Internet DRAFT - draft-smith-6man-accurate-ra-router-lifetime
draft-smith-6man-accurate-ra-router-lifetime
Internet Engineering Task Force M. Smith
Internet-Draft May 4, 2021
Updates: 4861 (if approved)
Intended status: Standards Track
Expires: November 5, 2021
More Accurately Naming IPv6 RA Router Lifetime
draft-smith-6man-accurate-ra-router-lifetime-00
Abstract
IPv6 Router Advertisements (RAs) have a "Router Lifetime" field,
which specifies how long the advertising router will act as a default
router for the receiving hosts, unless refreshed with another
advertisement. The field name "Router Lifetime" is quite general,
and could easily be misunderstood to mean the bounded lifetime of all
of the information contained in the RA. This memo more accurately
renames this field "Default Router Lifetime".
Status of This Memo
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provisions of BCP 78 and BCP 79.
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This Internet-Draft will expire on November 5, 2021.
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
2. Updates to RFC4861 . . . . . . . . . . . . . . . . . . . . . 3
3. Zero Value Default Router Lifetime Example Use Case . . . . . 3
4. Security Considerations . . . . . . . . . . . . . . . . . . . 4
5. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 4
6. Change Log [RFC Editor please remove] . . . . . . . . . . . . 4
7. Informative References . . . . . . . . . . . . . . . . . . . 4
Author's Address . . . . . . . . . . . . . . . . . . . . . . . . 4
1. Introduction
According to [RFC4861], Router Advertisements (RAs) are used by IPv6
routers to
[...] advertise their presence together with various link and
Internet parameters either periodically, or in response to a
Router Solicitation message. Router Advertisements contain
prefixes that are used for determining whether another address
shares the same link (on-link determination) and/or address
configuration, a suggested hop limit value, etc.
The Router Lifetime field of an RA indicates whether or not the
advertising router will act as a default router for the receiving
IPv6 hosts, and if so, for how many seconds it will perform that
role, unless it is refreshed by a subsequent RA from the router. The
router is identified by its sending interface's Link-Local address
[RFC4861].
If the RA Router Lifetime field value is zero, it means that the
router is not or will no longer be acting as a default router.
Router Advertisements can carry options such as the Prefix
Information option. These options are required to have their own
lifetime fields if necessary [RFC4861].
As the field name "Router Lifetime" is quite general, and is a
permanent field in a Router Advertisement, the purpose of this field
can be easily misunderstood. It could easily be misinterpreted as a
maximum lifetime value applying to all of the parameters and options
in the RA, acting as a constraint on all other lifetime values within
the RA and its options. A Router Lifetime value of zero could seem
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to indicate that the RA is entirely invalid and that all of its
contents should or must be ignored by the receivers of the RA.
This memo renames the Router Lifetime field to "Default Router
Lifetime", more accurately and explicitly describing its purpose.
2. Updates to RFC4861
For all instances of the term "router lifetime", the term "default
router lifetime" is to be used, independent of letter case.
When the term "lifetime" is used in the context of an IPv6 Router
Advertisment, implying "router lifetime", it will now imply "default
router lifetime."
No other updates are needed, as the Default Router List host
conceptual data structure, and the AdvDefaultLifetime router
interface configuration variable, already use "default" terminology.
3. Zero Value Default Router Lifetime Example Use Case
The use of a non-zero Default Router Lifetime is obvious; the router
sending these RAs is willing to act as a default router for the
receiving hosts.
An example of a router sending a zero value Default Router Lifetime
is as follows.
On a link, there is a router acting as a default router for the
attached hosts. This router is providing forwarding to default,
unspecified destinations, such as the IPv6 Internet. The router's
RAs have a non-zero value Default Router Lifetime, such as the
[RFC4861] AdvDefaultLifetime default value of 1800 seconds (30
minutes).
Also attached to the link is another router that is sending RAs with
a zero value Default Router Lifetime. This router is also attached
to another link and path to a specific destination. Within these RAs
is a Route Information Option (RIO) [RFC4191], specifying an IPv6
prefix covering the IPv6 address space reachable over the other link
and path.
Hosts receiving these zero value Default Router Lifetime RAs, that
understand the Route Information Option, will send packets towards
destinations within the prefix directly to the RIO advertising
router, benefitting from a more optimal forwarding path, and also
removing traffic forwarding load from the link's default router.
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The router advertising itself as a default router will need to know
about this other router and the address space reachable beyond it, so
that it can forward traffic towards the the other link and path, for
hosts that do not understand the Route Information Option.
4. Security Considerations
Security vulnerabilties can be created if the purpose or function of
a mechanism is misunderstood. Renaming the IPv6 RA Router Lifetime
field "Default Router Lifetime" will make it clearer what the purpose
and function of this field in IPv6 RAs is.
5. Acknowledgements
Review and comments were provided by YOUR NAME HERE!
This memo was prepared using the xml2rfc tool.
6. Change Log [RFC Editor please remove]
draft-smith-6man-accurate-ra-router-lifetime-00, initial version,
2021-03-09
7. Informative References
[RFC4191] Draves, R. and D. Thaler, "Default Router Preferences and
More-Specific Routes", RFC 4191, DOI 10.17487/RFC4191,
November 2005, <https://www.rfc-editor.org/info/rfc4191>.
[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>.
Author's Address
Mark Smith
PO BOX 521
HEIDELBERG, VIC 3084
AU
Email: markzzzsmith@gmail.com
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