Internet DRAFT - draft-lz-isis-relax-interfaces-limit
draft-lz-isis-relax-interfaces-limit
Network Working Group C. Lin
Internet-Draft H. Zhang
Intended status: Standards Track HangZhou H3C Co. Limited
Expires: January 4, 2014 V. Manral
Hewlett-Packard Co.
July 5, 2013
Simplified Extension of interface Space for IS-IS
draft-lz-isis-relax-interfaces-limit-00
Abstract
This document describes a simplified method for extending the
interface space beyond the 255 interfaces limit. The proposed
mechanism does not require any changes to the IS-IS protocol.
Status of this Memo
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This Internet-Draft will expire on December 19, 2013.
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3
2. Requirements Language . . . . . . . . . . . . . . . . . . . . . 3
3. Definition of Commonly Used Terms . . . . . . . . . . . . . . . 3
4. Proposed Solution . . . . . . . . . . . . . . . . . . . . . . . 4
5. Security Considerations . . . . . . . . . . . . . . . . . . . . 5
6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . . 5
7. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 5
8. References . . . . . . . . . . . . . . . . . . . . . . . . . . 5
8.1. Normative References . . . . . . . . . . . . . . . . . . . 5
8.2. Informative References . . . . . . . . . . . . . . . . . . 5
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 5
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1. Introduction
The IS-IS specification has an implicit limit of 255 interfaces, as
constrained by the eight-bit Circuit ID field carried in various
packets. Moderately clever implementers have realized that the only
true constraint is that of 255 LAN interfaces, and for that matter
only 255 LAN interfaces for which a system is the Designated IS.
This is because the only place that the circuit ID is advertised in
LSPs is in the pseudo-node LSP ID.
Implementers have treated the point-to-point circuit ID number space
as being independent from that of the LAN interfaces, since these
circuit IDs appear only in IIH PDUs and are only used for detection
of a change in identity at the other end of a link. More than 255
point-to-point interfaces have been supported by sending the same
circuit ID on multiple interfaces. See [RFC5303].
However, that solution suffers from restrictions required to maintain
interoperability with systems that do not support the extensions.
This document defines extensions that allow a system to exceed the
255 interfaces limit and do so in a way that has no interoperability
issues with systems that do not support the extension.
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. Definition of Commonly Used Terms
This section provides definitions for terms that are used throughout
the text. The terminology is consistent with that used in RFC 5311.
Originating IS: A physical IS running the IS-IS protocol. As
this document describes a method that allows a single physical IS to
run additional interfaces in name of multiple extend ISs, the
Originating IS represents the single physical IS.
Normal system-id: The system-id of an Originating IS as defined by
[IS-IS].
Additional system-id: A system-id other than the "Normal system-id",
that is assigned by the network administrator to an Extend-IS in
order to extend the interface range. The Additional system-id, like
the Normal system-id, must be unique throughout the routing area
(Level-1) or domain (Level-2), and must be different with the
Additional system-id used to extend LSPs in RFC5311.
Extending IS: The system, identified by an Additional system-id, for
the interfaces beyond 255 to enabled with.
Local System: A physical IS running the IS-IS protocol, including
Originating IS and Extending ISs.
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4. Proposed Solution
The extension proposed to IS-IS to relax the 255 interfaces limit,
Extending IS, same defined as Virtual IS in RFC 5311, is introduced
to be only used for extending the interfaces. Circuit index is
allocated based on IS, one extended IS 255 more interfaces. Here's
the diagrams:
R1 R255
\ /
I1 ... I255
____\_______________________/_________
| |
| Originating IS |
|______________________________________|
/ \
/ \
/ \
________/______ ___\___________
| extending IS' | ... | extending IS" |
|_______________| |_______________|
/ \ / \
I'1 ... I'255 I"1 ... I"255
/ \ / \
R'1 R'255 R"1 R"255
Figure 1: Extend interface space by extending IS
where Rx are remote routers, Ix are interface to remote routers.
When interface space is exceeded, for example I'x and I"x as
illustrated in Figure 1 is enabled in the name of extending IS, which
means R'x is peered with extending IS' and R"x is peered with
extending IS", NOT with Originating IS. The Originating IS MUST
specify extending ISs as a neighbor, with metric set to zero.
Extending ISs MUST specify the Originating IS as a neighbor with
metric set to zero. The adjacency between Originating IS and
Extending ISs SHOULD be considered as point-to-point.
Hello packet sending
Additional system-id is used for the Hello Packets sending on The
interface which is running in Extending IS.
LSP FLOOD
When a new LSP has been received, it must be flooded out some set
of the local system's interfaces including Original IS's interfaces
and all Extending ISs's interfaces. Also, a self-originated LSP must
be flooded out all the local system's interfaces including Original
IS's interfaces and all Extending ISs's interfaces.
Route Calculation
In local system, LSP Database including all Extending ISs's LSP
should be used in route calculation. All Extending ISs's interfaces
should be used in nexthop calculation.
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5. Security Considerations
This document raises no new security issues for IS-IS. IS-IS
security may be used to secure the IS-IS messages discussed here.
See [RFC5304].
6. IANA Considerations
This document has no IANA actions.
7. Acknowledgements
8. References
8.1. Normative References
[IS-IS] 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, Second Edition.
[RFC5303] D. Katz,R. Saluja,D. Eastlake 3rd,
"Three-Way Handshake for IS-IS Point-to-Point Adjacencies."
[RFC5311] Hermelin, A., Previdi, S., and M. Shand,
"Simplified Extension of Link State PDU (LSP) Space for
IS-IS",RFC 5311, February 2009.
8.2. Informative References
[draft-ietf-isis-wg-255adj-02.txt] T. Przygienda, Maintaining more
than 255 circuits in IS-IS
Authors' Addresses
Changwang Lin
Oriental Electronic Bld.,2 Chuangye Road,
Shang-Di Information Industry Base,Hai-Dian District
Beijing
P.R.China
Email: linchangwang.04414@h3c.com
Haifeng Zhang
HangZhou H3C Co. Limited
310 Liuhe Road, Zhijiang Science Park
Hangzhou
P.R. China
Email: zhanghf@h3c.com
Manral Vishwas
Hewlett-Packard Co.
USA
Email: vishwas.manral@hp.com
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