Internet DRAFT - draft-olopade-6man-slaac-signaling
draft-olopade-6man-slaac-signaling
IPv6 Maintenance (6man) Working Group Loba Olopade
Internet-Draft Virgin Media
Updates: 4862 (if approved) October 19, 2020
Intended status: Standards Track
Expires: April 22, 2021
Explicit signaling of Stateless Address Autoconfiguration (SLAAC)
to Renumbering Events
draft-olopade-6man-slaac-signaling-00
Abstract
After a renumbering event in an IPv6 network utilizing SLAAC, hosts
might continue to use stale addresses, as they are unaware of the
changes. Likewise, routers, who may deprecate the use of these
prefixes, are unaware of their use on the hosts. This scenario could
have an adverse effect on communication with the host. This document
proposes changes to the SLAAC algorithm that will explicitly allow
routers to learn of these stale prefixes that are still assigned on
the network.
Status of This Memo
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This Internet-Draft will expire on November 19, 2020.
Copyright Notice
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3
2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 3
3. SLAAC reaction to new PIOs . . . . . . . . . . . . . . . . . . 3
3.1. Proposed Change . . . . . . . . . . . . . . . . . . . . . 4
4. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 4
5. Security Considerations . . . . . . . . . . . . . . . . . . . 4
6. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 4
7. References . . . . . . . . . . . . . . . . . . . . . . . . . . 4
7.1. Normative References . . . . . . . . . . . . . . . . . . . 4
7.2. Informative References . . . . . . . . . . . . . . . . . . 6
Appendix A. Suggested Garbage collection of stale prefix
information . . . . . . . . . . . . . . . . . . . . . . . 6
A.1 Prefix Validation . . . . . . . . . . . . . . . . . . . . . 7
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 7
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1. Introduction
After a renumbering event in an IPv6 network utilizing SLAAC, hosts
might continue to use stale addresses, as they are unaware of the
changes. Likewise, routers, who may deprecate the use of these
prefixes, are unaware of their use on the hosts. This scenario, with
its causes and impacts are well documented in [I-D.ietf-v6ops-slaac-
renum] and [I-D.linkova-6man-default-addr-selection-update]. A key
factor with this issue is the lack of explicit signaling. For various
reasons, routers might not explicitly signal the network that there
is a renumbering event. Once the renumbering event has occurred,
there are no means to learn of the stale prefixes that might still be
present on the network. Without a means to do a garbage collection,
the network is limited to the aging out process of stale
information.
Rather than aging out, it would be better for routers to learn of
this information, in a proactive manner. Using Neighbor Discovery
messages, the router could learn of the stale prefixes.
While it is not the objective of this document to propose how the
stale prefix information is validated and deprecated, an example of
how this might be done is given in Appendix A.
2. Terminology
The term "globally reachable" is used in this document as defined in
[RFC8190].
The term "Global Unicast Address" (or its acronym "GUA") is used
throughout this document to refer to "globally reachable" [RFC8190]
addresses. That is, when used throughout this document, GUAs do NOT
include Unique Local Addresses (ULAs) [RFC4193]. Similarly, the term
"Global Unicast prefix" (or "GUA prefix") is employed throughout this
document to refer to network prefixes that specify GUAs, and does NOT
include the ULA prefix (FC00::/7) [RFC4193].
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and
"OPTIONAL" in this document are to be interpreted as described in BCP
14 [RFC2119] [RFC8174] when, and only when, they appear in all
capitals, as shown here.
3. SLAAC reaction to new PIOs
In the absence of RA messages to deprecate stale prefixes, when RAs
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are received with new PIO information, SLAAC hosts will form
additional IPv6 address on the interface. This could lead to a
situation where there are multiple addresses assigned to an
interface, while only a subset of them are valid. As previously
stated, with the current algorithm, there is no explicit way to
inform routers of the stale prefixes that are currently assigned to
the interfaces.
3.1. Proposed Change
When an address transitions from being tentative to preferred, for
each SLAAC assigned GUA address on the interface, the host should
send router solicitation messages, using the GUA as the source
address. Routers receiving the solicitation messages can deduce the
prefixes that are currently assigned to interfaces on the network.
They can then determine if these prefixes are still valid, and
proceed to deprecate them if they are not.
An alternate solution would use unsolicited Neighbor Advertisement,
similar to what is proposed in [I-D.ietf-6man-grand-03]. This would
still require NA messages for each SLAAC assigned GUA address on the
interface.
4. IANA Considerations
This document has no actions for IANA.
5. Security Considerations
It is not believed that this introduces any additional security risk.
6. Acknowledgments
The author would like to acknowledge Jen Linkova, Fernando Gont, Jan
Zorz and Richard Patterson for the work they have previously done on
this issue.
7. References
7.1. Normative References
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119,
DOI 10.17487/RFC2119, March 1997,
<https://www.rfc-editor.org/info/rfc2119>.
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[RFC4193] Hinden, R. and B. Haberman, "Unique Local IPv6 Unicast
Addresses", RFC 4193, DOI 10.17487/RFC4193, October 2005,
<https://www.rfc-editor.org/info/rfc4193>.
[RFC4861] Narten, T., Nordmark, E., Simpson, W., and H. Soliman,
"Neighbor Discovery for IP version 6 (IPv6)", RFC 4861,
DOI 10.17487/RFC4861, September 2007,
<https://www.rfc-editor.org/info/rfc4861>.
[RFC4862] Thomson, S., Narten, T., and T. Jinmei, "IPv6 Stateless
Address Autoconfiguration", RFC 4862,
DOI 10.17487/RFC4862, September 2007,
<https://www.rfc-editor.org/info/rfc4862>.
[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,
<https://www.rfc-editor.org/info/rfc8028>.
[RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC
2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174,
May 2017, <https://www.rfc-editor.org/info/rfc8174>.
[RFC8190] Bonica, R., Cotton, M., Haberman, B., and L. Vegoda,
"Updates to the Special-Purpose IP Address Registries",
BCP 153, RFC 8190, DOI 10.17487/RFC8190, June 2017,
<https://www.rfc-editor.org/info/rfc8190>.
[RFC8504] Chown, T., Loughney, J., and T. Winters, "IPv6 Node
Requirements", BCP 220, RFC 8504, DOI 10.17487/RFC8504,
January 2019, <https://www.rfc-editor.org/info/rfc8504>.
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7.2. Informative References
[I-D.ietf-v6ops-cpe-slaac-renum]
Gont, F., Zorz, J., Patterson, R., and B. Volz, "Improving
the Reaction of Customer Edge Routers to Renumbering
Events", draft-ietf-v6ops-cpe-slaac-renum-02 (work in
progress), May 2020.
[I-D.ietf-v6ops-slaac-renum]
Gont, F., Zorz, J., and R. Patterson, "Reaction
of Stateless Address Autoconfiguration (SLAAC) to Flash-
Renumbering Events", draft-ietf-v6ops-slaac-renum-04
(work in progress), September 2020.
[I-D.ietf-6man-slaac-renum]
Gont, F., Zorz, J., and R. Patterson, "Improving the
Robustness of Stateless Address Autoconfiguration (SLAAC)
to Flash Renumbering Events",
draft-ietf-6man-slaac-renum-01 (work in progress),
September 2020.
[I-D.linkova-6man-default-addr-selection-update]
Linkova, J., "Default Address Selection and Subnet
Renumbering",
draft-linkova-6man-default-addr-selection-00
(work in progress), March 2017.
[I-D.ietf-6man-grand-03]
Linkova, J., "Gratuitous Neighbor Discovery: Creating
Neighbor Cache Entries on First-Hop Routers",
draft-ietf-6man-grand-03 (work in progress), March 2017.
Appendix A. Suggested Garbage collection of stale prefix information
Consider a scenario where a service provider is using non-persistent
prefixes. If the router were to reboot, for whatever reason, then the
a new PD is assigned to the router. The router will then start to
include the new PIOs in its RA messages. At this point, hosts on the
LAN will assign additional IPv6 addresses from the new prefix, on
their interface. Using the proposed algorithm, the router will
receive RS messages from hosts with source address from the stale
prefixes.
Upon receipt of the RS messages, the router can proceed to create a
neighbor cache for the address. Before creating the neighbor cache,
it should validate that the prefix is valid for the LAN interface.
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Once validated, the neighbor cache entry can be created. A list of
unmanaged on-link prefixes should also be maintained. These prefixes
should not be included in its RA messages.
If the prefix validation is not successful, the router should
deprecate the prefix in its RA messages.
A.1 Prefix Validation
Routers should maintain a list for "unmanaged on-link prefixes".
These are prefixes that the router has determined are on-link, but
are not included in its RA messages. The list may be maintained by
static configuration, dynamic methods or both.
To validate a prefix, the router may do the following
o Check if the prefix is included in the list of unmanaged on-link
prefixes for the received interface. If not included, continue
with other validation steps. Otherwise, conclude the validation
with a success.
o Use a protocol (e.g. DHCPv6 leasequery) to check who the prefix is
assigned to. If assigned to itself, it should begin to include the
prefix in its RA messages and conclude the validation process with
a success.
o Send a RS message on the interface, and listen to see if the
prefix is included in received RA messages. RS messages must be
sent with unspecified source address, so that hosts will not
change the IsRouter flag for the router. If the prefix is
included, the unmanaged on-link list should be updated, and the
validation concluded as successful.
Authors' Addresses
Loba Olopade
Virgin Media
Email: loba.olopade@virginmedia.co.uk
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