Categories R&S

BGP – implement and troubleshoot Peerings – Multihop eBGP Peerings

 

When we were implementing eBGP peering, remember that we saw that the outgoing TTL was set to 1.

So what happen if we want to establish an eBGP peering with a couple of routers between our peer ?

 

Requirements:

Establish an eBGP session between R10 and R20 loopbacks.

 

Diagram:

update_source

 

Configuration and verification:

So this seems to be easy, let’s just add a network statement on both R10 and R20.

R10(config)#router bgp 10
R10(config-router)#neigh 10.20.1.20 remote-as 20
R10(config-router)#neigh 10.20.1.20 update-source lo0

R20(config)#router bgp 20
R20(config-router)#neigh 10.10.1.10 remote-as 10
R20(config-router)#neigh 10.10.1.10 update-source lo0

 

As expected, the BGP session is not coming UP.

 

 

Let’s try to use the ebgp multi hop command.

So from R10, R20 is 5 hop away.

R10(config-router)#neighbor 10.20.1.20 ebgp-multihop 5

R20(config-router)#neigh 10.10.1.10 ebgp-multihop 5

 

And now the session is UP !

%BGP-5-ADJCHANGE: neighbor 10.20.1.20 Up

R10#sh ip bgp sum
Neighbor        V           AS MsgRcvd MsgSent   TblVer  InQ OutQ Up/Down  State/PfxRcd
10.20.1.20      4           20      11      11       11    0    0 00:00:07        7

 

That’s all for this ebgp multihop command.

 

 

Thank you for reading.

 

 

 

BGP – implement and troubleshoot Peerings – Multihop eBGP Peerings