bgp-control inbound traffic（第2部分）

　　要求：对于as2内部的用户，去往1.1.0.0/24和1.1.2.0/24默认从r2走，去往1.1.2.0/24和1.1.3.0/24默认从r3走，并且保证r2或r3任意一台down掉，网络仍然那保持连通性。

　　option 2就是使用as-path prepend，对r2来说，如果他想从r3去1.1.2.0/24和1.1.3.0/24，那只要把这2条路由的as-path加长就可以了

　　R1

　　hostname R1

　　!

　　interface Loopback0

　　ip address 1.1.0.1 255.255.255.0

　　!

　　interface Loopback1

　　ip address 1.1.1.1 255.255.255.0

　　!

　　interface Loopback2

　　ip address 1.1.2.1 255.255.255.0

　　!

　　interface Loopback3

　　ip address 1.1.3.1 255.255.255.0

　　!

　　interface FastEthernet0/0

　　ip address 192.168.12.1 255.255.255.0

　　speed 100

　　full-duplex

　　!

　　interface FastEthernet0/1

　　ip address 192.168.13.1 255.255.255.0

　　speed 100

　　full-duplex

　　!

　　router bgp 10

　　no synchronization

　　bgp router-id 1.1.1.1

　　bgp log-neighbor-changes

　　network 1.1.0.0 mask 255.255.255.0

　　network 1.1.1.0 mask 255.255.255.0

　　network 1.1.2.0 mask 255.255.255.0

　　network 1.1.3.0 mask 255.255.255.0

　　neighbor 192.168.12.2 remote-as 20

　　neighbor 192.168.12.2 soft-reconfiguration inbound

　　neighbor 192.168.12.2 route-map r2 out

　　neighbor 192.168.13.3 remote-as 20

　　neighbor 192.168.13.3 soft-reconfiguration inbound

　　neighbor 192.168.13.3 route-map r3 out

　　no auto-summary

　　!

　　ip prefix-list detail1 seq 5 permit 1.1.0.0/24

　　ip prefix-list detail1 seq 10 permit 1.1.1.0/24

　　!

　　ip prefix-list detail2 seq 5 permit 1.1.2.0/24

　　ip prefix-list detail2 seq 10 permit 1.1.3.0/24

　　!

　　route-map r2 permit 10

　　match ip address prefix-list detail2

　　set as-path prepend 10 10

　　!

　　route-map r2 permit 20

　　!

　　route-map r3 permit 10

　　match ip address prefix-list detail1

　　set as-path prepend 10 10

　　!

　　route-map r3 permit 20

　　!

　　end

　　R2

　　hostname R2

　　!

　　interface Loopback0

　　ip address 2.2.2.2 255.255.255.255

　　!

　　interface FastEthernet0/0

　　ip address 192.168.12.2 255.255.255.0

　　speed 100

　　full-duplex

　　!

　　interface FastEthernet0/1

　　ip address 192.168.23.2 255.255.255.0

　　speed 100

　　full-duplex

　　!

　　router bgp 20

　　no synchronization

　　bgp router-id 2.2.2.2

　　bgp log-neighbor-changes

　　network 192.168.23.0

　　neighbor 192.168.12.1 remote-as 10

　　neighbor 192.168.12.1 soft-reconfiguration inbound

　　neighbor 192.168.23.3 remote-as 20

　　neighbor 192.168.23.3 next-hop-self

　　neighbor 192.168.23.3 soft-reconfiguration inbound

　　no auto-summary

　　!

　　end

　　R3

　　hostname R3

　　!

　　interface Loopback0

　　ip address 3.3.3.3 255.255.255.255

　　!

　　interface FastEthernet0/0

　　ip address 192.168.13.3 255.255.255.0

　　speed 100

　　full-duplex

　　!

　　interface FastEthernet0/1

　　ip address 192.168.23.3 255.255.255.0

　　speed 100

　　full-duplex

　　!

　　router bgp 20

　　no synchronization

　　bgp router-id 3.3.3.3

　　bgp log-neighbor-changes

　　network 192.168.23.0

　　neighbor 192.168.13.1 remote-as 10

　　neighbor 192.168.13.1 soft-reconfiguration inbound

　　neighbor 192.168.23.2 remote-as 20

　　neighbor 192.168.23.2 next-hop-self

　　neighbor 192.168.23.2 soft-reconfiguration inbound

　　no auto-summary

　　!

　　end

　　verification

　　R2#sho ip bgp 1.1.3.0

　　BGP routing table entry for 1.1.3.0/24, version 13

　　Paths: (2 available, best #2, table Default-IP-Routing-Table)

　　Advertised to update-groups:

　　1

　　10 10 10, (received &used)

　　192.168.12.1 from 192.168.12.1 (1.1.1.1)

　　Origin IGP, metric 0, localpref 100, valid, external

　　10, (received &used)

　　192.168.23.3 from 192.168.23.3 (3.3.3.3)

　　Origin IGP, metric 0, localpref 100, valid, internal, best

　　R2#sho ip route 1.1.3.0

　　Routing entry for 1.1.3.0/24

　　Known via "bgp 20", distance 200, metric 0

　　Tag 10, type internal

　　Last update from 192.168.23.3 00:33:57 ago

　　Routing Descriptor Blocks:

　　* 192.168.23.3, from 192.168.23.3, 00:33:57 ago

　　Route metric is 0, traffic share count is 1

　　AS Hops 1

　　Route tag 10

　　R2#tra

　　R2#traceroute 1.1.3.1 pro

　　R2#traceroute 1.1.3.1 probe 1

　　Type escape sequence to abort.

　　Tracing the route to 1.1.3.1

　　1 192.168.23.3 128 msec

　　2 192.168.13.1 300 msec

　　R3#sho ip route 1.1.1.0

　　Routing entry for 1.1.1.0/24

　　Known via "bgp 20", distance 200, metric 0

　　Tag 10, type internal

　　Last update from 192.168.23.2 00:33:49 ago

　　Routing Descriptor Blocks:

　　* 192.168.23.2, from 192.168.23.2, 00:33:49 ago

　　Route metric is 0, traffic share count is 1

　　AS Hops 1

　　Route tag 10

　　R3#tra

　　R3#traceroute 1.1.1.1 pro

　　R3#traceroute 1.1.1.1 probe 1

　　Type escape sequence to abort.

　　Tracing the route to 1.1.1.1

　　1 192.168.23.2 48 msec

　　2 192.168.12.1 360 msec