Lab aims

Get the students familiar with the basic operation principles of MPLS. The followed technologies were used in the lab: IPv4, CEF, MPLS, OSPF, and BGP.

The lab is performed using GNS3 emulator. It is expected that the student is already acquainted with the corresponding theoretical material, which is not explained in this lab.

Network scheme


Lab description

On the scheme above one can see a small network of a certain company (R1-R6 routers) connected to two Internet service providers (routers ISP1 and ISP2). The network of the company must perform functions of a transit autonomous system for connection between the providers' networks. In other words, it must transfer traffic between ISP1 and ISP2 routers. Use 7200 series routers and the latest stable IOS.

  1. Try suggesting an IP address plan for the sceme presented above and assign IP addresses to the interfaces that are used for connection between the routers. Create a Loopback 0 interface on every router and assign them IP addresses. Create Loopback 0 interfaces, which will emulate certain networks in the Internet, on ISP1 and ISP2 routers too.
  2. Adjust OSPF on every company's router in a way so that it works on all links inside of the company and doesn't work between you and the service provider's equipment.
  3. Redistribute info about the networks connected to the company's routers into the dynamic routing protocol.
  4. Make sure that every of the six routers gets info about all company's prefixes as well as IP networks used between the company and service providers.
  5. Configure BGP between your edge routers (R1 and R6) and the service providers' equipment.
  6. Configure BGP between your edge routers (R1 and R6). R2-R5 routers do not participate in BGP. Loopback 0 interfaces should be used in order to establish an iBGP session between R1 and R6.
  7. Make sure that every of the service providers can see prefixes announced by the other service provider in their routing tables.
  8. Make sure that there is no connectivity between networks of the first and second providers. Please explain this occurrence.
  9. Configure routes redistribution from OSPF to BGP on R1 and R6 routers. Make sure that the service providers received the updates about existing prefixes.
  10. Make sure that routes from BGP  don’t exist in OSPF.
  11. Make sure that every service provider can gain access to the local networks of your company but can't get connected to each other. Please explain this occurrence.
  12. Enable CEF support on R1-R6 routers using ip cef command. The latest versions of IOS have settings that use CEF by default, but it won't do any bad if we double-check that Cisco Express Forwarding technology is used. Review the output of sho ip cef command and explain what exactly you are seeing.
  13. Use mpls ip command in the global configuration mode in order to enable MPLS support on R1-R6 routers.
  14. Use mpls ip command to enable MPLS support on the internal interfaces of R1-R6 routers, or in other words not on the links between the company and the service providers.
  15. Use mpls mtu override 1540 interface command in order to adjust the value of MPLS MTU on the links from the previous item. This has to be done because the additional MPLS label located between Ethernet and IP headers increases the frame length.
  16. Make sure that the command from the previous item has been entered correctly by using show mpls interface interface_name detail command where the names of the interfaces you have configured should be used instead of interface_name parameter.
  17. Use mpls ldp router-id loopback0 force command in the global configuration mode in order to set the router ID for LDP.
  18. Make sure that every of R1-R6 routers can see all its LDP neighbors using sho mpls ldp neighbor command.
  19. Check the LIB table contents on R1-R6 routers using sho mpls ldp binding command. Explain which prefixes are present and absent there  and why.
  20. Make sure that R2-R5 routers don't have the external prefixes (from the service providers' ISP1 and ISP2 devices) in the LIB table. Explain why they must not be there.
  21. Use sho mpls forwarding-table command in order to review the LFIB table contents on R1-R6 routers.
  22. Make sure that the data transfer between ISP1 and ISP2 is taking place.
  23. Enable traffic capturing on R1-R2, R2-R3, and R2-R4 links. Review the contents of packets transferred between ISP1 and ISP2. Compare the used labels with the ones you saw in the LIB and LFIB tables. Explain why certain packets don't have any labels.

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