Advertising Service Functions Using OSPF

Status of This Memo

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Table of Contents

1. Introduction

[I-D.xu-spring-sfc-use-case] describes a particular use case for SPRING where the Segment Routing (SR) mechanism is leveraged to realize the service path layer functionality of the Service Function Chaining (SFC), i.e, steering traffic through the service function path. To allow a service classifier to encode the segment list representing a particular service function path, the classifier needs to know on which service node(s) a given service function is located and what segment ID (SID) is used to indicate that service function on a given service node. This document describes how to advertise service functions and their corresponding attributes (e.g., SID) using OSPF. Here the OSPF means both OSPFv2 [RFC2328] and OSPFv3 [RFC5340].¶

2. Terminology

This memo makes use of the terms defined in [RFC7770] and [I-D.xu-spring-sfc-use-case].¶

The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and "OPTIONAL" in this document are to be interpreted as described in BCP 14 [RFC2119] [RFC8174] when, and only when, they appear in all capitals, as shown here.¶

3. Advertising Service Functions and Corresponding SIDs

Service nodes within the network need to advertise each service function they are offering by using a TLV within the body of the OSPF Router Information (RI) Opaque LSA [RFC7770]. This new TLV is called as Service Function TLV. The Service Function TLV is applicable to both OSPFv2 and OSPFv3. The Service Function TLV could appear multiple times within a given Router Information (RI) Opaque LSA when more than one service function needs to be advertised by a given service node. The scope of the advertisement depends on the application but it is recommended that it SHOULD be domain-wide. Furthermore, service nodes need to allocate a corresponding SID to each service function and meanwhile advertise it by using a sub-TLV of the above Service Function TLV. In the MPLS-SR case, service nodes within the network would allocate a locally significant MPLS label to each service function they are offering. In the IPv6-SR case, service nodes within the network would allocate a locally unique link-local IPv6 address to each service function they are offering. For a given service function, the service node offering that service function could advertise the corresponding SID in the format of an MPLS label, an IPv6 address, or both.¶

 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=TBD            |            Length             |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|                  Service Function Identifier                  |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
~                          Sub-TLVs                             ~
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

 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=TBD            |            Length             |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
~                    Service Function SID                       ~
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

4. IANA Considerations

This memo includes a request to IANA for allocating type codes for the Service Function sub-TLV and the Service Function SID sub-TLV.¶

5. Security Considerations

This document does not introduce any new security risk.¶

6. Acknowledgements

TBD.¶

7. Contributors

Nan Wu
Huawei
eric.wu@huawei.com¶

Authors' Addresses