How to advertise networks in BGP

Lessons Discussion
27

Hello Hussein,

That is no problem. You advertise the network with the network command and then use route-maps to filter what you need.

Here’s R1 advertising to R2:

R1#show ip bgp neighbors 192.168.12.2 advertised-routes 
BGP table version is 4, local router ID is 1.1.1.1
Status codes: s suppressed, d damped, h history, * valid, > best, i - internal, 
              r RIB-failure, S Stale, m multipath, b backup-path, f RT-Filter, 
              x best-external, a additional-path, c RIB-compressed, 
              t secondary path, 
Origin codes: i - IGP, e - EGP, ? - incomplete
RPKI validation codes: V valid, I invalid, N Not found

     Network          Next Hop            Metric LocPrf Weight Path
 *>   1.1.1.1/32       0.0.0.0                  0         32768 i

Total number of prefixes 1

And to R3:

R1#show ip bgp neighbors 192.168.13.3 advertised-routes 
BGP table version is 4, local router ID is 1.1.1.1
Status codes: s suppressed, d damped, h history, * valid, > best, i - internal, 
              r RIB-failure, S Stale, m multipath, b backup-path, f RT-Filter, 
              x best-external, a additional-path, c RIB-compressed, 
              t secondary path, 
Origin codes: i - IGP, e - EGP, ? - incomplete
RPKI validation codes: V valid, I invalid, N Not found

     Network          Next Hop            Metric LocPrf Weight Path
 *>   1.1.1.1/32       0.0.0.0                  0         32768 i
 *>   2.2.2.2/32       192.168.12.2             0             0 2 i

Total number of prefixes 2

If you want to filter 1.1.1.1/32 from being advertised to R3, do something like this:

R1(config)#ip prefix-list R1_L0 permit 1.1.1.1/32

R1(config)#route-map TO_R3 deny 10
R1(config-route-map)#match ip address prefix-list R1_L0
R1(config)#route-map TO_R3 permit 20         

R1(config)#router bgp 1
R1(config-router)#neighbor 192.168.13.3 route-map TO_R3 out

And it’s gone:

R1#show ip bgp neighbors 192.168.13.3 advertised-routes 
BGP table version is 4, local router ID is 1.1.1.1
Status codes: s suppressed, d damped, h history, * valid, > best, i - internal, 
              r RIB-failure, S Stale, m multipath, b backup-path, f RT-Filter, 
              x best-external, a additional-path, c RIB-compressed, 
              t secondary path, 
Origin codes: i - IGP, e - EGP, ? - incomplete
RPKI validation codes: V valid, I invalid, N Not found

     Network          Next Hop            Metric LocPrf Weight Path
 *>   2.2.2.2/32       192.168.12.2             0             0 2 i

Total number of prefixes 1

Hope this helps!

Rene

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