Signaling Entropy Label Capability Using OSPF
draft-xu-ospf-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 via signaling that it can process ELs on that tunnel. This draft defines a mechanism to signal that capability using OSPF. This mechanism is useful when the label advertisement is also done via OSPF.

Status of This Memo

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Table of Contents

• 1. Introduction
• 1.1. Requirements Language
• 2. Terminology
• 3. Advertising ELC Using OSPF
• 4. Advertising RLSDC Using OSPF
• 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 on 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 OSPF [I-D.ietf-ospf-segment-routing-extensions] . In such scenario the signaling mechanisms defined in [RFC6790] are inadequate. This draft defines a mechanism to signal the ELC using OSPF. This mechanism is useful when the label advertisement is also done via OSPF. 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 [RFC4970].

3. Advertising ELC Using OSPF

The OSPF Router Information (RI) Opaque LSA defined in [RFC4970] is used by OSPF routers to announce their capabilities. A new TLV within the body of this LSA, called ELC TLV is defined to advertise the capability of the router to process the ELs. It is formatted as described in Section 2.1 of [RFC4970]. This TLV is applicable to both OSPFv2 and OSPFv3. The Type for the ELC TLV needs to be assigned by IANA and it has a Length of zero. The scope of the advertisement depends on the application but it is recommended that it SHOULD be AS-scoped.

4. Advertising RLSDC Using OSPF

A new TLV within the body of the OSPF RI LSA, called RLSDC TLV is defined to advertise the capability of the router to read the maximum label stack depth. It is formatted as described in Section 2.1 of [RFC4970] 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 TLV. This TLV is applicable to both OSPFv2 and OSPFv3.

5. Acknowledgements

The authors would like to thank Yimin Shen and George Swallow for their comments.

6. IANA Considerations

This memo includes a request to IANA to allocate two TLV types from the OSPF RI TLVs registry.

7. Security Considerations

This document does not introduce any new security risk.

8. References

8.1. Normative References

8.2. Informative References

Authors' Addresses