This is sort of filtering, but this will only send the 192.168.1.0/24 network if the 192.168.2.0/24 is down. Conditional Advertisement, another option. The exist-map and non-exist-map looks for prefixes in the BGP table only and not the routing table. Then enable OSPF on the 192.168.2.0/24 link. If the link goes down, the prefix will be sent to AS 100 and propogate to AS 300.
R3: router bgp 200 network 192.168.1.0 mask 255.255.255.0 network 192.168.2.0 mask 255.255.255.0 neighbor 192.168.5.5 remote-as 100 advertise-map send-1-0 non-exist-map detect-2-0 neighbor 192.168.1.1 remote-as 200 access-list 10 permit 192.168.1.0 0.0.0.255 access-list 20 permit 192.168.2.0 0.0.0.255 route-map send-1-0 permit 10 match ip address 10 route-map send-2-0 permit 10 match ip address 20 ________________________________ From: Jason Maynard <[email protected]> To: [email protected] Sent: Sun, October 24, 2010 2:40:36 PM Subject: [OSL | CCIE_RS] Troubleshooting #4 Trouble Shooting #4 The routing table on R3 should be able to reach 192.168.1.0/24 through 192.168.2.2 and not through 192.168.3.5. Restrictions: You cannot modify administrative distance or do any type of filtering. The network 192.168.1.0/24 must be advertised on R2 in both OSPF and BGP. You must ensure that R2 and R3 are not sending OSPF advertisements to R5. R5 can only use BGP as its routing protocol and must advertise its loopback.
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