From: Brian Dennis (bdennis@internetworkexpert.com)
Date: Thu Dec 04 2003 - 14:10:02 GMT-3
Look over section 3 of RFC 1403 (BGP OSPF Interaction). It is a very short
and straight forward section.
<RFC 1403>
3. BGP Identifier and OSPF router ID
The BGP identifier MUST be the same as the OSPF router id at all
times that the router is up.
This characteristic is required for two reasons.
i Synchronisation between OSPF and BGP
Consider the scenario in which 3 ASBRs, RT1, RT2, and RT3,
belong to the same autonomous system.
+-----+
| RT3 |
+-----+
|
Autonomous System running OSPF
/ \
+-----+ +-----+
| RT1 | | RT2 |
+-----+ +-----+
Both RT1 and RT2 have routes to an external network X and
import it into the OSPF routing domain. RT3 is advertising
the route to network X to other external BGP speakers. RT3
must use the OSPF router ID to determine whether it is using
RT1 or RT2 to forward packets to network X and hence build the
correct AS_PATH to advertise to other external speakers.
More precisely, RT3 must determine which ASBR it is using to
reach network X by matching the OSPF router ID for its route
to network X with the BGP Identifier of one of the ASBRs, and
use the corresponding route for further advertisement to
external BGP peers.
ii It will be convenient for the network administrator looking at
an ASBR to correlate different BGP and OSPF routes based on
the identifier.
</RFC 1403>
Brian Dennis, CCIE #2210 (R&S/ISP-Dial/Security)
bdennis@internetworkexpert.com
Toll Free: 877-224-8987
Direct: 775-745-6404 (Outside the US and Canada)
Internetwork Expert, Inc.
http://www.InternetworkExpert.com
-----Original Message-----
From: nobody@groupstudy.com [mailto:nobody@groupstudy.com] On Behalf Of
JamesGEF
Sent: Thursday, December 04, 2003 8:55 AM
To: ccielab@groupstudy.com
Subject: OSPF/BGP Router-ID
There was a good document on CCO showing exactly the problem with
redistribution of routes between OSPF and BGP with different router-id and
synchronization enabled. It had sample outputs.
I can't find it any more. Didn't bookmark it.
Does someone have it?
TIA,
James
This archive was generated by hypermail 2.1.4 : Sat Jan 03 2004 - 08:25:35 GMT-3