Network Working Group Robert Raszuk (Editor)
Internet Draft Cisco Systems, Inc
Category: Standards Track June 2003
Expires: December 2003
ISIS Extensions for BGP Peer Discovery
draft-raszuk-isis-peer-discovery-00.txt
Status of this Memo
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Abstract
This document proposes an extension to IS-IS protocol [ISO10589] to
support BGP peer auto discovery.
We propose the addition of new information that an Intermediate
System can flood in it's LSPDU. Such information is required for
network based auto discovery of IBGP peers as described in [IBGP-AM].
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1. Specification of Requirements
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].
2. Introduction
Today all BGP peering configuration is manual and requires action on
both sides of any given peering. In IBGP Auto Mesh draft [IBGP-AM] we
propose the automation of this task for IBGP sessions. As a
distribution of required information IS-IS [ISO10589] native flooding
layer is being proposed for reuse.
The information required to be flooded is static and can change only
by operator's manual configuration action.
It is envisioned that in the future when new and better approaches
for flooding information are available and deployed BGP Auto
Discovery TLV could also be migrated from ISIS to such a new
transport.
3. The BGP Auto Discovery TLV
BGP Auto Discovery TLV is an IS-IS TLV of type code 243 (to be
confirmed).
The format of BGP Auto Discovery TLV is indicated for reference in
Figure 1 below.
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| TLV Type | Length | FLOODING RESERVED |F|D|
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| BGP Identifier |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| FRAG | BGP RESERVED | 16 bit CHECKSUM |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Autonomous System(s) or confederation sub-AS(s) sub-TLV |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| IPv4/IPv6 Peering Address sub-TLV |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| AFI/SAFI for mesh topologies sub-TLV |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| AFI/SAFI for reflection topologies sub-TLV |
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+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Old BGP Identifier sub-TLV (opt) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 1. BGP Auto Discovery TLV
Type - Code 243 (to be confirmed)
Length - Total length in octets
Control Flags related to IGP operation:
Symbol Capabilities
F Flooding scope
D Down Bit
"F" {flooding} flooding scope of this TLV, when set domain wide
flooding scope is required, when not set TLV should not be
flooded into other areas or levels. Default not set
indicating area/level wide flooding only.
"D" {down} down bit set by IGP when leaked to other levels.
BGP Auto Discovery TLV can be contained in any LSP fragment. It also
can be repeated. BGP itself will take all necessary filtering/update
actions on reception of this information from ISIS.
The minimum TLV length can be 10 octets.
When a size of the TLV reaches 255 octets BGP will fragment the TLV.
A special "FRAG" 4 bit counter has been allocated in the BGP Control
Information section for unlikely cases where BGP Auto Discovery TLV
needs to be splitted across multiple TLVs for a given BGP speaker.
Fragmentation should be fully transparent to ISIS component.
The specific information and encoding of BGP sub-TLVs is discussed in
[IBGP-AM].
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4. Operation
It should be important to emphasize the fact that ISIS interaction
with the new information is to remain minimal. BGP component will
prepare the necessary information to be flooded as well as keep the
received information in it's own data structure (cache). BGP
component will also inform ISIS about required flooding scope for
it's information by setting the F bit.
It is assumed that all global LSP comparison will still take place.
On the other hand it is not required that ISIS will try to parse and
compare the TLV itself and based on the result initiate BGP
notification or not. Added checksum field should make comparison done
by BGP much less CPU intensive.
Forced reflooding should only take place based on the manual
configuration change of session related parameters. During normal
network operation when BGP configuration related to peer maintenance
is constant BGP Auto Discovery TLV should not cause any extra
processing or flooding for ISIS.
5. Deployment Considerations
The new proposed data to be flooded has an informational character.
Routers which do not understand new information will not be able to
participate in the IBGP auto mesh.
Deployment of new code which supports new information can be
incremental. Also enabling information distribution itself can also
have an incremental character.
It should be up to operator's decision to switch from informational
use of BGP Auto Discovery TLV to operational IBGP auto mesh benefits.
6. IANA Considerations
A new ISIS TLV type will need to be assigned by IANA. The TLV
assignee will be responsible for allocation of any sub-TLVs for the
IANA assigned TLV.
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7. Security Considerations
It is highly encouraged to use existing ISIS security mechanism when
transporting BGP Auto Discovery TLV.
While addition of new information does not present any additional
risks, potential consequences of injection of not authorized BGP Auto
Discovery TLVs into routing domain could by minimized by
implementation of additional filtering before attempting to establish
IBGP sessions.
8. Acknowledgments
I would like to express special thanks to Stefano Previdi, Steven
Luong & Abhay Roy for their comments.
9. Normative References
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", RFC 2119, March 1997.
[RFC2434] Narten, T., Alvestrand, H., "Guidelines for Writing an
IANA Considerations Section in RFCs", RFC 2434, October 1998.
[ISO10589] "Intermediate System to Intermediate System Intra-Domain
Routing Exchange Protocol for use in Conjunction with the
Protocol for Providing the Connectionless-mode Network Service
(ISO8473)" [Also republished as RFC 1142]
[RFC2966] T. Li, T. Przygienda, H. Smit, "Domain-wide Prefix
Distribution with Two-Level IS-IS", October 2000.
10. Informative References
[IBGP-AM] Raszuk, R., "IBGP Auto Mesh", draft-raszuk-ibgp-auto-
mesh-00.txt, June 2003
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11. Authors' Addresses
Robert Raszuk
Cisco Systems, Inc.
Al. Jerozolimskie 146C
02-305 Warsaw, Poland
Email: rraszuk@cisco.com
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