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Kompella 7 Juniper Networks 8 February 16, 2013 10 The Use of MPLS Special Purpose Labels for the Computation of Load 11 Balancing 12 draft-pignataro-mpls-reserved-labels-lb-01 14 Abstract 16 In addition to being used for forwarding, an MPLS label stack may 17 also be used as an entropy source to perform load balancing 18 computation in various ways. RFC 4928 and RFC 6790 describe this 19 mechanism in great detail. However, those two RFCs differ in the use 20 of MPLS special purpose labels (previously referred to as "reserved 21 labels") for computation of load balancing. This document addresses 22 this difference in specifications by providing a more comprehensive 23 set of recommendations. 25 This document updates RFC 4928 and RFC 6790. 27 Requirements Language 29 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", 30 "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this 31 document are to be interpreted as described in [RFC2119]. 33 Status of this Memo 35 This Internet-Draft is submitted in full conformance with the 36 provisions of BCP 78 and BCP 79. 38 Internet-Drafts are working documents of the Internet Engineering 39 Task Force (IETF). Note that other groups may also distribute 40 working documents as Internet-Drafts. The list of current Internet- 41 Drafts is at http://datatracker.ietf.org/drafts/current/. 43 Internet-Drafts are draft documents valid for a maximum of six months 44 and may be updated, replaced, or obsoleted by other documents at any 45 time. It is inappropriate to use Internet-Drafts as reference 46 material or to cite them other than as "work in progress." 48 This Internet-Draft will expire on August 20, 2013. 50 Copyright Notice 52 Copyright (c) 2013 IETF Trust and the persons identified as the 53 document authors. All rights reserved. 55 This document is subject to BCP 78 and the IETF Trust's Legal 56 Provisions Relating to IETF Documents 57 (http://trustee.ietf.org/license-info) in effect on the date of 58 publication of this document. Please review these documents 59 carefully, as they describe your rights and restrictions with respect 60 to this document. Code Components extracted from this document must 61 include Simplified BSD License text as described in Section 4.e of 62 the Trust Legal Provisions and are provided without warranty as 63 described in the Simplified BSD License. 65 Table of Contents 67 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3 68 2. MPLS Special Purpose Labels and Load Balancing . . . . . . . . 3 69 2.1. Current Specifications . . . . . . . . . . . . . . . . . . 3 70 2.2. Detail of Updates . . . . . . . . . . . . . . . . . . . . . 4 71 3. IANA Considerations . . . . . . . . . . . . . . . . . . . . . . 4 72 4. Security Considerations . . . . . . . . . . . . . . . . . . . . 4 73 5. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 4 74 6. Normative References . . . . . . . . . . . . . . . . . . . . . 5 75 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 5 77 1. Introduction 79 In addition to being used for forwarding, an MPLS label stack may 80 also be used as an entropy source to perform load balancing 81 computation in various ways. RFC 4928 [RFC4928] and RFC 6790 82 [RFC6790] describe this mechanism in great detail. However, those 83 two RFCs differ in the use of MPLS special purpose labels (previously 84 referred to as "reserved labels") for computation of load balancing. 85 This document addresses this difference in specifications by 86 providing a more comprehensive set of recommendations. 88 This document updates RFC 4928 and RFC 6790. 90 2. MPLS Special Purpose Labels and Load Balancing 92 2.1. Current Specifications 94 This section highlights current specifications relating to the usage 95 of MPLS special purpose labels for purposes of load balancing 96 computation. 98 [RFC4928] states that special purpose labels ("reserved labels") may 99 be used for load balancing, and describes current ECMP practice as 100 follows: 102 It must also be noted that LSRs that correctly identify a payload 103 as not being IP most often will load-share traffic across multiple 104 equal-cost paths based on the label stack. Any reserved label, no 105 matter where it is located in the stack, may be included in the 106 computation for load balancing. Modification of the label stack 107 between packets of a single flow could result in re-ordering that 108 flow. That is, were an explicit null or a router-alert label to 109 be added to a packet, that packet could take a different path 110 through the network. 112 [RFC6790], conversely, succintly states that special purpose labels 113 ("reserved labels") MUST NOT be used for load balancing: 115 If a transit LSR recognizes the ELI, it MAY choose to load balance 116 solely on the following label (the EL); otherwise, it SHOULD use 117 as much of the whole label stack as feasible as keys for the load- 118 balancing function. In any case, reserved labels MUST NOT be used 119 as keys for the load-balancing function. 121 2.2. Detail of Updates 123 There are several MPLS special purpose labels. MPLS special purpose 124 labels have special meaning both in the control plane and the data 125 plane, including an indication for OAM. OAM packets not taking the 126 same path as data packets defeats their purpose. 128 On the other hand, it is existing practice that MPLS equipment load 129 balances on the full label stack, or on portions of the full label 130 stack irrespective of the value of the label, as documented in 131 [RFC4928]. A new specification cannot automatically render obsolete 132 equipment that conformed to a prior documented specification. 134 Consequently, this document updates RFC 4928 and RFC 6790 by 135 specifying that: 137 1. It is RECOMMENDED that new implementations of MPLS equipment do 138 not use MPLS special purpose labels as input into the load 139 balancing computation. 141 2. MPLS forwarding equipment SHOULD document their load-balancing 142 behavior in presence of MPLS special purpose labels. 144 3. IANA Considerations 146 This document makes no request of IANA. 148 [Note to RFC Editor: this section may be removed on publication as 149 an RFC.] 151 4. Security Considerations 153 This document updates RFC 4928 and RFC 6790 by providing a more 154 comprehensive set of recommendation on the use of MPLS special 155 purpose labels as input into the load-balancing computations. The 156 security considerations of these two RFCs are unchanged. This update 157 does not impose any new security considerations. 159 5. Acknowledgements 161 The authors would like to thank thorough reviews and useful comments 162 and suggestions from Stewart Bryant, Adrian Farrel, and John E. 163 Drake. 165 6. Normative References 167 [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate 168 Requirement Levels", BCP 14, RFC 2119, March 1997. 170 [RFC4928] Swallow, G., Bryant, S., and L. Andersson, "Avoiding Equal 171 Cost Multipath Treatment in MPLS Networks", BCP 128, 172 RFC 4928, June 2007. 174 [RFC6790] Kompella, K., Drake, J., Amante, S., Henderickx, W., and 175 L. Yong, "The Use of Entropy Labels in MPLS Forwarding", 176 RFC 6790, November 2012. 178 Authors' Addresses 180 Carlos Pignataro 181 Cisco Systems, Inc. 183 Email: cpignata@cisco.com 185 Loa Andersson 186 Huawei Technologies 188 Email: loa@mail01.huawei.com 190 Kireeti Kompella 191 Juniper Networks 193 Email: kireeti.kompella@gmail.com