eBGP neighbourship

[Srin_G]

Can we form eBGP neighborship b/w two peers where one peer take physical interface address of remote-peer and 2nd peer taking loopback address of remote-peer?

[MHM Cisco World]

Yes I think
first you must sure that LO is learn from IGP 
the config ebgp multi-hop 
and it will work.

[Flavio Miranda]

Hi

  Yes you can but you need to do some ajustments. 

Use :

neighbor x.x.x.x remote-as xxxx

neighbor x.x.x.x update-source loopback x

neighbor x.x.x.x ebgp-multhop 2

[Srin_G]

Thanks for the replies! What is the rationale behind increasing the multihop value? could you please explain?

[Flavio Miranda]

eBGP is meant to be configured between two physical interfaces and for security reason it consider one hop away; a BGP speaker have a TTL of one. When you use Loopback, you are using more then one hop to get to the other router´s interface. that´s why you need to use multhop option.

[paul driver]

Hello
The prefered way to peer direct ebgp neighbours via thier loopbacks (physically 1 hop away) would keep the TTL to 1 but disable the nexthop check (no  ebgp-multhop required) 

neighbour x.x.x.x disable-connected-check

[emurray]

If the  EBGP session to an IP address on a directly connected router does not belong to a directly connected subnet, it is preferred to use the neighbor disable-connected-check statement. 

[MHM Cisco World]

for me best answer why and where we use multi-hop and disable-connected-check is found in below link 

https://ccieblog.co.uk/bgp/bgp-disable-connected-check-vs-ebgp-multi-hop

[emurray]

Yes, you have to configure the source loopback address on the router you will be using the loopback as the peer. Otherwise, he will keep using the outgoing interface IP address for the keepalive and all BGP-related traffic

Router1(config-bgp)# neighbor 172.16.222.2
Router1(config-bgp-neighbor)# remote-as 65005


Router1(config-bgp-neighbor)# update-source 5.5.5.5

On the router that is peering with the neighbor with a loopback interface

neighbor 5.5.5.5 ebgp-multihop 2