Network Working Group Robert Raszuk (Editor)
Internet Draft Cisco Systems, Inc
Category: Standards Track June 2003
Expires: December 2003
OSPF Extensions for BGP Peer Discovery
draft-raszuk-ospf-bgp-peer-discovery-00.txt
Status of this Memo
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Abstract
This document proposed an extension to OSPF Router Information LSA
[LINDEM1] to distribute selected information about BGP process on a
router to other routers in the same area or in the same domain. 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. In IBGP Auto Mesh draft [IBGP-AM] we propose the
automation of this task for IBGP sessions. As a distribution of
required information OSPF [RFC2328] native flooding is being
proposed.
The information required to be flooded is static and can change only
by operator's manual configuration.
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 OSPF to be flooded over
such a new transport.
3. The BGP Auto Discovery TLV
BGP Auto Discovery TLV is proposed to be flooded inside OSPF Router
Information LSA.
The format of OSPF Router Information LSA is indicated for reference
in Figure 1 as proposed in [LINDEM1]
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| LS age | Options | 10 or 11 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| 4 | 0 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Advertising Router |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| LS sequence number |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| LS checksum | length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
+- TLVs -+
| ... |
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Figure 1. OSPF Router Information LSA
For the application of distribution of BGP Auto Discovery TLV only
area wise flooding scope (code 10) and domain wide flooding scope
(code 11) are applicable.
As described in IBGP Auto Mesh document [IBGP-AM] BGP Auto Discovery
TLV will have the format presented in figure 2.
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 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Old BGP Identifier sub-TLV (opt) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 1. BGP Auto Discovery TLV
Type One octet set to 2 (to be confirmed).
Length One octet indicating the length of the TLV
Control Flags related to IGP operation:
Symbol Capabilities
F Flooding scope
D Down Bit
Reserved Set to all zeros
"F" {flooding} flooding scope of this TLV, when set domain wide
flooding scope is required (type 11), when not set TLV should
not be flooded into other areas or levels (type 10). Default
"F" not set indicating area wide flooding only (type 10).
"D" {down} down bit is not relevant to OSPF and should be ignored by
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OSPF. It is present in the BGP Auto Discovery TLV to achieve
identical encapsulation syntax independent from flooding protocol
being selected by the operator.
The specific information and encoding of BGP sub-TLVs is discussed in
[IBGP-AM].
4. Operation
It should be important to emphasize the fact that OSPF 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 cache. BGP component will also
inform OSPF about required flooding scope for it's information.
OSPF role in new information interpretation is limited to selectively
pass BGP Auto Discovery TLV to BGP component of the router. It is
assumed that all global LSA comparisons will still take place. On the
other hand it is not required that OSPF 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 itself
much less CPU intensive.
Forced reflooding should only take place based on the manual
configuration change. 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
OSPF.
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 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.
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6. IANA Considerations
A new opaque LSA type for OSPF Router Information LSA will need to be
assigned by IANA. Additionally, IANA will need to have registries for
the OSPF Router Information opaque LSA TLVs.
The TLV assignee will be responsible for allocation of any sub-TLVs
for the IANA assigned TLV.
7. Security Considerations
It is highly encouraged to use existing OSPF security mechanism when
transporting BGP Auto Discovery TLV [RFC2328]. While addition of new
information does not present any additional risks injection of not
authorized OSPF Router Information LSAs containing unreal BGP Auto
Discovery TLVs could require an implementation of additional
filtering before attempting to establish IBGP sessions.
8. Acknowledgments
I would like to express special thanks to Abhay Roy & Peter Psenak
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.
10. Informative References
[IBGP-AM] Raszuk, R., "IBGP Auto Mesh", draft-raszuk-ibgp-auto-
mesh-00.txt, June 2003
[LINDEM1] Lindem, A. at all, "Extensions to OSPF for Advertising
Optional Router Capabilities", draft-lindem-ospf-cap-00.txt, May
2003
[RFC2328] J. Moy. OSPF version 2. Technical Report RFC 2328,
Internet Engineering Task Force, 1998.
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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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