Signaling Entropy Label Capability and Readable Label-stack Depth Using OSPF
draft-ietf-ospf-mpls-elc-05

Abstract

Multiprotocol Label Switching (MPLS) has defined a mechanism to load balance traffic flows using Entropy Labels (EL). An ingress Label Switching Router (LSR) cannot insert ELs for packets going into a given tunnel unless an egress LSR has indicated via signaling that it has the capability of processing ELs, referred to as Entropy Label Capability (ELC), on that tunnel. In addition, it would be useful for ingress LSRs to know each LSR's capability of reading the maximum label stack depth, referred to as Readable Label-stack Depth (RLD), in the cases where stacked LSPs are used for whatever reasons. This document defines mechanisms to signal these two capabilities using OSPF. These mechanisms are useful when the label advertisement is also done via OSPF. In addition, this document introduces the Router Non-OSPF Functional Capabilities TLV for advertising OSPF router's actual non-OSPF functional capabilities. ELC is one of such non-OSPF functional capabilities.

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.

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 https://datatracker.ietf.org/drafts/current/.

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This Internet-Draft will expire on July 7, 2018.

Copyright Notice

Copyright (c) 2018 IETF Trust and the persons identified as the document authors. All rights reserved.

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Table of Contents

• 1. Introduction
• 2. Terminology
• 3. Non-OSPF Functional Capabilities TLV
• 4. Advertising ELC Using OSPF
• 5. Advertising RLD Using OSPF
• 6. Acknowledgements
• 7. IANA Considerations
• 8. Security Considerations
• 9. References
• 9.1. Normative References
• 9.2. Informative References
• Authors' Addresses

1. Introduction

[RFC6790] describes a method to load balance Multiprotocol Label Switching (MPLS) traffic flows using Entropy Labels (EL). [RFC6790] introduces the concept of Entropy Label Capability (ELC) and defines the signalings of this capability via MPLS 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 [RFC6790] 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.ietf-spring-segment-routing-mpls]), it would be useful for ingress LSRs to know each LSR's capability of reading the maximum label stack depth. This capability, referred to as Readable Label-stack Depth (RLD) may be used by ingress LSRs to determine whether it's necessary to insert an EL for a given LSP of the stacked LSP tunnel in the case where there has already been at least one EL in the label stack [I-D.ietf-mpls-spring-entropy-label].

2. Terminology

This memo makes use of the terms defined in [RFC6790] and [RFC7770].

3. Non-OSPF Functional Capabilities TLV

This document defines the Router Non-OSPF Functional Capabilities TLV for advertisement in the OSPF Router Information LSA. An OSPF router advertising an OSPF RI LSA MAY include the Router Non-OSPF Functional Capabilities TLV. If included, it MUST be included in the first instance of the LSA. Additionally, the TLV MUST reflect the advertising OSPF router's actual non-OSPF functional capabilities in the flooding scope of the containing OSPF RI LSA.

      0                   1                   2                   3
      0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |           Type=TBD1           |            Length             |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |                 Non-OSPF Functional Capabilities              |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
           Figure 1: Non-OSPF Functional Capabilities TLV Format

The format of the Router Non-OSPF Functional Capabilities TLV is as follows:

• Type: TBD1.
• Length: Indicates the length of the value portion in octets and will be a multiple of 4 octets dependent on the number of capabilities advertised. Initially, the length will be 4, denoting 4 octets of non-OSPF functional capability bits.
• Value: A variable-length sequence of capability bits rounded to a multiple of 4 octets padded with undefined bits. Initially, there are 4 octets of capability bits. Bits are numbered left to right starting with the most significant bit being bit 0.

The Non-OSPF Functional Capabilities TLV MAY be followed by optional TLVs that further specify a non-OSPF functional capability. In contrast to the OSPF Router Functional Capabilities TLV, the non-OSPF functional capabilities advertised in this TLV have no impact on the OSPF protocol operation. The specifications for non-OSPF functional capabilities advertised in this TLV MUST describe protocol behavior and address backwards compatibility.

4. Advertising ELC Using OSPF

One bit of the Non-OSPF Functional Capability Bits is to be assigned by the IANA for the ELC [RFC6790]. If a router has multiple line cards, the router MUST NOT announce the ELC [RFC6790] unless all of its linecards are capable of processing ELs.

5. Advertising RLD Using OSPF

A new TLV within the body of the OSPF RI LSA, called RLD TLV is defined to advertise the capability of the router to read the maximum label stack depth. As showed in Figure 2, it is formatted as described in Section 2.3 of [RFC7770] 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 depth 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 line cards with different capabilities of reading the maximum label stack depth, the router MUST advertise the smallest one in the RLD TLV. This TLV is applicable to both OSPFv2 and OSPFv3.

      0                   1                   2                   3
      0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |           Type=TBD2           |            Length             |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |     RLD       |
     +-+-+-+-+-+-+-+-+
                        Figure 2: RLD TLV Format

6. Acknowledgements

The authors would like to thank Yimin Shen, George Swallow, Acee Lindem, Carlos Pignataro and Bruno Decraene for their valuable comments and suggestions.

7. IANA Considerations

This document requests IANA to allocate one TLV type from the OSPF RI TLVs registry for the Non-OSPF Functional Capabilities TLV. Futhermore, this document requests IANA to creat a subregistry for "Non-OSPF Functional Capability Bits" within the "Open Shortest Path First v2 (OSPFv2) Parameters" registry. This subregistry is comprised of the fields Bit Number, Capability Name, and Reference. Initially, one bit is reqested to be assigned for the ELC. All Non-OSPF Functional Capability TLV additions are to be assigned through IETF Review [RFC5226].

This document also requests IANA to allocate one TLV type from the OSPF RI TLVs registry for the RLDC TLV.

8. Security Considerations

The security considerations as described in [RFC7770] is applicable to this document. This document does not introduce any new security risk.

9. References

9.1. Normative References

9.2. Informative References

Authors' Addresses