IS-IS purge originator: Purge Originator Identification TLV for IS-IS
A small IS-IS extension that stamps each purge with the system ID of the router that created it.
Wei, F., Qin, Y., Li, Z., Li, T., and J. Dong, "Purge Originator Identification TLV for IS-IS", RFC 6232, DOI 10.17487/RFC6232, May 2011, <https://www.rfc-editor.org/info/rfc6232>.
@misc{rfc6232,
series = {Request for Comments},
number = 6232,
howpublished = {RFC 6232},
publisher = {RFC Editor},
doi = {10.17487/RFC6232},
url = {https://www.rfc-editor.org/info/rfc6232},
author = {F. Wei and Y. Qin and Z. Li and T. Li and J. Dong},
title = {{Purge Originator Identification TLV for IS-IS}},
pagetotal = 6,
year = 2011,
month = may,
} RFC text
Contents
Internet Engineering Task Force (IETF) F. Wei
Request for Comments: 6232 Y. Qin
Updates: 5301, 5304, 5310 Z. Li
Category: Standards Track China Mobile
ISSN: 2070-1721 T. Li
Cisco Systems, Inc.
J. Dong
Huawei Technologies
May 2011
Purge Originator Identification TLV for IS-IS
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
Link State Protocol Data Unit (LSP) flooding does not change LSP
contents, this TLV should propagate with the purge.
This document updates RFC 5301, RFC 5304, and RFC 5310.
Status of This Memo
This is an Internet Standards Track document.
This document is a product of the Internet Engineering Task Force
(IETF). It represents the consensus of the IETF community. It has
received public review and has been approved for publication by the
Internet Engineering Steering Group (IESG). Further information on
Internet Standards is available in Section 2 of RFC 5741.
Information about the current status of this document, any errata,
and how to provide feedback on it may be obtained at
http://www.rfc-editor.org/info/rfc6232.
Copyright Notice
Copyright (c) 2011 IETF Trust and the persons identified as the
document authors. All rights reserved.
This document is subject to BCP 78 and the IETF Trust's Legal
Provisions Relating to IETF Documents
(http://trustee.ietf.org/license-info) in effect on the date of
publication of this document. Please review these documents
carefully, as they describe your rights and restrictions with respect
to this document. Code Components extracted from this document must
include Simplified BSD License text as described in Section 4.e of
the Trust Legal Provisions and are provided without warranty as
described in the Simplified BSD License.
Table of Contents
1. Introduction ....................................................2
2. Requirements Language ...........................................3
3. The Purge Originator Identification (POI) TLV ...................3
4. Using the Dynamic Hostname TLV in Purges ........................3
5. Security Considerations .........................................4
6. IANA Considerations .............................................4
7. Acknowledgments .................................................4
8. Normative References ............................................4
1. Introduction
The IS-IS [ISO-10589] 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 shown several circumstances where an IS can
improperly generate a purge. These are all due to implementation
deficiencies or implementations that predate [ISO-TC1] and generate a
purge when they receive a corrupted Link State Protocol Data Unit
(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].
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 from which it received the purge. 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 from which the purge was
received (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] to further aid in the rapid identification of
the system that generated the purge. This TLV MAY be included in
purges. Implementations SHOULD include one instance of the Dynamic
hostname TLV if the POI TLV is included. Only the local hostname
should be inserted.
5. Security Considerations
Use of the extensions defined here, with authentication as defined in
[RFC5304] or [RFC5310], will result in the discarding of purges by
legacy systems that 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.
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 [RFC6233].
6. IANA Considerations
IANA has assigned 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, and
Purge:y.
7. Acknowledgments
Many thanks to Adrian Farrel and Daniel King for their comments to
improve this document and move it forward.
The first version of this document was mainly composed by
Lianyuan Li.
Acknowledgments are given to the discussion in the mailing list.
Some improvements to this document are based on the discussion.
8. Normative References
[ISO-10589] 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)",
ISO/IEC 10589:2002.
[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", ISO/IEC 10589:1992/
Cor.1:1993.
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
[RFC5301] McPherson, D. and N. Shen, "Dynamic Hostname Exchange
Mechanism for IS-IS", RFC 5301, October 2008.
[RFC5304] Li, T. and R. Atkinson, "IS-IS Cryptographic
Authentication", RFC 5304, October 2008.
[RFC5310] Bhatia, M., Manral, V., Li, T., Atkinson, R., White, R.,
and M. Fanto, "IS-IS Generic Cryptographic
Authentication", RFC 5310, February 2009.
[RFC6233] Li, T. and L. Ginsberg, "IS-IS Registry Extension for
Purges", RFC 6233, May 2011.
Authors' Addresses
Fang Wei
China Mobile
No. 29, Financial Street, Xicheng District
Beijing 100032
P.R. China
EMail: weifang@chinamobile.com
Yue Qin
China Mobile
No. 29, Financial Street, Xicheng District
Beijing 100032
P.R. China
EMail: qinyue@chinamobile.com
Zhenqiang Li
China Mobile
Unit2, Dacheng Plaza, No. 28 Xuanwumenxi Ave., Xuanwu District
Beijing 100053
P.R. China
EMail: lizhenqiang@chinamobile.com
Tony Li
Cisco Systems, Inc.
170 W. Tasman Dr.
San Jose, CA 95134
USA
EMail: tony.li@tony.li
Jie Dong
Huawei Technologies
KuiKe Building, No. 9 Xinxi Rd., Haidian District
Beijing 100085
P.R. China
EMail: dongjie_dj@huawei.com
AI ELI5
On this page
§1Why Purges Need a Name Tag
IS-IS floods purges throughout an area no matter which IS started them. A purge is a link state PDU (LSP) that tells the other routers to remove old information. If an operator wants to investigate why a purge happened, the protocol gives no way to find out where it came from.
The RFC notes that field experience has shown several cases where an IS improperly generates a purge. These come from implementation deficiencies, or from implementations that predate ISO Technical Corrigendum 1 and generate a purge when they receive a corrupted LSP. This document adds a TLV to purges that records the system ID of the IS generating the purge.
Imagine a class where anyone can shout 'erase the board!' and nobody sees who did it. It is hard to find out why the board keeps getting erased. A name tag on every shout fixes that.
§3The Purge Originator Identification TLV
The POI TLV uses CODE 13. Its LENGTH is the total length of the value field. The value holds a one-octet count of system IDs (only the values 1 and 2 are defined), then the system ID of the IS that inserted the TLV, and optionally the system ID of the IS from which the purge was received.
The TLV SHOULD be found in all purges. It MUST NOT be found in LSPs with a non-zero Remaining Lifetime, so it only ever appears on purges and not on live LSPs.
The tag has a small number saying how many names are on it (one or two), then the name of the router that wrote it and, sometimes, the name of the neighbor who passed it along.
§3.1Who Adds the TLV
If an IS generates a purge, it SHOULD include the POI TLV with its own system ID. If an IS receives a purge that has no POI TLV, it SHOULD add one carrying both its own system ID and the system ID of the IS from which it received the purge.
This lets routers that receive purges log the originator or the upstream source. The RFC says this makes it much easier for a network administrator to locate the origin of a purge and so its cause, and that the TLV also helps developers in lab situations. Because normal LSP flooding does not change LSP contents, the TLV propagates along with the purge.
The router that starts the purge signs it. If a purge shows up unsigned, the first router to notice signs it with its own name and the name of the neighbor who handed it over.
| Situation | System IDs in the TLV | Count field |
|---|---|---|
| IS generates the purge | Its own system ID | 1 |
| IS receives a purge with no POI TLV THIS RFC | Its own system ID and the system ID of the IS it received the purge from | 2 |
§4Adding the Dynamic Hostname TLV
The RFC also extends the use of the Dynamic hostname TLV (type 137, from RFC 5301) to help identify the system that generated the purge. This TLV MAY be included in purges. Implementations SHOULD include one instance of it if the POI TLV is included, and only the local hostname should be inserted.
A hostname is easier for a person to recognize than a raw system ID.
A router can also write its friendly name on the tag, because names are easier for people to read than ID numbers.
§5Authentication and Mixed Networks
Using these extensions with authentication as defined in RFC 5304 or RFC 5310 will cause purges to be discarded by legacy systems that strictly conform to either of those RFCs. That may compromise the correctness and consistency of the routing database unless all ISs in the network support the extensions.
For that reason, all implementations in a domain that use authentication MUST be upgraded to receive the POI TLV before any IS is allowed to generate a purge with the POI TLV. Further interactions between the POI TLV, the Dynamic hostname TLV and the Authentication TLV are described in RFC 6233.
If some routers do not understand the new tag, they may throw the whole message away. So every router must learn about the tag before anyone starts using it.
§6The Code Point
IANA assigned code point 13 for the Purge Originator Identification TLV in the IS-IS TLV Codepoints registry. The additional values for this TLV are IIH:n, LSP:y, SNP:n and Purge:y, meaning it is not carried in IS-IS hello PDUs or sequence number PDUs, but is allowed in LSPs and in purges.
The tag was given its own official number, 13, so every router recognizes it the same way.