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OSPF NBRS not forming on ethernet

Hi,

We have connected two routers on ethernet. We can ping to other router from other router. We have given loopback zero address to each router which is in the same subnet. We have also published ethernet address in ospf process. But still it is not forming OSPF neighbor relationship with each other. when checked with command

# show ip ospf interface fast0/0 , it shows all default times of OSPF.

What is stopping them for forming neighbor relationship.

Is it possible to debug the problem.

Does speed of each ethernet port will cause any problem? As one is fast ethernet and other is gigabit ethernet. But as routers are finally connected to switch ,I dont think it will matter.

Is there is any way with which we can find out that ospf hellos are blocked preventing routers from forming neighbor relationship.

Can some one help us out

Any link on cisc.com is highly appreciable

Thanx in advance

Subodh

5 REPLIES
Gold

Re: OSPF NBRS not forming on ethernet

Debug IP OSPF ADJ

Will give you all kinds of information

You can also see with SHOW IP OSPF NEI if it got stuck.

This link has a flow chart of how to fix ospf but I suspect the debug command will tell you everything you need to know.

http://www.cisco.com/en/US/tech/tk365/technologies_tech_note09186a00800949f7.shtml

Hall of Fame Super Gold

Re: OSPF NBRS not forming on ethernet

Subodh

I agree with Tim that debug ip ospf adj is a very excellent place to start and that it is likely to identify the problem.

There are a number of things that can prevent OSPF forming neighbor relationship with a connected router. You might check for these things:

- OSPF timers must match. though the original post seems to indicate that they do match.

- OSPF interface type must be the same. though it is not so likely to be an issue on Ethernet connected interfaces.

- The interfaces must be in a common subnet. though the original post says that they can ping so it seems likely that they are in a common subnet.

- the OSPF area assigned to each interface must be the same.

- at least one of the routers must have a non-zero priority on the interface.

- the OSPF network statement must include the address of the physical interface.

If Tim's suggestion and mine do not help you find the issue then I suggest that you post the config of both routers and of ospf on both routers.

HTH

Rick

Purple

Re: OSPF NBRS not forming on ethernet

Check your connecting interfaces , by default I think all are passive interfaces which means they will not form an adjacency . Under the ospf process do a "no passive interface slot/port or if its a layer 3 switch no passive interface vlan XX . Also make sure your network statements are correct . To check to see if the interface is passive I believe it is "show ip ospf interface slot/port or show ip ospf interface vlan XX for a layer 3 switch .

Hall of Fame Super Gold

Re: OSPF NBRS not forming on ethernet

Glen

The passive interface is an interesting point and I should have thought to include it in my list of what would prevent OSPF from forming neighbors.

But I am interested in your statement about by default interfaces are passive. In my experience of configuring OSPF the default is for interfaces to be active. There is a command to set the default to interface passive, but that is not the default behavior. Perhaps you can tell us a bit more about situations in which you have experienced configuring OSPF and the default was for interfaces to be passive.

HTH

Rick

Purple

Re: OSPF NBRS not forming on ethernet

Not sure about routers but it seems to me like a native 720 or any l2/3 switch was passive default out of the box and we had to non passive the connecting links. But then again maybe I'm wrong , just seems like in some instances it was default out of the box though it probably wasn't a router .

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