1、首先来介绍下网络拓扑图：路由器r1、r2、r3属于 AS 100并且内部运行ospf协议。r4属于AS 200。r5、6、7属于AS 300并且内部运行ospf协议。本例中a路径：1.1.1.1 访问172.16.10.1 走 r1-r2-r4-r5-r7。b路径:1.1.1.1 访问172.16.20.1 走路径r1-r3-r4-r6-r7。介绍完拓扑图后接下来将为大家依次介绍每个路由器的配置！
2、路由器r1的核心配置：#interface GigabitEthernet0/0/0ip address 10.0.12.1 255.255.255.0#interface GigabitEthernet0/0/1ip address 10.0.13.1 255.255.255.0#interface GigabitEthernet0/0/2#interface NULL0#interface LoopBack0ip address 1.1.1.1 255.255.255.255#interface LoopBack10ip address 192.168.10.1 255.255.255.0#interface LoopBack20ip address 192.168.20.1 255.255.255.0#bgp 100router-id 1.1.1.1peer 10.0.12.2 as-number 100peer 10.0.13.3 as-number 100#ipv4-family unicast undo synchronization network 1.1.1.1 255.255.255.255 network 192.168.10.0 network 192.168.20.0 peer 10.0.12.2 enable peer 10.0.13.3 enable#ospf 1 router-id 1.1.1.1area 0.0.0.0 network 1.1.1.1 0.0.0.0 network 10.0.12.0 0.0.0.255 network 10.0.13.0 0.0.0.255#
3、路由器r2的核心配置：#interface GigabitEthernet0/0/0ip address 10.0.12.2 255.255.255.0#interface GigabitEthernet0/0/1ip address 10.0.24.2 255.255.255.0#interface GigabitEthernet0/0/2#interface NULL0#interface LoopBack0ip address 2.2.2.2 255.255.255.255#bgp 100router-id 2.2.2.2peer 10.0.12.1 as-number 100peer 10.0.24.4 as-number 200#ipv4-family unicast undo synchronization network 2.2.2.2 255.255.255.255 peer 10.0.12.1 enable peer 10.0.24.4 enable#ospf 1 router-id 2.2.2.2area 0.0.0.0 network 2.2.2.2 0.0.0.0 network 10.0.12.0 0.0.0.255 network 10.0.24.0 0.0.0.255#路由器r3的核心配置：#interface GigabitEthernet0/0/0ip address 10.0.34.3 255.255.255.0#interface GigabitEthernet0/0/1ip address 10.0.13.3 255.255.255.0#interface GigabitEthernet0/0/2#interface NULL0#interface LoopBack0ip address 3.3.3.3 255.255.255.255#bgp 100router-id 3.3.3.3peer 10.0.13.1 as-number 100peer 10.0.34.4 as-number 200#ipv4-family unicast undo synchronization network 3.3.3.3 255.255.255.255 peer 10.0.13.1 enable peer 10.0.34.4 enable#ospf 1 router-id 3.3.3.3area 0.0.0.0 network 3.3.3.3 0.0.0.0 network 10.0.13.0 0.0.0.255 network 10.0.34.0 0.0.0.255#
4、路由器r4的核心配置：#interface GigabitEthernet0/0/0ip address 10.0.34.4 255.255.255.0#interface GigabitEthernet0/0/1ip address 10.0.24.4 255.255.255.0#interface GigabitEthernet4/0/0ip address 10.0.46.4 255.255.255.0#interface GigabitEthernet4/0/1ip address 10.0.45.4 255.255.255.0#interface LoopBack0ip address 4.4.4.4 255.255.255.255#bgp 200router-id 4.4.4.4peer 10.0.24.2 as-number 100peer 10.0.34.3 as-number 100peer 10.0.45.5 as-number 300peer 10.0.46.6 as-number 300#ipv4-family unicast undo synchronization network 4.4.4.4 255.255.255.255 peer 10.0.24.2 enable peer 10.0.24.2 route-policy med10 export peer 10.0.24.2 advertise-community peer 10.0.34.3 enable peer 10.0.34.3 route-policy med20 export peer 10.0.34.3 advertise-community peer 10.0.45.5 enable peer 10.0.45.5 route-policy 10 import peer 10.0.46.6 enable peer 10.0.46.6 route-policy 10 import#route-policy 10 permit node 10if-match community-filter 10apply ip-address next-hop 10.0.45.5#route-policy 10 permit node 20if-match community-filter 20apply ip-address next-hop 10.0.46.6#route-policy med10 permit node 10if-match community-filter 10apply cost 100#route-policy med10 permit node 20if-match community-filter 20apply cost 200#route-policy med20 permit node 10if-match community-filter 20apply cost 100#route-policy med20 permit node 20if-match community-filter 10apply cost 200#ip community-filter 10 permit 300:100ip community-filter 20 permit 300:200#
5、路由器r5核心配置：#interface GigabitEthernet0/0/1ip address 10.0.45.5 255.255.255.0#interface GigabitEthernet0/0/2ip address 10.0.57.5 255.255.255.0#interface NULL0#interface LoopBack0ip address 5.5.5.5 255.255.255.255#bgp 300router-id 5.5.5.5peer 10.0.45.4 as-number 200peer 10.0.57.7 as-number 300#ipv4-family unicast undo synchronization network 5.5.5.5 255.255.255.255 peer 10.0.45.4 enable peer 10.0.45.4 advertise-community peer 10.0.57.7 enable#ospf 1 router-id 5.5.5.5area 0.0.0.0 network 5.5.5.5 0.0.0.0 network 10.0.45.0 0.0.0.255 network 10.0.57.0 0.0.0.255#路由器r6核心配置：#interface GigabitEthernet0/0/0ip address 10.0.46.6 255.255.255.0#interface GigabitEthernet0/0/1ip address 10.0.67.6 255.255.255.0#interface LoopBack0ip address 6.6.6.6 255.255.255.255#bgp 300router-id 6.6.6.6peer 10.0.46.4 as-number 200peer 10.0.67.7 as-number 300#ipv4-family unicast undo synchronization network 6.6.6.6 255.255.255.255 peer 10.0.46.4 enable peer 10.0.46.4 advertise-community peer 10.0.67.7 enable#ospf 1 router-id 6.6.6.6area 0.0.0.0 network 6.6.6.6 0.0.0.0 network 10.0.46.0 0.0.0.255 network 10.0.67.0 0.0.0.255#
6、路由器r7核心配置：#interface GigabitEthernet0/0/1ip address 10.0.67.7 255.255.255.0#interface GigabitEthernet0/0/2ip address 10.0.57.7 255.255.255.0#interface NULL0#interface LoopBack0ip address 7.7.7.7 255.255.255.255#interface LoopBack10ip address 172.16.10.1 255.255.255.0#interface LoopBack20ip address 172.16.20.1 255.255.255.0#bgp 300router-id 7.7.7.7peer 10.0.57.5 as-number 300peer 10.0.67.6 as-number 300#ipv4-family unicast undo synchronization network 7.7.7.7 255.255.255.255 network 172.16.10.0 255.255.255.0 route-policy com10 network 172.16.20.0 255.255.255.0 route-policy com20 peer 10.0.57.5 enable peer 10.0.57.5 advertise-community peer 10.0.67.6 enable peer 10.0.67.6 advertise-community#ospf 1 router-id 7.7.7.7area 0.0.0.0 network 7.7.7.7 0.0.0.0 network 10.0.57.0 0.0.0.255 network 10.0.67.0 0.0.0.255#route-policy com10 permit node 10apply community 300:100#route-policy com20 permit node 10apply community 300:200#
7、配置好所有设备后我们在r4上查看172.16.10.0和172.16.20.0网段的community值：<ar4>dis bgp routing-table 172.16.10.1BGP local router ID : 4.4.4.4Local AS number : 200Paths: 2 available, 1 best, 1 selectBGP routing table entry information of 172.16.10.0/24:From: 10.0.45.5 (5.5.5.5)Route Duration: 01h13m49sDirect Out-interface: GigabitEthernet4/0/1Original nexthop: 10.0.45.5Qos information : 0x0Community:<300:100>AS-path 300, origin igp, pref-val 0, valid, external, best, select, active, pre255Advertised to such 4 peers: 10.0.45.5 10.0.46.6 10.0.24.2 10.0.34.3BGP routing table entry information of 172.16.10.0/24:From: 10.0.46.6 (6.6.6.6)Route Duration: 01h13m39sRelay IP Nexthop: 0.0.0.0Relay IP Out-Interface: GigabitEthernet4/0/1Original nexthop: 10.0.45.5Qos information : 0x0Community:<300:100>通过上面输出的信息可以看到172.16.10.1的Community属性值是<300:100>！
8、最后我们在r1上使用tracert命令查看路径是否如我们所设置的那样：<ar1>tracert -a 1.1.1.1 172.16.10.1traceroute to 172.16.10.1(172.16.10.1), max hops: 30 ,packet length: 40,pressCTRL_C to break1 10.0.12.2 20 ms 20 ms 20 ms2 10.0.24.4 20 ms 30 ms 30 ms3 10.0.45.5 30 ms 30 ms 30 ms4 10.0.57.7 30 ms 40 ms 40 ms<ar1>tr <ar1>tracert -a 1.1.1.1 172.16.20.1traceroute to 172.16.20.1(172.16.20.1), max hops: 30 ,packet length: 40,pressCTRL_C to break1 10.0.13.3 20 ms 20 ms 20 ms2 10.0.34.4 20 ms 30 ms 20 ms3 10.0.46.6 30 ms 30 ms 40 ms4 10.0.67.7 30 ms 20 ms 30 ms输出结果与路由器的输出结果路线均正确，配置成功！
