Signaling Entropy Label Capability Using IS-IS
draft-xu-isis-mpls-elc-01

Abstract

Multi Protocol Label Switching (MPLS) has defined a mechanism to load balance traffic flows using Entropy Labels (EL). An ingress LSR cannot insert ELs for packets going into a given tunnel unless an egress LSR has indicated that it can process ELs for that tunnel. This draft defines a mechanism to signal that capability using IS-IS. This mechanism is useful when the label advertisement is also done via IS-IS.

Status of This Memo

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This Internet-Draft will expire on April 2, 2015.

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Table of Contents

• 1. Introduction
• 1.1. Requirements Language
• 2. Terminology
• 3. Advertising ELC using IS-IS
• 4. Advertising RLSDC using IS-IS
• 5. Acknowledgements
• 6. IANA Considerations
• 7. Security Considerations
• 8. References
• 8.1. Normative References
• 8.2. Informative References
• Authors' Addresses

1. Introduction

Multi Protocol Label Switching (MPLS) has defined a method in [RFC6790] to load balance traffic flows using Entropy Labels (EL). An ingress LSR cannot insert ELs for packets going into a given tunnel unless an egress LSR has indicated that it can process ELs for that tunnel. [RFC6790] defines the signaling of this capability (a.k.a Entropy Label Capability - ELC) via signaling protocols. Recently, mechanisms are being defined to signal labels via link state Interior Gateway Protocols (IGP) such as IS-IS [I-D.ietf-isis-segment-routing-extensions]. In such scenario the signaling mechanisms defined in [RFC6790] are inadequate. This draft defines a mechanism to signal the ELC using IS-IS. This mechanism is useful when the label advertisement is also done via IS-IS. [In addition, in the cases where stacked LSPs are used for whatever reasons (e.g., SPRING-MPLS [I-D.gredler-spring-mpls] [I-D.filsfils-spring-segment-routing-mpls]), it would be useful for ingress LSRs to know each LSR's capability of reading the maximum label stack deepth. This capability, referred to as Readable Label Stack Deepth Capability (RLSDC) can be used by ingress LSRs to determine whether it's necessary to insert an EL for a given LSP tunnel in the case where there has already been at least one EL in the label stack [I-D.kini-mpls-spring-entropy-label] . Of course, even it has been determined that it's neccessary to insert an EL for a given LSP tunnel, if the egress LSR of that LSP tunnel has not yet indicated that it can process ELs for that tunnel, the ingress LSR MUST NOT include an entropy label for that tunnel as well. ]

1.1. 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 RFC 2119 [RFC2119].

2. Terminology

This memo makes use of the terms defined in [RFC6790] and [RFC4971].

3. Advertising ELC using IS-IS

The IS-IS Router CAPABILITY TLV defined in [RFC4971] is used by IS-IS routers to announce their capabilities. A new sub-TLV of this TLV, called ELC sub-TLV is defined to advertise the capability of the router to process the ELs. It is formatted as described in [RFC5305] with a Type code to be assigned by IANA and a Length of zero. The scope of the advertisement depends on the application but it is RECOMMENDED that it SHOULD be domain-wide. If a router has multiple linecards, the router MUST NOT advertise the ELC unless all of the linecards are capable of processing ELs.

4. Advertising RLSDC using IS-IS

A new sub-TLV of the IS-IS Router CAPABILITY TLV, called RLSDC sub-TLV is defined to advertise the capability of the router to read the maximum label stack depth. It is formatted as described in [RFC5305] with a Type code to be assigned by IANA and a Length of one. The Value field is set to the maximum readable label stack deepth in the range between 1 to 255. The scope of the advertisement depends on the application but it is RECOMMENDED that it SHOULD be domain-wide. If a router has multiple linecards with different capabilities of reading the maximum label stack deepth, the router MUST advertise the smallest one in the RLSDC sub-TLV.

5. Acknowledgements

The authors would like to thank Yimin Shen and George Swallow for their valuable comments on the draft.

6. IANA Considerations

This memo includes a request to IANA to allocate two sub-TLV types within the IS-IS Router Capability TLV.

7. Security Considerations

This document does not introduce any new security risk.

8. References

8.1. Normative References

8.2. Informative References

Authors' Addresses