The aggregate command is changed to stop announcing the component routes. R3 and R4 get just the aggregate.
Before the change.
R4#show ip bgp
BGP table version is 14, local router ID is 172.17.0.4
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
*> 10.10.0.0/16 192.168.100.9 0 0 100 i
*> 10.10.10.0/24 192.168.100.9 0 100 80 1000 2000 3000 i
*> 10.10.11.0/24 192.168.100.9 0 100 80 i
*> 10.10.20.0/24 192.168.100.9 0 100 80 777 888 999 i
... output omitted ...
The aggregate gets the "summary-only" option.
R2#configure terminal
Enter configuration commands, one per line. End with CNTL/Z.
R2(config)#router bgp 100
R2(config-router)#aggregate-address 10.10.0.0 255.255.0.0 summary-only
R2#
The change is effective at once, the BGP table of R4 is much smaller.
R4#show ip bgp
BGP table version is 24, local router ID is 172.17.0.4
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
*> 10.10.0.0/16 192.168.100.9 0 0 100 i
R4#
Sometimes a few of the component routes should be announced to the neighbors, but not all. Omitting the "summary-only" command and suppressing some prefixes with the suppress-map makes this possible. We now suppress all prefixes with an odd 3rd octed and 10.10.40.0/24. All other prefixes should be announced as usual.
R2(config-router)#aggregate-address 10.10.0.0 255.255.0.0 suppress-map SUPP
R2(config)#ip prefix-list SUPP permit 10.10.40.0/24
R2(config)#access-list 10 permit 0.0.1.0 255.255.254.255
R2(config)#route-map SUPP permit 10
R2(config-route-map)#match ip address prefix-list SUPP
R2(config-route-map)#exit
R2(config)#route-map SUPP permit 20
R2(config-route-map)#match ip address 10
R2(config-route-map)#exit
The BGP table on R4 looks now like this.
R4#show ip bgp
BGP table version is 6, local router ID is 172.17.0.4
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
*> 10.10.0.0/16 192.168.100.9 0 0 100 i
*> 10.10.10.0/24 192.168.100.9 0 100 80 1000 2000 3000 i
*> 10.10.20.0/24 192.168.100.9 0 100 80 777 888 999 i
*> 10.10.30.0/24 192.168.100.9 0 100 80 i
*> 10.10.50.0/24 192.168.100.9 0 100 80 i
The prefixes with an odd 3rd octed and 10.10.40.0/24 are missing from the BGP table. The BGP table of R2 shows the suppressed prefixes, marked with a "s" in the first column.
R2#show ip bgp
BGP table version is 18, local router ID is 172.17.0.2
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
*> 10.10.0.0/16 0.0.0.0 32768 i
*> 10.10.10.0/24 192.168.100.1 0 0 80 1000 2000 3000 i
s> 10.10.11.0/24 192.168.100.1 0 0 80 i
*> 10.10.20.0/24 192.168.100.1 0 0 80 777 888 999 i
s> 10.10.21.0/24 192.168.100.1 0 0 80 i
*> 10.10.30.0/24 192.168.100.1 0 0 80 i
s> 10.10.31.0/24 192.168.100.1 0 0 80 i
s> 10.10.40.0/24 192.168.100.1 0 0 80 i
s> 10.10.41.0/24 192.168.100.1 0 0 80 i
*> 10.10.50.0/24 192.168.100.1 0 0 80 i
s> 10.10.51.0/24 192.168.100.1 0 0 80 i
Part 1, Setup
Part 2, Setting the Aggregate
Part 4, Unsuppress the Suppressed
Part 5, Modification of Attributes
Part 6, Playing with the AS-SET
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