Lab 8.7.9 Next Hop Attribute

Objectives:

  • Use the neighbor next-hop-self command to prevent routing failure between 2 routers that do not have a direct connection.

Scenario:

Router C learns about network 192.68.11.0/24 via EBGP from Router B with a next hop of 10.1.1.1, which is the IP address of the external neighbor to router B. However, Router C does not have a direct connection to Router A and therefore cannot reach the next hop. This will cause routing to fail. You will need to use the neighbor next-hop-self command to remedy this situation.

Tasks:

  1. Cable the lab and all interfaces as shown in the diagram. Don't forget the no shutdown command!




  2. Configure OSPF routing between routers B and C. Put both routers in area 0.
  3. Router B(config)#router ospf 1
    Router B(config-router)#network 10.2.2.0 0.0.0.255 area 0
    Router B(config-router)#network 10.3.3.0 0.0.0.255 area 0
    Router B(config-router)#passive-interface serial 0

    Router C(config)#router ospf 1
    Router C(config-router)#network 10.2.2.0 0.0.0.255 area 0
    Router C(config-router)#network 10.4.4.0 0.0.0.255 area 0

  4. Verify that Router B can successfully ping 10.1.1.1 and all interfaces on Router C.




  5. Configure BGP on Router A.
  6. Router A(config)#router BGP 1
    Router A(config-router)#neighbor 10.1.1.2 remote-as 65000
    Router A(config-router)#network 192.68.11.0
    Router A(config-router)#no synchronization

  7. Configure BGP on Routers B and C.
  8. Router B(config)#router BGP 65000
    Router B(config-router)#neighbor 10.1.1.1 remote-as 1
    Router B(config-router)#neighbor 10.2.2.2 remote-as 65000
    Router B(config-router)# network 10.2.2.0 mask 255.255.255.0
    Router B(config-router)#no synchronization

    Router C(config)#router BGP 65000
    Router C(config-router)#neighbor 10.2.2.1 remote-as 65000
    Router C(config-router)#network 10.4.4.0 mask 255.255.255.0
    Router C(config-router)#no synchronization

  9. Save your configurations.




  10. From Router C, can you ping 192.68.11.0?




  11. View the BGP routing table with the show ip bgp command, what can you say about network 192.168.11.0?
     



  12. Time to fix the problem! Router B needs to advertise itself as the next hop to Router C. To do this, issue the following commands:
  13. Router B(config-router)#neighbor 10.2.2.2 next-hop-self

  14. Now try to ping 192.68.11.1 from Router C. Were you successful?




  15.  Save your configuration and view the routing table of Router C again. What is different?