Internet DRAFT - draft-ietf-6man-maxra
draft-ietf-6man-maxra
IPv6 Maintenance S. Krishnan
Internet-Draft Kaloom
Updates: 4861 (if approved) J. Korhonen
Intended status: Standards Track Broadcom
Expires: June 1, 2018 S. Chakrabarti
Ericsson
E. Nordmark
Arista Networks
A. Yourtchenko
cisco
November 28, 2017
Support for adjustable maximum router lifetimes per-link
draft-ietf-6man-maxra-04
Abstract
The IPv6 Neighbor Discovery protocol specifies the maximum time
allowed between sending unsolicited multicast Router Advertisements
from a router interface as well as the maximum router lifetime. It
also allows the limits to be overridden by link-layer specific
documents. This document allows for overriding these values on a
per-link basis.
Status of This Memo
This Internet-Draft is submitted in full conformance with the
provisions of BCP 78 and BCP 79.
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This Internet-Draft will expire on June 1, 2018.
Copyright Notice
Copyright (c) 2017 IETF Trust and the persons identified as the
document authors. All rights reserved.
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 3
3. Relationship between AdvDefaultLifetime and MaxRtrAdvInterval 3
4. Updates to RFC4861 . . . . . . . . . . . . . . . . . . . . . 4
5. Host Behavior . . . . . . . . . . . . . . . . . . . . . . . . 4
6. Security Considerations . . . . . . . . . . . . . . . . . . . 4
7. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 4
8. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 4
9. References . . . . . . . . . . . . . . . . . . . . . . . . . 5
9.1. Normative References . . . . . . . . . . . . . . . . . . 5
9.2. Informative References . . . . . . . . . . . . . . . . . 5
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 5
1. Introduction
IPv6 Neighbor Discovery relies on IP multicast based on the
expectation that multicast makes efficient use of available bandwidth
and avoids generating interrupts in the network nodes. On some
datalink layers multicast may not be natively supported. On such
links, any possible reduction of multicast traffic will be highly
beneficial. Unfortunately, due to the fixed protocol constants
specified in [RFC4861], it is difficult to relax the multicast timers
for neighbor discovery. There are already link technology specific
clarifications describing how to tune the Neighbor Discovery Protocol
(NDP) constants for certain systems with in order to reduce excess
NDP traffic. e.g. [RFC6459][RFC7066] contain such clarifications for
3GPP cellular links.
This document specifies updates to the IPv6 Neighbor Discovery
Protocol [RFC4861] for increasing the the maximum time allowed
between sending unsolicited multicast Router Advertisements (RA) from
a router interface as well as for the maximum router lifetime.
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2. Terminology
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. Relationship between AdvDefaultLifetime and MaxRtrAdvInterval
MaxRtrAdvInterval is an upper bound on the time between which two
successive Router Advertisement messages are sent. Therefore one
might reason about the relationship between these two values in terms
of a ratio K=AdvDefaultLifetime/MaxRtrAdvInterval, which expresses
how many Router Advertisements will be guaranteed to be sent before
the router lifetime expires.
Assuming unicast Solicited Router Advertisements or a perfectly
stable network, on a theoretically perfect link with no losses, it
would have been sufficient to have K just above 1 - so that the sent
Router Advertisement refreshes the router entry just before it
expires. On the real links which allow for some loss, one would need
to use K>2 in order to minimize the chances of a single router
advertisement loss causing a loss of the router entry.
The exact calculation will depend on the packet loss probability. An
example: if we take a ballpark value of 1% probability of a packet
loss, then K=2 will give 0.01% percent chance of an outage due to a
packet loss, K=3 will give 0.0001% chance of an outage, and so forth.
To reverse the numbers, with these parameters, K~=1 gives 99%
reliability, K~=2 gives 99.99% reliability, and K~=3 gives 99.9999%
reliability - the latter should be good enough for a lot of
scenarios.
In a network with higher packet loss probabilities or if the higher
reliability is desired, the K might be chosen to be even higher. On
the other hand, some of the data link layers provide reliable
delivery at layer 2 - so there one might even consider using the
"theoretical" value of K just above 1. Since the choice of these two
parameters does not impact interoperability per se, this document
does not impose any specific constraints on their values other than
providing the guidelines in this section, therefore each individual
link can optimize accordingly to its use case.
Also AdvDefaultLifetime MUST be set to a value greater than or equal
to the selected MaxRtrAdvInterval. Otherwise, a router lifetime is
guaranteed to expire before the new Router Advertisement has a chance
to be sent, thereby creating an outage.
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4. Updates to RFC4861
This document updates Section 4.2 and Section 6.2.1. of [RFC4861] to
update the following router configuration variables.
In Section 4.2, inside the paragraph that defines Router Lifetime,
change 9000 to 65535 seconds.
In Section 6.2.1, inside the paragraph that defines
MaxRtrAdvInterval, change 1800 to 65535 seconds.
In Section 6.2.1, inside the paragraph that defines
AdvDefaultLifetime, change 9000 to 65535 seconds.
As explained in Section 3, the relationship between MaxRtrAdvInterval
and AdvDefaultLifetime must be chosen to take into account the
probability of packet loss.
5. Host Behavior
Legacy hosts on a link with updated routers may have issues with a
Router Lifetime of more than 9000 seconds. In the few
implementations we have tested with general purpose operating
systems, there does not seem to be any issues with setting this field
to more than 9000, but there might be implementations that
incorrectly (since RFC4861 requires receivers to handle any value)
reject such RAs.
6. Security Considerations
On a link where router advertisements are few and far between, the
detrimental effects of a rogue router that sends an unsolicited RA
are greatly increased. These rogue RAs can be prevented by using
approaches like RA-Guard [RFC6105] and SeND [RFC3971]
7. IANA Considerations
This document does not require any IANA action.
8. Acknowledgements
The authors would like to thank the members of the 6man efficient ND
design team for their comments that led to the creation of this
draft. The authors would also like to thank Lorenzo Colitti, Erik
Kline, Jeena Rachel John, Brian Carpenter, Tim Chown, Fernando Gont,
Warren Kumari and Adam Roach for their comments and suggestions that
improved this document.
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9. References
9.1. 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>.
[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>.
9.2. Informative References
[RFC3971] Arkko, J., Ed., Kempf, J., Zill, B., and P. Nikander,
"SEcure Neighbor Discovery (SEND)", RFC 3971,
DOI 10.17487/RFC3971, March 2005,
<https://www.rfc-editor.org/info/rfc3971>.
[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,
<https://www.rfc-editor.org/info/rfc6105>.
[RFC6459] Korhonen, J., Ed., Soininen, J., Patil, B., Savolainen,
T., Bajko, G., and K. Iisakkila, "IPv6 in 3rd Generation
Partnership Project (3GPP) Evolved Packet System (EPS)",
RFC 6459, DOI 10.17487/RFC6459, January 2012,
<https://www.rfc-editor.org/info/rfc6459>.
[RFC7066] Korhonen, J., Ed., Arkko, J., Ed., Savolainen, T., and S.
Krishnan, "IPv6 for Third Generation Partnership Project
(3GPP) Cellular Hosts", RFC 7066, DOI 10.17487/RFC7066,
November 2013, <https://www.rfc-editor.org/info/rfc7066>.
Authors' Addresses
Suresh Krishnan
Kaloom
335 Rue Peel
Montreal, QC
Canada
Email: suresh@kaloom.com
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Jouni Korhonen
Broadcom
Porkkalankatu 24
FIN-00180 Helsinki
Finland
Email: jouni.nospam@gmail.com
Samita Chakrabarti
Ericsson
USA
Email: samita.chakrabarti@ericsson.com
Erik Nordmark
Arista Networks
Santa Clara, CA
USA
Email: nordmark@acm.org
Andrew Yourtchenko
cisco
6b de Kleetlaan
Diegem 1831
Belgium
Email: ayourtch@cisco.com
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