OSPF neigbour routers not exchanging information

[mohit_kakkar]

Hello,

I am  newbie network administrator at work coming in with a linux backgroud so I am new to routing protocols.

I have to setup two routers, one called Montreal and the other Toronto.

We will be using a frame relay eventually but for testing purposes I just wanted to connect the two routers with a serial cable to test for connectivity.

I set up a serial cable, configured clock rate, and ran ospf. The two do not even seem to be exchaning hello packets.

I spent hours trying to figure out what is wrong but to no avail.

I attach my VLSM scheme as well as 5.3.1 packet analyzer file. If someone could point out the problem so I could fix it I wold appreciate it.

Thanks,

[Jon Marshall]

Mohit

Can you ping one router from the other ?

Have you included the subnet of the serial link under your OSPF config on both routers.

If yes to both answers can you post the router configs as text as some of use can't read packet tracer files

Jon

[mohit_kakkar]

Hi John,

I can ping from one serial interface to another. I checked that

As for your second concern, I just advertised the networks assigned to the subinterfaces of fa0/0 on both routers as these are the interfaces that have PC's and servers attached to them.

In my limited training, I was never told that we had to advertise the subnet of the serial interfaces themselves. Does  it have to be advertised?

I am more of a Linux Administrator being trained to do network administration hence my "simple" questions.

I am not on a windows machine so I cannot run packet anayzer so what I can give you is the VLSM outline detailing the networks of the routers:

Router1:

192.168.100.0 with a subnet mask of 255.255.255.192

192.168.100.128 with a subnet mask of 255.255.255.224

192.168.100.192 with a subnet mask of 

255.255.255.240

Router 2:

192.68.100.64          

255.255.255.19

192.168.100.128

255.255.255.224

192.168.100.208

255.255.255.240

The serial connections are on these IP's and subnet mask:

192.168.100.225 and 192.168.100.226 with subnet mask

255.255.255.252

Do you think the problem is that the subnet with the serial connections was not advertised?

[cadet alain]

Hi,

in every IGP(RIP,EIGRP,OSPF), the network command is used to enable the routing protocol on the interfaces whose IP address falls into the network command and it will also advertise those subnets.

Regards.

Alain

[mohit_kakkar]

Thank you for your answer Alain. So if I follow you correctly I have to make sure that the networks having my PC'/Servers are advertised as well as the subnets of the serial interfaces?

--Mohit

[cadet alain]

Hi,

if you want them to be reachable via OSPF yes you must but as there is no OSPF neighbour on the other side  you should also in the routing process declare these interfaces as passive.

eg:

router ospf 1

network x.x.x.x area x

passive-interface fx/x

Regards.

Alain

[mohit_kakkar]

There is just one serial connection between serial 0/0/0 on router 1 and between serial 0/0/0 on router 2. fa0/0 on both routers are in use and that's it. The passive interface directive is not mandatory is it?

[cadet alain]

Hi,

no it's not mandatory.this is a security feature here because then these networks will still be advertised but the router won't be sending OSPF messages and so there won't be no adjacency on these links.

Regards.

Alain

[mohit_kakkar]

How will the networks on the other fa interfaces be advertised if I do not explicity advertise them with the network command?

[cadet alain]

Hi,

What do you mean? You want full reachability from end to end with OSPF?

I'm gonna take a look at your PT file but I encourage you to use GNS3 to test routing because PT is a tool mainly used for CCNA and there a a lot of things that ain't working  and you don't have all the debug commands available.

EDIT: ok just enable OSPF on the serial connecting the 2 routers on both and the other network commands are comprising the subnets from the subinterfaces and so the subnets from the machines on each LAN.You can ping all Toronto's machines from Montreal's machines so there is end-to-end connectivity.

Regards.

Alain

[mohit_kakkar]

On both routers Alain, I just have switches connected to three subinterface of fa0 since I am using VLANS. s0/0/0 connects both routers on that serial. So I am only using fa0 and s0/0/0 on both routers. There are no other networks on other interfaces that need to be advertised. SO there are no other networks to advertise on any other interfaces so OSPF cannot advertise them. Hence my point that there is no need to deactivate them.

[cadet alain]

Hi,

ok but if you put a sniffer on one of the machine in any vlan you'll see OSPF hellos and putting these interfaces as passive( the subinterfaces) will prevent these hellos to be sent which is a security feature.Furthermore as it is sent to a multicast address it will be flooded out all ports in this vlan.

Regards.

Alain

[mohit_kakkar]

Got it. One more thing. I only assign IP's to the subinterfaces of fa0 on both routers but not to the interface itself. Will this pose any problem?

[cadet alain]

Hi,

No it won't. you can put one  if you want the physical interface to take care of native vlan ( untagged frames) if it is the vlan 1 otherwise you don't and use a subinterface for untagged traffic by specifying it with dot1q x native command.

Regards.

Alain