操纵BGP AS-PATH 属性案例（配图+详细验证过程）
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 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 192.1.1.1 255.255.255.0
int f3/0
ip ad 193.1.1.1 255.255.255.0
int lo0
ip ad 1.1.1.1 255.255.255.0
int lo1
ip ad 2.2.2.2 255.255.255.0
router 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 out
access-list 1 permit 1.0.0.0 0.255.255.255
route-map aspath 10
match ip ad 1
set as-path prepend 300 400
route-map aspath 20
//// r2 ////
int f2/0
ip ad 192.1.1.2 255.255.255.0
int f4/0
ip ad 194.1.1.2 255.255.255.0
router os 1
netw 0.0.0.0 255.255.255.255 a 0
passive-interface f2/0
router 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 193.1.1.3 255.255.255.0
int f5/0
ip ad 195.1.1.3 255.255.255.0
router os 1
netw 0.0.0.0 255.255.255.255 a 0
passive-interface f3/0
router 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 194.1.1.4 255.255.255.0
int f5/0
ip ad 195.1.1.4 255.255.255.0
int lo0
ip ad 4.4.4.4 255.255.255.0
router os 1
netw 0.0.0.0 255.255.255.255 a 0
router 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 i r3#sh ip ro
B 1.0.0.0/8 [200/0] via 192.1.1.1, 00:05:23 B 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 masks O 4.4.4.4/32 [110/65] via 195.1.1.4, 00:10:38, Serial5/0 B 4.0.0.0/8 [200/0] via 195.1.1.4, 00:10:13 C 193.1.1.0/24 is directly connected, Serial3/0 O 192.1.1.0/24 [110/192] via 195.1.1.4, 00:10:38, Serial5/0 C 195.1.1.0/24 is directly connected, Serial5/0 O 194.1.1.0/24 [110/128] via 195.1.1.4, 00:10:38, Serial5/0 本文出自 “CiscoDocu（屎壳Ｑ岛）” 博客，转载请与作者联系！ 本文出自 51CTO.COM技术博客 |
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