From: Edwards, Andrew M (andrew.m.edwards@boeing.com)
Date: Fri Apr 02 2004 - 15:08:45 GMT-3
I wanted to ask one question for my own edification... I noticed an eBGP
speaker will put the routes learned via eBGP into its routing table.
Then, the eBGP speaker will tell its iBGP counterparts about those eBGP
learned routes. These routes will be put into the local routing table
of an iBGP speaker, with synchronization ENABLED, as long as the eBGP
learned route has a next-hop address that is reachable by the iBGP
speaker. If the next-hop is not reachable, then it doesn't go into the
BGP table, and therefore, the local IP routing table.
At least that's what I saw... And that's why using route-maps for these
eBGP speakers becomes important for BGP route redistribution with
synchronization enabled.
Can someone confirm my understanding... ?
Thx
andy
-----Original Message-----
From: Packet Man [mailto:ccie2b@hotmail.com]
Sent: Thursday, April 01, 2004 2:28 PM
To: bill@eccie.com; gladston@br.ibm.com; ccielab@groupstudy.com
Subject: RE: BGP and OSPF RID [bcc][faked-from][bayes]
Bill,
You have some of the best written and most informative and insightful
posts
I've seen here on GS. I always learn something new whenever I read your
posts even when it's on a topic I'm very knowledgable about. So, I hope
you'll keep sending in your thoughts.
thanks, pm
>From: Bill Lijewski <bill@eccie.com>
>Reply-To: Bill Lijewski <bill@eccie.com>
>To: gladston@br.ibm.com, ccielab@groupstudy.com
>Subject: RE: BGP and OSPF RID [bcc][faked-from][bayes]
>Date: Thu, 1 Apr 2004 13:44:57 -0800
>
>Synchronization only comes into play for iBGP routes. With
>synchronization on the router will check its IGP table for all iBGP
>routes it learns to make sure that it has a matching entry before it
>will ever put the route into its BGP table as a best route.
>Synchronization does not check for a match in the IGP table for eBGP
>routes. If no match is found in the IGP table for the iBGP routes they
>will not be marked as best, and the routes will not be passed to any
>other BGP neighbors.
>
>There is one extra step that BGP goes through for iBGP routes when
>synchronization is on and OSPF is the underlying IGP. BGP will check
>for a matching route in the IGP table, if one is found it will check to
>see which IGP protocol is running. If the router is running OSPF as
>its IGP, BGP will check and make sure that the origin of the routes for
>both OSPF and BGP are the same. In other words BGP will make sure that
>the OSPF and BGP router IDs of the source of the route match before it
>will put it into the BGP table.
>
>You can check these Router ID origins with the following two commands:
>
>For the OSPF route: show ip route x.x.x.x
>
>For an example we can see what the origin of the 210.10.10.0/24
>network:
>
>Routing entry for 210.10.10.0/24
> Known via "ospf 1", distance 110, metric 1, type extern 2, forward
>metric 10
> Last update from 172.168.1.2 on Ethernet0, 1d03h ago
> Routing Descriptor Blocks:
> * 172.168.1.2, from 5.5.5.5, 1d03h ago, via Ethernet0
> Route metric is 1, traffic share count is 1
>
>The second line up from the bottom is the important one. It shows
>'from 5.5.5.5', 5.5.5.5 is the OSPF origin ID for this route.
>
>
>For the BGP route: show ip bgp x.x.x.x
>
>Again we can take a look at the origin of the 210.10.10.0/24 network:
>
>BGP routing table entry for 210.10.10.0/24, version 2
>Paths: (1 available, best #1, table Default-IP-Routing-Table)
> Advertised to non peer-group peers:
> 192.168.2.2
> Local
> 172.168.1.2 from 5.5.5.5
>Origin IGP, metric 0, localpref 100, valid, internal, synchronized,
>best
>
>Again the second line up from the bottom shows 'from 5.5.5.5', 5.5.5.5
>is the BGP origin ID for this route.
>
>In this case both the BGP and the OSPF origin Router ID's match so this
>route could be placed into the BGP table as a best route.
>
>
>- Bill Lijewski
>CCIE#8642
>Network Learning Inc
>5 Day R&S CCIE Bootcamp Instructor
>http://www.ccbootcamp.com
>bill@eccie.com
>
>
>-----Original Message-----
>From: nobody@groupstudy.com [mailto:nobody@groupstudy.com] On Behalf Of
>gladston@br.ibm.com
>Sent: Thursday, April 01, 2004 1:25 PM
>To: ccielab@groupstudy.com
>Subject: BGP and OSPF RID [bcc][faked-from][bayes]
>Importance: Low
>
>I remember to see a problem related to OSPF and BGP RID, redistribution
>and Route Refletor.
>
>Any help on where it is on the DOCCD or cisco.com?
>
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