Using the IPv6 Flow Label for Load Balancing in Server Farms
RFC 7098

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Internet Engineering Task Force (IETF)                      B. Carpenter
Request for Comments: 7098                             Univ. of Auckland
Category: Informational                                         S. Jiang
ISSN: 2070-1721                             Huawei Technologies Co., Ltd
                                                              W. Tarreau
                                              HAProxy Technologies, Inc.
                                                            January 2014

      Using the IPv6 Flow Label for Load Balancing in Server Farms

Abstract

   This document describes how the currently specified IPv6 flow label
   can be used to enhance layer 3/4 (L3/4) load distribution and
   balancing for large server farms.

Status of This Memo

   This document is not an Internet Standards Track specification; it is
   published for informational purposes.

   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).  Not all documents
   approved by the IESG are a candidate for any level of Internet
   Standard; see 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/rfc7098.

Copyright Notice

   Copyright (c) 2014 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
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   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, et al.             Informational                     [Page 1]
RFC 7098          Flow Label for Server Load Balancing      January 2014

Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   2
   2.  Summary of Flow Label Specification . . . . . . . . . . . . .   2
   3.  Summary of Server Farm Load-Balancing Techniques  . . . . . .   4
   4.  Applying the Flow Label to Layer 3/4 Load Balancing . . . . .   8
   5.  Security Considerations . . . . . . . . . . . . . . . . . . .  10
   6.  Acknowledgements  . . . . . . . . . . . . . . . . . . . . . .  11
   7.  References  . . . . . . . . . . . . . . . . . . . . . . . . .  12
     7.1.  Normative References  . . . . . . . . . . . . . . . . . .  12
     7.2.  Informative References  . . . . . . . . . . . . . . . . .  12

1.  Introduction

   The IPv6 flow label has been redefined [RFC6437] and is now a
   recommended IPv6 node requirement [RFC6434].  Its use for load
   sharing in multipath routing has been specified [RFC6438].  Another
   scenario in which the flow label could be used is in load
   distribution for large server farms.  Load distribution is a slightly
   more general term than load balancing, but the latter is more
   commonly used.  In the context of a server farm, both terms refer to
   mechanisms that distribute the workload of a server farm among
   different servers in order to optimize performance.  Server load
   balancing commonly applies to HTTP traffic, but most of the
   techniques described would apply to other upper-layer applications as
   well.  This document starts with brief introductions to the flow
   label and to server load-balancing techniques, and then describes how
   the flow label can be used to enhance load balancers operating on IP
   packets and TCP sessions, commonly known as layer 3/4 load balancers.

   The motivation for this approach is to improve the performance of
   most types of layer 3/4 load balancers, especially for traffic
   including multiple IPv6 extension headers and in particular for
   fragmented packets.  Fragmented packets, often the result of
   customers reaching the load balancer via a VPN with a limited MTU,
   are a common performance problem.

2.  Summary of Flow Label Specification

   The IPv6 flow label [RFC6437] is a 20-bit field included in every
   IPv6 header [RFC2460].  It is recommended to be supported in all IPv6
   nodes by [RFC6434].  There is additional background material in
   [RFC6436] and [RFC6294].  According to its definition, the flow label
   should be set to a constant value for a given traffic flow (such as
   an HTTP connection), and that value will belong to a uniform
   statistical distribution, making it potentially valuable for load-
   balancing purposes.

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