bgp AS-path选路
## 拓扑
需求
1、按照IP地址规划，配置接口IP地址；
2、RT1、RT2、RT3配置OSPF协议，仅宣告互联网段以及loopback0接口；
3、RT1、RT2、RT3通过loopback0接口建立对等体组IBGP全互联，RT2——RT4通过物理接口建立EBGP对等体，RT3——RT5通过物理接口建立EBGP对等体，RT4——RT6通过物理接口建立EBGP对等体；RT5——RT6通过物理接口库建立IBGP对等体。
4、RT1在BGP中宣告loopback 10、20、30。
5、出于安全角度，要求AS300仅访问192.168.1.0网段时，正常情况下通过专线访问，专线出现问题时通过ISP访问，其他网段通过ISP访问。请在RT2、RT3上通过合适的地址前缀列表、路由策略来修改BGP的AS_PATH属性，以实现上述要求。
6、为防止ISP路由通过企业网络传递，通过在RT3、RT5上配置AS-PATH list仅允许本地始发路由向外传递；
配置地址
R1
[H3C]interface g0/0
[H3C-GigabitEthernet0/0]ip address 10.255.12.1 30
[H3C-GigabitEthernet0/0]in g0/1
[H3C-GigabitEthernet0/1]ip address 10.255.13.1 30
[H3C-GigabitEthernet0/1]qu
[H3C]interface LoopBack 0
[H3C-LoopBack0]ip address 192.168.255.1 32
[H3C-LoopBack0]qu
[H3C]interface LoopBack 10
[H3C-LoopBack10]ip address 192.168.0.1 24
[H3C-LoopBack10]qu
[H3C]interface LoopBack 20
[H3C-LoopBack20]ip address
[H3C-LoopBack20]ip address 192.168.1.1 24
[H3C-LoopBack20]qu
[H3C]interface LoopBack 30
[H3C-LoopBack30]ip address 192.168.2.1 24
[H3C-LoopBack30]qu
R2
[H3C]interface g0/0
[H3C-GigabitEthernet0/0]ip address 10.255.12.2 30
[H3C-GigabitEthernet0/0]in g0/2
[H3C-GigabitEthernet0/2]ip address 10.255.23.1 30
[H3C-GigabitEthernet0/2]in s1/0
[H3C-Serial1/0]ip address 10.255.24.1 30
[H3C-Serial1/0]qu
[H3C]interface LoopBack 0
[H3C-LoopBack0]ip address 192.168.255.2 32
[H3C-LoopBack0]qu
R3
[H3C]interface g0/2
[H3C-GigabitEthernet0/2]ip address 10.255.23.2 30
[H3C-GigabitEthernet0/2]in g0/1
[H3C-GigabitEthernet0/1]ip address 10.255.13.2 30
[H3C-GigabitEthernet0/1]in s1/0
[H3C-Serial1/0]ip address 10.255.35.1 30
[H3C-Serial1/0]qu
[H3C]interface LoopBack 0
[H3C-LoopBack0]ip address 192.168.255.3 32
[H3C-LoopBack0]qu
R4
[H3C]in s1/0
[H3C-Serial1/0]ip address 10.255.24.2 30
[H3C-Serial1/0]in s2/0
[H3C-Serial2/0]ip address 10.255.46.1 30
[H3C-Serial2/0]qu
[H3C]in
[H3C]interface LoopBack 0
[H3C-LoopBack0]ip address 192.168.255.4 32
[H3C-LoopBack0]qu
R5
[H3C]interface s1/0
[H3C-Serial1/0]ip address 10.255.35.2 30
[H3C-Serial1/0]in g0/0
[H3C-GigabitEthernet0/0]ip address 10.255.56.1 30
[H3C-GigabitEthernet0/0]qu
[H3C]interface LoopBack 0
[H3C-LoopBack0]ip address 192.168.255.5 32
[H3C-LoopBack0]qu
R6
[H3C]interface s2/0
[H3C-Serial2/0]ip address 10.255.46.2 30
[H3C-Serial2/0]in g0/0
[H3C-GigabitEthernet0/0]ip address 10.255.56.2 30
[H3C-GigabitEthernet0/0]qu
[H3C]interface LoopBack 0
[H3C-LoopBack0]ip address 192.168.255.6 32
[H3C-LoopBack0]qu
PPP认证
R3
[H3C]local-user r5 class network
New local user added.
[H3C-luser-network-r5]service-type ppp
[H3C-luser-network-r5]password simple 123456
[H3C-luser-network-r5]qu
[H3C]interface s1/0
[H3C-Serial1/0]ppp authentication-mode chap
[H3C-Serial1/0]ppp chap user r3
R5
[H3C]local-user r3 class network
New local user added.
[H3C-luser-network-r3]password simple 123456
[H3C-luser-network-r3]service-type ppp
[H3C-luser-network-r3]qu
[H3C]interface s1/0
[H3C-Serial1/0]ppp authentication-mode chap
[H3C-Serial1/0]ppp chap user r5
ospf
R1
[H3C]ospf 1
[H3C-ospf-1]area 0
[H3C-ospf-1-area-0.0.0.0]network 10.255.12.1 0.0.0.0
[H3C-ospf-1-area-0.0.0.0]network 10.255.13.1 0.0.0.0
[H3C-ospf-1-area-0.0.0.0]network 192.168.255.1 0.0.0.0
[H3C-ospf-1-area-0.0.0.0]network 192.168.0.1 0.0.0.0
[H3C-ospf-1-area-0.0.0.0]network 192.168.1.1 0.0.0.0
[H3C-ospf-1-area-0.0.0.0]network 192.168.2.1 0.0.0.0
[H3C-ospf-1]qu
R2
[H3C]ospf 1
[H3C-ospf-1]area 0
[H3C-ospf-1-area-0.0.0.0]network 10.255.12.2 0.0.0.0
[H3C-ospf-1-area-0.0.0.0]network 10.255.23.1 0.0.0.0
[H3C-ospf-1-area-0.0.0.0]network 192.168.255.2 0.0.0.0
[H3C-ospf-1-area-0.0.0.0]qu
R3
[H3C]ospf 1
[H3C-ospf-1]area 0
[H3C-ospf-1-area-0.0.0.0]network 10.255.13.2 0.0.0.0
[H3C-ospf-1-area-0.0.0.0]network 10.255.23.2 0.0.0.0
[H3C-ospf-1-area-0.0.0.0]network 192.168.255.3 0.0.0.0
bgp
R1
[H3C]bgp 100
[H3C-bgp-default]router-id 192.168.255.1
[H3C-bgp-default]group 100 internal
[H3C-bgp-default]peer 192.168.255.2 group 100
[H3C-bgp-default]peer 192.168.255.3 group 100
[H3C-bgp-default]peer 100 connect-interface LoopBack 0
[H3C-bgp-default]address-family ipv4
[H3C-bgp-default-ipv4]peer 100 enable
[H3C-bgp-default-ipv4]network 192.168.0.1 24
[H3C-bgp-default-ipv4]network 192.168.1.1 24
[H3C-bgp-default-ipv4]network 192.168.2.1 24
R2
[H3C]bgp 100
[H3C-bgp-default]router-id 192.168.255.2
[H3C-bgp-default]group 100 internal
[H3C-bgp-default]peer 192.168.255.1 group 100
[H3C-bgp-default]peer 192.168.255.3 group 100
[H3C-bgp-default]peer 100 connect-interface LoopBack 0
[H3C-bgp-default]address-family ipv4
[H3C-bgp-default-ipv4]peer 100 enable
[H3C-bgp-default-ipv4]qu
[H3C-bgp-default]peer 10.255.24.2 as-number 200
[H3C-bgp-default]address-family ipv4
[H3C-bgp-default-ipv4]peer 10.255.24.2 enable
[H3C-bgp-default-ipv4]peer 100 next-hop-local
R3
[H3C]bgp 100
[H3C-bgp-default]router-id 192.168.255.3
[H3C-bgp-default]group 100 internal
[H3C-bgp-default]peer 192.168.255.1 group 100
[H3C-bgp-default]peer 192.168.255.2 group 100
[H3C-bgp-default]peer 100 connect-interface LoopBack 0
[H3C-bgp-default]address-family ipv4
[H3C-bgp-default-ipv4]peer 100 enable
[H3C-bgp-default-ipv4]qu
[H3C-bgp-default]peer 10.255.35.2 as-number 300
[H3C-bgp-default]address-family ipv4
[H3C-bgp-default-ipv4]peer 10.255.35.2 enable
[H3C-bgp-default-ipv4]peer 100 next-hop-local
R4
[H3C]bgp 200
[H3C-bgp-default]peer 10.255.24.1 as-number 100
[H3C-bgp-default]peer 10.255.46.2 as-number 300
[H3C-bgp-default]address-family ipv4
[H3C-bgp-default-ipv4]peer 10.255.24.1 enable
[H3C-bgp-default-ipv4]peer 10.255.46.2 enable
R5
[H3C]bgp 300
[H3C-bgp-default]peer 10.255.56.2 as-number 300
[H3C-bgp-default]peer 10.255.35.1 as-number 100
[H3C-bgp-default]address-family ipv4
[H3C-bgp-default-ipv4]peer 10.255.56.2 enable
[H3C-bgp-default-ipv4]peer 10.255.35.1 enable
R6
[H3C]bgp 300
[H3C-bgp-default]peer 10.255.46.1 as-number 200
[H3C-bgp-default]peer 10.255.56.1 as-number 300
[H3C-bgp-default]address-family ipv4
[H3C-bgp-default-ipv4]peer 10.255.46.1 enable
[H3C-bgp-default-ipv4]peer 10.255.56.1 enable
AS-path选路
在R3上面匹配0.0和2.0网段，使之在发送给R5的时候加上AS400 500 600，也就是出接口方向
或者在R5上匹配0.0和2.0网段，使之接收到R3发来的路由时，加上as 400 500 600也就是入口方向
R3
[H3C]ip prefix-list 123 index 10 permit 192.168.0.0 24
[H3C]ip prefix-list 123 index 20 permit 192.168.2.0 24
[H3C]route-policy 123 permit node 10
[H3C-route-policy-123-10]if-match ip address prefix-list 123
[H3C-route-policy-123-10]apply as-path 400 500 600
[H3C-route-policy-123-10]qu
[H3C]bgp 100
[H3C-bgp-default]address-family ipv4
[H3C-bgp-default-ipv4]peer 10.255.35.2 route-policy 123 export
[H3C-bgp-default-ipv4]qu
始发路由
[H3C]ip as-path 1 permit ^$
[H3C]route-policy shifa permit node 10
[H3C-route-policy-shifa-10]if-match as-path 1
[H3C-route-policy-shifa-10]qu
[H3C]bgp 300
[H3C-bgp-default]address-family ipv4
[H3C-bgp-default-ipv4]peer 10.255.35.1 route-policy shifa export