How to properly configure OSPF protocol?

Question

I have this simple 3 router network that I need to configure the OSPF for, when using two routers every thing works fine and i can ping but when I add the third router nothing works

left router

interface se0/1/0
    ip address 200.20.20.1  255.255.255.252 
    no sh 

interface gig0/0/0 
    ip address 192.168.3.1 255.255.255.224
    no sh 


router ospf 1 
    network 200.20.20.0 0.0.0.3  area 0 
    network 192.168.3.0 0.0.0.31 area 0
    interface loopback 100 
    ip address 100.0.0.1/30 

middle router

interface se0/1/0
    ip address 200.20.20.2
    no sh 
interface se0/1/1
    ip address 200.20.20.10 
    no sh 

interface gig0/0/0 
    ip address 192.168.3.33 255.255.255.224
    no sh 

router ospf 1
    network 200.20.20.0 0.0.0.3 area 0 
    network 200.20.20.8 0.0.0.3 area 0 
    network 192.168.3.32 0.0.0.31 area 0

right router

interface se0/1/0
    ip address 200.20.20.9  255.255.255.252 
    no sh 

interface gig0/0/0 
    ip address 192.168.3.65 255.255.255.224
    no sh 


router ospf 1 
    network 200.20.20.8 0.0.0.3  area 0 
    network 192.168.3.65 0.0.0.31 area 0

Can somebody please explain what is am I missing here?

Answer 1

Apart from your configuration excerpts on the middle router missing the subnet mask:

interface se0/1/0
    ip address 200.20.20.2
    no sh 
interface se0/1/1
    ip address 200.20.20.10 
    no sh 

Everything seems to be configured correctly. I expect it wouldn't have allowed you to proceed without entering the subnet mask anyway, so I'm going to assume you entered it correctly and didn't just make a typo or something.

My suggestion would be to just walk through some of the typical troubleshooting steps;

• Check the OSPF database and make sure everything you expect is there: show ip ospf database router
• Check if the routers are establishing adjacency: show ip ospf neighbor
• Check the timers: show ip ospf interface
• If you have no clues at this point, turn on OSPF adjacency/event debugging and look at what's going on, bring down/up the interfaces to trigger stuff if needs be: debug ip ospf adj, debug ip ospf events

---

Edit: I replicated basically the same setup you have like this and it works fine for me (tracert looks a little wonky, but hop count is correct so probably not a big deal), my guess would be you just made a typo or two when you were doing it.