Network Working Group C. Pignataro Internet-Draft Cisco Systems, Inc. Updates: 4928, 6790 (if approved) L. Andersson Intended status: Standards Track Huawei Technologies Expires: August 20, 2013 K. Kompella Juniper Networks February 16, 2013 The Use of MPLS Special Purpose Labels for the Computation of Load Balancing draft-pignataro-mpls-reserved-labels-lb-01 Abstract In addition to being used for forwarding, an MPLS label stack may also be used as an entropy source to perform load balancing computation in various ways. RFC 4928 and RFC 6790 describe this mechanism in great detail. However, those two RFCs differ in the use of MPLS special purpose labels (previously referred to as "reserved labels") for computation of load balancing. This document addresses this difference in specifications by providing a more comprehensive set of recommendations. This document updates RFC 4928 and RFC 6790. Requirements Language 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]. Status of this Memo This Internet-Draft is submitted in full conformance with the provisions of BCP 78 and BCP 79. Internet-Drafts are working documents of the Internet Engineering Task Force (IETF). Note that other groups may also distribute working documents as Internet-Drafts. The list of current Internet- Drafts is at http://datatracker.ietf.org/drafts/current/. Internet-Drafts are draft documents valid for a maximum of six months and may be updated, replaced, or obsoleted by other documents at any time. It is inappropriate to use Internet-Drafts as reference material or to cite them other than as "work in progress." This Internet-Draft will expire on August 20, 2013. Pignataro, et al. Expires August 20, 2013 [Page 1] Internet-Draft MPLS Reserved Labels and LB February 2013 Copyright Notice Copyright (c) 2013 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. Table of Contents 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3 2. MPLS Special Purpose Labels and Load Balancing . . . . . . . . 3 2.1. Current Specifications . . . . . . . . . . . . . . . . . . 3 2.2. Detail of Updates . . . . . . . . . . . . . . . . . . . . . 4 3. IANA Considerations . . . . . . . . . . . . . . . . . . . . . . 4 4. Security Considerations . . . . . . . . . . . . . . . . . . . . 4 5. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 4 6. Normative References . . . . . . . . . . . . . . . . . . . . . 5 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 5 Pignataro, et al. Expires August 20, 2013 [Page 2] Internet-Draft MPLS Reserved Labels and LB February 2013 1. Introduction In addition to being used for forwarding, an MPLS label stack may also be used as an entropy source to perform load balancing computation in various ways. RFC 4928 [RFC4928] and RFC 6790 [RFC6790] describe this mechanism in great detail. However, those two RFCs differ in the use of MPLS special purpose labels (previously referred to as "reserved labels") for computation of load balancing. This document addresses this difference in specifications by providing a more comprehensive set of recommendations. This document updates RFC 4928 and RFC 6790. 2. MPLS Special Purpose Labels and Load Balancing 2.1. Current Specifications This section highlights current specifications relating to the usage of MPLS special purpose labels for purposes of load balancing computation. [RFC4928] states that special purpose labels ("reserved labels") may be used for load balancing, and describes current ECMP practice as follows: It must also be noted that LSRs that correctly identify a payload as not being IP most often will load-share traffic across multiple equal-cost paths based on the label stack. Any reserved label, no matter where it is located in the stack, may be included in the computation for load balancing. Modification of the label stack between packets of a single flow could result in re-ordering that flow. That is, were an explicit null or a router-alert label to be added to a packet, that packet could take a different path through the network. [RFC6790], conversely, succintly states that special purpose labels ("reserved labels") MUST NOT be used for load balancing: If a transit LSR recognizes the ELI, it MAY choose to load balance solely on the following label (the EL); otherwise, it SHOULD use as much of the whole label stack as feasible as keys for the load- balancing function. In any case, reserved labels MUST NOT be used as keys for the load-balancing function. Pignataro, et al. Expires August 20, 2013 [Page 3] Internet-Draft MPLS Reserved Labels and LB February 2013 2.2. Detail of Updates There are several MPLS special purpose labels. MPLS special purpose labels have special meaning both in the control plane and the data plane, including an indication for OAM. OAM packets not taking the same path as data packets defeats their purpose. On the other hand, it is existing practice that MPLS equipment load balances on the full label stack, or on portions of the full label stack irrespective of the value of the label, as documented in [RFC4928]. A new specification cannot automatically render obsolete equipment that conformed to a prior documented specification. Consequently, this document updates RFC 4928 and RFC 6790 by specifying that: 1. It is RECOMMENDED that new implementations of MPLS equipment do not use MPLS special purpose labels as input into the load balancing computation. 2. MPLS forwarding equipment SHOULD document their load-balancing behavior in presence of MPLS special purpose labels. 3. IANA Considerations This document makes no request of IANA. [Note to RFC Editor: this section may be removed on publication as an RFC.] 4. Security Considerations This document updates RFC 4928 and RFC 6790 by providing a more comprehensive set of recommendation on the use of MPLS special purpose labels as input into the load-balancing computations. The security considerations of these two RFCs are unchanged. This update does not impose any new security considerations. 5. Acknowledgements The authors would like to thank thorough reviews and useful comments and suggestions from Stewart Bryant, Adrian Farrel, and John E. Drake. Pignataro, et al. Expires August 20, 2013 [Page 4] Internet-Draft MPLS Reserved Labels and LB February 2013 6. Normative References [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, March 1997. [RFC4928] Swallow, G., Bryant, S., and L. Andersson, "Avoiding Equal Cost Multipath Treatment in MPLS Networks", BCP 128, RFC 4928, June 2007. [RFC6790] Kompella, K., Drake, J., Amante, S., Henderickx, W., and L. Yong, "The Use of Entropy Labels in MPLS Forwarding", RFC 6790, November 2012. Authors' Addresses Carlos Pignataro Cisco Systems, Inc. Email: cpignata@cisco.com Loa Andersson Huawei Technologies Email: loa@mail01.huawei.com Kireeti Kompella Juniper Networks Email: kireeti.kompella@gmail.com Pignataro, et al. Expires August 20, 2013 [Page 5]