Protocol (RSVP)
Reservations" [RFC4860]: This document also discusses aggregation
of individual RSVP reservations. Here again, group keying applies
and is mentioned in the Security Considerations section.
o "Aggregation of Resource ReSerVation Protocol (RSVP) Reservations
over MPLS TE/DS-TE Tunnels" [RFC4804]: This scheme also defines a
form of aggregation of RSVP reservation, but this time over
MPLS-TE tunnels. Similarly, group keying may be used in such an
environment.
o "Pre-Congestion Notification (PCN) Architecture" [RFC5559]:
defines an architecture for flow admission and termination based
on aggregated pre-congestion information. One deployment model
for this architecture is based on Intserv over Diffserv: the
Diffserv region is PCN-enabled. Also, RSVP signaling is used end-
to-end, but the PCN-domain is a single RSVP hop, i.e., only the
PCN-boundary-nodes process RSVP messages. In this scenario, RSVP
authentication may be required among PCN-boundary-nodes, and the
considerations about keying approaches discussed earlier in this
document apply. In particular, group keying may facilitate
operations since the ingress PCN-boundary-node does not
necessarily know ahead of time which PCN-egress-node will
intercept and process the initial end-to-end Path message. From
the viewpoint of securing end-to-end RSVP in this scenario (from
the end host to the PCN-ingress-node, to the PCN-egress-node, to
the other end host), there are a lot of similarities in scenarios
involving RSVP Aggregation over aggregate RSVP reservations
[RFC3175] [RFC4860], RSVP Aggregation over MPLS-TE tunnels
[RFC4804], and RSVP (Aggregation) over PCN ingress-egress
aggregates.
9. Summary
The following table summarizes the various approaches for RSVP
keying, and their applicability to various RSVP scenarios. In
particular, such keying can be used for RSVP authentication (e.g.,
using the RSVP INTEGRITY object or AH) and/or for RSVP encryption
(e.g., using ESP in tunnel mode).
+----------------------------+-----------------+--------------------+
| | per-neighbor / | group keys |
| | per-interface | |
| | keys | |
+----------------------------+-----------------+--------------------+
| Works intra-domain | Yes | Yes |
| Works inter-domain | Yes | No |
| Works over non-RSVP hops | No | Yes (1) |
| Dynamic keying | Yes (IKE) | Yes (e.g., GDOI) |
+----------------------------+-----------------+--------------------+
Table 1: Overview of Keying Approaches and Their Applicability
(1): RSVP integrity with group keys works over non-RSVP nodes; RSVP
encryption with ESP and RSVP authentication with AH work over
non-RSVP nodes in tunnel mode with address preservation; RSVP
encryption with ESP and RSVP authentication with AH do not work
over non-RSVP nodes in tunnel mode.
We also make the following observations:
o All key types can be used statically, or with dynamic key
negotiation. This impacts the manageability of the solution, but
not the applicability itself.
o For encryption of RSVP messages, IPsec ESP in tunnel mode can be
used.
o There are some special cases in RSVP, like non-RSVP hosts, the
Notify message (as discussed in Section 5.1, the various RSVP
deployment models discussed in Section 8, and MPLS Traffic
Engineering and GMPLS discussed in Section 5.2, which would
benefit from a group-keying approach.
10. Security Considerations
This entire document discusses RSVP security; this section describes
specific security considerations relating to subverted RSVP nodes.
10.1. Subverted Nodes
An undetected subverted node, for example, one that an intruder has
gained control over, is still implicitly a trusted node. However, it
is a threat to the security of RSVP. Since RSVP authentication is
hop by hop and not end to end, a subverted node in the path breaks
the chain of trust. This is, to a large extent, independent of the
type of keying used.
For per-interface or per-neighbor keying, the subverted node can now
introduce fake messages to its neighbors. This can be used in a
variety of ways, for example, by changing the receiver address in the
Path message or by generating fake Path messages. This allows path
states to be created on every RSVP router along any arbitrary path
through the RSVP domain. That in itself could result in a form of
denial of service by allowing exhaustion of some router resources
(e.g., memory). The subverted node could also generate fake Resv
messages upstream corresponding to valid Path states. In doing so,
the subverted node can reserve excessive amounts of bandwidth thereby
possibly performing a denial-of-service attack.
Group keying allows the additional abuse of sending fake RSVP
messages to any node in the RSVP domain, not just adjacent RSVP
nodes. However, in practice, this can be achieved to a large extent
also with per-neighbor or per-interface keys, as discussed above.
Therefore, the impact of subverted nodes on the path is comparable
for all keying schemes discussed here (per-interface, per-neighbor,
and group keys).
11. Acknowledgements
The authors would like to thank everybody who provided feedback on
this document. Specific thanks to Bob Briscoe, Hannes Tschofenig,
Ran Atkinson, Stephen Kent, and Kenneth G. Carlberg.
12. Informative References
[GDOI-MAC] Weis, B. and S. Rowles, "GDOI Generic Message
Authentication Code Policy", Work in Progress, September
2011.
[RFC2205] Braden, B., Zhang, L., Berson, S., Herzog, S., and S.
Jamin, "Resource ReSerVation Protocol (RSVP) -- Version 1
Functional Specification", RFC 2205, September 1997.
[RFC2747] Baker, F., Lindell, B., and M. Talwar, "RSVP
Cryptographic Authentication", RFC 2747, January 2000.
[RFC3175] Baker, F., Iturralde, C., Le Faucheur, F., and B. Davie,
"Aggregation of RSVP for IPv4 and IPv6 Reservations", RFC
3175, September 2001.
[RFC3182] Yadav, S., Yavatkar, R., Pabbati, R., Ford, P., Moore,
T., Herzog, S., and R. Hess, "Identity Representation for
RSVP", RFC 3182, October 2001.
[RFC3209] Awduche, D., Berger, L., Gan, D., Li, T., Srinivasan, V.,
and G. Swallow, "RSVP-TE: Extensions to RSVP for LSP
Tunnels", RFC 3209, December 2001.
[RFC3473] Berger, L., "Generalized Multi-Protocol Label Switching
(GMPLS) Signaling Resource ReserVation Protocol-Traffic
Engineering (RSVP-TE) Extensions", RFC 3473, January
2003.
[RFC3740] Hardjono, T. and B. Weis, "The Multicast Group Security
Architecture", RFC 3740, March 2004.
[RFC4090] Pan, P., Swallow, G., and A. Atlas, "Fast Reroute
Extensions to RSVP-TE for LSP Tunnels", RFC 4090, May
2005.
[RFC4206] Kompella, K. and Y. Rekhter, "Label Switched Paths (LSP)
Hierarchy with Generalized Multi-Protocol Label Switching
(GMPLS) Traffic Engineering (TE)", RFC 4206, October
2005.
[RFC4216] Zhang, R. and J. Vasseur, "MPLS Inter-Autonomous System
(AS) Traffic Engineering (TE) Requirements", RFC 4216,
November 2005.
[RFC4230] Tschofenig, H. and R. Graveman, "RSVP Security
Properties", RFC 4230, December 2005.
[RFC4301] Kent, S. and K. Seo, "Security Architecture for the
Internet Protocol", RFC 4301, December 2005.
[RFC4302] Kent, S., "IP Authentication Header", RFC 4302, December
2005.
[RFC4303] Kent, S., "IP Encapsulating Security Payload (ESP)", RFC
4303, December 2005.
[RFC4804] Le Faucheur, F., "Aggregation of Resource ReSerVation
Protocol (RSVP) Reservations over MPLS TE/DS-TE Tunnels",
RFC 4804, February 2007.
[RFC4860] Le Faucheur, F., Davie, B., Bose, P., Christou, C., and
M. Davenport, "Generic Aggregate Resource ReSerVation
Protocol (RSVP) Reservations", RFC 4860, May 2007.
[RFC4875] Aggarwal, R., Papadimitriou, D., and S. Yasukawa,
"Extensions to Resource Reservation Protocol - Traffic
Engineering (RSVP-TE) for Point-to-Multipoint TE Label
Switched Paths (LSPs)", RFC 4875, May 2007.
[RFC5374] Weis, B., Gross, G., and D. Ignjatic, "Multicast
Extensions to the Security Architecture for the Internet
Protocol", RFC 5374, November 2008.
[RFC5559] Eardley, P., "Pre-Congestion Notification (PCN)
Architecture", RFC 5559, June 2009.
[RFC5945] Le Faucheur, F., Manner, J., Wing, D., and A. Guillou,
"Resource Reservation Protocol (RSVP) Proxy Approaches",
RFC 5945, October 2010.
[RFC6407] Weis, B., Rowles, S., and T. Hardjono, "The Group Domain
of Interpretation", RFC 6407, October 2011.
Authors' Addresses
Michael H. Behringer
Cisco Systems
Village d'Entreprises Green Side
400, Avenue Roumanille, Batiment T 3
Biot - Sophia Antipolis 06410
France
EMail: mbehring@cisco.com
URI: http://www.cisco.com
Francois Le Faucheur
Cisco Systems
Village d'Entreprises Green Side
400, Avenue Roumanille, Batiment T 3
Biot - Sophia Antipolis 06410
France
EMail: flefauch@cisco.com
URI: http://www.cisco.com
Brian Weis
Cisco Systems
170 W. Tasman Drive
San Jose, California 95134-1706
USA
EMail: bew@cisco.com
URI: http://www.cisco.com