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Community Member

OSPF Routing Prob

Hi All.

I do have scenario like,

I have 5 routers in my lab environment configured with OSPF running on all the routers. All are running well having all the updates except R1, which dose not have any update in its routing table except the its directly connected network.

But if lookin after the SHOW IP OSPF NEIGHBOR and SHOW IP OSPF DATABASE commands on R1 as well its directly connected router R3 both are showing eachother as neighbors as well the STATE is FULL. so they are scnchronizing with each other. even R1 dosent have any route to any destination.

--so what could be the prob is.?

--and what are the parameters to be checked fot makin routers adjacent.?

My Connectivity is like,

R1------R3------R4-------R5--------R2

|_______||_______________||_________|

area 1 area 0 area 2

Update me for possible solution....

Thanks

Dhaval Tandel.

14 REPLIES
Purple

Re: OSPF Routing Prob

How many LSAs do you see in R1's OSPF database ?

Paresh

Re: OSPF Routing Prob

paresh...

will various network types will affact this routing or some thing else? what will be the possible cause for such a scenarios...?

regards

Devang

Purple

Re: OSPF Routing Prob

Devang,

One example is an ethernet link where one end is configured as point-to-point and the other is configured as broadcast. The neighbor relationship is Full but the routes will not be properly installed.

Paresh

Re: OSPF Routing Prob

hi paresh...

so what is the cause in the above example given by you can you explain me it in detail...???

but here he is having both the end with the serial connection...so in this case also the same thing will happend...?

regards

Devang

Community Member

Re: OSPF Routing Prob

Router Link States (Area 1)

Two Link ID is there

one is of its own and other of R3.

Summary Net Link States (Area 1)

Six Link Id is there

Thanks

Silver

Re: OSPF Routing Prob

Could you please provide the R1 & R3 configurtion ? Is it a Frame-Relay link between them ? If yes, try to configure the broadcast at FR.

Community Member

Re: OSPF Routing Prob

Hello Jackyoung,

Thanks for taking interest.

As you asked i am not connected by FR i am using serial links only and am also atteching the sh run here, just go through and update me if you found something...

Thanks

Purple

Re: OSPF Routing Prob

Hi,

On R3, remove the following statement from under 'interface Serial0':

ip ospf network broadcast

That should fix things up.

Paresh

PS. Pls do remember to rate posts that help

Community Member

Re: OSPF Routing Prob

Hi,

Thanks for reply.

I got the update after removing the ip ospd network broadcast. But still Can you tell me what is the logic behinfd that...?

Bcoz i think if two router exchanging the hello packets and makin the adjacancies as FULL at both side than they should exchange routes too.

Thanks again...

Dhaval Tandel

Purple

Re: OSPF Routing Prob

If you really want to understand this, put that statement back in on R3, and then issue the 'sh ip ospf database router' command on R3. You will find that R3's router LSA will have a 'Link connected to: a Transit Network' which refers to the link to R1. R1, on the other hand, will have a 'Link connected to: another Router (point-to-point)'. Now, when OSPF is building it's routing table, it will expect to see each router reporting the same type of link to the other. If that is not the case, then it will not recognise the link between the two; that's what happened in your case.

Hope that helps - pls do remember to rate posts.

Paresh

Community Member

Re: OSPF Routing Prob

Hello,

Mr. Paresh..

I got your point. and thanks for explanation...

Dhaval Tandel

Re: OSPF Routing Prob

hi Pareshbhai...

still i m not clear with your explanation will you explain me in some detail???

and as you said R1 is on other hand having some Link connected to another router ...right...

but what happen when R1 is the last router and its connected to R3 and all other routers are connected with the R3... no more router connected with R1 ...so at that time what will happend???

regards

Devang

Silver

Re: OSPF Routing Prob

Let me try to explain. The point that Pareshbai told is the OSPF network type should be the same in the same link. So, if there are other routers connecting to the R3, we just need to configure the network type the same at both ends per link. If it is a LAN connection, we can use broadcast; if it is also serial, we can use point-to-point. The hello and deaf interval are the same in different network type. It will also create the problem.

Check here for OSPF design guide for details.

http://www.cisco.com/en/US/tech/tk365/technologies_white_paper09186a0080094e9e.shtml#t27

Hope this helps.

Purple

Re: OSPF Routing Prob

Devang,

Adding to what Jack wrote: OSPF, being a link-state protocol, works on the basis of reporting the links that each router has got. This information is carried in type-1, or router LSAs. Now, there are 4 types of links that the router could report about:

- router link

- link to a transit (multiaccess) network

- link to a stub network

- virtual link

When OSPF builds its routing table, it goes through each link that each router reports. If R1 reports a link to R2, it checks that R2 also reports the same type of link to R1. If R1 reports a 'router link' to R2 but R2 reports a 'link to a transit network' to R2, the router will not use this link for the purpose of OSPF. That is exactly what happens when one end configures the link as point-to-point (router link) while the other end configures it as broadcast (link to a transit network).

Paresh

PS. Pls do remember to rate posts.

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