BGP backdoor route

[ajitkgiri]

Hi,

It is very confusing for me why shall I advertise subnet of one AS Edge router to other AS Edge router for Backdoor configuration which is connected through eBGP connectivity. As we know that after configuring the backdoor route command under eBGP config, will increase AD value (200) of eBGP for that subnet which was earlier learned via eBGP.So obviously any other IGP will take place whose AD is less than 200.

Please find the network diagram mentioned below. For normal scenario subnets 10,20 and 30 network will get installed in R2 by eBGP (AD 20) and next hop would be 5.5.5.1 for R2 and 192.168.10.1 and other network will get installed in R1 by eBGP (AD 20) and next-hop would be 5.5.5.2

But In case of BGP backdoor route 10 networks are advertised in local R2 using network and backdoor command in order to make it as a local route and not to advertise other eBGP peer.

But why it is being configured in opponent router using network and backdoor command why not from same router with network and backdoor command.

I am very new into BGP study and preparing for CCIE. So please clarify me if I am asking any foolish question at all.

Regards

Ajit

[Jose Jara]

Hi,

because the goal with the backdoor command is to change the AD from 20 (routes learned by eBGP) to 200 and make it less preferable than other routes learned by IGP´s. The local prefixes you are advertising are connected with an AD of 0.