eBGP neighbourship
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06-26-2022 05:53 PM
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?
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Routing Protocols
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06-26-2022 05:58 PM
Yes I think
first you must sure that LO is learn from IGP
the config ebgp multi-hop
and it will work.
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06-26-2022 06:01 PM
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
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06-26-2022 06:10 PM
Thanks for the replies! What is the rationale behind increasing the multihop value? could you please explain?
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06-26-2022 06:19 PM
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.
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06-26-2022 11:50 PM - edited 06-26-2022 11:51 PM
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
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This then could assist others on these forums to find a valuable answer and broadens the community’s global network.
Kind Regards
Paul
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06-27-2022 05:58 AM
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.
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06-27-2022 01:08 AM
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
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06-27-2022 05:45 AM - edited 06-27-2022 05:51 AM
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
