question about BGP Loopback interface

[hanyawad]

dear experts,

in the attached document, i've read in page number 5 (BGP and Loopback interfaces) section that we can use loopback interface with iBGP if there isn't a direct connection between the iBGP peers and we don't need it with eBGP peers because they have a direct connection so the loopback interface doesn't apply.

but in page number 7 in eBGP Multihop (load balancing) section i found that it uses the loopback interface between the two eBGP peers in the command update-source loopback 0

because i'm confused between the two statments, i want to know we can use the Loopback interface in iBGP only or also in eBGP?

thanks for your help

Labib

[Edison Ortiz · Accepted solution]

It depends on the technical/business requirements - best practice indicates iBGP to use Loopback for peering while physical interface for eBGP peering but it's not set in stone - you can interchange the design with iBGP and eBGP.

[Reza Sharifi]

Hi Labib,

For IBGP you always use loopback interfaces to peer.  For EBGP, you use physical interface.

now, if you are not directly connected to the device you want to peer with, you use neighbor ebgp-multihop command.

for example if you have r1------sw1-------r2 in this example if you are trying to establish a eBGP neigbor between r1 and r2 you use neighbor ebgp-multihop because r1 and r2 are not physically/directly connected.

HTH

[hanyawad]

Hi Reza,

thanks alot for your help, but actually i was focusing in something else that confused me, which is the command update-source loopback 0 can be used while connecting indirect eBGP routers ?

thanks

Labib

[Reza Sharifi · Accepted solution]

That is correct.  If you are using a loopback interface to peer (IBGP or EBGP) and not a physical interface you need pdate-source loopback command

HTH