Advertising Service Functions Using OSPF
draft-xu-ospf-service-function-adv-01

Abstract

The Segment Routing mechanism can be leveraged to realize the service path layer functionality of the Service Function Chaining (i.e, steering traffic through the service function path). This document describes how to advertise service functions and their corresponding characters (e.g.,service function segment ID) using OSPF. Here the OSPF means both OSPFv2 and OSPFv3.

Status of This Memo

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This Internet-Draft will expire on December 20, 2014.

Copyright Notice

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Table of Contents

• 1. Introduction
• 1.1. Requirements Language
• 2. Terminology
• 3. Advertising Service Functions and Corresponding SIDs
• 3.1. Service Function TLV
• 3.2. Service Function SID Sub-TLV
• 4. Acknowledgements
• 5. IANA Considerations
• 6. Security Considerations
• 7. References
• 7.1. Normative References
• 7.2. Informative References
• Authors' Addresses

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 characters (e.g.,service function segment ID) using OSPF. Here the OSPF means both OSPFv2 [RFC2328] and OSPFv3 [RFC2740].

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 [RFC4970].

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 [RFC4970]. 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 wihin 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.

3.1. Service Function TLV

 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                             ~
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

• Type: TBD.
• Length: variable.
• Service Function Identifier: A unique identifier that represents a service function within an SFC-enabled domain.
• Sub-TLVs: contains zero or more sub-TLVs related to service functions. Besides the Service Function SID sub-TLV as defined in Section 3.2, other sub-TLVs (to be defined in future) which are used to describe some characters of a given service function could also be added.

3.2. Service Function SID Sub-TLV

 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                       ~
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

• Type: TBD
• Length: variable (3 or 16).
• Value: if the Length is set to 3, the rightmost 20 bits represent an MPLS label. If the length is set to 16, the value represents an IPv6 address.

4. Acknowledgements

TBD.

5. IANA Considerations

This memo includes a request to IANA for allocating one TLV type code for the Service Function TLV, and one sub-TLV type code for the Service Function SID sub-TLV.

6. Security Considerations

This document does not introduce any new security risk.

7. References

7.1. Normative References

7.2. Informative References

Authors' Addresses