BGP选路原则之local preference

我们先做下配置：

R1:interface Serial1/0

ip address 13.1.1.1 255.255.255.0

serial restart-delay 0

interface Serial1/1

ip address 14.1.1.1 255.255.255.0

serial restart-delay 0

interface Serial1/2

ip address 15.1.1.1 255.255.255.0

serial restart-delay 0

interface Loopback0

ip address 1.1.1.1 255.255.255.0

router ospf 10

router-id 1.1.1.1

log-adjacency-changes

network 1.1.1.0 0.0.0.255 area 0

network 13.1.1.0 0.0.0.255 area 0

router bgp 1

no synchronization

bgp router-id 1.1.1.1

bgp log-neighbor-changes

neighbor liang peer-group

neighbor liang remote-as 2

neighbor liang ebgp-multihop 255

neighbor liang update-source Loopback0

neighbor 3.3.3.3 remote-as 1

neighbor 3.3.3.3 update-source Loopback0

neighbor 3.3.3.3 next-hop-self

neighbor 4.4.4.4 peer-group liang

neighbor 5.5.5.5 peer-group liang

no auto-summary

ip route 4.4.4.4 255.255.255.255 14.1.1.4

ip route 5.5.5.5 255.255.255.255 15.1.1.5

R2:

interface Loopback0

ip address 2.2.2.2 255.255.255.0

interface Serial1/0

ip address 24.1.1.2 255.255.255.0

serial restart-delay 0

interface Serial1/1

ip address 23.1.1.2 255.255.255.0

serial restart-delay 0

interface Serial1/2

no ip address

shutdown

serial restart-delay 0

inteface Serial1/3

ip address 25.1.1.2 255.255.255.0

serial restart-delay 0

router ospf 10

router-id 2.2.2.2

log-adjacency-changes

network 2.2.2.0 0.0.0.255 area 0

network 23.1.1.0 0.0.0.255 area 0

router bgp 1

no synchronization

bgp router-id 2.2.2.2

bgp log-neighbor-changes

neighbor liang peer-group 为了简化配置我们用peer-group

neighbor liang remote-as 2

neighbor liang ebgp-multihop 255

neighbor liang update-source Loopback0

neighbor 3.3.3.3 remote-as 1

neighbor 3.3.3.3 update-source Loopback0

neighbor 3.3.3.3 next-hop-self

neighbor 4.4.4.4 peer-group liang

neighbor 5.5.5.5 peer-group liang

no auto-summary

ip route 4.4.4.4 255.255.255.255 24.1.1.4

ip route 5.5.5.5 255.255.255.255 25.1.1.5

R3:

interface Loopback0

ip address 3.3.3.3 255.255.255.0

interface Serial1/0

ip address 13.1.1.3 255.255.255.0

serial restart-delay 0

interface Serial1/1

ip address 23.1.1.3 255.255.255.0

serial restart-delay 0

router ospf 10

router-id 3.3.3.3

log-adjacency-changes

network 3.3.3.0 0.0.0.255 area 0

network 13.1.1.0 0.0.0.255 area 0

network 23.1.1.0 0.0.0.255 area 0

router bgp 1

no synchronization

bgp router-id 3.3.3.3

bgp log-neighbor-changes

neighbor 1.1.1.1 remote-as 1

neighbor 1.1.1.1 update-source Loopback0

neighbor 2.2.2.2 remote-as 1

neighbor 2.2.2.2 update-source Loopback0

no auto-summary

其他的配置都差不多不在贴出来了

我们看下BGP表

R1#show ip bgp

BGP table version is 3, local router ID is 1.1.1.1

Status codes: s suppressed, d damped, h history, * valid, > best, i - internal,

r RIB-failure, S Stale

Origin codes: i - IGP, e - EGP, ? - incomplete

Network Next Hop Metric LocPrf Weight Path

* 6.6.6.0/24 4.4.4.4 0 2 i

*> 5.5.5.5 0 2 i

* 8.8.8.0/24 5.5.5.5 0 2 i

*> 4.4.4.4 0 2 i

R2#show ip bgp

BGP table version is 3, local router ID is 2.2.2.2

Status codes: s suppressed, d damped, h history, * valid, > best, i - internal,

r RIB-failure, S Stale

Origin codes: i - IGP, e - EGP, ? - incomplete

Network Next Hop Metric LocPrf Weight Path

* 6.6.6.0/24 4.4.4.4 0 2 i

*> 5.5.5.5 0 2 i

* 8.8.8.0/24 5.5.5.5 0 2 i

*> 4.4.4.4 0 2 i

R3# show ip bgp

BGP table version is 9, local router ID is 3.3.3.3

Status codes: s suppressed, d damped, h history, * valid, > best, i - internal,

r RIB-failure, S Stale

Origin codes: i - IGP, e - EGP, ? - incomplete

Network Next Hop Metric LocPrf Weight Path

* i6.6.6.0/24 2.2.2.2 0 100 0 2 i

*>i 1.1.1.1 0 100 0 2 i

* i8.8.8.0/24 2.2.2.2 0 100 0 2 i

*>i 1.1.1.1 0 100 0 2 i

发现R3到6.6.6.0和8.8.8.0 下一跳都是R1

我们的要求是R3访问6.6.6.0/24 走R1 R4 访问8.8.8.0/24走R2 R5

第一种方式我们在R1 R2的out方向做





R1

access-list 1 permit 6.6.6.0

access-list 2 permit 8.8.8.0

route-map to-r3 permit 10

match ip address 1

set local-preference 400

route-map to-r3 permit 20

match ip address 2

set local-preference 300

route-map to-r3 permit 30

R1(config)#router bgp 1

R1(config-router)#neighbor 3.3.3.3 route-map to-r3

R2

access-list 1 permit 6.6.6.0

access-list 2 permit 8.8.8.0

route-map to-r3 permit 10

match ip address 1

set local-preference 300

route-map to-r3 permit 20

match ip address 2

set local-preference 400

R2(config)#router bgp 1

R2(config-router)#neighbor 3.3.3.3 route-map to-r3 out

我们需要的R3上软清下

R3#clear ip bgp * soft

R3# show ip bgp

BGP table version is 12, local router ID is 3.3.3.3

Status codes: s suppressed, d damped, h history, * valid, > best, i - internal,

r RIB-failure, S Stale

Origin codes: i - IGP, e - EGP, ? - incomplete

Network Next Hop Metric LocPrf Weight Path

* i6.6.6.0/24 2.2.2.2 0 300 0 2 i

*>i 1.1.1.1 0 400 0 2 i

*>i8.8.8.0/24 2.2.2.2 0 400 0 2 i

* i 1.1.1.1 0 300 0 2 i

发现第一跳确实变了，但我们看下R2 R1的BGP表

R1#show ip bgp

BGP table version is 3, local router ID is 1.1.1.1

Status codes: s suppressed, d damped, h history, * valid, > best, i - internal,

r RIB-failure, S Stale

Origin codes: i - IGP, e - EGP, ? - incomplete

Network Next Hop Metric LocPrf Weight Path

* 6.6.6.0/24 4.4.4.4 0 2 i

*> 5.5.5.5 0 2 i

* 8.8.8.0/24 5.5.5.5 0 2 i

*> 4.4.4.4 0 2 i

R2#show ip bgp 直接走R4了 还不是我们想要的要求

BGP table version is 3, local router ID is 2.2.2.2

Status codes: s suppressed, d damped, h history, * valid, > best, i - internal,

r RIB-failure, S Stale

Origin codes: i - IGP, e - EGP, ? - incomplete

Network Next Hop Metric LocPrf Weight Path

* 6.6.6.0/24 4.4.4.4 0 2 i

*> 5.5.5.5 0 2 i

* 8.8.8.0/24 5.5.5.5 0 2 i

*> 4.4.4.4 0 2 i

我们只是控制了R3到R1R2的选路

我们在R3 R4的in方向做





R1

access-list 1 permit 6.6.6.0

route-map liang permit 10

match ip address 1

set local-preference 500

route-map liang permit 20

neighbor 4.4.4.4 route-map liang in

R2

access-list 1 permit 8.8.8.0

route-map liang permit 10

match ip address 1

set local-preference 500

route-map liang permit 20

neighbor 5.5.5.5 route-map liang in

软清一下在R1 R2 R3

R1#show ip bgp

BGP table version is 4, local router ID is 1.1.1.1

Status codes: s suppressed, d damped, h history, * valid, > best, i - internal,

r RIB-failure, S Stale

Origin codes: i - IGP, e - EGP, ? - incomplete

Network Next Hop Metric LocPrf Weight Path

*> 6.6.6.0/24 4.4.4.4 500 0 2 i

* 5.5.5.5 0 2 i

* 8.8.8.0/24 5.5.5.5 0 2 i

*> 4.4.4.4 0 2 i

R2#show ip bgp

BGP table version is 4, local router ID is 2.2.2.2

Status codes: s suppressed, d damped, h history, * valid, > best, i - internal,

r RIB-failure, S Stale

Origin codes: i - IGP, e - EGP, ? - incomplete

Network Next Hop Metric LocPrf Weight Path

* 6.6.6.0/24 4.4.4.4 0 2 i

*> 5.5.5.5 0 2 i

*> 8.8.8.0/24 5.5.5.5 500 0 2 i

* 4.4.4.4 0 2 i

R3# show ip bgp

BGP table version is 17, local router ID is 3.3.3.3

Status codes: s suppressed, d damped, h history, * valid, > best, i - internal,

r RIB-failure, S Stale

Origin codes: i - IGP, e - EGP, ? - incomplete

Network Next Hop Metric LocPrf Weight Path

* i6.6.6.0/24 2.2.2.2 0 100 0 2 i

*>i 1.1.1.1 0 500 0 2 i

*>i8.8.8.0/24 2.2.2.2 0 500 0 2 i

* i 1.1.1.1 0 100 0 2 i

我们的目的达到了！

总结：

loacl preference 有三种不同的方法进行配置

1.通过IGP路由引入BGP是关联route-map

2.针对IBGP peer 应用in and out 方向进行配置，对从peer收到或者通过的给peer的所有或部分进行设置

3.针对EBGP peer 应用in 方向的route-map针对peer接受到的所有或部分路由进行设置