In the previous article, if we could exclude the 192.168.1.0/24 prefix from being part of the prefixes that form the aggregate, the aggregate would not inherit the no-export community attribute.
The advertise map is another form of route maps that determines the formation of the aggregate based on a limited selection of the more-specific prefixes.
Below shows the BGP tables on RT1 and RT2 prior to implementing any aggregation configuration on RT3.
RT1#sh ip bgp BGP table version is 3, local router ID is 192.168.1.1 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 *> 192.168.1.0 0.0.0.0 0 32768 i *> 192.168.2.0 13.13.13.3 0 300 200 i RT1# ================================================================================ RT2#sh ip bgp BGP table version is 3, local router ID is 192.168.2.1 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 *> 192.168.1.0 24.24.24.4 0 300 100 i *> 192.168.2.0 0.0.0.0 0 32768 i RT2#
Below shows that upon implementing an AS_SET aggregation 192.168.0.0/16 on RT3, RT1 and RT2 denied the aggregate as it contains {100 200} in the AS path, a normal BGP behavior in detecting loops.
RT3#conf t Enter configuration commands, one per line. End with CNTL/Z. RT3(config)#router bgp 300 RT3(config-router)#aggregate-address 192.168.0.0 255.255.0.0 as-set RT3(config-router)#end RT3# RT3#sh ip bgp BGP table version is 4, local router ID is 34.34.34.3 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 *> 192.168.0.0/16 0.0.0.0 100 32768 {100,200} i *> 192.168.1.0 13.13.13.1 0 0 100 i *>i192.168.2.0 34.34.34.4 0 100 0 200 i RT3# ================================================================================ RT4#sh ip bgp BGP table version is 4, local router ID is 34.34.34.4 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 *>i192.168.0.0/16 34.34.34.3 0 100 0 {100,200} i *>i192.168.1.0 34.34.34.3 0 100 0 100 i *> 192.168.2.0 24.24.24.2 0 0 200 i RT4#
RT1#debug ip bgp updates BGP updates debugging is on RT1# 00:01:40: BGP(0): 13.13.13.3 computing updates, afi 0, neighbor version 2, table version 3, starting at 0.0.0.0 00:01:40: BGP(0): 13.13.13.3 update run completed, afi 0, ran for 0ms, neighbor version 2, start version 3, throttled to 3 00:02:06: BGP(0): 13.13.13.3 rcv UPDATE w/ attr: nexthop 13.13.13.3, origin i, metric 0, aggregated by 300 34.34.34.3, originator 0.0.0.0, path 300 {100,200}, community , extended community 00:02:06: BGP(0): 13.13.13.3 rcv UPDATE about 192.168.0.0/16 -- DENIED due to: AS-PATH contains our own AS; RT1# ================================================================================ RT2#debug ip bgp updates BGP updates debugging is on RT2# 00:02:08: BGP(0): 24.24.24.4 rcv UPDATE w/ attr: nexthop 24.24.24.4, origin i, aggregated by 300 34.34.34.3, originator 0.0.0.0, path 300 {100,200}, community , extended community 00:02:08: BGP(0): 24.24.24.4 rcv UPDATE about 192.168.0.0/16 -- DENIED due to: AS-PATH contains our own AS; RT2#
Below shows how to use an advertise map to cause RT3 to base the aggregate upon 192.168.2.0/24 only, and excludes 192.168.1.0/24 from the formation of the aggregate.
RT3#conf t Enter configuration commands, one per line. End with CNTL/Z. RT3(config)#access-list 1 permit 192.168.2.0 0.0.0.255 RT3(config)#route-map SPEC-ROUTES permit 10 RT3(config-route-map)#match ip address 1 RT3(config-route-map)#exit RT3(config)# RT3(config)#router bgp 300 RT3(config-router)#aggregate-address 192.168.0.0 255.255.0.0 as-set advertise-map SPEC-ROUTES RT3(config-router)#end RT3# RT3#sh ip bgp BGP table version is 5, local router ID is 34.34.34.3 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 *> 192.168.0.0/16 0.0.0.0 100 32768 200 i *> 192.168.1.0 13.13.13.1 0 0 100 i *>i192.168.2.0 34.34.34.4 0 100 0 200 i RT3# ================================================================================ RT4#sh ip bgp BGP table version is 5, local router ID is 34.34.34.4 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 *>i192.168.0.0/16 34.34.34.3 0 100 0 200 i *>i192.168.1.0 34.34.34.3 0 100 0 100 i *> 192.168.2.0 24.24.24.2 0 0 200 i RT4#
RT1 accepted the route as the AS path no longer includes its AS number.
RT1# 00:09:47: BGP(0): 13.13.13.3 rcvd UPDATE w/ attr: nexthop 13.13.13.3, origin i, metric 0, atomic-aggregate, aggregated by 300 34.34.34.3, path 300 200 00:09:47: BGP(0): 13.13.13.3 rcvd 192.168.0.0/16 00:09:47: BGP(0): Revise route installing 1 of 1 route for 192.168.0.0/16 -> 13.13.13.3 to main IP table 00:09:47: BGP(0): 13.13.13.3 computing updates, afi 0, neighbor version 3, table version 4, starting at 0.0.0.0 00:09:47: BGP(0): 13.13.13.3 update run completed, afi 0, ran for 0ms, neighbor version 3, start version 4, throttled to 4 RT1# RT1#sh ip bgp BGP table version is 4, local router ID is 192.168.1.1 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 *> 192.168.0.0/16 13.13.13.3 0 0 300 200 i *> 192.168.1.0 0.0.0.0 0 32768 i *> 192.168.2.0 13.13.13.3 0 300 200 i RT1# ================================================================================ RT2# 00:09:47: BGP(0): 24.24.24.4 rcv UPDATE w/ attr: nexthop 24.24.24.4, origin i, atomic-aggregate, aggregated by 300 34.34.34.3, originator 0.0.0.0, path 300 200, community , extended community 00:09:47: BGP(0): 24.24.24.4 rcv UPDATE about 192.168.0.0/16 -- DENIED due to: AS-PATH contains our own AS; RT2#
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