操纵BGP多出口区分属性（MED）案例MED属性与本地优先级属性（localpref）不同，MED在AS间交换，但进入AS的MED不能离开该AS。AS使用Localpref来影响它自已的出站选择处理。MED是用来影响另一个AS的出站选择。MED越小，路由优先级越高。R1将1.0.0.0的MED属性在通告给R3之前设置为50，在通告给R2前设置为100。/ r1 /int f2/0 ip ad 192.1.1.1 255.255.255.0int f3/0 ip ad 193.1.1.1 255.255.255.0int lo0 ip ad 1.1.1.1 255.255.255.0int lo1 ip ad 2.2.2.2 255.255.255.0router 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 neighbor 192.1.1.2 route-map setmed100 out neighbor 193.1.1.3 route-map setmed50 outaccess-list 1 permit 1.0.0.0 0.255.255.255route-map setmed50 10 match ip ad 1 set metric 50route-map setmed50 20 set metricroute-map setmed100 10 match ip ad 1 set metric 100route-map setmed100 20 set metric/ r2 /int f2/0 ip ad 192.1.1.2 255.255.255.0int f4/0 ip ad 194.1.1.2 255.255.255.0router os 1 netw 0.0.0.0 255.255.255.255 a 0 passive-interface f2/0router 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 193.1.1.3 255.255.255.0int f5/0 ip ad 195.1.1.3 255.255.255.0router os 1 netw 0.0.0.0 255.255.255.255 a 0 passive-interface f3/0router 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/ r4 /int f4/0 ip ad 194.1.1.4 255.255.255.0int f5/0 ip ad 195.1.1.4 255.255.255.0int lo0 ip ad 4.4.4.4 255.255.255.0router os 1 netw 0.0.0.0 255.255.255.255 a 0router 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：r2#sh ip bgp Network Next Hop Metric LocPrf Weight Path*i1.0.0.0 193.1.1.1 50 100 0 100 i* 192.1.1.1 100 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 ir2#注意MED值比较低的被选为最佳路径。r2#sh ip roB 1.0.0.0/8 200/50 via 193.1.1.1, 00:02:00B 2.0.0.0/8 20/0 via 192.1.1.1, 00:02:00 4.0.0.0/8 is variably subnetted, 2 subnets, 2 masksO 4.4.4.4/32 110/65 via 194.1.1.4, 00:41:09, Serial4/0B 4.0.0.0/8 200/0 via 194.1.1.4, 00:17:42O 193.1.1.0/24 110/192 via 194.1.1.4, 00:41:09, Serial4/0C 192.1.1.0/24 is directly connected, Serial2/0O 195.1.1.0/24 110/128 via 194.1.1.4, 00:41:09, Serial4/0C 194.1.1.0/24 is directly connected, Serial4/0