Advertising Service Functions Using IS-IS
draft-xu-isis-service-function-adv-02

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 attributes (e.g.,segment ID) using IS-IS.

Status of This Memo

This Internet-Draft is submitted in full conformance with the provisions of BCP 78 and BCP 79.

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This Internet-Draft will expire on December 30, 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 Sub-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 attributes (e.g.,SID) using IS-IS.

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 [RFC4971] and [I-D.xu-spring-sfc-use-case].

3. Advertising Service Functions and Corresponding SIDs

Service nodes within the network need to advertise each service function they are offering by using a new sub-TLV of the IS-IS Router CAPABILITY TLV [RFC4971]. This new sub-TLV is called as Service Function sub-TLV. The Service Function sub-TLV could appear multiple times wihin a given IS-IS Router CAPABILITY TLV 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 they are offering and advertise it by using a sub-TLV of the above Service Function sub-TLV, called Service Function SID sub-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 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 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 corresponding to the particular attributes of a given service function. The Service Function SID sub-TLV as defined in Section 3.2 is one such sub-TLV which is used to indicate the corrresponding service function SID. Other sub-TLVs are to be defined in the future.

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 type codes for the Service Function sub-TLV and 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