操纵BGP AS-PATH 属性案例.doc

操纵BGP AS-PATH 属性案例（配图+详细验证过程） BGP总是优先选择具有最短AS路径的路由。本案例中，我们将配置R1，将1.0.0.0通告给R2、R3之前预先添加两个额外的AS路径到1.0.0.0上（AS300、AS400）具体配置如下：/ 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 193.1.1.3 route-map aspath outaccess-list 1 permit 1.0.0.0 0.255.255.255route-map aspath 10 match ip ad 1 set as-path prepend 300 400route-map aspath 20/ 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：r3#sh ip b Network Next Hop Metric LocPrf Weight Path*i1.0.0.0 192.1.1.1 0 100 0 100 i* 193.1.1.1 0 0 100 300 400 i* i2.0.0.0 192.1.1.1 0 100 0 100 i* 193.1.1.1 0 0 100 i*i4.0.0.0 195.1.1.4 0 100 0 ir3#sh ip roB 1.0.0.0/8 200/0 via 192.1.1.1, 00:05:23B 2.0.0.0/8 20/0 via 193.1.1.1, 00:05:23 4.0.0.0/8 is variably subnetted, 2 subnets, 2 masksO 4.4.4.4/32 110/65 via 195.1.1.4, 00:10:38, Serial5/0B 4.0.0.0/8 200/0 via 195.1.1.4, 00:10:13C 193.1.1.0/24 is directly connected, Serial3/0O 192.1.1.0/24 110/192 via 195.1.1.4, 00:10:38, Serial5/0C