关于BGP的中转AS 其它頭條網

实验拓扑图

本实验涉及的知识点：

中转AS；
路由黑洞问题，BGP水平分割原理，如何解决路由黑洞？见3
逻辑全互联，指定下一跳 next-hop-local ，因为宣告路由器和接收路由器是内部对等体，且 update 消息的 NLRI 指向的是外部 AS 的目的地，那么 NEXT_HOP 是外部对等体的IP地址。也就是说R2将R1的路由器通告给R3的时候，它的下一跳地址为R1的接口IP，但R3并没有去往R1接口IP的路由，所以需要对R3进行指定下一跳，同时由于 BGP 水平分割原则，R3知道如何去往R1的路由时，它并不会传递给R4，所以此时可以进行逻辑全互联（并不是最优方案，通常可以使用路由反射器或 BGP 联邦）
转发路径上的每台BGP路由器都必须知道路由器与外部对等体使用的BGP路由，也就是说转发AS内的每台路由器要知道外部BGP路由，否则无法通信。
EBGP多跳问题（默认状态下 EBGP 之间 TTL=1）

<code>R1配置：
interface GigabitEthernet0/0/0
ip address 12.1.1.1 255.255.255.0
# 

interface LoopBack0
ip address 1.1.1.1 255.255.255.255
#
interface LoopBack1
ip address 1.1.1.3 255.255.255.255
#
bgp 100
router-id 1.1.1.1
peer 2.2.2.2 as-number 200
peer 2.2.2.2 ebgp-max-hop 2
peer 2.2.2.2 connect-interface LoopBack0
peer 2.2.2.2 password cipher cisco
#
ipv4-family unicast
  undo synchronization
  network 1.1.1.3 255.255.255.255
  peer 2.2.2.2 enable
#
ip route-static 2.2.2.2 255.255.255.255 12.1.1.2
#

R2配置：
interface GigabitEthernet0/0/0
ip address 12.1.1.2 255.255.255.0
#
interface GigabitEthernet0/0/1
ip address 23.1.1.2 255.255.255.0
ospf authentication-mode hmac-md5 1 cipher cisco
#
interface LoopBack0
ip address 2.2.2.2 255.255.255.255
#
bgp 200
router-id 2.2.2.2
peer 1.1.1.1 as-number 100
peer 1.1.1.1 ebgp-max-hop 2
peer 1.1.1.1 connect-interface LoopBack0
peer 1.1.1.1 password cipher cisco
peer 3.3.3.3 as-number 200
peer 3.3.3.3 connect-interface LoopBack0
peer 4.4.4.4 as-number 200
peer 4.4.4.4 connect-interface LoopBack0
ipv4-family unicast
  undo synchronization
  peer 1.1.1.1 enable
  peer 3.3.3.3 enable
  peer 3.3.3.3 next-hop-local
  peer 4.4.4.4 enable
  peer 4.4.4.4 next-hop-local
# 

ospf 1 router-id 2.2.2.2
area 0.0.0.0
  authentication-mode md5 1 cipher cisco
  network 2.2.2.2 0.0.0.0
  network 23.1.1.0 0.0.0.255
#
ip route-static 1.1.1.1 255.255.255.255 12.1.1.1
#

R3配置：
interface GigabitEthernet0/0/1
ip address 23.1.1.3 255.255.255.0
ospf authentication-mode hmac-md5 1 cipher cisco
#
interface GigabitEthernet0/0/2
ip address 34.1.1.3 255.255.255.0
ospf authentication-mode hmac-md5 1 cipher cisco
#
interface LoopBack0
ip address 3.3.3.3 255.255.255.255
#
bgp 200
router-id 3.3.3.3
peer 2.2.2.2 as-number 200
peer 2.2.2.2 connect-interface LoopBack0
peer 4.4.4.4 as-number 200
peer 4.4.4.4 connect-interface LoopBack0
ipv4-family unicast
  undo synchronization
  peer 2.2.2.2 enable
  peer 4.4.4.4 enable
#
ospf 1 router-id 3.3.3.3
area 0.0.0.0
  authentication-mode md5 1 cipher cisco
  network 3.3.3.3 0.0.0.0
  network 23.1.1.0 0.0.0.255
  network 34.1.1.0 0.0.0.255
#

R4配置：
interface GigabitEthernet0/0/0
ip address 45.1.1.4 255.255.255.0
#
interface GigabitEthernet0/0/2
ip address 34.1.1.4 255.255.255.0
ospf authentication-mode hmac-md5 1 cipher cisco
#
interface LoopBack0
ip address 4.4.4.4 255.255.255.255 

#
bgp 200
router-id 4.4.4.4
peer 2.2.2.2 as-number 200
peer 2.2.2.2 connect-interface LoopBack0
peer 3.3.3.3 as-number 200
peer 3.3.3.3 connect-interface LoopBack0
peer 45.1.1.5 as-number 300
peer 45.1.1.5 password cipher cisco
ipv4-family unicast
  undo synchronization
  peer 2.2.2.2 enable
  peer 2.2.2.2 next-hop-local
  peer 3.3.3.3 enable
  peer 3.3.3.3 next-hop-local
  peer 45.1.1.5 enable
#
ospf 1 router-id 4.4.4.4
area 0.0.0.0
  authentication-mode md5 1 cipher cisco
  network 4.4.4.4 0.0.0.0
  network 34.1.1.0 0.0.0.255
#

R5配置：
interface GigabitEthernet0/0/0
ip address 45.1.1.5 255.255.255.0
#
interface LoopBack0
ip address 5.5.5.5 255.255.255.255
#
bgp 300
router-id 5.5.5.5
peer 45.1.1.4 as-number 200
peer 45.1.1.4 password cipher cisco
ipv4-family unicast
  undo synchronization
  network 5.5.5.5 255.255.255.255
  peer 45.1.1.4 enable
#/<code>