From: John Conzone (jkconzone@xxxxxxxx)
Date: Sat Sep 09 2000 - 19:14:57 GMT-3
Aaron, I had a similar experience with lab 8, which I never did rectify.
I had my OSPF into BGP back into OSPF and yes, when I did I debug IP OSPF
packet, my problem was an external LSA being generated everytime my isdn
went down.
The link would go down, would send that into BGP on 1 router, who would
then send that back into OSPF, who would genreate the external LSA, and the
cycle continued.
If you debug ip ospf packet, you should see the route that is generating
the loop.
One good thing is I am going over route redistribution in both Doyles
and Caslows book.
Whenever I redistribute routes mutually, I filter out the native routes
from the other protocol's routes. So if I redistribute rip into ospf and
ospf back into rip, I filter out the rip routes inbound on the ospf process,
and the ospf routes in on the rip processes to prevent feedback. Of course
on the lab it won't be so easy!
Please let me know what you find out.
----- Original Message -----
From: "Aaron DuShey" <aaron.dushey@dushey-consulting.com>
To: "CCIE (E-mail)" <ccielab@groupstudy.com>
Sent: Saturday, September 09, 2000 5:39 PM
Subject: routing loops
> as3---r6---r5----r1-----as1
> 172.168.80.x as2 172.168.70.x
>
> OSPF is running only on r5
> r1 & r6 are doing mutal redistribution and running both ospf & bgp
> Looking at the results below my redistribution filtering isn't working as
> planned
>
> I want to make sure I understand what's happening here clearly-can someone
> verify please?
>
> r1 is redistibuting route 172.168.80.x in from BGP into OSPF, r6 ospf then
> adv to r5, r5ospf adv to r1 and BGP route is removed. BGP route is then
> re-entered, and loop is formed.
> Am I correct in saying this happens with type 5 (External) only since they
> are treated in a distance vector sort of manner in which they are
advertised
> by next-hops vs the normal LS behaviour of flooding?
> thanks,
>
> 01:43:00: RT: add 172.168.80.0/24 via 137.20.60.1, bgp metric [200/0]
> 01:43:05: RT: closer admin distance for 172.168.80.0, flushing 1 routes
> 01:43:05: RT: add 172.168.80.0/24 via 137.20.25.2, ospf metric [110/30]
> 01:43:10: OSPF: Rcv hello from 137.20.224.5 area 2 from Ethernet0/0
> 137.20.25.2
> 01:43:10: OSPF: End of hello processing
> 01:43:11: RT: del 172.168.80.0/24 via 137.20.25.2, ospf metric [110/30]
> 01:43:11: RT: delete subnet route to 172.168.80.0/24
> 01:43:13: RT: add 172.168.80.0/24 via 137.20.60.1, bgp metric [200/0]
> 01:43:16: RT: closer admin distance for 172.168.80.0, flushing 1 routes
> 01:43:16: RT: add 172.168.80.0/24 via 137.20.25.2, ospf metric [110/30]
> 01:43:20: OSPF: Rcv hello from 137.20.224.5 area 2 from Ethernet0/0
> 137.20.25.2
> 01:43:20: OSPF: End of hello processing
> 01:43:21: RT: del 172.168.80.0/24 via 137.20.25.2, ospf metric [110/30]
> 01:43:21: RT: delete subnet route to 172.168.80.0/24
> 01:43:23: RT: add 172.168.80.0/24 via 137.20.60.1, bgp metric [200/0]
> 01:43:26: RT: closer admin distance for 172.168.80.0, flushing 1 routes
> 01:43:26: RT: add 172.168.80.0/24 via 137.20.25.2, ospf metric [110/30]
> 01:43:30: OSPF: Rcv hello from 137.20.224.5 area 2 from Ethernet0/0
> 137.20.25.2
> 01:43:30: OSPF: End of hello processing
> Aaron DuShey
>
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