Internet DRAFT - draft-krishnan-6man-maxra
draft-krishnan-6man-maxra
IPv6 Maintenance S. Krishnan
Internet-Draft Ericsson
Updates: 4861 (if approved) J. Korhonen
Intended status: Standards Track Broadcom
Expires: April 20, 2016 S. Chakrabarti
Ericsson
E. Nordmark
Arista Networks
A. Yourtchenko
cisco
October 18, 2015
Support for adjustable maximum router lifetimes per-link
draft-krishnan-6man-maxra-03
Abstract
The 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 April 20, 2016.
Copyright Notice
Copyright (c) 2015 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
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 2
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 . . . . . . . . . . . . . . . . . . . . . . . . . 4
9.1. Normative References . . . . . . . . . . . . . . . . . . 5
9.2. Informative References . . . . . . . . . . . . . . . . . 5
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 5
1. Introduction
IPv6 Neighbor Discovery relies on IP multicast with the expectation
to be efficient with respect to available bandwidth and to avoid
generating interrupts in the network nodes. On some datalink-layer
network, for example IEEE 802.11 WiFi, this is not the case because
of limitations in the services offered by the datalink-layer network
[draft-vyncke-6man-mcast-not-efficient-01]. 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
how to tune protocol constants for certain system with the
expectation to reduce excess Neighbor Discovery Protocol (NDP)
traffic. 3GPP cellular links are one existing example
[RFC6459][RFC7066].
This document specifies updates to the IPv6 Neighbor Discovery
Protocol [RFC4861] for relaxing the the maximum time allowed between
sending unsolicited multicast Router Advertisements (RA) from a
router interface as well as for the maximum router lifetime.
2. Terminology
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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 the two
successive Router Advertisement messages are sent, therefore one
might reason about the relationship between these two values in terms
of the ratio K=AdvDefaultLifetime/MaxRtrAdvInterval, which expresses
how many Router Advertisements will be guaranteed to be sent before
the router lifetime expiry.
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 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 the 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 6.2.1. of [RFC4861] to update the
following router configuration variables. MaxRtrAdvInterval MUST be
no greater than 65535. AdvDefaultLifetime MUST be between
MaxRtrAdvInterval and 65535.
This document also updates Sections 6.2.1., 6.2.2., 6.2.4. and 6.2.5.
of [RFC4861] so that AdvSendAdvertisements can be set "FALSE" but the
router would still continue be a router and respond with RAs to
solicited RSes .
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
attack window for a rogue router to send an unsolicited RA is greatly
increased. These attacks can easily be prevented by using 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 and Jeena Rachel John for their comments and suggestions that
improved this document.
9. References
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9.1. Normative References
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
[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.
9.2. Informative References
[RFC6459] Korhonen, J., Soininen, J., Patil, B., Savolainen, T.,
Bajko, G., and K. Iisakkila, "IPv6 in 3rd Generation
Partnership Project (3GPP) Evolved Packet System (EPS)",
RFC 6459, January 2012.
[RFC7066] Korhonen, J., Arkko, J., Savolainen, T., and S. Krishnan,
"IPv6 for Third Generation Partnership Project (3GPP)
Cellular Hosts", RFC 7066, November 2013.
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
Jouni Korhonen
Broadcom
Porkkalankatu 24
FIN-00180 Helsinki
Finland
Email: jouni.nospam@gmail.com
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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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