Lab 9.1.1: Solutions Guide Link Failure Dial Backup

Objective:

Implement an ISDN dial backup system for your Frame Relay network between Orlando and Atlanta.

Scenario:

You have just installed an ISDN line to be used as a dial backup line to your Frame Relay connection between the Atlanta (hub) and Orlando (stub) office. Configure DDR on the BRI interface of the Orlando router. Configure Frame Relay on the serial interfaces connecting to the Frame Relay network. Use floating static routes to control which link is used.

Lab Tasks:

  1. Cable the lab as shown in the diagram. Use the Adtran Atlas 550 as your ISDN and Frame Relay networks. Start with a clean config on both routers.
  2. First configure your ISDN BRI lines. Assign the appropriate SPIDs and dialer maps to implement DDR. Be sure to configure the following items:
    • PPP encapsulation
    • CHAP authentication
    • ISDN Spid numbers
    • Idle timeouts
    • Map statements

    Test your DDR configuration to make sure it is functional.

  3. Next, setup your Frame Relay network. Configure Frame Relay encapsulation on your serial links. Use the DLCIs specified in the above diagram.

    Use ANSI as your LMI type.

    Use sub-interfaces. Configure the appropriate IP addresses.

    Test your Frame Relay configuration to make sure it is functional

  4. When you are satisfied that both components are functional, turn on the link down dial backup feature on the Orlando Frame Relay interface. This will enable the BRI line to use DDR when the Frame Relay link goes down.
    • On the Orlando router:

    Orlando(config)#int s0.16
    Orlando(config-if)#backup interface bri0/0
    Orlando(config-if)#backup delay 30 60

  5. Now install your floating static routes:

    • For the Orlando router, you need a default route that prefers the Frame Relay link. If the Frame Relay link is down, there should be a second default route that uses the BRI link.

    What commands would you use to install these routes?

    • For the Atlanta router, you need a static route to Orlando's Ethernet (192.168.1.0) that first prefers the Frame Relay link. If the Frame Relay link is down, there should a second route to that network that uses the BRI link.

    What commands would you use to install these routes?


  6. At this point, your Frame Relay network should be up. From the Orlando router, look at your routing table. What is the next hop address of your default route?


    In what state is your BRI interface?


  7. Simulate a link down condition on your Frame Relay network by removing the Orlando serial cable to the Frame Relay network. Watch your console session on the Orlando router to see what happens to the BRI interface.

    What happened?

    Did the BRI line dial yet?  

     

    Why?


    Ping to 192.168.2.1 - What happens?


    Look at the routing table on the Orlando router. What do you notice?


    Look at the status of the dial backup link with the show backup command.

     

  8. Plug the Frame Relay serial link back in to the Orlando router.

 What happens?


While you are waiting for the BRI line to go back down, check the status of the dial backup link using the show backup command.

When everything is back to normal, check the status of the dial backup link using the
show backup command.