Exchange Point Lab Exercise

Configuring peering with an Upstream and Configuring Local Peering across IXP


  1. Remove the entire old configuration from your router with the exception of the interface configurations and user access permissions. We will be using one Serial and two Ethernet links for this exercise.

  3. Confirm that you are not longer receiving OSPF or BGP routes by doing a show ip route
  4. Connect your routerís serial port to the upstream router according to the diagram.

    We will now set up eBGP between all of the routers in the classroom and the corresponding upstream router. Each table is its own AS. For example, Table A is AS 100. Table B is AS 1100, etc.


  5. Figure out your AS number.
  6. AS:


    Verify your addressing scheme.

  7. We will set up peering sessions according the map. Contact your upstream provider for the IP addresses you are going to use for your Point-to-Point serial link.

  9. Configure BGP on your router to announce your network.

  11. Set up a peering session with the upstream router.

    Router(config)#router bgp 100 //use your AS number

    Router(config-router)#neighbor remote-as 1

    // use the IP address and AS number of your neighbor

    Router(config-router)#neighbor description My-Peer-with-AS1

    Router(config-router)#neighbor update-source loopback0

    Router(config-router)#neighbor prefix-list my-routes out

    Router(config-router)#neighbor prefix-list my-peer in


  13. Define the prefix-lists that you will need. This specifies which routes you will send out and which routes you will accept.
  14. Router(config)#ip prefix-list my-routes seq 5 permit

    Router(config)#ip prefix-list my-routes seq 10 deny le 32


    Router(config)#ip prefix-list my-upstream seq 5 deny le 32

    Router(config)#ip prefix-list my-upstream seq 10 deny le 32

    Router(config)#ip prefix-list my-upstream seq 15 deny le 32

    Router(config)#ip prefix-list my-upstream seq 20 deny le 32

    Router(config)#ip prefix-list my-upstream seq 25 deny le 32

    Router(config)#ip prefix-list my-upstream seq 50 permit le 32

    Notice that you will have to confirm with your upstream as to what routes they are planning

    to send you. In the case above, the neighbor is sending everything. Double check

    that you set your "my-routes" outbound filter to contain the network you wish to announce.

    The entries with sequence number 50 are used to deny default routes.



  15. Check to see if the peering session is up:
  16. Router#show ip bgp sum

    BGP router identifier, local AS number 100

    BGP table version is 3, main routing table version 3

    Neighbor V AS MsgRcvd MsgSent TblVer InQ OutQ Up/Down State/PfxRcd 4 1 0 0 3 0 0 never Idle



  17. Check to see if you are receiving routes from your upstream. You should accept "full" routes or default from your upstream.
  18. Router#show ip bgp

    What routes are you receiving?

    Other commands to monitor BGP:

    Router#sh ip route

    Router#sh ip bgp

    Router#sh ip bgp neighbor

    Router#sh ip bgp neighbor x.x.x.x received-routes [*]

    [*] Only works if "soft-reconfiguration inbound" has been configured for this peer


  19. Traceroute to all of the other networks in the classroom. Notice the path that they take.





  21. Set up an exchange point for all of the classroom peers. J Find a switch to use to connect everyone to a shared medium. Use as the exchange point address space.




  23. Gather the necessary information from all of your peers:
  24. AS number of neighbor Prefixes they will be announcing Ip address for peering

    ----------------------------- ---------------------------------------- ---------------------------


























  25. Negotiate peering sessions with all your neighbors (local ISPs). Set these eBGP peering sessions up. Be sure to configure your filters correctly! Only accept customer routes from your peers. Only announce your routes (donít provide transit!) to your peers.
  26. Note:

    Often, in a BGP speaker, many neighbors are configured with the same update policies (that is, the same outbound route maps, distribute lists, filter lists, update source, and so on). Neighbors with the same update policies can be grouped into peer groups to simplify configuration and, more importantly, to make updating more efficient. When you have many peers, this approach is highly recommended.

    We can use this to simplify our outbound configuration for our peers. We should be announcing just our prefix to our Exchange Point peers:

    For example:

    router bgp 100
     neighbor XP-peers peer-group
     neighbor XP-peers filter-list 99 out
     neighbor XP-peers description Exchange Point Peers
     neighbor remote-as 200
     neighbor peer-group XP-peers
     neighbor filter-list 43 in
     neighbor remote-as 300
     neighbor peer-group XP-peers
     neighbor filter-list 45 in
     neighbor remote-as 400
     neighbor peer-group XP-peers
     neighbor filter-list 47 in


    ip as-path access-list 99 permit ^$


    Our Inbound prefix lists will vary for each peer as we will only be accepting only our peersí prefix from each.



  27. Use a hold-down route for your aggregate for stability

  29. Traceroute to all of the networks in the class now. What path do you take? Do you see the improvement?