From: Hoyle, Anthony (AL) (ALHoyle@dow.com)
Date: Sat Feb 28 2004 - 17:15:03 GMT-3
You gave the answer. The external distance of BGP is 20. Disappearing from the database..well you are redistributing the connected route into ISIS. You are then redistributing isis into OSPF. This route will always be in the OSPF database regardless(unless you have a filter), however it won't be placed in the routing table under OSPF -if there is another protocol (like BGP) advertising the same route with a lower admin distance (BGP external routes).
When you say disappear from the OSPF database, you mean when you do a "show ip route ospf" ?
Did I understand your question correctly..?
Anthony Hoyle
-----Original Message-----
From: nobody@groupstudy.com [mailto:nobody@groupstudy.com] On Behalf Of Ahmed Mustafa
Sent: Saturday, February 28, 2004 3:22 AM
To: ccielab@groupstudy.com
Subject: BGP versus OSPF/ISIS
Can someone look into this
R6 connected to R2 via ISIS level 1
R2 connected to R3 via HDLC link/ISIS Level 2
R2 connected to R3 via Frame-Relay link/OSPF-----> R2 is also doing mutual redistribution
I announced r6 loopback interface 132.1.6.0/24 to ISIS via redistribute connected.
R3 learned that route obviously through Frame-Relay due to lower admin distance. I then changed the admin distance of ISIS to 106, and r3 installed this route via ISIS. So far so good
Now comes BGP, and totally screwed this nice scenerio above
R6 is in AS 100
R2 and R3 are in AS 300
I redistributed r6 loopback now into BGP via redistribute connected, not through network command.
r2 will obviously install this route as a BGP route because of lower adminstrative distance External BGP 20 over ISIS 115.
Now r3 learns that route via BGP as well with the distance 200 since r2 and r3 are in same AS. I thought that the route 132.1.6.0 should have learned through ISIS or OSPF if I removed the admin distance command of ISIS from 106 to default 115 because both OSPF and ISIS have lower admin distance than IBGP 200.
My guesses:
The route learned via BGP since it is in r2 routing table regardless of r2 should have this route in ISIS database as well as in OSPF database since r2 is also doing redistribution.
Issues: If I shut down the BGP link between r2 and r6, bingo, the route will appear in OSPF database as an external route on r2, but when the BGP link is up between r2 and r6, the route will disappear from OSPF database.
Any ideas !!!
Sorry for the tedious email, but Group can learn from this and also advise.
Regards,
Ahmed
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