OSPF Configuration

[jordanmc31]

Hi,

I have a question about ospf i'm having trouble understanding some of these concepts.

Say you have 2 routers

Router A
int s0 ip address 192.168.1.1
int E0 ip address 172.16.1.1

router ospf 1


network 192.168.1.0 area 0
network 172.16.1.0 area 0


router B
int s0 ip address 192.168.1.2
int E0 ip address 172.16.1.2
int S1 ip address 192.168.2.1
router ospf 2

network 192.168.1.0 area 0
network 172.16.2.0 area 0

These two routers can communicate fine ping all interfaces. But then say router C is added afterwards and can only ping directly connected interfaces. But router A can ping router c's s0 interface but not Ethernet0's.

Router C

router ospf 1
int S0 ip address 192.168.2.2
int e0 ip address 172.16.3.0

network 192.168.2.0 area 0
network 172.16.3.0 area 0



RouterA S0 connected to router B S0.
Router B S1's connected to Router C's S0.

i'm having trouble with this problem routing setup. Any Help would be greatly appreciated.

 

[lambent]

I think you forgot to enable OSPF on S1 in router B.

 

[jordanmc31]

My mistake that is enabled just forgot to add it to the original post.

 

[jneiberger]

Do you really have routers A and B directly connected both serially and via ethernet?

 

[lambent]

I suggest you copy and paste your configurations of your 3 routers here.

 

[jordanmc31]

no the ethernets stub off into their own networks. the routers are only attached via serial interfaces.

 

[jneiberger]

The configuration you pasted above shows they A and B have two connections: 1) directly connected via serial cable, 2) connected on the 192.168.1.0 LAN. However, that may be a typo. For the e0 interface on Router B did you mean to type 192.168.2.1 instead of 1.2?

 

[jordanmc31]

Yeh my mistake thats what i meant. I'm doing this from memory from a simulation test.

 

[jordanmc31]

Well since router C was added later can it still be put into area 0 or would it need to be say area 1 or something else?

 

[lambent]

All routers can be in the same area. And be sure that router C can form a full neighbour state with router B.

 

[jordanmc31]

How do I go about the neighbor state? I've been reading about it but i'm more of a hands on person and unfortanetly can't get ahold of my instructor.

 

[lambent]

show ip ospf nei

make sure it's in a "FULL" state.

You still have your configurations? Or it's all from your memory?

 

[jordanmc31]

Its all from memory. If you know something specific I might be able to recall it. The ip addresses arent exactly the same but its the same idea and what not.

 

[lambent]

Make sure both sides are reachable from each others...
Make sure the subnet mask on both side matches
Make sure the router ID is unique in your network
Make sure you have enable OSPF on the interface with the "network" statement
Make sure that the ospf network type on both side match in the following ways:

A) broadcast/non-broadcast to broadcast/non-broadcast
B) p2p/p2mp/p2mp-broadcast to p2p/p2mp/p2mp-broadcast

And there's DR election in A), but no election in B).

And the default network types are:

Serial physical interfaces = non-broadcast
Ethernet physical interfaces = broadcast
p2p sub-interfaces = p2p
multipoint sub-interfaces = p2mp

Also be sure to match the hello/holdtime timers in different network types

Well there're still other things for multiple area implementation. If you're just using single area, then this should be enough. And btw, for single area implementation, you do not necessarily use Area 0 but then you'll lose the scalability.

 

[jordanmc31]

The networks are all connected via serial connections so they would be nonbroadcast to nonbroadcast. Do i have to set that in the configuration somewhere? Hello/holdtime timers i never thought about but that could have been the problem. Routers A and B were already configured for me and were set to area 0. I had to get Router C to communicate properly.

 

[lambent]

Can you access router A and B? If yes then you should be able to check the OSPF configuration as well as the OSPF interface configuration.

One more thing, you can set OSPF authentication using clear-text or MD5 passwords or null. So make sure that the authentication type matches if it's configured on router B. It can be configured globally or per interface.

 

[lambent]

and "debug" is always your friend in your lab

 

[jordanmc31]

Yeh I didn't notice any authentication. That is something I looked for. I unfortanetly didn't get much into each interfaces config which was a mistake on my part. Thanks for the help.


Jordan