Lab 9.1.4.2: Load Sharing IGRP-EIGRP

Objective:

Implement a standby ISDN DDR system for your Frame Relay network between Orlando and Atlanta for on-demand bandwidth when the Frame Relay interface is overloaded using a dynamic routing protocol.

Scenario:

You have just installed an ISDN line to be used as standby reserve bandwidth for your Frame Relay connection between the Atlanta and Orlando office. Configure DDR using a dialer interface on the Orlando router. Configure Frame Relay on the serial interfaces connecting to the Frame Relay network. Configure this to work successfully with IGRP. EIGRP could also be 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 configuration.
  2.  First configure your ISDN BRI lines. Assign the appropriate SPIDs and dialer profiles to implement DDR. Be sure to configure the following items:
    • PPP encapsulation
    • CHAP authentication
    • ISDN Spid numbers
    • Idle timeouts

    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 standby dial feature on the Orlando Frame Relay interface. This will enable the dialer interface to help out when the Frame Relay link is overloaded.
    • On the Orlando router:

    Orlando(config)#int s0/0
    Orlando(config-if)#backup interface dialer 1
    Orlando(config-if)#backup load 2 1

  5. Configure IGRP on both routers so that they are exchanging information about all networks in the above diagram including both the Frame Relay network and the ISDN network.

    What commands would you use to turn on these protocols?




  6. At this point, your Frame Relay network should be up. From the Orlando router, look at your routing table. What is the route to 192.168.3.0? Does anything look strange?

    It appears like this because load backup command puts the dialer interface into a shutdown state to keep our standby routes from interfering with real traffic. But the BRI interface on the Atlanta side does not have load backup configured. Remember by default BRI lines spoof that they are active in order to allow DDR to work properly. Because the Atlanta BRI is spoofing that it is up the Atlanta router is announcing the BRI network in its routing updates.

    Is this a problem?

    In what state is your dialer interface?

  7. Check the serial interface to verify the backup interface load levels with the show interface s0/0 command.

    What load level is the back setup to kick in at?


  8. Create a large amount of traffic destined for the Atlanta router. Create a telnet session into the Orlando router from the Atlanta router. This will allow you to keep the Orlando console free to see console messages.

    From the telnet session to Orlando do an extended ping using very large packet sizes. This will saturate the link and cause the backup to kick in. Make sure you create enough of them to keep the traffic going for a while. This will give you more time to observe what is happening.

    Orlando#ping
    Protocol [ip]:
    Target IP address: 192.168.2.1
    Repeat count [5]: 500
    Datagram size [100]: 1460
    Timeout in seconds [2]:
    Extended commands [n]:
    Sweep range of sizes [n]:
    Type escape sequence to abort.
    Sending 500, 1460-byte ICMP Echos to 192.168.2.1, timeout is 2 seconds:
    !!!!!!!!!!!!!!!!

  9. Watch your console session on the Orlando router to see what happens to the BRI interface.

    What happened?

    Once the link comes up, wait a few moments for IGRP to learn the new routes.

    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 to make sure you are in overload mode.

    What do you see?



    Check the bandwidth values on the dialer 1 interface and the Frame Relay serial interface. What do you notice?

    What problem will this cause?

    We can tweak how IGRP looks at routes using the variance command. This command allows you to specify a multiplier to calculate acceptable metric values.

    Configure a variance of 4 on both the Atlanta and Orlando routers:

    Orlando(config)#router igrp 100
    Orlando(config-router)#variance 4

    Atlanta(config)#router igrp 100
    Atlanta(config-router)#variance 4

    Do a
    clear ip route * command on both routers, create traffic to bring up the line again, and check the route table.

    What do you see now?

  10. Stop your ping.

    What happens?

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