Lab 4.2.4.1 OSPF DR And BDR Selection

Objective:

Observe the DR and BDR selection process.

WARNING: There is a known bug in some 12.X IOS versions, where after the DR/BDR election process has completed, the DR can be replaced by a router with a higher ID.

Scenario:

You are the network administrator for the above network. You wish to see the interaction of OSPF routers in your broadcast network.

  1. Write the running-configurations of all three routers to memory and turn off all three routers
  2. Turn on "Router B" only
  3. Enter show ip ospf neighbor and show ip ospf database

What did the router respond with?

  1. Enter show ip ospf interface

What did the router respond with?

  1. Turn on "Router A" only and wait one minute

From the "Router A" console

  1. Enter show ip ospf neighbor and show ip ospf database

What did the router respond with

From the "Router A" console

  1. Enter debug ip ospf adjacencies from "Router A" and then turn on "Router C"

Report your findings concerning the DR/BDR election process.

  1. Enter undebug all on "Router A"
  2. Enter show ip ospf neighbor and show ip ospf database

What did the router respond with

  1. Enter show ip ospf interface

Which router is the DR and which router is the BDR? Why?

  1. Turn off all the routers and then turn on "Router A" only and wait one minute

From the "Router A" console

  1. Enter enable exec mode and turn on the other two routers at the same time
  2. Continuously issue the command show ip ospf neighbor as the other routers boot
  3. Examine the router states as they boot. Report your findings.

From the "Router C" console

  1. Enter show ip ospf neighbor detail

What is the priority of all the routers in Area 0

From the "BDR Router" console

  1. Enter debug ip ospf events turn off "The router that is the DR" only and wait one minute

Predict which routers will become the DR and BDR after the DR router is dead

  1. Enter show ip ospf neighbor after the election process has stopped

Which router became the DR and which became the BDR? Why?

  1. Turn on "the old DR router" only and wait one minute

Did "the old DR router" became the DR again? Why?

  1. Reboot all three routers at the same time

Predict which routers will become the DR and BDR

  1. Enter enable exec mode and issue the command show ip ospf neighbor

Which routers became the DR and BDR? Why?