Internet DRAFT - draft-pignataro-mpls-reserved-labels-lb
draft-pignataro-mpls-reserved-labels-lb
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.
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This Internet-Draft will expire on August 20, 2013.
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Copyright Notice
Copyright (c) 2013 IETF Trust and the persons identified as the
document authors. All rights reserved.
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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
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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.
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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.
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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
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