IS-IS Working Group Z. Li
Internet-Draft Y. Qin
Intended status: BCP China Mobile
Expires: September 8, 2010 J. Dong
Huawei Technologies
March 7, 2010
Recommendations for LSP Checksum Calculation and Related Processing in
multi-vendor Networks using Intermediate System to Intermediate System
draft-li-isis-error-lsp-processing-03
Abstract
Recommendations for Interoperable Networks using Intermediate System
to Intermediate System (IS-IS) [RFC3719] highlights a number of
differences between the IS-IS protocol as described in ISO 10589 and
the protocol as it is deployed today.
This document outlines a number of differences found in the China
Mobile backbone network, which is constructed using routers from
several manufacturers. These differences include LSP checksum
calculation, zero checksum LSP processing, zero remaining lifetime
LSP processing, and corrupt LSP processing. This document is
intended to provide best current practices to facilitate
interoperability and maintain network stability.
Status of this Memo
This Internet-Draft is submitted to IETF in full conformance with the
provisions of BCP 78 and BCP 79.
Internet-Drafts are working documents of the Internet Engineering
Task Force (IETF), its areas, and its working groups. Note that
other groups may also distribute working documents as Internet-
Drafts.
Internet-Drafts are draft documents valid for a maximum of six months
and may be updated, replaced, or obsoleted by other documents at any
time. It is inappropriate to use Internet-Drafts as reference
material or to cite them other than as "work in progress."
The list of current Internet-Drafts can be accessed at
http://www.ietf.org/ietf/1id-abstracts.txt.
The list of Internet-Draft Shadow Directories can be accessed at
http://www.ietf.org/shadow.html.
Li, et al. Expires September 8, 2010 [Page 1]
Internet-Draft draft-li-isis-error-lsp-processing March 2010
This Internet-Draft will expire on September 8, 2010.
Copyright Notice
Copyright (c) 2010 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 BSD License.
Li, et al. Expires September 8, 2010 [Page 2]
Internet-Draft draft-li-isis-error-lsp-processing March 2010
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3
2. Requirements Language . . . . . . . . . . . . . . . . . . . . 4
3. Checksum Calculation . . . . . . . . . . . . . . . . . . . . . 5
4. Zero Checksum LSP Processing . . . . . . . . . . . . . . . . . 6
5. Zero Remaining Lifetime LSP Processing . . . . . . . . . . . . 8
6. Corrupt LSP Processing . . . . . . . . . . . . . . . . . . . . 9
7. Security Considerations . . . . . . . . . . . . . . . . . . . 10
8. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 11
9. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 12
10. Normative References . . . . . . . . . . . . . . . . . . . . . 13
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 14
Li, et al. Expires September 8, 2010 [Page 3]
Internet-Draft draft-li-isis-error-lsp-processing March 2010
1. Introduction
IS-IS Protocol [ISO10589] is one of the Interior Gateway Protocols.
It is widely deployed in the carrier backbone networks.
[RFC3719] discusses a number of differences between the IS-IS
protocol as described in ISO 10589 and the protocol as it is deployed
today.
In the China Mobile backbone network, constructed with hundreds of
routers from several manufacturers, some differences in IS-IS
implementations were identified. These differences contribute to
instability across the whole network. The differences discussed in
this document include Link State Protocol Data Unit (LSP) checksum
calculation, zero checksum LSP processing, zero remaining lifetime
LSP processing, and corrupt LSP processing.
This document is intended to provide best current practices for LSP
checksum calculation and related processing to facilitate
interoperability and maintain network stability. The following
sections describe the problems and possible solutions in multi-vendor
IS-IS environments.
Li, et al. Expires September 8, 2010 [Page 4]
Internet-Draft draft-li-isis-error-lsp-processing March 2010
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 [RFC 2119].
Li, et al. Expires September 8, 2010 [Page 5]
Internet-Draft draft-li-isis-error-lsp-processing March 2010
3. Checksum Calculation
ISO 10589, section 7.3.16.4, note 36, prescribes that examining the
checksum of a zero Remaining Lifetime LSP is always successful.
Thus, some implementations fill in the checksum field with zero in
the zero Remaining Lifetime LSP.
However, some implementations check the checksum regardless of the
value of the Remain Lifetime. 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.
Li, et al. Expires September 8, 2010 [Page 6]
Internet-Draft draft-li-isis-error-lsp-processing March 2010
4. Zero Checksum LSP Processing
Section 7 of [RFC3719] suggests an implementation SHOULD treat all
LSPs with a zero checksum and a non-zero remaining lifetime, as if
they had a checksum error.
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 an LSP with the
correct checksum.
Considering the above two conditions together, the implementation
SHOULD check the remaining lifetime first, then check the checksum.
In practice, some implementations perform the check in reverse. The
suggested processing procedure is shown in Figure 1.
+--------------+
+---| LSP Received |
| +--------------+
|
| +----------------+
+-->| zero remaining | Yes +------------------------+
+---| lifetime? |----->|Zero remaining lifetime |
| +----------------+ |LSP processing specified|
|No | in Section 4 |
| +------------------------+
| +--------------+
+-->|Zero checksum?| Yes +---------------------+
+---| |----->| |
| +--------------+ | Corrupt LSP |
| |processing specified |
| +----->| in Section 5 |
|No | +---------------------+
| |
| +----------+ |
+-->| Checksum |Yes|
+---| error? |---+
| +----------+
|No
| +----------------------+
+-->|Correct LSP processing|
+----------------------+
Figure 1 Suggested LSP Processing Procedure
Equipment with on-off switches of "ignore LSP errors" SHOULD treat
Li, et al. Expires September 8, 2010 [Page 7]
Internet-Draft draft-li-isis-error-lsp-processing March 2010
LSPs with a zero checksum and a non-zero remaining lifetime according
to the processing mechanism mentioned in Section 5 of this document.
That is treating this kind of LSPs as corrupt LSPs.
As for the LSPs with a zero checksum and a zero remaining lifetime,
the processing mechanism SHOULD NOT be affected by the state of the
switch. That is treating this kind of LSPs as correct zero remaining
lifetime LSPs. The suggested process mechanism is specified in
Section 4 of this document.
Li, et al. Expires September 8, 2010 [Page 8]
Internet-Draft draft-li-isis-error-lsp-processing March 2010
5. Zero Remaining Lifetime LSP Processing
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 a correct LSP, no matter whether its checksum is
correct or not.
Some implementations, however, still check the checksum of a zero
Remaining Lifetime LSP.
The processing mechanism SHOULD NOT be affected by the on-off switch
and the details can be seen in section 7.3.16.4, ISO 10589.
Li, et al. Expires September 8, 2010 [Page 9]
Internet-Draft draft-li-isis-error-lsp-processing March 2010
6. Corrupt LSP Processing
Section 7.3.14.2 e) of [ISO10589] states: An IS receiving a LSP with
an incorrect LSP Checksum or with an invalid PDU syntax shall 1)
generate a corruptedLSPReceived circuit event, 2) discard the PDU.
In order to control the processing mechanism of Checksum error LSP,
some equipment manufacturers provide an on-off configuration switch.
However, the default state of the switch is different, thus the
processing mechanism of checksum error LSP is not the same.
From the carrier's perspective, such on-off configuration switch is
welcome, because the carrier can determine the processing mechanism
through the switch. But the behavior of the switch SHOULD be the
same, as follows.
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 [ISO10589]. 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, i.e. treating the
checksum error LSP as zero remaining lifetime LSP. The processing
mechanism is specified in Section 4 of this document.
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 [ISO10589].
Li, et al. Expires September 8, 2010 [Page 10]
Internet-Draft draft-li-isis-error-lsp-processing March 2010
7. Security Considerations
The suggestions and clarifications in this document will not cause
any new security concerns.
Li, et al. Expires September 8, 2010 [Page 11]
Internet-Draft draft-li-isis-error-lsp-processing March 2010
8. IANA Considerations
This document makes no requests for IANA action.
Li, et al. Expires September 8, 2010 [Page 12]
Internet-Draft draft-li-isis-error-lsp-processing March 2010
9. Acknowledgments
Many thanks to Adrian Farrel for your comments to push this document
forward. Daniel King reviewed this document and gave lots of sound
advice.
Support and discussion from Lianyuan Li, Xiaodong Duan are greatly
appreciated. Lianyuan Li presented this document at IETF 75 in
Stockholm.
Acknowledgments to the efforts and discussion from Fang Wei, Zhaorui
Huang, Xiaodong Wei, Jingxi Zho, Xiaobo He, Jun Zhu when doing the
test in lab.
Li, et al. Expires September 8, 2010 [Page 13]
Internet-Draft draft-li-isis-error-lsp-processing March 2010
10. Normative References
[ISO10589]
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)", ISO/IEC 10589:2002.
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
[RFC3719] Parker, J., "Recommendations for Interoperable Networks
using Intermediate System to Intermediate System (IS-IS)",
RFC 3719, February 2004.
Li, et al. Expires September 8, 2010 [Page 14]
Internet-Draft draft-li-isis-error-lsp-processing March 2010
Authors' Addresses
Zhenqiang Li
China Mobile
Unit2, Dacheng Plaza, No. 28 Xuanwumenxi Ave, Xuanwu District
Beijing 100053
P.R. China
Email: lizhenqiang@chinamobile.com
Yue Qin
China Mobile
No. 29, Financial Street, Xicheng District
Beijing 100032
P.R. China
Email: qinyue@chinamobile.com
Jie Dong
Huawei Technologies
KuiKe Building, No.9 Xinxi Rd., Haidian District
Beijing 100085
P.R. China
Email: dongjie_dj@huawei.com
Li, et al. Expires September 8, 2010 [Page 15]