Prerequisites: CCNP level skills.
Topology
Task 1
Configure EBGP between R1 and R3 in such a way that it can survive either Frame-Relay or HDLC link failure. Do not use ebgp-multihop command.
Lab Solution
Task 1
Configure EBGP between R1 and R3 in such a way that it can survive either Frame-Relay or HDLC link failure. Do not use ebgp-multihop command.
R1 Configuration:
!
ip route 172.16.103.0 255.255.255.0 10.1.0.3
ip route 172.16.103.0 255.255.255.0 10.1.13.3
ip route 172.16.103.0 255.255.255.0 10.1.13.3
!
router bgp 10
no synchronization
bgp router-id 1.1.1.1
bgp log-neighbor-changes
neighbor 172.16.103.3 remote-as 30
neighbor 172.16.103.3 disable-connected-check
neighbor 172.16.103.3 update-source Loopback0
no auto-summary
no synchronization
bgp router-id 1.1.1.1
bgp log-neighbor-changes
neighbor 172.16.103.3 remote-as 30
neighbor 172.16.103.3 disable-connected-check
neighbor 172.16.103.3 update-source Loopback0
no auto-summary
!
R3 Configuration:
!
ip route 172.16.101.0 255.255.255.0 10.1.0.1
ip route 172.16.101.0 255.255.255.0 10.1.13.1
!
ip route 172.16.101.0 255.255.255.0 10.1.13.1
!
router bgp 30
no synchronization
bgp router-id 3.3.3.3
bgp log-neighbor-changes
neighbor 172.16.101.1 remote-as 10
neighbor 172.16.101.1 disable-connected-check
neighbor 172.16.101.1 update-source Loopback0
no auto-summary
no synchronization
bgp router-id 3.3.3.3
bgp log-neighbor-changes
neighbor 172.16.101.1 remote-as 10
neighbor 172.16.101.1 disable-connected-check
neighbor 172.16.101.1 update-source Loopback0
no auto-summary
!
Notice!
This option (disable-connected-check) does not increment TTL but relies on the fact that the routers ARE directly connected only peering between loopbacks is used. The difference between this and ebgp-multihop is that in the latter one we can tune TTL value allowing multiple transit routers between the two BGP peers. In the former option (disable-connected-check), the routers must be directly connected (1 hop since TTL=1).
Pic. 2 - Neighbor Details.
Notice!
Consider the topology (pic. 1). Assume there are three paths between R1 and R3 in the routing table via S0/0, S0/1 and F1/0. Both S0/0 and S0/1 are down. The remaining path from R1 to R3 loopback is via F1/0 (R2 is the next-hop).
- If I use the command: neighbor disable-connected-check, the BGP session is going to time out after 180 seconds (neighbor down).
- If I use the command: neighbor ebgp-multihop 2, the BGP session is going to survive.