Network Working Group Naiming Shen
INTERNET DRAFT Albert Tian
Expiration Date: October 2004 Redback Networks
Derek Yeung
Procket Networks
April 2004
Inter-Area IP Route Attribute in IS-IS
<draft-shen-isis-interarea-route-attr-00.txt>
1. Status of this Memo
This document is an Internet-Draft and is in full conformance with
all provisions of Section 10 of RFC2026.
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.
2. Abstract
This document describes an extension to the IS-IS protocol to allow
some routing attributes to be associated with advertised inter-area
prefixes. The extension allows routers to learn this routing
information without the knowledge of the link-state topology in
another IS-IS level. The initial applications for this extension
are inter-area IP MPLS fast reroute for node protection and
inter-area TE LSPs.
3. Introduction
An IS-IS [1][2] routing domain can be partitioned into multiple
levels with L1/L2 border routers redistributing routes between
levels. When routes are leaked into another level most of the
routing or topology information is lost. However, certain
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applications requiring network topology information may not be
bounded by the IGP area/level. This document proposes to add
additional routing attributes during the inter-area route
redistribution in inter-area prefix advertisement.
IP fast re-route for node protection [3][4] uses the link-state
topology information to compute alternative paths to reach
next-nexthop IP nodes. When the nexthop node is a border router
and the next-nexthop router resides in another IS-IS level,
the PLR node won't have the topology information needed to
select an inter-area next-nexthop node for node protection.
This IS-IS inter-area route attribute extension provides a
mechanism for IS-IS border routers to include the required
topology information along with intra-area prefixes.
4. Terminology
FRR Fast Reroute.
Level IS-IS routing level, it is inter-changeable with
"area" in this document.
Next-Nexthop Node The router is the Nexthop node of PLR's Nexthop
node.
PLR Point of Local Repair. This node detects the link
or nexthop node failure and performs the fast
reroute operation.
TE LSP MPLS traffic engineer LSP or label switched path.
5. Inter-Area Route Attribute Sub-TLV
This document proposes a new "Inter-Area Route Attribute"
sub-TLV to be added to TLVs 135 and 235 [5][6]. This sub-TLV
includes a list of "Attribute Flag" and a "Router ID". This
sub-TLV is only used for IS-IS L1/L2 border router for advertising
leaked IP prefixes.
The Inter-Area Route Attribute sub-TLV has the following
structure:
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type | Length | Attr Flag 1 | Router-ID 1 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Router-ID 1 (continued) | Attr Flag 2 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
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| Router-ID 2 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
// // Attr Flag N |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Router-ID N |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Type An 8 bit field. The Sub-TLV code value is 4.
Length An 8 bit field and the value is 5 * N. N is the number
of route attributes in the list. Each route attribute
contains an 8-bit attribute flag and a 32-bit Router-ID.
Attribute Flag
This is a 8-bit field with three bits currently defined.
0 1 2 3 4 5 6 7
+-+-+-+-+-+-+-+-+
|N|O|B| reserved|
+-+-+-+-+-+-+-+-+
Bits Description
N Nexthop Bit. If set, the router advertising this
IP prefix with this sub-TLV uses router specified
in the Router-ID field as the nexthop node.
O Origination Bit. If set, the router advertising this
IP prefix with this sub-TLV had learnt this prefix
from the router specified in the Router-ID field.
B Non-Best Path Bit. The N bit and B bit are mutually
exclusive. If set, the border router advertising this
this sub-TLV does not consider router specified in
the Router-ID field to be on the IGP best path to
reach the IP prefix. For some applications such as
traffic engineering, the LSP path setup may not
follow the shortest path.
Router-ID
This is a 32-bit unsigned number representing the router which
can be used to forward traffic towards the destination for
the prefixes.
The list may contain multiple (Attribute Flag, Router-ID) tuples to
handle ECMP or non-ECMP cases.
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6. Applications
Determination of when to advertise route attribute associated with
an IP prefix using the proposed sub-TLV is application dependent.
This document only describes the mechanism for node protection
of IP fast reroute. Other applications, such as inter-area TE LSP
setup mechanism, are beyond the scope of this document.
6.1. Inter-Area IP node protection using FRR
In the IP fast reroute for node protection case, the IS-IS border
router can be configured to advertise Inter-Area Route Attribute
sub-TLVs along with inter-area prefixes. This can be used by the
adjacent PLR nodes to fast reroute traffic to inter-area
next-nexthop nodes when the IS-IS border router fails. The Router-ID
is the TE router-id [5] advertised by the nexthop router. The
Nexthop bit in the Attribute Flag must be set. Whether an
inter-area prefix should include this Inter-Area Route Attribute
sub-TLV can be determined based on local policy or on the
administrative route tags associated with the prefix. The sub-TLV
may contain a list of the route attributes in ECMP case.
When the IS-IS node (PLR) adjacent to the area border router has an
alternative path to a next-nexthop node (in another area) which does
not go through the area border router, it can pre-build an
alternative IP path for the prefixes and perform the node protection
fast switchover when the area border router fails.
7. Security Considerations
This document raises no new security issues.
8. Acknowledgments
The authors would like to thank Tony Li and Acee Lindem for their
comments to this document.
9. IANA Considerations
The authors have chosen "4" as the type code for this sub-TLV.
This value must be allocated by IANA.
10. Full Copyright Statement
Copyright (C) The Internet Society (2002). All Rights Reserved.
This document and translations of it may be copied and furnished to
others, and derivative works that comment on or otherwise explain it
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Internet Draft Inter-Area Route Attr April 2004
or assist in its implementation may be prepared, copied, published
and distributed, in whole or in part, without restriction of any
kind, provided that the above copyright notice and this paragraph are
included on all such copies and derivative works. However, this
document itself may not be modified in any way, such as by removing
the copyright notice or references to the Internet Society or other
Internet organizations, except as needed for the purpose of
developing Internet standards in which case the procedures for
copyrights defined in the Internet Standards process must be
followed, or as required to translate it into languages other than
English.
The limited permissions granted above are perpetual and will not be
revoked by the Internet Society or its successors or assigns.
This document and the information contained herein is provided on an
"AS IS" basis and THE INTERNET SOCIETY AND THE INTERNET ENGINEERING
TASK FORCE DISCLAIMS ALL WARRANTIES, EXPRESS OR IMPLIED, INCLUDING
BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF THE INFORMATION
HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED WARRANTIES OF
MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE.
11. References
[1] "Intermediate System to Intermediate System Intra-Domain Routeing
Exchange Protocol for use in Conjunction with the Protocol for
Providing the Connectionless-mode Network Service (ISO 8473)",
ISO 10589.
[2] Callon, R., RFC 1195, "Use of OSI IS-IS for routing in TCP/IP and
dual environments", RFC 1195, December 1990.
[3] Shen, N., Pan, P., "Nexthop Fast ReRoute for IP and MPLS",
Internet draft, draft-shen-nhop-fastreroute-00.txt, work in
progress.
[4] Smit, H., Shen, N., "Calculating IGP Routes Over Traffic
Engineering Tunnels", draft-ietf-rtgwg-igp-shortcut-00.txt,
Work In Progress.
[5] Li, T., and Smit, H., "IS-IS extensions for Traffic
Engineering", draft-ietf-isis-traffic-05.txt, Work in Progress,
August 2003.
[6] Przygienda, Shen, Sheth, "Multi Topology (MT) Routing in IS-IS",
draft-ietf-isis-wg-multi-topology-06.txt, Work in progress.
12. Authors' Addresses
Naiming Shen
Redback Networks, Inc.
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300 Holger Way
San Jose, CA 95134
Email: naiming@redback.com
Albert Tian
Redback Networks, Inc.
300 Holger Way
San Jose, CA 95134
Email: tian@redback.com
Derek M. Yeung
Procket Networks, Inc.
1100 Cadillac Court
Milpitas, CA 95035 USA
Email: myeung@procket.com
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