Route Information Options in IPv6 Neighbor Discovery
draft-templin-6man-rio-redirect-04
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| Authors | Fred Templin , james woodyatt | ||
| Last updated | 2017-08-16 | ||
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draft-templin-6man-rio-redirect-04
Network Working Group F. Templin, Ed.
Internet-Draft Boeing Research & Technology
Updates: rfc4191 (if approved) J. Woodyatt
Intended status: Standards Track Google
Expires: February 17, 2018 August 16, 2017
Route Information Options in IPv6 Neighbor Discovery
draft-templin-6man-rio-redirect-04.txt
Abstract
The IPv6 Neighbor Discovery (ND) protocol allows nodes to discover
neighbors on the same link. Router Advertisement (RA) messages can
also convey routing information by including 1) a non-zero (default)
Router Lifetime, and/or 2) Route Information Options (RIOs). This
document specifies backward-compatible extensions that permit nodes
to include RIOs in other IPv6 ND messages to support the discovery of
more-specific routes.
Status of This Memo
This Internet-Draft is submitted in full conformance with the
provisions of BCP 78 and BCP 79.
Internet-Drafts are working documents of the Internet Engineering
Task Force (IETF). Note that other groups may also distribute
working documents as Internet-Drafts. The list of current Internet-
Drafts is at http://datatracker.ietf.org/drafts/current/.
Internet-Drafts are draft documents valid for a maximum of six months
and may be updated, replaced, or obsoleted by other documents at any
time. It is inappropriate to use Internet-Drafts as reference
material or to cite them other than as "work in progress."
This Internet-Draft will expire on February 17, 2018.
Copyright Notice
Copyright (c) 2017 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
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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 . . . . . . . . . . . . . . . . . . . . . . . . 2
2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 3
3. Motivation . . . . . . . . . . . . . . . . . . . . . . . . . 3
4. Route Information Options (RIOs) in IPv6 Neighbor Discovery
Messages . . . . . . . . . . . . . . . . . . . . . . . . . . 5
4.1. RIO Update . . . . . . . . . . . . . . . . . . . . . . . 5
4.2. RIO Requirements . . . . . . . . . . . . . . . . . . . . 7
4.3. Classic Redirection Scenario . . . . . . . . . . . . . . 8
4.4. RIO Redirection Scenario . . . . . . . . . . . . . . . . 9
4.4.1. Router Specification . . . . . . . . . . . . . . . . 10
4.4.2. Source Specification . . . . . . . . . . . . . . . . 10
4.4.3. Target Specification . . . . . . . . . . . . . . . . 11
4.5. Operation Without Redirects . . . . . . . . . . . . . . . 12
4.6. Multiple RIOs . . . . . . . . . . . . . . . . . . . . . . 12
4.7. Multicast . . . . . . . . . . . . . . . . . . . . . . . . 12
4.8. Backward Compatibility . . . . . . . . . . . . . . . . . 13
4.9. Why NS/NA? . . . . . . . . . . . . . . . . . . . . . . . 13
5. Implementation Status . . . . . . . . . . . . . . . . . . . . 14
6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 14
7. Security Considerations . . . . . . . . . . . . . . . . . . . 14
8. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 15
9. References . . . . . . . . . . . . . . . . . . . . . . . . . 15
9.1. Normative References . . . . . . . . . . . . . . . . . . 15
9.2. Informative References . . . . . . . . . . . . . . . . . 16
Appendix A. Link-layer Address Changes . . . . . . . . . . . . . 17
Appendix B. Interfaces with Multiple Link-Layer Addresses . . . 17
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 17
1. Introduction
"Neighbor Discovery for IP version 6 (IPv6)" [RFC4861] (IPv6 ND)
provides a Router Solicitation (RS) function allowing nodes to
solicit a Router Advertisement (RA) response from an on-link router,
a Neighbor Solicitation (NS) function allowing nodes to solicit a
Neighbor Advertisement (NA) response from an on-link neighbor, and a
Redirect function allowing routers to inform nodes of a better next
hop neighbor on the link toward the destination. Further guidance
for processing Redirect messages is given in "First-Hop Router
Selection by Hosts in a Multi-Prefix Network" [RFC8028].
"Default Router Preferences and More-Specific Routes" [RFC4191]
specifies a Route Information Option (RIO) that routers can include
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in RA messages to inform recipients of more-specific routes (section
1 of that document provides rationale for the use of RA messages
instead of an adjunct routing protocol). This document specifies a
backward-compatible and incrementally-deployable extension to allow
nodes to include RIOs in other IPv6 ND messages to support the
dynamic discovery of more-specific routes. This allows nodes to
discover a better neighbor for more-specific routes to both increase
performance and reduce the workload on default routers.
This approach applies to any link type on which there may be many
nodes that are holders of more-specific routes and do not act as
default routers. These nodes can either be routers that forward
packets on behalf of their downstream-attached networks, or hosts
that use a delegated prefix for their own multi-addressing purposes
[RFC7934].
This work benefits from the experience of [RFC6706] - an experimental
protocol that uses UDP-based "pseudo-ND" messages instead of actual
ICMPv6 message codes. That experience has shown that using
synthesized UDP messages in conjunction with the IPv6 ND messaging
already present on the link is inefficient. Furthermore, the UDP
approach is neither backward-compatible nor incrementally-deployable,
since sending UDP messages blindly to a node that does not have the
port open can trigger excessive "Port Unreachable" messages and
(worse) could be mis-interpreted as indications of a UDP port scan
attack. This specification avoids these issues by using the already-
present and natural IPv6 ND messaging available on the link, as
specified in this document.
2. Terminology
The terminology in the normative references applies.
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]. Lower case
uses of these words are not to be interpreted as carrying RFC2119
significance.
3. Motivation
An example of a good application for RIO is the local-area subnets
served by the routers described in "Basic Requirements for IPv6
Customer Edge Routers" [RFC7084]. While many customer edge routers
are capable of operating in a mode with a dynamic routing protocol
operating in the local-area network, the default mode of operation is
typically designed for unmanaged operation without any dynamic
routing protocol. On these networks, the only means for any node to
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learn about routers on the link is by using the Router Discovery
protocol described in [RFC4861].
Nevertheless, hosts on unmanaged home subnets may use "IPv6 Prefix
Options for DHCPv6" [RFC3633] (DHCPv6 PD) to receive IPv6 routing
prefixes for additional subnets allocated from the space provided by
the service provider, and operate as routers for other links where
hosts in delegated subnets are attached. Hosts may even learn about
more specific routes than the default route by processing RIOs in RA
messages as described in [RFC4191].
However, due to perceptions of the security considerations for hosts
in processing RIOs on unmanaged networks, the default configuration
for common host IPv6 implementations is to ignore RIOs. Accordingly,
on typical home networks the forwarding path from hosts on one subnet
to destinations on every off-link local subnet always passes through
the customer edge router, even when a shorter path would otherwise be
available through an on-link router. This adds costs for
retransmission on shared LAN media, often adding latency and jitter
with queuing delay and delay variability. This is not materially
different under the scenarios described in "IPv6 Home Networking
Architecture Principles" [RFC7368] except that routers may use an
interior dynamic routing protocol to coordinate sending of RIOs in RA
messages, which as explained above, are not processed by typical
hosts.
In increasingly common practice, a node that receives a prefix
delegation can use the prefix for its own multi-addressing purposes
or can connect an entourage of "Internet of Things" back end devices
(an approach sometimes known as "tethering" [RFC7934]). On many link
types, the number of such nodes may be quite large which would make
running a dynamic routing protocol between the nodes impractical.
Example use cases include:
o IETF conference, airport, and hotel WiFi networks, where large
numbers of nodes on the link could receive IPv6 prefix
delegations. Using the extensions described in this document, the
nodes could dynamically discover more-specific routes to enable
direct neighbor-to-neighbor communications.
o Mobile enterprise devices that connect into a corporate network
via VPN links. Using the extensions described in this document,
mobile devices could dynamically establish pair-wise VPN links
between themselves without having to use the enterprise network as
transit.
o Civil aviation networks where an aircraft holds an IPv6 prefix
derived from the identification value assigned to it by the
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International Civil Aviation Organization (ICAO). Using the
extensions described in this document, direct paths between the
aircraft and Air Traffic Control (ATC) can be established to
provide a more direct route for communications.
By using RIOs in IPv6 ND messages, the forwarding path between
subnets can be shortened while accepting a much narrower opening of
attack surfaces on general purpose hosts related to the Router
Discovery protocol. The basic idea is simple: hosts normally send
packets for off-link destinations to their default router unless they
receive ND Redirect messages designating another on-link node as the
target. This document allows ND Redirects additionally to suggest
another on-link node as the target for one or more routing prefixes,
including one with the destination. Hosts that receive RIOs in ND
Redirect messages then send NS messages to the target containing
those RIOs, and process the NA messages the target sends in reply.
If hosts only process RIOs in NA messages when they have previously
sent them in NS messages to the targets of received ND Redirect
messages, then hosts only process RIO at the initiative of routers
they already accept as authoritative.
4. Route Information Options (RIOs) in IPv6 Neighbor Discovery Messages
The RIO is specified for inclusion in RA messages in Section 2.3 of
[RFC4191], while the neighbor discovery functions are specified in
[RFC4861]. This specification permits routers to include RIOs in
other IPv6 ND messages so that recipients can discover a better next
hop for a destination *prefix* instead of just a specific destination
address. This specification therefore updates [RFC4191] as discussed
in the following sections.
4.1. RIO Update
The RIO format given in Section 2.3 of [RFC4191] is updated by this
specification as shown in Figure 1:
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0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type | Length | Prefix Length |Ver|S|Prf|Resvd|
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Route Lifetime |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Prefix (Variable Length) |
. .
. .
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Attributes ...
+-+-+-+-+-+-+-+-+-+-+-+-
Figure 1: Updated RIO Format
This format introduces a new Ver field, a new S flag and variable-
length Attributes. The fields of the main body of the RIO are set as
follows:
o Type, Prefix Length, Prf, Route Lifetime and Prefix are set
exactly as specified in Section 2.3 of [RFC4191].
o Length MUST be initialized to exactly 1 when Prefix Length is 0,
to exactly 2 when Prefix Length is between 1 and 64, and to
exactly 3 when Prefix Length is greater than 64; Length is then
incremented by the length of all included Attributes in units of
8-octets (see below).
o Ver is set to '01' to indicate that this is Version 1 of the RIO
format ([RFC4191] is considered as the Version 0 format).
o S is set to '1' to "Solicit" route information or to '0' (i.e.,
the default value) to "Assert" route information.
o Resvd is reserved and MUST be set to '0'.
Attributes MAY be included as ancillary route information. Each
Attribute is formatted in the same manner as specified for IPv6 ND
options in Section 4.6 of [RFC4861] and as shown in Figure 2:
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0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type | Length | ... |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
~ ... ~
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 2: RIO Attribute Format
This document defines the NULL Attribute with Type '0'. Other
Attribute Types are assigned through IANA action.
When Type is '0', Length MUST be set to the total number of 8-octet
blocks in the Attribute, and the Attribute body MUST include a
corresponding number of '0' octets. For example, for Lengths of 1,
2, 3, etc., the Attribute body includes 6, 14, 22, etc. '0' octets,
respectively.
Receivers ignore any NULL, unknown or malformed Attributes and
continue to process any other Attributes in the RIO that follow.
4.2. RIO Requirements
This specification updates [RFC4191] by allowing RIOs to appear in
any IPv6 ND messages with the following requirements:
o The RIOs of all IPv6 ND messages that conform to this
specification MUST set Ver to '01'. Any RIOs with Ver set to '00'
in RA messages are accepted as legacy RIOs that MUST conform to
the specification in [RFC4191]. Any RIOs in IPv6 ND messages that
encode any other value in the Ver field MUST be silently ignored.
o Redirect, NA and RA messages MUST NOT include RIOs with the S flag
set to '1'; any RIOs received in Redirect, NA and RA messages with
S set to '1' MUST be silently ignored.
o NS and RS messages MAY include some RIOs with S set to '1' and
others with S set to '0'.
o NA/RA responses to RIOs in NS/RS messages with S set to '1' MUST
include RIOs with the solicited route information and with S set
to '0'. (If the route information solicited by the NS/RS message
is incorrect or unrecognized, however, the RIO MUST be silently
ignored.)
o Asserted route information in any RIOs received with S set to '0'
SHOULD be considered as "unconfirmed" until the assertion can be
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verified. Assertion verification can be through a trust anchor
such as a trusted on-link router, through a static routing table,
or through some other means outside the scope of this document.
Any route information that cannot be verified SHOULD be rejected.
The following sections present the classic redirection scenario
illustrating an exchange where a trusted on-link router is used to
verify RIO assertions. Other IPv6 ND messaging scenarios that can
employ some other means of verifying RIO assertions are also
acceptable.
4.3. Classic Redirection Scenario
In the classical redirection scenario there are three actors, namely
the Source, Router and Target as shown in Figure 3:
+-------------------+
| |
| Router |
| |
+---------+---------+
|
|
X---------+----------------+---------------+---------X
| Link |
| |
+---------+---------+ +----------+--------+
| | | |
| Source | | Target |
| | | |
+-------------------+ +---------+---------+
|
2001:db8::/N
|
X-+----+--+-------+-X
| | |
+--+ +--+ +--+
|H1| |H2| .... |Hn|
+--+ +--+ +--+
Figure 3: Classical Redirection Scenario
In addition, the Target may be a router that connects an arbitrarily-
complex set of IPv6 networks (e.g., as depicted by 2001:db8::/N in
the figure) with hosts H(i).
In this scenario, the Source initially has no route for 2001:db8::/N
and must send initial packets destined to correspondents H(i) via a
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first-hop Router. Upon receiving the packets, the Router forwards
the packets to the Target and may also send a Redirect message back
to the Source with the Destination Address field set to the
destination of the packet that triggered the Redirect, the Target
Address field set to the target link-local address and with a Target
Link Layer Address Option (TLLAO) that includes the target link-layer
address. After receiving the message, the Source may begin sending
packets destined to H(i) directly to the Target, which will then
forward them to its connected networks.
This specification augments the classical Redirection scenario by
allowing the Router to include entire prefixes (e.g., 2001:db8::/N)
in RIOs in the Redirect message, and thereafter allowing the Source
to include RIOs in an NS message and the Target to include RIOs in
its NA response. The following sections present this "augmented" RIO
redirection scenario.
4.4. RIO Redirection Scenario
In the RIO redirection scenario, the Source sends initial packets via
the Router the same as in the classical scenario. When the Router
receives the packets, it searches its routing tables for a route that
is assigned to the Target and that covers the destination address of
the packet. The Router then includes the route in an RIO in a
Redirect message to send back to the Source. The Router sets the S
flag in the RIO to '0' to indicate that a prefix is being asserted.
When the Source receives the Redirect message, it prepares an NS
message that includes the route information received in the RIO from
the Redirect message and with S set to '1 to indicate that route
information is being solicited. At the same time, if the Source
needs to assert any route information to the Target, it includes the
information in RIOs with S set to '0'. The Source then sends the NS
message to the Target.
When the Target receives the NS message, it records any route
information in RIOs with S set to '0' as unconfirmed route
information for the Source pending verification. At the same time,
it determines whether the route information included in any RIOs with
S set to '1' matches one of its own routes. If so, the Target
includes the route information in an RIO with S set to '0' to return
in an NA message reply to the Source.
When the Source receives the NA message it can install any RIO
information that matches the Redirect RIOs in its routing table. The
following sections present more detailed specifications for the
Router, Source and Target.
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4.4.1. Router Specification
When the Router receives a packet from the Source it searches its
routing table for a prefix that covers the destination address (e.g.,
2001:db8::/N as depicted in Figure 1), where prefix could be
populated in the routing table during DHCPv6 Prefix Delegation
[RFC3633], via manual configuration, etc. If the next hop for the
prefix is on-link (i.e., a "Target" in the terms of [RFC4861]), the
Router then prepares a Redirect message with the Destination Address
field set to the packet's IPv6 destination address, with the Target
Address field set to the link-local address of the Target, with a
TLLAO set to the link-layer address of the Target, and with an RIO
that includes route information for the prefix with Route Lifetime,
Prf, and S set to 0. The Router then sends the Redirect message to
the Source (subject to rate limiting).
4.4.2. Source Specification
According to [RFC4861], a Source that receives a valid Redirect
message updates its destination cache per the Destination Address and
its neighbor cache per the Target Address. According to [RFC4191],
Sources can be classified as Type "A", "B" or "C" based on how they
process RIOs, where a Type "C" Source updates its routing table per
any RIO elements included in an RA message. Finally, according to
[RFC8028], a Type "C" Source operating on a Multi-Prefix Network with
multiple default routes can make source address selection decisions
based on information in its routing table decorated with information
derived from the source of the RIO element.
In light of these considerations, this document introduces a new Type
"D" behavior for Sources with the same behavior as a Type "C" Source,
but which also process RIO elements in other IPv6 ND messages. Type
"D" Sources process Redirect messages with RIO elements by first
verifying that the Prefix in the first RIO matches the Destination
Address. If the Destination Address does not match the Prefix, the
Source discards the Redirect message. Otherwise, the Source updates
its neighbor cache per the Target Address and its destination cache
per the Destination Address the same as for classical redirection.
Next, the Source MAY send an NS message to the Target containing an
RIO with the Prefix and Prefix Length and with S set to '1' to elicit
an NA response (at the same time, the Source MAY include RIOs with S
set to '0' if it needs to assert any route information to the
Target).
When the Type 'D' Source receives the solicited NA message from the
Target, if the NA includes an RIO with S set to '0' and with a Prefix
corresponding to the one received in the Redirect message, the Source
installs the route information in its routing table with the Target's
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address as the next hop. (Note that the Prefix Length received in
the NA message MAY be different than the Prefix Length received in
the Redirect message. If the Prefix Length in the NA is the same or
longer, the Source accepts the Prefix as verified by the Router; if
the Prefix Length is shorter, the Source considers the Prefix as
unconfirmed.)
After the Source installs the route information in its routing table,
it MAY begin sending packets with destination addresses that match
the Prefix directly to the Target Instead of sending them to the
Router. The Source SHOULD decrement the Route Lifetime and MAY send
new NS messages to receive a fresh Route Lifetime (if the Route
Lifetime decrements to 0, the Source instead deletes the route
information from its routing table). The Source MAY furthermore
delete the route information at any time and again allow packets to
flow through the Router which may send a fresh Redirect. The Source
SHOULD then again test the route by performing an NS/NA exchange with
the Target the same as described above.
After updating its routing table, the Source MAY receive an
unsolicited NA message from the Target with an RIO with new route
information. If the RIO Prefix is in its routing table, and if the
RIO Route Lifetime value is 0, the Source deletes the corresponding
route.
After updating its routing table, the Source MAY subsequently receive
a Destination Unreachable message from the Target with Code '0' ("no
route to destination"). If so, the Source again deletes the
corresponding route information from its routing table.
4.4.3. Target Specification
When the Target receives an NS message from the Source containing an
RIO with S set to '1', it examines the Prefix and Prefix Length to
see if it matches one of the prefixes in its routing table. If so,
the Target prepares an NA message with an RIO including a Prefix and
Prefix Length, any necessary route information, and with S set to
'0'. The Target then sends the NA message back to the Source.
If the NS included any RIO options with S set to '0', the Target
SHOULD employ a suitable means to verify the asserted route
information, and SHOULD reject any route information that cannot be
verified.
At some later time, the Target may either alter or deprecate one of
its routes. If the Target has asserted route information in RIOs to
one or more Sources, the Target SHOULD send (unsolicited) NA messages
with RIOs that assert new route information to alter the route (where
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a new Route Lifetime value of '0' deprecates the route). If the
Target receives a packet with a destination addresses for which there
is no matching route for one of its downstream-attached networks, the
Target sends a Destination Unreachable message to the Source with
Code '0' ("no route to destination"), subject to rate limiting.
4.5. Operation Without Redirects
If the Source has some way to determine the Target's link-local
address without receiving a Redirect message from the Router, the
Source MAY send an NS message with an RIO directly to the Target with
S set to 1, Prefix set to the destination address of an IPv6 packet,
Prefix Length set to 128 and all other route information is set to 0.
When the Target receives the NS message, it prepares an NA response
with an RIO that includes route information for one of its prefixes
that covers the destination address. The Target then sends the NA
message to the Source.
When the Source receives the NA message, it SHOULD consider the route
information asserted in the RIO as unconfirmed until it can verify
the Target's claim (i.e., as described in Section 4.2).
Any node may also assert route information at any time by sending
unsolicited IPv6 ND messages with RIOs with S set to 0. Recipients
of such messages SHOULD consider the route information as unconfirmed
until the information can be verified.
4.6. Multiple RIOs
If a Redirect includes multiple RIOs, the Source only checks the
destination address for a match against the Prefix in the first RIO.
If an NS/RS message includes multiple RIOs with S set to '1', the
neighbor only responds to those RIOs which match entries in its
routing table.
If an NS/NA/RS/RA message includes multiple RIOs with S set to '0',
the neighbor considers all of the route information as unconfirmed
until the information can be verified.
4.7. Multicast
Nodes MAY send IPv6 ND messages with RIOs to link-scoped multicast
destination addresses including All Nodes, All Routers, and
Solicited-Node multicast (see: [RFC4291]. As an example, a node
could send unsolicited NA messages to the All Nodes multicast address
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to alter or deprecate a route it had previously asserted to one or
more neighbors.
Nodes MUST be conservative in their use of multicast IPv6 ND
messaging to avoid unnecessarily disturbing other nodes on the link.
4.8. Backward Compatibility
[RFC4191] only allows RIOs to appear in RA messages, and requires
that the bits corresponding to the Ver field in this specification be
set to '00'. In cases where legacy Type 'C' hosts may be on the
link, implementation of this protocol SHOULD only send multicast RAs
with RIOs formatted per [RFC4191]. RA responses to RS messages with
RIOs formatted per this specificaiton SHOULD be sent as unicast and
SHOULD include RIOs formatted per this specifcation.
4.9. Why NS/NA?
Since [RFC4191] already specifies the inclusion of RIOs in RA
messages, a natural question is why use NS/NA instead of RS/RA?
First, NS/NA exchanges used by the IPv6 Neighbor Unreachability
Detection (NUD) procedure are unicast-based whereas RA responses to
RS messages are typically sent as multicast. Since this mechanism
must support unicast operation, the use of unicast exchanges is
required.
Second, the IPv6 ND specification places restrictions on minimum
delays between RA messages. Since this mechanism expects an
immediate advertisement from the Target in response to the Source's
solicitation, only the NS/NA exchange can satisfy this property.
Third, the RA message is the "swiss army knife" of the IPv6 ND
protocol. RA messages carry numerous configuration parameters for
the link, including Cur Hop Limit, M/O flags, Router Lifetime,
Reachable Time, Retrans Time, Prefix Information Options, MTU
options, etc. The Target must not advertise any of this information
to the soliciting Source.
Fourth, RIOs in legacy RA messages cannot encode attributes and
therefore may be limited in the route information they can carry.
Finally, operators are deeply concerned about the security of RA
messages - so much so that they deploy link security mechanisms that
drop RA messages originating from nodes claiming to be an
authoritative router for the link [RFC6105].
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5. Implementation Status
The IPv6 ND functions and RIOs are widely deployed in IPv6
implementations, however these implementations do not currently
include RIOs in IPv6 ND messages other than RAs.
An experimental implementation of [RFC6706] exists, and demonstrates
how the Redirect function can be used to carry route information.
6. IANA Considerations
IANA is instructed to create a registry for "RIO Attributes" as
discussed in Section 4.1. The registry includes the following
initial entry:
0 - the NULL Attribute [draft-templin-6man-rio-redirect]
Other Attribute types are defined through standards action or expert
review.
7. Security Considerations
The Redirect message validation rules in Section 8.1 of [RFC4861]
require recipients to verify that the IP source address of the
Redirect is the same as the current first-hop router for the
specified ICMP Destination Address. Recipients therefore naturally
reject any Redirect message with an incorrect source address.
Other security considerations for IPv6 ND messages that include RIOs
are the same as specified in Section 11 of [RFC4861]. Namely, the
protocol must take measures to secure IPv6 ND messages on links where
spoofing attacks are possible.
A spoofed ND message containing no RIOs could cause corruption in the
recipient's destination cache, while a spoofed ND message containing
RIOs could corrupt the host's routing tables. While the latter would
seem to be a more onerous result, the possibility for corruption is
unacceptable in either case.
"IPv6 ND Trust Models and Threats" [RFC3756] discusses spoofing
attacks, and states that: "This attack is not a concern if access to
the link is restricted to trusted nodes". "SEcure Neighbor Discovery
(SEND)" [RFC3971] provides one possible mitigation for other cases.
In some scenarios, it may be sufficient to include only the Timestamp
and Nonce options defined for SEND without implementing other aspects
of the protocol.
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"IPv6 Router Advertisement Guard" [RFC6105] ("RA Guard") describes a
layer-2 filtering technique intended for network operators to use in
protecting hosts from receiving RA messages sent by nodes that are
not among the set of routers regarded as legitimate by the network
operator.
Nodes must have some form of trust basis for knowing that the sender
of an ND message is authoritative for the prefixes it asserts in
RIOs. For example, when an NS/NA exchange is triggered by the
receipt of a Redirect, the soliciting node can verify that the RIOs
in the NA message match the ones it received in the Redirect message
(which originally came from a trusted router).
8. Acknowledgements
Joe Touch suggested a standalone draft to document this approach in
discussions on the intarea list. The work was subsequently
transferred to the 6man list, where the following individuals
provided valuable feedback: Mikael Abrahamsson, Zied Bouziri, Brian
Carpenter, Steinar Haug, Christian Huitema, Tatuya Jinmei, Tomoyuki
Sahara.
Discussion with colleagues during the "bits-and-bites" session at
IETF98 helped shape this document. Those colleagues are gratefully
acknowledged for their contributions.
This work was sponsored through several ongoing initiatives,
including 1) the NASA Safe Autonomous Systems Operation (SASO)
program under NASA contract number NNA16BD84C, 2) the FAA SE2025
contract number DTFAWA-15-D-00030, 3) the Boeing Information
Technology (BIT) MobileNet program, and 4) the Boeing Research &
Technology (BR&T) enterprise autonomy program.
9. References
9.1. Normative References
[RFC0791] Postel, J., "Internet Protocol", STD 5, RFC 791,
DOI 10.17487/RFC0791, September 1981,
<http://www.rfc-editor.org/info/rfc791>.
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119,
DOI 10.17487/RFC2119, March 1997,
<http://www.rfc-editor.org/info/rfc2119>.
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[RFC2460] Deering, S. and R. Hinden, "Internet Protocol, Version 6
(IPv6) Specification", RFC 2460, DOI 10.17487/RFC2460,
December 1998, <http://www.rfc-editor.org/info/rfc2460>.
[RFC4191] Draves, R. and D. Thaler, "Default Router Preferences and
More-Specific Routes", RFC 4191, DOI 10.17487/RFC4191,
November 2005, <http://www.rfc-editor.org/info/rfc4191>.
[RFC4443] Conta, A., Deering, S., and M. Gupta, Ed., "Internet
Control Message Protocol (ICMPv6) for the Internet
Protocol Version 6 (IPv6) Specification", STD 89,
RFC 4443, DOI 10.17487/RFC4443, March 2006,
<http://www.rfc-editor.org/info/rfc4443>.
[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,
<http://www.rfc-editor.org/info/rfc4861>.
9.2. Informative References
[RFC3633] Troan, O. and R. Droms, "IPv6 Prefix Options for Dynamic
Host Configuration Protocol (DHCP) version 6", RFC 3633,
DOI 10.17487/RFC3633, December 2003,
<http://www.rfc-editor.org/info/rfc3633>.
[RFC3756] Nikander, P., Ed., Kempf, J., and E. Nordmark, "IPv6
Neighbor Discovery (ND) Trust Models and Threats",
RFC 3756, DOI 10.17487/RFC3756, May 2004,
<http://www.rfc-editor.org/info/rfc3756>.
[RFC3971] Arkko, J., Ed., Kempf, J., Zill, B., and P. Nikander,
"SEcure Neighbor Discovery (SEND)", RFC 3971,
DOI 10.17487/RFC3971, March 2005,
<http://www.rfc-editor.org/info/rfc3971>.
[RFC4291] Hinden, R. and S. Deering, "IP Version 6 Addressing
Architecture", RFC 4291, DOI 10.17487/RFC4291, February
2006, <http://www.rfc-editor.org/info/rfc4291>.
[RFC6105] Levy-Abegnoli, E., Van de Velde, G., Popoviciu, C., and J.
Mohacsi, "IPv6 Router Advertisement Guard", RFC 6105,
DOI 10.17487/RFC6105, February 2011,
<http://www.rfc-editor.org/info/rfc6105>.
[RFC6706] Templin, F., Ed., "Asymmetric Extended Route Optimization
(AERO)", RFC 6706, DOI 10.17487/RFC6706, August 2012,
<http://www.rfc-editor.org/info/rfc6706>.
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[RFC7084] Singh, H., Beebee, W., Donley, C., and B. Stark, "Basic
Requirements for IPv6 Customer Edge Routers", RFC 7084,
DOI 10.17487/RFC7084, November 2013,
<http://www.rfc-editor.org/info/rfc7084>.
[RFC7368] Chown, T., Ed., Arkko, J., Brandt, A., Troan, O., and J.
Weil, "IPv6 Home Networking Architecture Principles",
RFC 7368, DOI 10.17487/RFC7368, October 2014,
<http://www.rfc-editor.org/info/rfc7368>.
[RFC7934] Colitti, L., Cerf, V., Cheshire, S., and D. Schinazi,
"Host Address Availability Recommendations", BCP 204,
RFC 7934, DOI 10.17487/RFC7934, July 2016,
<http://www.rfc-editor.org/info/rfc7934>.
[RFC8028] Baker, F. and B. Carpenter, "First-Hop Router Selection by
Hosts in a Multi-Prefix Network", RFC 8028,
DOI 10.17487/RFC8028, November 2016,
<http://www.rfc-editor.org/info/rfc8028>.
Appendix A. Link-layer Address Changes
Type "D" hosts send unsolicited NAs to announce link-layer address
changes per standard neighbor discovery [RFC4861]. Link-layer
address changes may be due to localized factors such as hot-swap of
an interface card, but could also occur during movement to a new
point of attachment on the same link.
Appendix B. Interfaces with Multiple Link-Layer Addresses
Type "D" host interfaces may have multiple connections to the link;
each with its own link-layer address. Type "D" nodes can therefore
include multiple link-layer address options in IPv6 ND messages.
Neighbors that receive these messages can cache and select link-layer
addresses in a manner outside the scope of this specification.
Authors' Addresses
Fred L. Templin (editor)
Boeing Research & Technology
P.O. Box 3707
Seattle, WA 98124
USA
Email: fltemplin@acm.org
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James Woodyatt
Google
3400 Hillview Ave
Palo Alto, CA 94304
USA
Email: jhw@google.com
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