Using the IPv6 Flow Label for Equal Cost Multipath Routing and Link Aggregation in Tunnels
RFC 6438
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RFC - Proposed Standard
(November 2011; No errata)
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2015-10-14
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draft-carpenter-flow-ecmp
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RFC 6438 (Proposed Standard)
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Jari Arkko
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Brian Haberman (brian@innovationslab.net) is the document shepherd for this document.
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Internet Engineering Task Force (IETF) B. Carpenter
Request for Comments: 6438 Univ. of Auckland
Category: Standards Track S. Amante
ISSN: 2070-1721 Level 3
November 2011
Using the IPv6 Flow Label for
Equal Cost Multipath Routing and Link Aggregation in Tunnels
Abstract
The IPv6 flow label has certain restrictions on its use. This
document describes how those restrictions apply when using the flow
label for load balancing by equal cost multipath routing and for link
aggregation, particularly for IP-in-IPv6 tunneled traffic.
Status of This Memo
This is an Internet Standards Track document.
This document is a product of the Internet Engineering Task Force
(IETF). It represents the consensus of the IETF community. It has
received public review and has been approved for publication by the
Internet Engineering Steering Group (IESG). Further information on
Internet Standards is available in Section 2 of RFC 5741.
Information about the current status of this document, any errata,
and how to provide feedback on it may be obtained at
http://www.rfc-editor.org/info/rfc6438.
Copyright Notice
Copyright (c) 2011 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
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.
Carpenter & Amante Standards Track [Page 1]
RFC 6438 Flow Label for Tunnel ECMP/LAG November 2011
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 2
1.1. Choice of IP Header Fields for Hash Input . . . . . . . . . 3
1.2. Flow Label Rules . . . . . . . . . . . . . . . . . . . . . 4
2. Normative Notation . . . . . . . . . . . . . . . . . . . . . . 5
3. Guidelines . . . . . . . . . . . . . . . . . . . . . . . . . . 6
4. Security Considerations . . . . . . . . . . . . . . . . . . . . 7
5. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 7
6. References . . . . . . . . . . . . . . . . . . . . . . . . . . 8
6.1. Normative References . . . . . . . . . . . . . . . . . . . 8
6.2. Informative References . . . . . . . . . . . . . . . . . . 8
1. Introduction
When several network paths between the same two nodes are known by
the routing system to be equally good (in terms of capacity and
latency), it may be desirable to share traffic among them. Two such
techniques are known as equal cost multipath (ECMP) routing and link
aggregation (LAG) [IEEE802.1AX]. There are, of course, numerous
possible approaches to this, but certain goals need to be met:
o Maintain roughly equal share of traffic on each path.
(In some cases, the multiple paths might not all have the same
capacity, and the goal might be appropriately weighted traffic
shares rather than equal shares. This would affect the load-
sharing algorithm but would not otherwise change the argument.)
o Minimize or avoid out-of-order delivery for individual traffic
flows.
o Minimize idle time on any path when queue is non-empty.
There is some conflict between these goals: for example, strictly
avoiding idle time could cause a small packet sent on an idle path to
overtake a bigger packet from the same flow, causing out-of-order
delivery.
One lightweight approach to ECMP or LAG is this: if there are N
equally good paths to choose from, then form a modulo(N) hash
[RFC2991] from a defined set of fields in each packet header that are
certain to have the same values throughout the duration of a flow,
and use the resulting output hash value to select a particular path.
If the hash function is chosen so that the output values have a
uniform statistical distribution, this method will share traffic
roughly equally between the N paths. If the header fields included
in the hash input are consistent, all packets from a given flow will
generate the same hash output value, so out-of-order delivery will
Carpenter & Amante Standards Track [Page 2]
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