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
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

验证：
//// 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