操纵BGP路径选择---local preference属性案例（配图+详细验证过程）-白红宇

本地优先级（local pref）属性是分配给路由的一种优先级度量，用于和到同一目的地的其他路由相比较。这是BGP路由处理中的第二优先属性（WEIGHT是第一优先属性）。Local Pref属性只在本AS内部有效，不会被传送到EBGP邻居上。本地优先级越高，路由优先级越高。

以上案例中，我们通过对R3的配置，设置从R1学到的1.0.0.0的本地优先级（Localpref）设置为200，由于缺省的值为100，AS200中所有的路由器都会选择R3到达1.0.0.0。

int f2/0

ip ad 192.1.1.1 255.255.255.0

int f3/0

ip ad 193.1.1.1 255.255.255.0

int lo0

ip ad 1.1.1.1 255.255.255.0

int lo1

ip ad 2.2.2.2 255.255.255.0

router bgp 100

no syn

neighbor 192.1.1.2 remote-as 200

neighbor 193.1.1.3 remote-as 200

network 1.0.0.0

int f2/0

ip ad 192.1.1.2 255.255.255.0

int f4/0

ip ad 194.1.1.2 255.255.255.0

router os 1

netw 0.0.0.0 255.255.255.255 a 0

passive-interface f2/0

router bgp 200

no syn

neighbor 192.1.1.1 remote-as 100

neighbor 194.1.1.4 remote-as 200

neighbor 195.1.1.3 remote-as 200

neighbor 194.1.1.4 next-hop-self

int f3/0

ip ad 193.1.1.3 255.255.255.0

int f5/0

ip ad 195.1.1.3 255.255.255.0

router os 1

netw 0.0.0.0 255.255.255.255 a 0

passive-interface f3/0

router bgp 200

no syn

neighbor 193.1.1.1 remote-as 100

neighbor 195.1.1.4 remote-as 200

neighbor 195.1.1.4 next-hop-self

neighbor 194.1.1.2 remote-as 200

neighbor 193.1.1.1 route-map localpref in

access-list 1 permit 1.0.0.0 0.255.255.255

route-map localpref permit 10

match ip ad 1

set local-pref 200

route-map localpref permit 20

set local-pref 100

int f4/0

ip ad 194.1.1.4 255.255.255.0

int f5/0

ip ad 195.1.1.4 255.255.255.0

int lo0

ip ad 4.4.4.4 255.255.255.0

router os 1

netw 0.0.0.0 255.255.255.255 a 0

router bgp 200

no syn

neighbor 194.1.1.2 remote-as 200

neighbor 195.1.1.3 remote-as 200

netw 4.0.0.0

验证：

r4#sh ip bgp

Network Next Hop Metric LocPrf Weight Path

*>i1.0.0.0 195.1.1.3 0 200 0 100 i

* i2.0.0.0 195.1.1.3 0 100 0 100 i

*>i 194.1.1.2 0 100 0 100 i

*> 4.0.0.0 0.0.0.0 0 32768 i

r4#sh ip ro

B 1.0.0.0/8 [200/0] via 195.1.1.3, 00:02:20

B 2.0.0.0/8 [200/0] via 194.1.1.2, 00:02:24

4.0.0.0/24 is subnetted, 1 subnets

C 4.4.4.0 is directly connected, Loopback0

O 193.1.1.0/24 [110/128] via 195.1.1.3, 00:04:35, Serial5/0

O 192.1.1.0/24 [110/128] via 194.1.1.2, 00:04:35, Serial4/0

C 195.1.1.0/24 is directly connected, Serial5/0

C 194.1.1.0/24 is directly connected, Serial4/0

r2#sh ip bgp

Network Next Hop Metric LocPrf Weight Path

*>i1.0.0.0 193.1.1.1 0 200 0 100 i

* 192.1.1.1 0 0 100 i

* i2.0.0.0 193.1.1.1 0 100 0 100 i

*> 192.1.1.1 0 0 100 i

*>i4.0.0.0 194.1.1.4 0 100 0 i

r2#sh ip ro

B 1.0.0.0/8 [200/0] via 193.1.1.1, 00:06:00

B 2.0.0.0/8 [20/0] via 192.1.1.1, 00:06:04

4.0.0.0/8 is variably subnetted, 2 subnets, 2 masks

O 4.4.4.4/32 [110/65] via 194.1.1.4, 00:08:20, Serial4/0

B 4.0.0.0/8 [200/0] via 194.1.1.4, 00:06:55

O 193.1.1.0/24 [110/192] via 194.1.1.4, 00:08:20, Serial4/0

C 192.1.1.0/24 is directly connected, Serial2/0

O 195.1.1.0/24 [110/128] via 194.1.1.4, 00:08:20, Serial4/0

C 194.1.1.0/24 is directly connected, Serial4/0

本文转自 ciscodocu51CTO博客，原文链接：http://blog.51cto.com/ciscodocu/52814，如需转载请自行联系原作者