Lab 124 - BGP Aggregation Advertise Map

Lanjtut yaaa belajar BGP nya.. sekarang kita akan belajar fitur advertise map pada aggregation BGP.. langsung lab aja ya.. nanti teorinya saya jelaskan sambil ngelab nya.. Berikut topologi yang akan kita gunakan pada lab ini

Pertama kita konfig BGP nya dulu ya.. oya diasumsikan ip address sudah di konfig standard idn ya..

R1(config)#do sh run | s r b
router bgp 12
 bgp log-neighbor-changes
 network 1.1.0.0 mask 255.255.255.0
 network 1.1.1.0 mask 255.255.255.0
 network 1.1.2.0 mask 255.255.255.0
 network 1.1.3.0 mask 255.255.255.0
 neighbor 13.13.13.3 remote-as 3

neighbor 12.12.12.2 remote-as 12

R2(config-router)#do sh run | s r b
router bgp 12
 bgp log-neighbor-changes
 network 1.1.4.0 mask 255.255.255.0
 network 1.1.5.0 mask 255.255.255.0
 network 1.1.6.0 mask 255.255.255.0
 network 1.1.7.0 mask 255.255.255.0
 neighbor 23.23.23.3 remote-as 3

neighbor 12.12.12.1 remote-as 12

R3(config-router)#do sh run | s r b
router bgp 3
 bgp log-neighbor-changes
 neighbor 13.13.13.1 remote-as 12
 neighbor 23.23.23.2 remote-as 12
 neighbor 34.34.34.4 remote-as 4

R4(config-router)#do sh run | s r b
router bgp 4
 bgp log-neighbor-changes
 neighbor 34.34.34.3 remote-as 3

Kita lihat hasilnya di R3 yaa

R4(config-router)#do sh ip bgp
BGP table version is 27, 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, m multipath, b backup-path, f RT-Filter, 
              x best-external, a additional-path, c RIB-compressed, 
Origin codes: i - IGP, e - EGP, ? - incomplete
RPKI validation codes: V valid, I invalid, N Not found

     Network          Next Hop            Metric LocPrf Weight Path
 *>  1.1.0.0/24       34.34.34.3                             0 3 12 i
 *>  1.1.1.0/24       34.34.34.3                             0 3 12 i
 *>  1.1.2.0/24       34.34.34.3                             0 3 12 i
 *>  1.1.3.0/24       34.34.34.3                             0 3 12 i
 *>  1.1.4.0/24       34.34.34.3                             0 3 12 i
 *>  1.1.5.0/24       34.34.34.3                             0 3 12 i
 *>  1.1.6.0/24       34.34.34.3                             0 3 12 i
 *>  1.1.7.0/24       34.34.34.3                             0 3 12 i

Oke R3 sudah punya informasi prefix yang lengkap dalam BGP..

Sekarang kita lakukan summarization di R3 yaa

R3(config)#router bgp 3
R3(config-router)#aggregate-address 1.1.0.0 255.255.248.0 as-set summary-only 

Kita coba lihat hasilnya di R4..

R4(config-router)#do sh ip bgp
BGP table version is 38, 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, m multipath, b backup-path, f RT-Filter, 
              x best-external, a additional-path, c RIB-compressed, 
Origin codes: i - IGP, e - EGP, ? - incomplete
RPKI validation codes: V valid, I invalid, N Not found

     Network          Next Hop            Metric LocPrf Weight Path
 *>  1.1.0.0/21       34.34.34.3               0             0 3 12 i

Oke hasilnya normal ya...

Sekarang ada sedikit masalah nih.. R1 akan mengkonfigurasikan prefix 1.1.0.0/24 dengan community no-advertise

R1(config)#access-list 1 permit 1.1.0.0 0.0.0.255
R1(config)#route-map set-com
R1(config-route-map)#match ip address 1
R1(config-route-map)#set community no-advertise

R1(config-route-map)#router bgp 12
R1(config-router)#nei 13.13.13.3 route-map set-com out
R1(config-router)#nei 13.13.13.3 send-community
R1(config-router)#do cle ip bgp * soft

Sebenarnya ini masalah sepele.. tapi akibatnya bisa besar lho.. kita coba lihat R3 yaa

R4(config-router)#do sh ip bgp
R4(config-router)#

Tuh kannn.... di R4 jadi hilang prefix hasil summary nya.. kenapa demikian?? karena R3 melakukan summary pada network 1.1.0.0/21,, dan salah satu prefix nya (1.1.0.0/24) memiliki community no-advertise.. jadi akibatnya semua prefix akan terpengaruhi dan tidak akan diadvertise kemanapun...

Untuk mengatasi masalah ini.. kita bisa melakukan summary pada beberapa prefix saja menggunakan advertisemap pada R3 seperti berikut

R3(config)#ip prefix-list advertise-map deny 1.1.0.0/24 
R3(config)#ip prefix-list advertise-map permit 1.1.0.0/21 ge 24 le 24
R3(config)#route-map to-aggregate
R3(config-route-map)#match ip address prefix-list advertise-map

R3(config-route-map)#router bgp 3
R3(config-router)# aggregate-address 1.1.0.0 255.255.248.0 as-set summary-only 
advertise-map to-aggregate

Perhatikan bahwa kita membuat prefix list.. pertama mendeny network 1.1.0.0/24.. artinya nanti prefix 1.1.0.0/24 tidak akan diikutkan dalam summarization..

Kita coba cek hasilnya di R4 yaa

R4(config-router)#do sh ip bgp
BGP table version is 42, 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, m multipath, b backup-path, f RT-Filter, 
              x best-external, a additional-path, c RIB-compressed, 
Origin codes: i - IGP, e - EGP, ? - incomplete
RPKI validation codes: V valid, I invalid, N Not found

     Network          Next Hop            Metric LocPrf Weight Path
 *>  1.1.0.0/21       34.34.34.3               0             0 3 12 i

Okeee sudah berhasil kan..

Oke sampai disini dulu ya.. semoga bermanfaat..