BGP配置实验之Local preference选路
1、Local preference选路解析属性
传播范围
默认值
优先值方向
备注
weight本路由器本路由器32768，其他路由器0大值优先INCISCO私有
Local preferenceAS内部100：边界路由器，通告给IBGP邻居，告知如何离开本AS大值优先OUT
修改Local preference值的方法：
方法一：全部修改通告给IBGP邻居的路由的Local preference值，例如：
router bgp 4 bgp default local-preference 125方法二：部分修改通告给IBGP邻居的路由的Local preference值，例如：
2、实验拓扑3、基础配置R1配置
interface Loopback0 ip address 1.1.1.1 255.255.255.0interface Serial0/0 ip address 13.1.1.1 255.255.255.0interface Serial0/1 ip address 14.1.1.1 255.255.255.0router ospf 110 router-id 1.1.1.1 log-adjacency-changes network 1.1.1.0 0.0.0.255 area 0 network 14.1.1.0 0.0.0.255 area 0router bgp 4 no synchronization bgp router-id 1.1.1.1 neighbor 4.4.4.4 remote-as 4 neighbor 4.4.4.4 update-source Loopback0 neighbor 4.4.4.4 next-hop-self neighbor 13.1.1.3 remote-as 3 no auto-summary
R2配置interface Loopback0 ip address 2.2.2.2 255.255.255.0interface Serial0/1 ip address 23.1.1.2 255.255.255.0interface FastEthernet1/0 ip address 24.1.1.2 255.255.255.0router ospf 110 router-id 2.2.2.2 network 2.2.2.0 0.0.0.255 area 0 network 24.1.1.0 0.0.0.255 area 0router bgp 4 no synchronization bgp router-id 2.2.2.2 neighbor 4.4.4.4 remote-as 4 neighbor 4.4.4.4 update-source Loopback0 neighbor 4.4.4.4 next-hop-self neighbor 23.1.1.3 remote-as 3 no auto-summary
R3配置interface Loopback0 ip address 3.3.3.3 255.255.255.0interface Loopback1 ip address 33.33.33.33 255.255.255.0 interface Serial0/0 ip address 13.1.1.3 255.255.255.0interface Serial0/1 ip address 23.1.1.3 255.255.255.0router bgp 3 no synchronization bgp router-id 3.3.3.3 network 3.3.3.0 mask 255.255.255.0 network 33.33.33.0 mask 255.255.255.0 neighbor 13.1.1.1 remote-as 4 neighbor 23.1.1.2 remote-as 4 no auto-summary
R4配置interface Loopback0 ip address 4.4.4.4 255.255.255.0interface Serial0/1 ip address 14.1.1.4 255.255.255.0interface FastEthernet1/0 ip address 24.1.1.4 255.255.255.0router ospf 110 router-id 4.4.4.4 network 4.4.4.0 0.0.0.255 area 0 network 14.1.1.0 0.0.0.255 area 0 network 24.1.1.0 0.0.0.255 area 0router bgp 4 no synchronization bgp router-id 4.4.4.4 neighbor 1.1.1.1 remote-as 4 neighbor 1.1.1.1 update-source Loopback0 neighbor 2.2.2.2 remote-as 4 neighbor 2.2.2.2 update-source Loopback0 no auto-summary
4、默认选路根据BGP选路原则第八条可以知道，R4到达3.3.3.0/24、33.33.33.0/24都是经过R2。
5、全部修改通告给IBGP邻居的路由的Local preference值由前面可以R4到达3.3.3.0/24、33.33.33.0/24都是经过R2，我们通过修改Local preference值将R4到达3.3.3.0/24、33.33.33.0/24都是经过R1。R4配置router bgp 4
bgp default local-preference 125
6、部分修改通告给IBGP邻居的路由的Local preference值
R4到达3.3.3.0/24、33.33.33.0/24都是经过R2，我们通过修改Local preference值将R4到达3.3.3.0/24经过R2、达到33.33.33.0/24都是经过R1。
R4配置
ip prefix-list 1 seq 5 permit 33.33.33.0/24
no cdp log mismatch duplex
route-map L permit 10
match ip address prefix-list 1
set local-preference 125
route-map L permit 20
router bgp 4
neighbor 4.4.4.4 route-map L out
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