配置BGP联邦

 

涉及到的概念：BGP联邦即BGP Confederation。一般用在一个AS的内部，在一个大的AS内部可以拆分成数个小的AS，这样只要保证小的AS之间可以通过EBGP方式进行互联即可，不必每台路由器都互相建立IBGP连接。

BGP联邦和RR的对比：BGP联邦建立之后在联邦内跨越内部的AS的时候AS_PATH仍然会发生变化，可以针对AS_PATH的变化做出更精确的控制。

配置如下：

routerE:
router bgp 100
 no synchronization
 bgp log-neighbor-changes
 network 1.1.1.1 mask 255.255.255.255
 neighbor 152.1.1.9 remote-as 200
 neighbor 152.1.2.5 remote-as 200
 no auto-summary 

routerB:
router ospf 1
 log-adjacency-changes
 redistribute connected subnets
 network 152.1.1.6 0.0.0.0 area 0
!
router bgp 65050
 no synchronization
 bgp log-neighbor-changes
 bgp confederation identifier 200
 bgp confederation peers 65051
 neighbor 152.1.1.5 remote-as 65050
 neighbor 152.1.1.5 next-hop-self
 neighbor 152.1.1.10 remote-as 100
 neighbor 152.1.1.65 remote-as 65051
 no auto-summary
! 

routerA:
router ospf 1
 log-adjacency-changes
 network 152.1.1.0 0.0.0.255 area 0
!
router bgp 65050
 no synchronization
 bgp log-neighbor-changes
 network 152.1.1.1 mask 255.255.255.255
 neighbor 152.1.1.6 remote-as 65050
 no auto-summary
!

routerC:
router bgp 65051
 no synchronization
 bgp log-neighbor-changes
 bgp confederation identifier 200
 bgp confederation peers 65050
 network 152.1.2.1 mask 255.255.255.255
 neighbor 152.1.1.66 remote-as 65050
 neighbor 152.1.1.66 next-hop-self
 neighbor 152.1.2.6 remote-as 100
 neighbor 152.1.2.129 remote-as 65051
 no auto-summary
!

routerD:
router ospf 1
 log-adjacency-changes
 network 152.1.2.0 0.0.0.255 area 0
!
router bgp 65051
 no synchronization
 bgp log-neighbor-changes
 network 152.1.2.2 mask 255.255.255.255
 neighbor 152.1.2.130 remote-as 65051
 no auto-summary
!
 配置完毕后，在router E上show ip bgp可以看到：

E#sh ip bgp 
BGP table version is 7, 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
*> 1.1.1.1/32       0.0.0.0                  0         32768 i
*> 152.1.1.1/32     152.1.1.9                              0 200 i
*  152.1.2.1/32     152.1.1.9                              0 200 i
*>                  152.1.2.5                0             0 200 i
*  152.1.2.2/32     152.1.1.9                              0 200 i
*>                  152.1.2.5                              0 200 i 

由此可知，联邦对外的表现是一个整体，AS100看到的都是AS200，而不是内部的AS65050或65051。但是在联邦的内部执行show ip bgp仍然会看到联邦内的AS的信息：

b#sh ip bgp
BGP table version is 12, local router ID is 152.1.1.2
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
*  1.1.1.1/32       152.1.1.65               0    100      0 (65051) 100 i
*>                  152.1.1.10               0             0 100 i
r>i152.1.1.1/32     152.1.1.5                0    100      0 i
*> 152.1.2.1/32     152.1.1.65               0    100      0 (65051) i
*> 152.1.2.2/32     152.1.1.65               0    100      0 (65051) i