BGP neighbor command

[Roel Reyes]

hi guys, 

Who will prevail regarding these neighbor commands, i just dont understand why are these configurations enabled on the router

neighbor 192.168.1.2 prefix-list MyAS-ISP1 out
neighbor 192.168.1.2 filter-list 2 out

ip as-path access-list 2 permit ^$    - this command advertise routes local to my AS

ip prefix-list MyAS-ISP1 description Prefix Advertise to ISP1
ip prefix-list MyAS-ISP1 seq 100 permit 0.0.0.0/0 le 32   - this command advertise routes with prefix length less than 32 

Need your inputs, these configs were already configured before i taken the network administration in my company, and im planning to clean up the config since we will be migrating to new Core router. 

[Jon Marshall]

"sh ip bgp neighbor 192.168.1.2 advertised-routes" will show you what is being advertised. 

Jon

[Julio E. Moisa]

Hi

This AS-Path list (ip as-path access-list 2 permit ^$) is preventing your router become a transit router, in other words it will not allow that all the Internet traffic is passing through your router.

:-)

[Roel Reyes]

so you mean, my router will only advertise routes local to my AS, thus preventing other routes(not local) to be advertised, right? 

then do i still need these neighbor commands if i only allow routes local to my AS? i think these will only help if have longer and shorter prefix to filtered, right? like if i have 4 /24 and their /22, i can make my ip prefix list le 22 or le 24?

neighbor 192.168.1.2 prefix-list MyAS-ISP1 out

ip prefix-list MyAS-ISP1 description Prefix Advertise to ISP1
ip prefix-list MyAS-ISP1 seq 100 permit 0.0.0.0/0 le 32

[Julio E. Moisa]

Hi,

That is correct, it will advertise the local routes only, now it usually is configured when you have 2 ISPs a multihomed scheme.