| Rfc | 6059 |
|---|
| Title | Simple Procedures for Detecting Network Attachment in IPv6 |
|---|
| Author | S.
Krishnan, G. Daley |
|---|
| Date | November 2010 |
|---|
| Format: | TXT, HTML |
|---|
| Status: | PROPOSED STANDARD |
|---|
|
Internet Engineering Task Force (IETF) S. Krishnan
Request for Comments: 6059 Ericsson
Category: Standards Track G. Daley
ISSN: 2070-1721 Netstar Logicalis
November 2010
Simple Procedures for Detecting Network Attachment in IPv6
Abstract
Detecting Network Attachment allows hosts to assess if its existing
addressing or routing configuration is valid for a newly connected
network. This document provides simple procedures for Detecting
Network Attachment in IPv6 hosts, and procedures for routers to
support such services.
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 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/rfc6059.
Copyright Notice
Copyright (c) 2010 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 . . . . . . . . . . . . . . . . . . . . . . . . . 3
1.1. Goals . . . . . . . . . . . . . . . . . . . . . . . . . . 3
1.2. Applicability . . . . . . . . . . . . . . . . . . . . . . 3
1.3. Link Identification Model . . . . . . . . . . . . . . . . 4
1.4. DNA Overview . . . . . . . . . . . . . . . . . . . . . . . 4
1.5. Working Assumptions . . . . . . . . . . . . . . . . . . . 5
2. Requirements Notation . . . . . . . . . . . . . . . . . . . . 5
3. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 6
4. The Simple DNA Address Table (SDAT) . . . . . . . . . . . . . 7
5. Host Operations . . . . . . . . . . . . . . . . . . . . . . . 7
5.1. On Receipt of a Router Advertisement . . . . . . . . . . . 7
5.2. After Assignment of a DHCPv6 Address . . . . . . . . . . . 8
5.3. Steps Involved in Detecting Link Change . . . . . . . . . 8
5.4. Link-Layer Indication . . . . . . . . . . . . . . . . . . 8
5.5. Sending Neighbor Discovery probes . . . . . . . . . . . . 9
5.5.1. Sending Router Solicitations . . . . . . . . . . . . . 9
5.5.2. Sending Neighbor Solicitations . . . . . . . . . . . . 9
5.5.3. Concurrent Sending of RS and NS Probes . . . . . . . . 9
5.5.4. Initiating DHCPv6 Exchange . . . . . . . . . . . . . . 9
5.6. Contents of the Neighbor Discovery Messages . . . . . . . 10
5.6.1. Neighbor Solicitation Messages . . . . . . . . . . . . 10
5.6.2. Router Solicitation Messages . . . . . . . . . . . . . 10
5.7. Response Gathering . . . . . . . . . . . . . . . . . . . . 11
5.7.1. Receiving Neighbor Advertisements . . . . . . . . . . 11
5.7.2. Receiving Router Advertisements . . . . . . . . . . . 11
5.7.3. Conflicting Results . . . . . . . . . . . . . . . . . 11
5.8. Further Host Operations . . . . . . . . . . . . . . . . . 11
5.9. On Connecting to a New Point of Attachment . . . . . . . . 12
5.10. Periodic Maintenance of the SDAT . . . . . . . . . . . . . 12
5.11. Recommended Retransmission Behavior . . . . . . . . . . . 12
6. Pseudocode for Simple DNA . . . . . . . . . . . . . . . . . . 13
7. Constants . . . . . . . . . . . . . . . . . . . . . . . . . . 15
8. Relationship to DNAv4 . . . . . . . . . . . . . . . . . . . . 15
9. Security Considerations . . . . . . . . . . . . . . . . . . . 15
10. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 16
11. References . . . . . . . . . . . . . . . . . . . . . . . . . . 17
11.1. Normative References . . . . . . . . . . . . . . . . . . . 17
11.2. Informative References . . . . . . . . . . . . . . . . . . 17
Appendix A. Issues with Confirming Manually Assigned Addresses . 18
1. Introduction
Hosts require procedures to simply and reliably identify if they have
moved to a network to which they had been recently connected. In
order to detect reconnection to a previously visited network, router
and neighbor discovery messages are used to collect reachability and
configuration information. This information is used to detect if the
host has attached to a link for which it may still have valid address
and other configuration information, and which it can use until it
receives confirmation through either the Neighbor Discovery protocol
or DHCPv6.
This document incorporates feedback from host and router operating
systems implementors, which seeks to make implementation and adoption
of IPv6 change detection procedures simple for general use.
1.1. Goals
The goal of this document is to specify a simple procedure for
Detecting Network Attachment (Simple DNA) that has the following
characteristics.
o Routers do not have to be modified to support this scheme.
o The most common use cases are optimized.
o In the worst case, detection latency is equal to that of standard
neighbor discovery so that performance is never degraded.
o False positives are not acceptable. A host must not wrongly
conclude that it has reattached to a previously visited network.
o False negatives are acceptable. A host may fail to identify a
previously visited link correctly and attempt to acquire fresh
addressing and configuration information.
1.2. Applicability
The Simple DNA protocol provides substantial benefits over standard
neighbor discovery procedures [RFC4861] in some scenarios and does
not provide any benefit at all in certain other scenarios. This is
intentional as Simple DNA was designed for simplicity rather than
completeness. In particular, the Simple DNA protocol provides
maximum benefits when a host moves between a small set of known
links. When a host moves to a completely new link that is previously
unknown, the performance of the Simple DNA protocol will be identical
to that using standard neighbor discovery procedures [RFC4861]. In
this case, the main benefit of the Simple DNA protocol is to
immediately flush out the inoperable addresses and configuration
instead of timing them out. The Simple DNA procedure provides
support for addresses configured using either IPv6 Stateless Address
Autoconfiguration [RFC4862] or DHCPv6 [RFC3315]. It does not support
manually configured addresses since they are not widely used and can
cause unpredictable results and/or aggressive probing behavior (see
Appendix A).
1.3. Link Identification Model
Earlier methods of Detecting Network Attachment, e.g., the procedure
defined in [DNA-PROTOCOL], relied on detecting whether the host was
still connected to the same link. If the host was attached to the
same link, all information related to the link such as the routers,
prefixes, and configuration parameters was considered to be valid.
The Simple DNA protocol follows an alternate approach where it relies
on probing each previously known router to determine whether to use
information learnt from THAT router. This allows Simple DNA to probe
routers learnt from multiple earlier attachments to optimize movement
between a known set of links.
1.4. DNA Overview
Detecting Network Attachment is performed by hosts after detecting a
link-layer "up" indication. The host uses a combination of unicast
Neighbor Solicitations (NSs) and multicast Router Solicitations (RSs)
in order to determine whether previously encountered routers are
present on the link, in which case an existing configuration can be
reused. If previously encountered routers are not present, then
either IPv6 Stateless Address Autoconfiguration and/or DHCPv6 is used
for configuration.
Hosts implementing Simple DNA may also send DHCPv6 packets, as
described in Section 5.5.4. Since Simple DNA does not modify the
DHCPv6 protocol or state machine, the operation of DHCPv6 is
unchanged.
Routers that follow the standard neighbor discovery procedure
described in [RFC4861] will delay the router advertisement (RA) by a
random period between 0 and MAX_RA_DELAY_TIME (defined to be 500 ms)
as described in Section 6.2.6 of [RFC4861]. In addition, consecutive
RAs sent to the all-nodes multicast address are rate limited to no
more than one advertisement every MIN_DELAY_BETWEEN_RAS (defined to
be 3 seconds). This will result in a worst-case delay of 3.5 seconds
in the absence of any packet loss.
Hosts implementing Simple DNA can detect the presence of a previously
encountered router using unicast Neighbor Solicitations. As a
result, where the host with a valid configuration is returning to a
previously encountered link, delays in the sending of a Router
Advertisement (RA) will not delay configuration as long as NS probing
is successful. However, in situations where the host is attaching to
a link for the first time, or where it does not have a valid IP
address on the link, it will be dependent on the receipt of an RA for
stateless autoconfiguration. In these situations, delays in the
receipt of an RA can be significant and may result in service
disruption.
1.5. Working Assumptions
There are a series of assumptions about the network environment that
underpin these procedures.
o The combination of the link-layer address and the link-local IPv6
address of a router is unique across links.
o Hosts receive indications when a link layer comes up. Without
this, they would not know when to commence the DNA procedure.
If these assumptions do not hold, host change detection systems will
not function optimally. In that case, they may occasionally detect
change spuriously or experience some delay in Detecting Network
Attachment. The delays so experienced will be no longer than those
caused by following the standard neighbor discovery procedure
described in [RFC4861].
2. Requirements Notation
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in [RFC2119].
3. Terminology
+---------------------+---------------------------------------------+
| Term | Definition |
+---------------------+---------------------------------------------+
| Valid IPv6 address | An IPv6 address configured on the node that |
| | has a valid lifetime greater than zero. |
| | |
| Operable IPv6 | An IPv6 address configured on the node that |
| address | can be used safely on the current link. |
| | |
| Router identifier | Identifier formed using the link-local |
| | address of a router along with its |
| | link-layer address. |
| | |
| D-Flag | Flag indicating whether the address was |
| | obtained using Stateless Address |
| | Autoconfiguration (SLAAC) or DHCPv6. If it |
| | is set to 0, then SLAAC was used to |
| | configure the address. If it is set to 1, |
| | then DHCPv6 was used to configure the |
| | address. |
| | |
| O-Flag | Flag indicating whether the address is |
| | operable. If it is set to 0, the address |
| | is inoperable. If it is set to 1, the |
| | address is operable. |
| | |
| S-Flag | Flag indicating whether SEND [RFC3971] was |
| | used in the Router Advertisement that |
| | resulted in the creation/modification of |
| | this SDAT entry. If it is set to 0, then |
| | SEND was not used. If it is set to 1, then |
| | SEND was used. |
| | |
| Candidate Router | A router address in the SDAT that is |
| Address | associated with at least one valid address. |
| | |
| Candidate Router | A set of router addresses that has been |
| Set | identified for NS-based probing. |
+---------------------+---------------------------------------------+
Table 1: Simple DNA Terminology
4. The Simple DNA Address Table (SDAT)
In order to correctly perform the procedure described in this
document, the host needs to maintain a data structure called the
Simple DNA address table (SDAT). The host needs to maintain this
data structure for each interface on which it performs Simple DNA.
Each entry in the SDAT table will be indexed by the router identifier
(link-local + link-layer address of the router) and consists of at
least the following parameters. Fields tagged as [S] are used for
addresses configured using SLAAC. Fields tagged as [D] are used for
addresses obtained using DHCPv6. Fields tagged as [S+D] are used in
both cases.
o [S+D] Link-local IPv6 address of the router(s)
o [S+D] Link-layer (MAC) address of the router(s)
o [S+D] Flag indicating whether the address was obtained using SLAAC
or DHCPv6. (The D-Flag)
o [S+D] IPv6 address and its related parameters like valid lifetime,
preferred lifetime, etc.
o [S] Prefix from which the address was formed.
o [S] Flag indicating whether SEND was used. (The S-Flag)
o [D] DHCP-specific information in case DHCPv6 [RFC3315] was used to
acquire the address. This information includes the DUID, the
IAID, a flag indicating IA_NA/IA_TA, and configuration information
such as DNS server address, NTP server address, etc.
o [S+D] Flag indicating whether the address is operable. (The
O-Flag)
5. Host Operations
On connecting to a new point of attachment, the host performs the
Detecting Network Attachment procedure in order to determine whether
the existing addressing and configuration information are still
valid.
5.1. On Receipt of a Router Advertisement
When the host receives a Router Advertisement and the router
identifier of the sending router is not present in the SDAT, the host
processes the Router Advertisement as specified in Section 6.3.4 of
[RFC4861]. Additionally, the host performs the following operations.
If the Router Advertisement is protected by SEND, the S-Flag MUST be
set to 1 in the SDAT entries created/modified by this RA.
o The host configures addresses out of the autoconfigurable prefixes
advertised in the RA, as specified in [RFC4862]. The host MUST
add an SDAT entry (indexed by this router identifier) for each
such address the host configures.
o The host might have already configured addresses out of the
autoconfigurable prefixes advertised in the RA. This could be a
result of receiving the prefix in an RA from another router on the
same link. The host MUST add an SDAT entry (indexed by this
router identifier) for each such address the host had already
configured.
o The host might have DHCPv6-assigned addresses that are known to be
operable on the link. The host MUST add an SDAT entry (indexed by
this router identifier) for each such DHCPv6 address.
5.2. After Assignment of a DHCPv6 Address
After the host is assigned an address by a DHCPv6 server, it needs to
associate the address with the routers on link. The host MUST create
one SDAT entry for each of the on-link routers associated with the
DHCPv6-assigned address.
5.3. Steps Involved in Detecting Link Change
The steps involved in basic detection of network attachment are:
o Link-layer indication
o Sending of neighbor discovery probes
o Response gathering and assessment
These steps are described below.
5.4. Link-Layer Indication
In order to start detection of network attachment procedures, a host
typically requires a link-layer indication that the medium has become
available [RFC4957].
After the indication is received, the host MUST mark all currently
configured (non-tentative) IP addresses as inoperable until the
change detection process completes. It MUST also set all Neighbor
Cache (NC) entries for the routers on its Default Router List to
STALE. This is done to speed up the acquisition of a new default
router in case the host attaches to a previously unvisited link.
5.5. Sending Neighbor Discovery probes
5.5.1. Sending Router Solicitations
When a host receives a link-layer "up" indication, it SHOULD
immediately send a Router Solicitation (as specified in Section 6.3.7
of [RFC4861]). The Router Solicitation is sent to the all-routers
multicast address using a link-local address as the source address
[RFC4861]. Even if the host is in possession of more than one valid
IPv6 address, it MUST send only one router solicitation using a valid
link-local address as the source address.
5.5.2. Sending Neighbor Solicitations
The host iterates through the SDAT to identify a set of candidate
routers for NS-based probing. Each router in the SDAT that is
associated with at least one valid address is added to the candidate
router set exactly once. For each router in the candidate router
set, the host MUST send a unicast Neighbor Solicitation to the
router's link-local address it obtained from the lookup on the SDAT.
The host MUST set the link-layer destination address in each of these
neighbor solicitations to the link-layer address of the router stored
in the SDAT. The host MUST NOT send unicast Neighbor Solicitations
to a router that is not associated to a valid address in the SDAT.
If at least one entry in the SDAT for a given router had the S-Flag
set, the host SHOULD use SEND to secure the NS probe being sent to
the router.
5.5.3. Concurrent Sending of RS and NS Probes
The host SHOULD send the Neighbor-Solicitation-based unicast probes
in parallel with the multicast Router Solicitation. Since sending
NSs is just an optimization, doing the NSs and the RS in parallel
ensures that the procedure does not run slower than it would if it
only used a Router Solicitation.
NOTE: A Simple DNA implementation SHOULD limit its NS-based probing
to at most six previously seen routers.
5.5.4. Initiating DHCPv6 Exchange
On receiving a link-layer "up" indication, the host will initiate a
DHCPv6 exchange (with the timing and protocol as specified in
[RFC3315]) in order to verify whether the addresses and configuration
obtained using DHCPv6 are still usable on the link. Note that
DHCPv6, as specified today, only attempts to confirm addresses
obtained on the most recently attached link.
5.6. Contents of the Neighbor Discovery Messages
5.6.1. Neighbor Solicitation Messages
This section describes the contents of the neighbor solicitation
probe messages sent during the probing procedure.
Source Address: A link-local address assigned to the
probing host.
Destination Address: The link-local address of the router being
probed as learned from the SDAT.
Hop Limit: 255
ND Options:
Target Address: The link-local address of the router being
probed as learnt from the SDAT.
Link-Layer Header:
Destination Address: The link-layer (MAC) address of the router
being probed as learnt from the SDAT.
The probing node SHOULD include the source link-layer address option
in the probe messages.
5.6.2. Router Solicitation Messages
This section describes the contents of the router solicitation probe
message sent during the probing procedure.
Source Address: A link-local address assigned to the
probing host.
Destination Address: The all-routers multicast address.
Hop Limit: 255
The probing node SHOULD NOT include the source link-layer address
option in the probe messages.
5.7. Response Gathering
5.7.1. Receiving Neighbor Advertisements
When a Neighbor Advertisement is received from a router in response
to an NS probe, the host MUST verify that both the IPv6 and link-
layer (MAC) addresses of the router match the expected values before
utilizing the configuration associated with the detected network
(prefixes, MTU, etc.). The host MUST then go through the SDAT and
mark the addresses (both SLAAC and DHCPv6 acquired) associated with
the router as operable.
5.7.2. Receiving Router Advertisements
On reception of a Router Advertisement, the host MUST go through the
SDAT and mark all the addresses associated with the router (both
SLAAC and DHCPv6 acquired) as inoperable. The host MUST then process
the Router Advertisement as specified in Section 6.3.4 of [RFC4861].
5.7.3. Conflicting Results
5.7.3.1. Conflicting Results between RS and NS Probes
Where the conclusions obtained from the Neighbor Solicitation/
Advertisement from a given router and the RS/RA exchange with the
same router differ, the results obtained from the RS/RA will be
considered definitive. In case the Neighbor Advertisement was
secured using SEND and the Router Advertisement was not, the host
MUST wait for SEND_NA_GRACE_TIME to see if a SEND-secured RA is
received. If a SEND-secured RA is not received, the conclusions
obtained from the NS/NA exchange will be considered definitive.
5.7.3.2. Conflicting Results between DHCPv6 and NS Probes
Where the conclusions obtained from the Neighbor Solicitation/
Advertisement for a given DHCPv6-assigned address and the conclusions
obtained from the DHCPv6 exchange differ, the results obtained from
the DHCPv6 exchange will be considered definitive.
5.8. Further Host Operations
Operations subsequent to Detecting Network Attachment depend upon
whether or not the host has reconnected to a previously visited
network.
After confirming the reachability of the associated router using an
NS/NA pair, the host performs the following steps.
o The host SHOULD rejoin any solicited nodes' multicast groups for
addresses it continues to use.
o The host SHOULD select a default router as described in Section
6.3.6 of [RFC4861].
If the host has determined that it has reattached to a previously
visited link, it SHOULD NOT perform duplicate address detection on
the addresses that have been confirmed to be operable.
If the NS-based probe with a router did not complete or if the RS-
based probe on the same router completed with different prefixes than
the ones in the SDAT, the host MUST begin address configuration
techniques, as indicated in a received Router Advertisement [RFC4861]
[RFC4862].
5.9. On Connecting to a New Point of Attachment
A host usually maintains SDAT entries from some number of previously
visited networks. When the host attaches to a previously unknown
network, it MAY need to discard some older SDAT entries.
5.10. Periodic Maintenance of the SDAT
The host SHOULD maintain the SDAT table by removing entries when the
valid lifetime for the prefix and address expires, that is, at the
same time that the prefix is removed from the Prefix List in
[RFC4861]. The host SHOULD also remove a router from an SDAT entry
when that router stops advertising a particular prefix. When three
consecutive RAs from a particular router have not included a prefix,
then the router should be removed from the corresponding SDAT entry.
Likewise, if a router starts advertising a prefix for which there
already exists an SDAT entry,then that router should be added to the
SDAT entry.
5.11. Recommended Retransmission Behavior
Where the NS probe does not complete successfully, it usually implies
that the host is not attached to the network whose configuration is
being tested. In such circumstances, there is typically little value
in aggressively retransmitting unicast neighbor solicitations that do
not elicit a response.
Where unicast Neighbor Solicitations and Router Solicitations are
sent in parallel, one strategy is to forsake retransmission of
Neighbor Solicitations and to allow retransmission only of Router
Solicitations or DHCPv6. In order to reduce competition between
unicast Neighbor Solicitations and Router Solicitations and DHCPv6
retransmissions, a DNAv6 implementation that retransmits may utilize
the retransmission strategy described in the DHCPv6 specification
[RFC3315], scheduling DNAv6 retransmissions between Router
Solicitations or DHCPv6 retransmissions.
If a response is received to any unicast Neighbor Solicitation,
pending retransmissions of the same MUST be canceled. A Simple DNA
implementation SHOULD NOT retransmit a Neighbor Solicitation more
than twice. To provide damping in the case of spurious link-up
indications, the host SHOULD NOT perform the Simple DNA procedure
more than once a second.
6. Pseudocode for Simple DNA
/* Link-up indication received on INTERFACE */
/* Start Simple DNA process */
/* Mark all addresses as inoperable */
Configured_Address_List=Get_Address_List(INTERFACE);
for each Configured_Address in Configured_Address_List
{
if (Get_Address_State(Configured_Address)!=AS_TENTATIVE)
{
Set_Address_State(Configured_Address,AS_INOPERABLE);
}
}
/* Mark all routers' NC entries as STALE to speed up */
/* acquisition of new router if link change has occurred */
for each Router_Address in DEFAULT_ROUTER_LIST
{
NCEntry=Get_Neighbor_Cache_Entry(Router_Address);
Set_Neighbor_Cache_Entry_State(NCEntry,NCS_STALE);
}
/* Thread A : Send Router Solicitation */
RS_Target_Address=FF02::2;
RS_Source_Address=Get_Any_Link_Local_Address(INTERFACE);
Send_Router_Solicitation(RS_Source_Address,RS_Target_Address);
/* Thread B : Send Neighbor Solicitation(s) */
Previously_Known_Router_List=Get_Router_List_from_SDAT();
NS_Source_Address=Get_Any_Link_Local_Address(INTERFACE);
for each Router_Address in Previously_Known_Router_List
{
if (Get_Any_Valid_Address_from_SDAT(Router_Address))
{
Send_Neighbor_Solicitation(NS_Source_Address,
Router_Address.L3_Address,
Router_Address.L2_Address);
}
}
/* Thread C : Response collection of RAs */
/* Received Router Advertisement processing */
/* Only for RAs received from routers in the SDAT */
L3_Source=Get_L3_Source(RECEIVED_MESSAGE);
L2_Source=Get_L2_Source(RECEIVED_MESSAGE);
SDAT_Entry_List=Get_Entries_from_SDAT_L2L3(L3_Source,L2_Source));
/* Mark all the addresses associated with the router as inoperable */
for each SDAT_Entry in SDAT_Entry_List
{
Set_Address_State(SDAT_Entry,AS_INOPERABLE);
}
/* Ignore further NAs from this router */
/* after delaying for x milliseconds */
Add_Router_to_NA_Ignore_List(L3_Source,SEND_NA_GRACE_PERIOD);
/* Perform Standard RA processing as per RFC 4861 / RFC 4862 */
/* Thread D : Response collection of NAs */
/* Received Neighbor Advertisement processing */
/* Only for NAs received as response to DNA NSs */
L3_Source=Get_L3_Source(RECEIVED_MESSAGE);
L2_Source=Get_L2_Source(RECEIVED_MESSAGE);
if (Is_Router_on_NA_Ignore_List(L3_Source)) {
/* Ignore message and wait for next message */
continue;
}
SDAT_Entry_List=Get_Entries_from_SDAT_L2L3(L3_Source,L2_Source));
for each SDAT_Entry in SDAT_Entry_List
{
/* Address is operable. */
Set_Address_State(SDAT_Entry,AS_OPERABLE);
/* Configure on Interface */
}
Figure 1: Pseudocode for Simple DNA
NOTE: This section does not include any pseudocode for sending of the
DHCPv6 packets since the DHCPv6 exchange is orthogonal to the Simple
DNA process.
7. Constants
SEND_NA_GRACE_TIME
Definition: An optional period to wait after Neighbor
Solicitation before adopting a non-SEND RA's link change
information.
Value: 40 milliseconds
8. Relationship to DNAv4
DNAv4 [RFC4436] specifies a set of steps that optimize the (common)
case of reattachment to an IPv4 network that a host has been
connected to previously by attempting to reuse a previous (but still
valid) configuration. This document shares the same goal as DNAv4
(that of minimizing the handover latency in moving between points of
attachment) but differs in the steps it performs to achieve this
goal. Another difference is that this document supports stateless
autoconfiguration of addresses in addition to addresses configured
using DHCPv6.
9. Security Considerations
A host may receive Router Advertisements from non-SEND devices, after
receiving a link-layer indication. While it is necessary to assess
quickly whether a host has moved to another network, it is important
that the host's current secured SEND [RFC3971] router information is
not replaced by an attacker that spoofs an RA and purports to change
the link.
As such, the host SHOULD send a Neighbor Solicitation to the existing
SEND router upon link-up indication as described above in
Section 5.4. The host SHOULD then ensure that unsecured router
information does not cause deletion of existing SEND state, within
MIN_DELAY_BETWEEN_RAS, in order to allow for a present SEND router to
respond.
If the current default router is a SEND-secured router, the host
SHOULD wait SEND_NA_GRACE_TIME after transmission before adopting a
new default router.
Even if SEND signatures on RAs are used, it may not be immediately
clear if the router is authorized to make such advertisements. As
such, a host SHOULD NOT treat such devices as secure until and unless
authorization delegation discovery is successful.
Unless SEND or another form of secure address configuration is used,
the DNA procedure does not in itself provide positive, secure
authentication of the router(s) on the network, or authentication of
the network itself, as would be provided, e.g., by mutual
authentication at the link layer. Therefore, when such assurance is
not available, the host MUST NOT make any security-sensitive
decisions based on the DNA procedure alone. In particular, it MUST
NOT decide that it has moved from an untrusted to a trusted network,
and MUST NOT make any security decisions that depend on the
determination that such a transition has occurred.
10. Acknowledgments
This document is the product of a discussion the authors had with
Bernard Aboba, Thomas Narten, Erik Nordmark, and Dave Thaler at IETF
69. The authors would like to thank them for clearly detailing the
requirements of the solution and the goals it needed to meet and for
helping to explore the solution space. The authors would like to
thank the authors and editors of the complete DNA specification for
detailing the overall problem space and solutions. The authors would
like to thank Jari Arkko for driving the evolution of a simple and
probabilistic DNA solution. The authors would like to thank Bernard
Aboba, Thomas Narten, Jari Arkko, Sathya Narayan, Julien Laganier,
Domagoj Premec, Jin Hyeock-Choi, Alfred Hoenes, Frederic Rossi, Ralph
Droms, Ted Lemon, Erik Nordmark, Lars Eggert, Brian Carpenter, and
Yaron Sheffer for performing reviews on the document and providing
valuable comments to drive the document forward.
11. References
11.1. Normative References
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
[RFC3315] Droms, R., Bound, J., Volz, B., Lemon, T., Perkins,
C., and M. Carney, "Dynamic Host Configuration
Protocol for IPv6 (DHCPv6)", RFC 3315, July 2003.
[RFC3971] Arkko, J., Kempf, J., Zill, B., and P. Nikander,
"SEcure Neighbor Discovery (SEND)", RFC 3971, March
2005.
[RFC4861] Narten, T., Nordmark, E., Simpson, W., and H.
Soliman, "Neighbor Discovery for IP version 6
(IPv6)", RFC 4861, September 2007.
11.2. Informative References
[DNA-PROTOCOL] Narayanan, S., Ed., "Design Alternative for Detecting
Network Attachment in IPv6 Networks (DNAv6 Design
Alternative)", Work in Progress, November 2009.
[RFC4436] Aboba, B., Carlson, J., and S. Cheshire, "Detecting
Network Attachment in IPv4 (DNAv4)", RFC 4436, March
2006.
[RFC4862] Thomson, S., Narten, T., and T. Jinmei, "IPv6
Stateless Address Autoconfiguration", RFC 4862,
September 2007.
[RFC4957] Krishnan, S., Montavont, N., Njedjou, E., Veerepalli,
S., and A. Yegin, "Link-Layer Event Notifications for
Detecting Network Attachments", RFC 4957, August
2007.
Appendix A. Issues with Confirming Manually Assigned Addresses
Even though DNAv4 [RFC4436] supports verification of manually
assigned addresses, this feature of DNAv4 has not been widely
implemented or used. There are two major issues that come up with
confirming manually assigned addresses using Simple DNA.
o When DHCPv6 or SLAAC addresses are used for probing, there is no
need to aggressively retransmit lost probes. This is because the
address configuration falls back to vanilla DHCPv6 or SLAAC, and
the host will eventually obtain an address. This is not the case
with manually assigned addresses. If the probes are lost, the
host runs the risk of ending up with no addresses at all. Hence,
aggressive retransmissions are necessary.
o Another issue comes up when the host moves between two networks,
one where manual addressing is being used (say, NET1) and the
other where dynamic addressing (stateless autoconfiguration or
DHCPv6) is being used (say, NET2). Since the host can obtain a
dynamic address in some situations, it will need to send Simple
DNA probes and may also engage in a DHCPv6 exchange. In a
situation where the host moves to NET1 and the NS probes are lost
and in addition an RA is not received, the host will not be able
to confirm that it attached to NET1, and therefore that it should
use the manual configuration for that network. As a result, if
DHCPv6 is enabled on NET1, then the host could mistakenly obtain a
dynamic address and configuration instead of using the manual
configuration. To prevent this problem, Simple DNA probing needs
to continue even after the DHCPv6 exchange has completed, and DNA
probes need to take precedence over DHCPv6, contrary to the advice
provided in Section 5.7.3.
Given these issues, it is NOT RECOMMENDED to use manual addressing
with Simple DNA.
Authors' Addresses
Suresh Krishnan
Ericsson
8400 Decarie Blvd.
Town of Mount Royal, QC
Canada
Phone: +1 514 345 7900 x42871
EMail: suresh.krishnan@ericsson.com
Greg Daley
Netstar Logicalis
Level 6/616 St Kilda Road
Melbourne, Victoria 3004
Australia
Phone: +61 401 772 770
EMail: hoskuld@hotmail.com