IS-IS Working Group Z. Li
Internet Draft L. Li
Intended status: BEST CURRENT PRACTICE X. Duan
Expires: September 1, 2009 China Mobile
March 2, 2009
Recommendations for Processing Mechanism for Checksum Error LSP in
Interoperable Networks using Intermediate System to Intermediate
System (IS-IS)
draft-li-isis-error-lsp-processing-00.txt
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Abstract
This document discusses the processing mechanism for the Link State
Protocol Data Unit (LSP) with an incorrect LSP Checksum in the
interoperable networks using IS-IS. It is suggested to add a
configurable switch to control the processing mechanism of checksum
error LSP. This document clarifies the processing mechanism for zero
checksum LSP and zero remaining lifetime LSP, and gives advices to
calculate the checksum of all kinds of LSPs as well.
1. Introduction
Intermediate System to Intermediate System (IS-IS) Protocol [1] is
one of the Interior Gateway Protocols. It is widely deployed in the
carrier backbone networks.
Section 7.3.14.2 e) of [1] states: An Intermediate system receiving a
Link State PDU (LSP) with an incorrect LSP Checksum or with an
invalid PDU syntax shall
1) generate a corruptedLSPReceived circuit event,
2) discard the PDU.
However practically, operators usually request that equipments can
provide control switch in order to control the processing mechanism
of Checksum error LSP. Actually, some equipment manufacturers have
provided such configuration switch, such as Cisco's IGNORE-LSP-
ERRORS switch and Huawei's IGNORE-LSP-CHECKSUM-ERROR switch. But for
the lack of unified standards, the default state of the switch is
usually diverse, and the processing mechanism of checksum error LSP
is not exactly the same. Many unexpected failures may occur in the
multi-manufacture environment.
Besides, the processing mechanism of zero Remaining Lifetime LSP for
different manufacturers is not completely the same.
This document aims at posing these issues, and gives uniform
suggestion.
2. Terminology
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 [2].
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3. On-off Switch
All the devices implementing IS-IS SHOULD provide an on-off switch to
control the processing mechanism when they receive a LSP with an
incorrect LSP Checksum. The on-off switch SHOULD be configurable
through the Command Line Interface (CLI).
When the on-off switch is on, the processing mechanism for the
checksum error LSP SHOULD be accordant with what is stated in Section
7.3.14.2 e) of [1]. When the on-off switch is off, the equipment
SHOULD treat the received checksum error LSP in the same way as the
LSP whose remaining lifetime equals 0. The processing mechanism is
specified in Section 7.3.16.4 of [1].
It is RECOMMENDED that the default state of the on-off switch be on.
In this way, the default processing mechanism is in accordance with
Section 7.3.14.2 e) of [1].
4. Zero checksum
RFC 3719 [3], section 7, suggests an implementation SHOULD treat all
LSPs with a zero checksum and a non-zero remaining lifetime as if
they had as checksum error. Equipments with on-off switch SHOULD
treat such LSPs in accordance with the processing mechanism mentioned
in the previous section 3.
ISO 10589, section 7.3.16.4, note 36, states: A check of the checksum
of a zero Remaining Lifetime LSP succeeds even though the data
portion is not present. Therefore, the LSP with a zero checksum and a
zero remaining lifetime SHOULD be treated as the LSP with correct
checksum, and the processing mechanism SHOULD NOT be affected by the
switch state. To insure the interoperability and maintain network
stability, it is RECOMMENDED that the checksum of all LSPs, including
the LSP with a zero remaining lifetime, SHOULD be calculated
correctly, just as described in section 6.
5. Zero remaining lifetime
ISO 10589, section 7.3.16.4, note 36, states: A check of the checksum
of a zero Remaining Lifetime LSP succeeds even though the data
portion is not present. Therefore, a zero Remaining Lifetime LSP
SHOULD be treated as correct LSP, no matter whether its checksum is
correct or not. The processing mechanism SHOULD NOT be affected by
the on-off switch and the details can be seen in section 7.3.16.4.
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However, in order to insure the interoperability and maintain network
stability, the checksum of zero Remaining Lifetime LSP is RECOMMENDED
to be calculated correctly as well, as described in section 6.
6. Checksum calculation
Although note 36, section 7.3.16.4, ISO 10589 prescribes that
examining the checksum of a zero Remaining Lifetime LSP is always
successful, to insure the interoperability and maintain network
stability, it is RECOMMENDED to calculate the checksum of all LSPs
correctly, including zero Remaining Lifetime LSP. The calculation
method is presented in Section 7.3.11, ISO 10589.
7. Security Considerations
The suggestions and clarifications in this document will not cause
extra new security concerns.
8. References
[1] ISO 10589 V2 Telecommunications and information exchange
between systems-Intermediate System to Intermediate System
[2] Bradner, S., "Key words for use in RFCs to Indicate Requirement
Levels", BCP 14, RFC 2119, March 1997.
[3] J. Parker, Ed., "Recommendations for Interoperable Networks
using Intermediate System to Intermediate System (IS-
IS)", RFC 3719, February 2004.
Author's Addresses
Zhenqiang Li (editor)
China Mobile Research Institute
Gate 2 Dacheng Plaza
No. 28 Xuanwumen West Street
Xuanwu District, Beijing 100053
China
Phone: +86 1391 163 5816
Email: lizhenqiang@chinamobile.com
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Lianyuan Li
China Mobile Research Institute
Gate 2 Dacheng Plaza
No. 28 Xuanwumen West Street
Xuanwu District, Beijing 100053
China
Phone: +86 1391 178 9703
Email: lilianyuan@chinamobile.com
Xiaodong Duan
China Mobile Research Institute
Gate 2 Dacheng Plaza
No. 28 Xuanwumen West Street
Xuanwu District, Beijing 100053
China
Phone: +86 1391 019 1797
Email: duanxiaodong@chinamobile.com
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