Description

This article describes about how the BGP prevents the loop when there is two neighbours with same AS number.

Symptoms

192.168.1.1 R1[AS10]-------------R2[AS20]-------------R3[AS10] 172.168.1.1

 

Usually when the R2 receives the route from R1, it should sent route update to R3. However when you check "show route advertising-protocol bgp <R3-PEER-IP> ", 

 

It will have nothing, which means that R2 is not even sending update to R3 regarding the route update for IP:192.168.1.1

 

Solution

This is the expected way of working[loop prevention]. By default R2 should suppress it.

 

 

To change the behavior you can use the advertise-peer-as option.

 

https://www.juniper.net/documentation/us/en/software/junos/bgp/topics/ref/statement/advertise-peer-as-edit-protocols-bgp.html

Modification History

2024-09-27 : Article Created