Purge Originator Identification TLV for IS-IS
draft-ietf-isis-purge-tlv-02

Abstract

At present an IS-IS purge does not contain any information identifying the Intermediate System (IS) that generates the purge. This makes it difficult to locate the source IS.

To address this issue, this document defines a TLV to be added to purges to record the system ID of the IS generating it. Since normal LSP flooding does not change LSP contents, this TLV should propagate with the purge.

Status of this Memo

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Copyright Notice

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Table of Contents

1.  Introduction
2.  Requirements Language
3.  The Purge Originator Identification TLV
4.  Using the Dynamic Hostname TLV in Purges
5.  Security Considerations
6.  Functional Changes
7.  IANA Considerations
8.  Acknowledgments
9.  Normative References
§  Authors' Addresses

1.  Introduction

The IS-IS [ISO 10589] (ISO, “Intermediate system to Intermediate system routeing information exchange protocol for use in conjunction with the Protocol for providing the Connectionless-mode Network Service (ISO 8473),” .) routing protocol has been widely used in large-scale IP networks because of its strong scalability and fast convergence.

The IS-IS protocol floods purges throughout an area, regardless of which IS initiated the purge. If a network operator would like to investigate the cause of the purge, it is difficult to determine the origin of the purge. At present the IS-IS protocol has no mechanism to locate the originator of a purge. To address this problem, this document defines a TLV to be added to purges to record the system ID of the IS generating the purge.

Field experience has observed several circumstances where an IS can improperly generate a purge. These are all due to implementation deficiencies or implementations that predate [ISO TC1] (ISO, “Intermediate system to Intermediate system intra-domain routeing information exchange protocol for use in conjunction with the protocol for providing the connectionless-mode Network Service (ISO 8473) -- Technical Corrigendum 1,” .) and generate a purge when they receive a corrupted LSP.

2.  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 [RFC2119] (Bradner, S., “Key words for use in RFCs to Indicate Requirement Levels,” March 1997.).

3.  The Purge Originator Identification TLV

This document defines a TLV to be included in purges. This TLV carries the system ID of the IS generating the purge, or, in a proxy mode, carries the system ID of the IS that first saw the purge and inserted this TLV, as well as the system ID of the system that it received the purge from.

This allows ISs receiving purges to log the system ID of the originator, or the upstream source of the purge. This makes it much easier for the network administrator to locate the origin of the purge and thus the cause of the purge. Similarly, this TLV is helpful to developers in lab situations.

The Purge Originator Identification TLV is defined as:

CODE - 13

LENGTH - total length of the value field.

VALUE -

Number of system IDs carried in this TLV (1 octet) -- Only the values 1 and 2 are defined.

System ID of the Intermediate System that inserted this TLV.

The system ID of the Intermediate System that the purge was received from. (optional)

4.  Using the Dynamic Hostname TLV in Purges

This document also extends the use of the Dynamic hostname TLV (type 137) [RFC5301] (McPherson, D. and N. Shen, “Dynamic Hostname Exchange Mechanism for IS-IS,” October 2008.). This TLV MAY also be included in purges. This will further aid in the rapid identification of the system that generated the purge.

Implementations SHOULD include the Purge Originator Identification TLV in addition to the Dynamic hostname TLV.

5.  Security Considerations

If the proposed TLV or the Dynamic hostname TLV is used in conjunction with IS-IS authentication mechanisms [RFC5304] (Li, T. and R. Atkinson, “IS-IS Cryptographic Authentication,” October 2008.)[RFC5310] (Bhatia, M., Manral, V., Li, T., Atkinson, R., White, R., and M. Fanto, “IS-IS Generic Cryptographic Authentication,” February 2009.), the purge LSP is constructed as follows. First, the original contents of the LSP are removed, leaving only the LSP header, then the Purge Originator Identification TLV and/or the Dynamic hostname TLV are added, and then the IS-IS authentication TLV is added.

Legacy systems that implement [RFC5304] (Li, T. and R. Atkinson, “IS-IS Cryptographic Authentication,” October 2008.) or [RFC5310] (Bhatia, M., Manral, V., Li, T., Atkinson, R., White, R., and M. Fanto, “IS-IS Generic Cryptographic Authentication,” February 2009.) MUST discard purges with these additional TLVs. This is not thought to be a significant operational issue as the loss of purges is typically not critical.

6.  Functional Changes

This document amends the behavior specified in [RFC5301] (McPherson, D. and N. Shen, “Dynamic Hostname Exchange Mechanism for IS-IS,” October 2008.), [RFC5304] (Li, T. and R. Atkinson, “IS-IS Cryptographic Authentication,” October 2008.) and [RFC5310] (Bhatia, M., Manral, V., Li, T., Atkinson, R., White, R., and M. Fanto, “IS-IS Generic Cryptographic Authentication,” February 2009.). ISs that receive purges with the Purge Originator Identification TLV or the Dynamic hostname TLV with valid authentication MUST NOT discard the PDU and SHOULD process it normally. ISs that receive purges with the Purge Originator Identification TLV or the Dynamic hostname TLV MUST be accepted and processed as a normal purge. The Purge Originator Identification TLV or Dynamic hostname TLV MUST NOT be removed from the purge prior to propagation. If multiple purges are received for the same LSP fragment, then the implementation MAY propagate any one of the purges.

7.  IANA Considerations

RFC EDITOR NOTE: This section to be removed upon publication.

This document requests that IANA assign a code point for this TLV from the IS-IS 'TLV Codepoints Registry'.

8.  Acknowledgments

Many thanks to Adrian Farrel and Daniel King for your comments to improve this document and move it forward.

The first version of this document was mainly composed by Lianyuan Li.

Acknowledgments to the discussion in the mailing list. Some improvements of this document are based on the discussion.

9. Normative References

Authors' Addresses