BGP filtering with Prefix-Lists

BGP filtering with Prefix-Lists

In this example, we will filter the BGP routes by using prefix-list

Here is the initial configuration of the router:

interface Loopback4

 ip address 4.4.4.4 255.255.255.255

!

interface FastEthernet1/0

 ip address 192.168.45.4 255.255.255.0

 !

router bgp 4

 no synchronization

 bgp log-neighbor-changes

 network 4.4.4.4 mask 255.255.255.255

 neighbor 192.168.45.5 remote-as 5

 no auto-summary

Here is the BGP table:

R4#show ip bgp

BGP table version is 4, local router ID is 192.168.0.4

Status codes: s suppressed, d damped, h history, * valid, > best, i - internal,

              r RIB-failure, S Stale

Origin codes: i - IGP, e - EGP, ? - incomplete

   Network          Next Hop            Metric LocPrf Weight Path

*> 4.4.4.4/32       0.0.0.0                  0         32768 i

*> 5.5.5.5/32       192.168.45.5             0             0 5 i

*> 55.55.55.0/24    192.168.45.5             0             0 5 i

Lets filter the 55.55.55.0/24:

Firstly we will create a prefix-list  access-list.

Prefix-list name is R5-in

ip prefix-list R5-in seq 5 deny 55.55.55.0/24

ip prefix-list R5-in seq 10 permit 0.0.0.0/0 le 32

Then, we apply the prefix-list to the BGP configuration:

R4(config)#router bgp 4                                     

R4(config-router)#neighbor 192.168.45.5 prefix-list R5-in in

Then we see that 55.55.55.0/24 IP prefix is no longer exists:

R4#show ip bgp

BGP table version is 5, local router ID is 192.168.0.4

Status codes: s suppressed, d damped, h history, * valid, > best, i - internal,

              r RIB-failure, S Stale

Origin codes: i - IGP, e - EGP, ? - incomplete

   Network          Next Hop            Metric LocPrf Weight Path

*> 4.4.4.4/32       0.0.0.0                  0         32768 i

*> 5.5.5.5/32       192.168.45.5             0             0 5 i