The previous topology was concerned with establishing a E-BGP neighborings with two directly connected networks . Now lets turn our focus to the ones which are not directly connected but yet needs to be E-BGP peers
The following topology will be used by me
R2 ->R1 — 172.16.1.0/24
R1->R4 — 172.16.2.0/24
R4 :
router bgp 1
nei 172.16.1.2 remote-as 2
R4
router bgp 2
nei 172.16.2.2 remote-as 1
when we turn on debugging and wait for something to happen. Actually first we need see if we have network layer reachability to routers then we can worry about EBGP peerings . Hence i set up a static route and enable
DEBUG IP BGP IPV4 UNICAST
For EBgp relationships
Now if we are left with other configuration option such as Ttl-security lets see how things get worse from one end
even though the state changes from IDLE / ACTIVE -> OPEN SENT it never comes to established
The other router will always be in open confirm mode
Lets verify that
Because the other router is expecting a incoming ip packet value TTL should be atleast 253 or higher . so the solution is to configure R2 such that it sends TTL OF 255 so that by the time packet travels 2 hops its TTL would be 253 .
or the other option is to set ttl-security option to Router 2 also . But we would rather miss the fun Right
Ok lets do it on R2
Yaa can you see the multihop working now in accordance with TTL-SECURITY . Its bed Time . Meet you Tomorrow with some other fun stuff
Regards
Rakesh
