BGP交换前缀列表的出口路由过滤"ORF"技术

BGP交换前缀列表的出口路由过滤"ORF"技术

拓扑:

R5------------R7

R5用2个回环口模拟子网（5.5.5.5/32和 55.55.55.55/32）

R7用2个回环口模拟子网(7.7.7.7/32和77.77.77.77/32)

R5和R7之间是192.168.25.x/24

R5的AS号为5

R7的AS号为7

实验目的:

要过滤r7的77.77.77.77/32的条目,可以在r7的out方向做,也可以在r5的in方向做.显然在r7的out方向上做效率高,可以节省两端处理报文的cpu资源和链路负载(这里只有一条,但实际可是几百,千条呵呵).

如果r7是其它isp的路由器,对r5来讲,无权配置r7时,这里提供了一种可选方案:

在r5上配置

r5(config)#ip prefix-list abc seq 5 permit 7.7.7.7/32

r5(config)#ip prefix-list abc seq 10 permit 88.88.88.0/24

将prefix-list abc 用在neighbor 192.168.25.7 prefix-list abc in上(neighbor 192.168.25.7 prefix-list abc in),

仅仅做到这一步是可以实现目的.但意义不大的,因为报文已经是被传到了r5上后被过滤的.造成cpu,链路资源的浪费.这里提供了一种将本端的in方向的prefix-list"推到"对端邻居r7的out方向上去的能力,即ORF,列表不在本地起作用了,而是让对端去过滤.出口路由过滤:

r5(config-router)#nei 192.168.25.7 capability orf prefix-list both/receive/send [启用orf能力,both表示双向，即可以发送orf也可以接收orf，这里r5是发送]

r7(config-router)#nei 192.168.25.5 capability orf prefix-list both/receive/send
[r7也启用orf能力，这里r7为接收，只需要配置receive关键字也可]

r5#clear ip bgp 192.168.25.7 in prefix-filter [作用:向邻居r7推出前缀列表,以用于r7的out方向，地址是neighbor x.x.x.x remote num的建立邻居的地址]

结果:查看r7发给邻居192.168.25.5(r5)的条目,是没有77.77.77.77/32的,说明在出r7时就已经被前缀列表滤掉了.但这个列表却是在r5上配置的.

r7#sh ip bgp nei 192.168.25.5 advertised-routes

show ip bgp neighbors192.168.25.5
received prefix-filter

BGP table version is 14, local router ID is 7.7.7.7

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

*> 7.7.7.7/32 0.0.0.0 0 32768 i

*> 88.88.88.0/24 0.0.0.0 0 32768 i

hostname r5

!

logging queue-limit 100

!

ip subnet-zero

no ip domain lookup

!

!

!

!

interface Loopback0

ip address 5.5.5.5 255.255.255.255

no ip route-cache

no ip mroute-cache

!

interface Loopback1

ip address 55.55.55.55 255.255.255.255

!

interface Ethernet0

ip address 192.168.25.5 255.255.255.0

!

interface Serial0

no ip address

!

interface Serial1

no ip address

!

router bgp 5

no synchronization

bgp router-id 5.5.5.5

bgp log-neighbor-changes

network 5.5.5.5 mask 255.255.255.255

network 55.55.55.55 mask 255.255.255.255

neighbor 192.168.25.7 remote-as 7

neighbor 192.168.25.7 prefix-list abc in

nei 192.168.25.7
capability orf prefix-list both

no auto-summary

!

no ip http server

ip classless

!

!

!

ip prefix-list abc seq 5 permit 7.7.7.7/32

ip prefix-list abc seq 10 permit 88.88.88.0/24

!

!

!

hostname r7

!

logging queue-limit 100

!

ip subnet-zero

!

!

!

!

interface Loopback0

ip address 7.7.7.7 255.255.255.255

!

interface Loopback1

ip address 77.77.77.77 255.255.255.255

!

interface Loopback2

ip address 88.88.88.88 255.255.255.0

!

interface Ethernet0

ip address 192.168.25.7 255.255.255.0

!

interface Serial0

no ip address

shutdown

no fair-queue

!

interface Serial1

no ip address

shutdown

!

router bgp 7

no synchronization

bgp router-id 7.7.7.7

bgp log-neighbor-changes

network 7.7.7.7 mask 255.255.255.255

network 77.77.77.77 mask 255.255.255.255

network 88.88.88.0 mask 255.255.255.0

neighbor 192.168.25.5 remote-as 5

#nei 192.168.25.5
capability orf prefix-list both

no auto-summary