Lab 85 - BGP Attribute (Community Local-AS)

Pada lab sebelumnya kita telah belajar tentang Community No-Export dan Community No-Advertise. Selanjutnya pada lab ini kita akan belajar tentang Community Local AS. Berikut topologi yang akan kita gunakan pada lab ini

Gambar 1 Topologi jaringan BGP

Topologi ini merupakan topologi yang kita gunakan pada lab sebelumnya. Namun konfignya agak berbeda sih...

Pada lab sebelumnya, kita melakukan konfig BGP Confederation dengan Sub AS yang berbeda pada setiap router, yaitu AS 1 di R1, 2 di R2, dan AS 3 di R3. Padalah community dengan type local-as artinya bahwa network akan diadvertise ke router yang berada di AS Confederation yang sama. Dengan konfig sebelumnya, maka percuma saja kalo kita konfig community dengan local-as. Jadi kita bakal rubah penuh konfignya ya.. tapi yang di R1, R2 dan R3 aja.. yang di R4 udah gk perlu kita rombak

R1(config)#no router bgp 1

R2(config)#no router bgp 2

R3(config)#no router bgp 3

Oke kita konfig ulang BGP Confederationnya ya, nanti R1 ada di AS 1 dan R2 serta R3 ada di AS 23

R1(config)#router bgp 1
R1(config-router)#bgp confederation identifier 123
R1(config-router)#bgp confederation peers 23
R1(config-router)#neighbor 12.12.12.2 remote-as 23
R1(config-router)#net 1.1.1.1 mask 255.255.255.255

R2(config)#router bgp 23
R2(config-router)#bgp confederation identifier 123
R2(config-router)#bgp confederation peers 1
R2(config-router)#neighbor 12.12.12.1 remote-as 1
R2(config-router)#neighbor 12.12.12.1 next-hop-self 
R2(config-router)#neighbor 23.23.23.3 remote-as 23
R2(config-router)#neighbor 23.23.23.3 next-hop-self 
R2(config-router)#neighbor 24.24.24.4 remote-as 4
R2(config-router)#net 2.2.2.2 mask 255.255.255.255

R3(config)#router bgp 23
R3(config-router)#bgp confederation identifier 123
R3(config-router)#neighbor 23.23.23.2 remote-as 23
R3(config-router)#net 3.3.3.3 mask 255.255.255.255

Sekarang kita coba lihat tabel routing di seluruh router, pastikan semuanya sudah punya tabel routing yang lengkap

R1(config-router)#do sh ip ro
1.0.0.0/32 is subnetted, 1 subnets
C        1.1.1.1 is directly connected, Loopback0
      2.0.0.0/32 is subnetted, 1 subnets
B        2.2.2.2 [200/0] via 12.12.12.2, 00:03:52
      3.0.0.0/32 is subnetted, 1 subnets
B        3.3.3.3 [200/0] via 12.12.12.2, 00:03:52
      4.0.0.0/32 is subnetted, 1 subnets
B        4.4.4.4 [200/0] via 12.12.12.2, 00:06:59
      11.0.0.0/32 is subnetted, 1 subnets
C        11.11.11.11 is directly connected, Loopback1
      12.0.0.0/8 is variably subnetted, 2 subnets, 2 masks
C        12.12.12.0/24 is directly connected, Ethernet0/0

R2(config-router)#do sh ip ro

      1.0.0.0/32 is subnetted, 1 subnets
B        1.1.1.1 [200/0] via 12.12.12.1, 00:11:17
      2.0.0.0/32 is subnetted, 1 subnets
C        2.2.2.2 is directly connected, Loopback0
      3.0.0.0/32 is subnetted, 1 subnets
B        3.3.3.3 [200/0] via 23.23.23.3, 00:04:22
      4.0.0.0/32 is subnetted, 1 subnets
B        4.4.4.4 [20/0] via 24.24.24.4, 00:07:01
      12.0.0.0/8 is variably subnetted, 2 subnets, 2 masks
C        12.12.12.0/24 is directly connected, Ethernet0/0
      23.0.0.0/8 is variably subnetted, 2 subnets, 2 masks
C        23.23.23.0/24 is directly connected, Ethernet0/1
      24.0.0.0/8 is variably subnetted, 2 subnets, 2 masks
C        24.24.24.0/24 is directly connected, Ethernet0/2

R3(config-router)#do sh ip ro

      1.0.0.0/32 is subnetted, 1 subnets
B        1.1.1.1 [200/0] via 23.23.23.2, 00:04:27
      2.0.0.0/32 is subnetted, 1 subnets
B        2.2.2.2 [200/0] via 23.23.23.2, 00:04:04
      3.0.0.0/32 is subnetted, 1 subnets
C        3.3.3.3 is directly connected, Loopback0
      4.0.0.0/32 is subnetted, 1 subnets
B        4.4.4.4 [200/0] via 23.23.23.2, 00:04:27
      23.0.0.0/8 is variably subnetted, 2 subnets, 2 masks
C        23.23.23.0/24 is directly connected, Ethernet0/0

R4(config-router)#do sh ip ro

      1.0.0.0/32 is subnetted, 1 subnets
B        1.1.1.1 [20/0] via 24.24.24.2, 00:07:08
      2.0.0.0/32 is subnetted, 1 subnets
B        2.2.2.2 [20/0] via 24.24.24.2, 00:04:01
      3.0.0.0/32 is subnetted, 1 subnets
B        3.3.3.3 [20/0] via 24.24.24.2, 00:04:01
      4.0.0.0/32 is subnetted, 1 subnets
C        4.4.4.4 is directly connected, Loopback0
      24.0.0.0/8 is variably subnetted, 2 subnets, 2 masks
C        24.24.24.0/24 is directly connected, Ethernet0/0

Joozzzz udah lengkap semua kan.. sekarang kita konfig community local AS di R1

R1(config)#access-list 2 permit 1.1.1.1
R1(config)#route-map LOCAL-AS permit 10
R1(config-route-map)#match ip address 2
R1(config-route-map)#set community local-as
R1(config-route-map)#route-map LOCAL-AS permit 20

R1(config-route-map)#router bgp 1
R1(config-router)#neighbor 12.12.12.2 route-map LOCAL-AS out
R1(config-router)#neighbor 12.12.12.2 send-community 

Untuk pengujian, kita coba lihat statusnya di R2 dulu

R2(config-router)#do sh ip bgp 1.1.1.1
BGP routing table entry for 1.1.1.1/32, version 8
Paths: (1 available, best #1, table default, not advertised outside local AS)
  Advertised to update-groups:
     4         
  (1)
    12.12.12.1 from 12.12.12.1 (11.11.11.11)
      Origin IGP, metric 0, localpref 100, valid, confed-external, best
      Community: local-AS

Sip2 community nya udah local-AS ya.. lanjut kita coba lihat tabel routing di R3 dan R4

R3(config-router)#do sh ip ro

      1.0.0.0/32 is subnetted, 1 subnets
B        1.1.1.1 [200/0] via 23.23.23.2, 00:08:59
      2.0.0.0/32 is subnetted, 1 subnets
B        2.2.2.2 [200/0] via 23.23.23.2, 00:08:36
      3.0.0.0/32 is subnetted, 1 subnets
C        3.3.3.3 is directly connected, Loopback0
      4.0.0.0/32 is subnetted, 1 subnets
B        4.4.4.4 [200/0] via 23.23.23.2, 00:08:59
      23.0.0.0/8 is variably subnetted, 2 subnets, 2 masks
C        23.23.23.0/24 is directly connected, Ethernet0/0

R4(config-router)#do sh ip ro

      2.0.0.0/32 is subnetted, 1 subnets
B        2.2.2.2 [20/0] via 24.24.24.2, 00:08:33
      3.0.0.0/32 is subnetted, 1 subnets
B        3.3.3.3 [20/0] via 24.24.24.2, 00:08:33
      4.0.0.0/32 is subnetted, 1 subnets
C        4.4.4.4 is directly connected, Loopback0
      24.0.0.0/8 is variably subnetted, 2 subnets, 2 masks
C        24.24.24.0/24 is directly connected, Ethernet0/0

Udah jozzz kan?? R3 masih punya informasi tentang 1.1.1.1, namun R4 udah gk punya.. kenapa? karena R3 berada di AS Confederation yang sama dengan R2, yaitu 23. Bagaimana jika ternyata R3 berada di AS Confederation (Sub AS) 3?? ya R3 gak bakal punya informasi tentang 1.1.1.1, karena community local as hanya akan mengadvertise network ke AS yang sama!