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In the first post we explored the basic configuration of BGP route aggregation with and without the summary-only keyword.

In todays post our task is to explore the suppress-map keyword using the same topology used in the first post. “please refer Part1 or the series for R1&R2 configuration and network diagram“.

Task1: Configure route aggregation on R2 for its loopback networks and allow only networks 2.2.0.0/24 and 2.2.2.0/24 to be advertised to R1 with the summary.

It is known that the aggregate-address command advertises the aggregate plus the more specific networks by default. The suppress map technique can be used to manually suppress some of these networks that match a specific criteria defined in a route-map called the suppress map as shown in the solution of this task below.

BGP tables of R1 and R2 before aggregation

R1#sh ip bgp
BGP table version is 6, 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
Origin codes: i - IGP, e - EGP, ? - incomplete

   Network          Next Hop            Metric LocPrf Weight Path
*> 1.1.1.0/24       0.0.0.0                  0         32768 i
*> 2.2.0.0/24       192.168.12.2             0             0 2 i
*> 2.2.1.0/24       192.168.12.2             0             0 2 i
*> 2.2.2.0/24       192.168.12.2             0             0 2 i
*> 2.2.3.0/24       192.168.12.2             0             0 2 i

!-- R2 bgp table

R2#sh ip bgp
BGP table version is 6, local router ID is 2.2.2.2
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
*> 1.1.1.0/24       192.168.12.1             0             0 1 i
*> 2.2.0.0/24       0.0.0.0                  0         32768 i
*> 2.2.1.0/24       0.0.0.0                  0         32768 i
*> 2.2.2.0/24       0.0.0.0                  0         32768 i
*> 2.2.3.0/24       0.0.0.0                  0         32768 i

Aggregation Configuration on R2: All routes matched in the route-map will be suppressed and not advertised to any neighbor.

!-- routes to be suppressed
R2(config)#access-list 2 permit 2.2.1.0
R2(config)#access-list 2 permit 2.2.3.0

R2(config)#route-map SUPPRESS
R2(config-route-map)#match ip address 2

R2(config)#router bgp 2
R2(config-router)#aggregate-address 2.2.0.0 255.255.252.0 suppress-map SUPPRESS

Verification and troubleshooting:

!-- Notice the S character which indicates suppressed route.
R2(config-router)#do sh ip bgp
BGP table version is 9, local router ID is 2.2.2.2
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
*> 1.1.1.0/24       192.168.12.1             0             0 1 i
*> 2.2.0.0/24       0.0.0.0                  0         32768 i
*> 2.2.0.0/22       0.0.0.0                            32768 i
s> 2.2.1.0/24       0.0.0.0                  0         32768 i
*> 2.2.2.0/24       0.0.0.0                  0         32768 i
s> 2.2.3.0/24       0.0.0.0                  0         32768 i

!-- R1 has the summary route and only the allowed routes from R2
R1#sh ip bgp
BGP table version is 9, 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
Origin codes: i - IGP, e - EGP, ? - incomplete

   Network          Next Hop            Metric LocPrf Weight Path
*> 1.1.1.0/24       0.0.0.0                  0         32768 i
*> 2.2.0.0/24       192.168.12.2             0             0 2 i
*> 2.2.0.0/22       192.168.12.2             0             0 2 i
*> 2.2.2.0/24       192.168.12.2             0             0 2 i

Hope the post was descriptive and clear; please feel free to post your comments, questions and corrections.

1. BGP Routing Information Base (RIB)
2. BGP table analysis and statistics
3. BGP Route Refresh Capability

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