Cisco BGP AS-PATH配置实例如下图示：
R1: interface Loopback0 ip address 1.1.1.1 255.255.255.255 interface FastEthernet0/0 ip address 12.1.1.1 255.255.255.0 interface FastEthernet0/1 ip address 14.1.1.1 255.255.255.0 router eigrp 1 network 1.1.1.1 0.0.0.0 network 12.1.1.0 0.0.0.255 network 14.1.1.0 0.0.0.255 no auto-summary router bgp 100 bgp router-id 1.1.1.1 bgp log-neighbor-changes no synchronization neighbor 2.2.2.2 remote-as 100 neighbor 2.2.2.2 update-source Loopback0 neighbor 2.2.2.2 next-hop-self neighbor 3.3.3.3 remote-as 100 neighbor 3.3.3.3 update-source Loopback0 neighbor 3.3.3.3 next-hop-self neighbor 4.4.4.4 remote-as 200 neighbor 4.4.4.4 ebgp-multihop 255 neighbor 4.4.4.4 update-source Loopback0 neighbor 4.4.4.4 next-hop-self no auto-summary R2: interface Loopback0 ip address 2.2.2.2 255.255.255.255 interface FastEthernet0/0 ip address 12.1.1.2 255.255.255.0 interface FastEthernet0/1 ip address 23.1.1.2 255.255.255.0 router eigrp 1 network 2.2.2.2 0.0.0.0 network 12.1.1.0 0.0.0.255 network 23.1.1.0 0.0.0.255 no auto-summary router bgp 100 no synchronization bgp router-id 2.2.2.2 bgp log-neighbor-changes neighbor 1.1.1.1 remote-as 100 neighbor 1.1.1.1 update-source Loopback0 neighbor 1.1.1.1 next-hop-self neighbor 3.3.3.3 remote-as 100 neighbor 3.3.3.3 update-source Loopback0 neighbor 3.3.3.3 next-hop-self no auto-summary R3: interface Loopback0 ip address 3.3.3.3 255.255.255.255 interface FastEthernet0/0 ip address 34.1.1.3 255.255.255.0 interface FastEthernet0/1 ip address 23.1.1.3 255.255.255.0 router eigrp 1 network 3.3.3.3 0.0.0.0 network 23.1.1.0 0.0.0.255 network 34.1.1.0 0.0.0.255 no auto-summary router bgp 100 no synchronization bgp router-id 3.3.3.3 bgp log-neighbor-changes neighbor 1.1.1.1 remote-as 100 neighbor 1.1.1.1 update-source Loopback0 neighbor 1.1.1.1 next-hop-self neighbor 2.2.2.2 remote-as 100 neighbor 2.2.2.2 update-source Loopback0 neighbor 2.2.2.2 next-hop-self neighbor 4.4.4.4 remote-as 200 neighbor 4.4.4.4 ebgp-multihop 255 neighbor 4.4.4.4 update-source Loopback0 neighbor 4.4.4.4 next-hop-self no auto-summary R4: interface Loopback0 ip address 4.4.4.4 255.255.255.255 interface FastEthernet0/0 ip address 34.1.1.4 255.255.255.0 interface FastEthernet0/1 ip address 14.1.1.4 255.255.255.0 router eigrp 1 network 4.4.4.4 0.0.0.0 network 14.1.1.0 0.0.0.255 network 34.1.1.0 0.0.0.255 no auto-summary ip prefix-list 1 seq 5 permit 4.4.4.4/32 route-map as_path permit 10 match ip address prefix-list 1 set as-path prepend 600 700 router bgp 200 no synchronization bgp log-neighbor-changes neighbor 1.1.1.1 remote-as 100 neighbor 1.1.1.1 ebgp-multihop 255 neighbor 1.1.1.1 update-source Loopback0 neighbor 1.1.1.1 next-hop-self neighbor 3.3.3.3 remote-as 100 neighbor 3.3.3.3 ebgp-multihop 255 neighbor 3.3.3.3 update-source Loopback0 neighbor 3.3.3.3 next-hop-self neighbor 3.3.3.3 route-map as_path out no auto-summary R4(config-router)#do ping 1.1.1.1 Type escape sequence to abort. Sending 5, 100-byte ICMP Echos to 1.1.1.1, timeout is 2 seconds: !!!!! Success rate is 100 percent (5/5), round-trip min/avg/max = 32/36/40 ms R4(config-router)#do traceroute 1.1.1.1 Type escape sequence to abort. Tracing the route to 1.1.1.1 1 34.1.1.3 8 msec 12 msec 24 msec 2 23.1.1.2 32 msec 36 msec 44 msec 3 12.1.1.1 32 msec 44 msec 32 msec R4(config-router)# R4(config-router)#do show ip route Codes: C - connected, S - static, R - RIP, M - mobile, B - BGP D - EIGRP, EX - EIGRP external, O - OSPF, IA - OSPF inter area N1 - OSPF NSSA external type 1, N2 - OSPF NSSA external type 2 E1 - OSPF external type 1, E2 - OSPF external type 2 i - IS-IS, su - IS-IS summary, L1 - IS-IS level-1, L2 - IS-IS level-2 ia - IS-IS inter area, * - candidate default, U - per-user static route o - ODR, P - periodic downloaded static route Gateway of last resort is not set 34.0.0.0/24 is subnetted, 1 subnets C 34.1.1.0 is directly connected, FastEthernet0/0 1.0.0.0/32 is subnetted, 1 subnets D 1.1.1.1 [90/460800] via 34.1.1.3, 00:05:23, FastEthernet0/0 2.0.0.0/32 is subnetted, 1 subnets D 2.2.2.2 [90/435200] via 34.1.1.3, 00:03:07, FastEthernet0/0 3.0.0.0/32 is subnetted, 1 subnets D 3.3.3.3 [90/409600] via 34.1.1.3, 00:05:25, FastEthernet0/0 4.0.0.0/32 is subnetted, 1 subnets C 4.4.4.4 is directly connected, Loopback0 23.0.0.0/24 is subnetted, 1 subnets D 23.1.1.0 [90/307200] via 34.1.1.3, 00:05:36, FastEthernet0/0 12.0.0.0/24 is subnetted, 1 subnets D 12.1.1.0 [90/332800] via 34.1.1.3, 00:03:10, FastEthernet0/0 14.0.0.0/24 is subnetted, 1 subnets D 14.1.1.0 [90/358400] via 34.1.1.3, 00:05:37, FastEthernet0/0