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

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。

//// r1 ////

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

//// r2 ////

  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

  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

//// r3 ////

  ip ad 193.1.1.3 255.255.255.0

int f5/0

  ip ad 195.1.1.3 255.255.255.0

  passive-interface f3/0

  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

//// r4 ////

  ip ad 194.1.1.4 255.255.255.0

  ip ad 195.1.1.4 255.255.255.0

  ip ad 4.4.4.4 255.255.255.0

  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

*>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

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