BGP路由选择相关实验

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没文化 2019-07-13 00:16:58 ©著作权

文章标签 BGP 路由 文章分类 运维

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BGP有丰富的路由属性。我们通常控制BGP路由属性，来控制BGP路由流向。 cisco路由器常见路由属性如下：

1.优先选择最大weight（权重）的路由（范围：0~65535） 2.优先选择有最大LOCAL_OREF（本地优先级）的路由（范围：0~4294967295） 3.优先选择从本地路由器始发的路由（即下一跳0.0.0.0） 4.优先选择AS-path数量最少的路由 5.根据origin属性，优先选择具有最低起源类型的路由（IGP优先于EGP优先于incomplete） 6.优先选择具有最小MED值的路由（范围：0~4294967295） 7.EBGP优先于IBGP 8.优先选择能够通过最近的IGP邻居到达的路径（即对BGP下一跳具有最低IGP度量值的路径） 9.如果配置了maximum-path N（2≤N≤6），可实现负载均衡（但BGP会继续比较，只有一条路径被打上“>”标签） 10.如果都是external（外部的）路由，优先选择最老（即最早学到）的路由 11.优先选择拥有最小BGP-router-ID的路由 12.如果是从路由反射器（RR）学习到的路由，优先选择拥有最小cluster-ID（路由反射器的router-ID）的路由 13.优先选择具有最低对等体地址接收到的路由（即邻居IP地址最小的优先）

实验拓扑图

配置前R1上的路由 R1#sh 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

 172.16.0.0/24 is subnetted, 2 subnets

C 172.16.12.0 is directly connected, FastEthernet0/0 C 172.16.13.0 is directly connected, FastEthernet0/1 10.0.0.0/32 is subnetted, 2 subnets B 10.10.6.6 [20/0] via 172.16.12.2, 00:27:41 C 10.10.1.1 is directly connected, Loopback0

使用weight改变路由

R1(config-router)#neighbor 172.16.13.3 weight 10 R1#clear ip bgp * soft

更改weight后路由 R1#sh 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

 172.16.0.0/24 is subnetted, 2 subnets

C 172.16.12.0 is directly connected, FastEthernet0/0 C 172.16.13.0 is directly connected, FastEthernet0/1 10.0.0.0/32 is subnetted, 2 subnets B 10.10.6.6 [20/0] via 172.16.13.3, 00:01:09 C 10.10.1.1 is directly connected, Loopback0

使用local-preference更改路由

更改R1配置： R1(config)#ip prefix-list mei permit 10.10.6.6/32 R1(config)#route-map paul permit 10 R1(config-route-map)#match ip address prefix-list mei R1(config-route-map)#set local-preference 200 R1(config)#route-map paul permit 99 R1(config-route-map)#router bgp 100 R1(config-router)#neighbor 172.16.13.3 remote-as 2345 R1(config-router)#neighbor 172.16.13.3 route-map mei in

R1(config-router)#do clear ip bgp * so 1(config-router)#do sh ip bgp 10.10.6.6/32 BGP routing table entry for 10.10.6.6/32, version 4 Paths: (2 available, best #1, table Default-IP-Routing-Table) Flag: 0x840 Advertised to update-groups: 1 2345 600 172.16.13.3 from 172.16.13.3 (10.10.3.3) Origin IGP, localpref 200, valid, external, best 2345 600

** 使用AS-path更改路由** 更改R1配置 R1(config-route-map)#do sh run | s route-map route-map paul permit 10 match ip address prefix-list mei set as-path prepend 100 100 route-map paul permit 99

R1(config-router)#do sh run | s bgp router bgp 100 no synchronization bgp router-id 10.10.1.1 bgp log-neighbor-changes network 10.10.1.1 mask 255.255.255.255 neighbor 172.16.12.2 remote-as 2345 neighbor 172.16.12.2 route-map paul in neighbor 172.16.13.3 remote-as 2345 no auto-summary

R1(config-router)#do clear ip bgp * so R1(config-router)#do sh ip bgp 10.10.6.6 BGP routing table entry for 10.10.6.6/32, version 2 Paths: (2 available, best #2, table Default-IP-Routing-Table) Advertised to update-groups: 1 100 100 2345 600 172.16.12.2 from 172.16.12.2 (10.10.2.2) Origin IGP, localpref 100, valid, external 2345 600 172.16.13.3 from 172.16.13.3 (10.10.3.3) Origin IGP, localpref 100, valid, external, best

** 使用MED更改路由** 更改R1配置 R1(config-router)#do sh run | s route-map neighbor 172.16.12.2 route-map paul in route-map paul permit 10 match ip address prefix-list mei set metric 10000 route-map paul permit 99 R1(config-router)#do sh run | s bgp router bgp 100 no synchronization bgp router-id 10.10.1.1 bgp log-neighbor-changes network 10.10.1.1 mask 255.255.255.255 neighbor 172.16.12.2 remote-as 2345 neighbor 172.16.12.2 route-map paul in neighbor 172.16.13.3 remote-as 2345 no auto-summary

R1(config-router)#do clear ip bgp * soft R1(config-router)#do sh ip bgp 10.10.6.6/32 BGP routing table entry for 10.10.6.6/32, version 2 Paths: (2 available, best #1, table Default-IP-Routing-Table) Flag: 0x820 Advertised to update-groups: 1 2345 600 172.16.13.3 from 172.16.13.3 (10.10.3.3) Origin IGP, localpref 100, valid, external, best 2345 600 172.16.12.2 from 172.16.12.2 (10.10.2.2) Origin IGP, metric 10000, localpref 100, valid, external R1(config-router)#