Cisco提供一种方式强IGP路由优先于EBGP路由.这个概念也就是"后门链路"(backdoor link).EBGP路由可以标记为后门链路,它将设置这些路由的管理距离与BGP本地或200相同.因为这个管理距离要高于IGP,所以***IGP路由.
以下是具体配置:
//// r1 ////
int lo0 ip ad 1.1.1.1 255.255.255.0 int e1/0 ip ad 192.1.1.1 255.255.255.0 router os 1 network 0.0.0.0 255.255.255.255 a 0 //将所有接口宣告进OSPF router bgp 200 no syn //关闭同步,同时也注定了全互连的拓扑 neighbor 192.1.1.2 remote-as 200 neighbor 192.1.1.2 update-source lo0 //以lo0接口IP作为更新源地址 |
int lo0 ip ad 2.2.2.2 255.255.255.0 int e1/0 ip ad 192.1.1.2 255.255.255.0 int e0/0 ip ad 193.1.1.2 255.255.255.0 int e2/0 ip ad 195.1.1.2 255.255.255.0 router os 1 network 0.0.0.0 255.255.255.255 a 0 //宣告所有接口进OSPF router bgp 200 no syn neighbor 192.1.1.1 remote-as 200 neighbor 192.1.1.1 update-source lo0 neighbor 192.1.1.1 next-hop-self neighbor 195.1.1.5 remote-as 100 network 192.1.1.0 mask 255.255.255.0 |
//// r3 ////
int lo0 ip ad 3.3.3.3 255.255.255.0
int e0/0 ip ad 193.1.1.3 255.255.255.0
int e1/0 ip ad 194.1.1.3 255.255.255.0
int e3/0 ip ad 196.1.1.3 255.255.255.0
router os 1 netw 0.0.0.0 255.255.255.255 a 0
router bgp 300 no syn neighbor 196.1.1.5 remote-as 100 neighbor 194.1.1.4 remote-as 300 neighbor 194.1.1.4 update-source lo0 neighbor 194.1.1.4 next-hop-self network 194.1.1.0 mask 255.255.255.0 |
//// r4 ////
int lo0 ip ad 4.4.4.4 255.255.255.0 int e0/0 ip ad 194.1.1.3 255.255.255.0 router os 1 network 0.0.0.0 255.255.255.255 a 0 router bgp 300 no syn neighbor 194.1.1.3 remote-as 300 neighbor 194.1.1.3 update-source lo0 network 192.1.1.0 mask 255.255.255.0 backdoor |
//// r5 ////
int lo0 ip ad 5.5.5.5 255.255.255.0 int e2/0 ip ad 195.1.1.5 255.255.255.0 int e3/0 ip ad 196.1.1.5 255.255.255.0 router bgp 100 no syn neighbor 195.1.1.2 remote-as 200 neighbor 196.1.1.3 remote-as 300 |
验证:
//后门链路作用前
r2#sh ip bgp Network Next Hop Metric LocPrf Weight Path *> 192.1.1.0 0.0.0.0 0 32768 i *> 194.1.1.0 195.1.1.5 0 100 300 i r2# r2# r2# r2#sh ip ro bgp B 194.1.1.0/24 [20/0] via 195.1.1.5, 00:00:49 r3#sh ip bgp Network Next Hop Metric LocPrf Weight Path *> 192.1.1.0 196.1.1.5 0 100 200 i *> 194.1.1.0 0.0.0.0 0 32768 i r3#sh ip ro bgp B 192.1.1.0/24 [20/0] via 196.1.1.5, 00:02:28 |
r3#sh ip ro //后门链路作用前
1.0.0.0/32 is subnetted, 1 subnets O 1.1.1.1 [110/21] via 193.1.1.2, 00:04:22, Ethernet0/0 2.0.0.0/32 is subnetted, 1 subnets O 2.2.2.2 [110/11] via 193.1.1.2, 00:04:22, Ethernet0/0 3.0.0.0/24 is subnetted, 1 subnets C 3.3.3.0 is directly connected, Loopback0 4.0.0.0/32 is subnetted, 1 subnets O 4.4.4.4 [110/11] via 194.1.1.4, 00:04:22, Ethernet1/0 C 196.1.1.0/24 is directly connected, Serial3/0 C 193.1.1.0/24 is directly connected, Ethernet0/0 B 192.1.1.0/24 [20/0] via 196.1.1.5, 00:00:06 O 195.1.1.0/24 [110/74] via 193.1.1.2, 00:04:22, Ethernet0/0 C 194.1.1.0/24 is directly connected, Ethernet1/0 |
//后门链路作用后
r3#sh ip ro
1.0.0.0/32 is subnetted, 1 subnets O 1.1.1.1 [110/21] via 193.1.1.2, 00:06:38, Ethernet0/0 2.0.0.0/32 is subnetted, 1 subnets O 2.2.2.2 [110/11] via 193.1.1.2, 00:06:38, Ethernet0/0 3.0.0.0/24 is subnetted, 1 subnets C 3.3.3.0 is directly connected, Loopback0 4.0.0.0/32 is subnetted, 1 subnets O 4.4.4.4 [110/11] via 194.1.1.4, 00:06:38, Ethernet1/0 C 196.1.1.0/24 is directly connected, Serial3/0 C 193.1.1.0/24 is directly connected, Ethernet0/0 O 192.1.1.0/24 [110/20] via 193.1.1.2, 00:00:06, Ethernet0/0 O 195.1.1.0/24 [110/74] via 193.1.1.2, 00:06:38, Ethernet0/0 C 194.1.1.0/24 is directly connected, Ethernet1/0
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