Choose the DR
R1, R2 and R3 share one LAN (10.0.0.0/24) through SW1, and OSPF is already running. R3 is the DR and R2 the BDR, but R1 is the most powerful router, so the network team wants:
- R1 as the DR (give its Gi0/0 priority 100).
- R2 as the BDR (priority 50).
- R3 never DR or BDR.
Remember that the election isn't pre-emptive.
How it works: this is VulnTech NetLab, a network simulator running in your browser. Click a device in the diagram to open its console and type commands, just like on real equipment (? shows help, Tab finishes a word). Click a cable to inspect it. Tasks tick themselves off as you complete them; questions are answered in the box under each task. Your work is kept if you reload; Reset starts the network over.
Solution explanation
The priorities alone change nothing: the election only runs again when the DR goes away. Priority 0 on R3 makes it give up its role at once. The BDR (R2) then becomes DR and R1, with the highest priority left, becomes BDR. Clearing the process on R2 makes it drop the DR role, so R1 is promoted and R2 comes back as BDR. (Clearing R3 first isn't needed after priority 0, but it does no harm.)
Show solution
[R1]
enable
show ip ospf neighbor
configure terminal
interface g0/0
ip ospf priority 100
end
[R2]
enable
configure terminal
interface g0/0
ip ospf priority 50
end
[R3]
enable
configure terminal
interface g0/0
ip ospf priority 0
end
clear ip ospf process
yes
[R2]
clear ip ospf process
yes
[R1]
show ip ospf neighbor