操縱BGP路徑選擇---local preference屬性案例（配圖+詳細驗證過程）

本地優先級（local pref）屬性是分配給路由的一種優先級度量，用於和到同一目的地的其他路由相比較。這是BGP路由處理中的第二優先屬性（WEIGHT是第一優先屬 性）。Local Pref屬性只在本AS內部有效，不會被傳送到EBGP鄰居上。本地優先級越高，路由優先級越高。

 

以上案例中，我們通過對R3的配置，設置從R1學到的1.0.0.0的本地優先級（Localpref）設置爲200，由於缺省的值爲100，AS200中所有的路由器都會選擇R3到達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

  network 1.0.0.0

 

 

 

//// r2 ////

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

 

 

//// r3 ////

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

 

//// r4 ////

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

 

 

 

 

驗證：

//// r4 ////

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