Purge Originator Identification TLV for IS-IS
draft-ietf-isis-purge-tlv-04

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 (POI) TLV
4.  Using the Dynamic Hostname TLV in Purges
5.  Security Considerations
6.  IANA Considerations
7.  Acknowledgments
8.  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 (POI) TLV

This document defines a TLV to be included in purges. If an IS generates a purge, it SHOULD include this TLV in the purge with its own system ID. If an IS receives a purge that does not include this TLV, then it SHOULD add this TLV with both its own system ID and the system ID of the IS 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 POI 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.

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

The POI TLV SHOULD be found in all purges and MUST NOT be found in LSPs with a non-zero Remaining Lifetime.

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.) to further aid in the rapid identification of the system that generated the purge. This TLV MAY be included in purges. Implementations SHOULD include the Dynamic hostname TLV if the POI TLV is included.

5.  Security Considerations

Use of the extensions defined here with authentication as defined in [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.) will result in the discarding of purges by legacy systems which are in strict conformance with either of those RFCs. This may compromise the correctness/consistency of the routing database unless all ISs in the network support these extensions. NEW TEXT: Therefore, all implementations in a domain implementing authentication MUST be upgraded to receive the POI TLV before any IS is allowed to generate a purge with the POI TLV.

More interactions between the POI TLV, the Dynamic hostname TLV, and the Authentication TLV are described in [I‑D.li‑reg‑purge] (Li, T., “IS-IS Registry Extension for Purges,” August 2010.).

6.  IANA Considerations

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

This document requests that IANA assign code point 13 for the 'Purge Originator Identification' TLV from the IS-IS 'TLV Codepoints Registry'. The additional values for this TLV should be: IIH:n, LSP:y, SNP:n, Purge:y.

7.  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.

8. Normative References

Authors' Addresses