OSPF question

[anthony.marsh]

From new york router which will be my ABR/ASBR, I have redistributed ospf 200 with a default metric of 10 and from nycore router I've redistributed ospf 1000 default metric 10.

When I show ip route on corertr1 i see the O IA route for 192.168.13.0/28 from router 2, but I see no routes from nycore for 172.20.2.0/24.

On router 2 using the show ip route command displays O IA routes for 172.16.111.0/24, 172.16.112.0/24, 172.16.113.0/24, 172.16.114.0/24 but again no route from nycore for network 172.20.2.0/24.

However on nycore I see all routes advertised for OSPF 1000 in it's routing table.

What am I doing wrong if anything? You answers will be very much appreciated.

[anthony.marsh]

more attachments for the question above!

[Harold Ritter]

Make sure that you use the "subnet" keyword on the redistribute statement when redistributing subnet information (prefix with prefix length longer than natural netmask) into OSPF.

Hope this helps,

[anthony.marsh]

Thanks for your reply.

I've applied the "subnet" keyword to the redistribute statement, but it still hasn't allowed me to receive routes for the 172.20.2.0/24 subnet from NYCore.

Can you possibly elaborate further on what I need to do, as I am still learning OSPF and it's functions.

Thanks

[Harold Ritter]

So your redistribute statement on NYcore looks like this:

redistribute ospf 200 subnets

Can you do a "clear ip ospf redistribution" on Nycore to see if you start getting the routes.

Thanks,

[anthony.marsh]

Hi again,

I've did as you suggested with the "clear ip ospf redistribution" command on Nycore and I can see all the routes being advertised.

However, I cannot see any routes for 172.20.2.0/24 advertised on local routers!

[nycore]------[nyrouter]-----[switch]

|

|

[corertr01]

Again, thanks for your help, in making sense of this query!

[anthony.marsh]

Sorry,

corertr01 is meant to be connected to the switch also!

[Nycore]------[nyrouter]----[switch]----[corertr01]

ABR/ASBR P2P ABR/ASBR LAN Backbone

[Harold Ritter]

Anthony,

Can you explain what you mean by:

However, I cannot see any routes for 172.20.2.0/24 advertised on local routers!

What command did you use to determine that. Where is that route supposed to come from?

Can you do a "sh ip route 172.20.2.0 255.255.255.0" and "sh ip route 172.20.2.0" on NYcore if this is the router where this route is supposed to come from.

Thanks,

[anthony.marsh]

Hi,

On routers corertr01 and newyork i am using the sh ip route command to identify if the network 172.20.2.0/24 is being advertised from Nycore and this is what I get for output:-

corertr01.to>sh ip route 172.20.2.0 255.255.255.0

% Network not in table

newyork>sh ip route 172.20.2.0 255.255.255.0

% Network not in table

NYCore router has a point to point configuration on the fa0/0 interface and the same on the newyork fa0/1 interface for ospf routing between both devices.

Here is the output for NYCore

NYCore>sh ip route 172.20.2.10 255.255.255.0

Routing entry for 172.20.2.0/24

Known via "connected", distance 0, metric 0 (connected, via interface)

Redistributing via ospf 200

Routing Descriptor Blocks:

* directly connected, via Loopback0

Route metric is 0, traffic share count is 1

NYCore>sh ip route 172.20.2.0

Routing entry for 172.20.2.0/24

Known via "connected", distance 0, metric 0 (connected, via interface)

Redistributing via ospf 200

Routing Descriptor Blocks:

* directly connected, via Loopback0

Route metric is 0, traffic share count is 1

[Harold Ritter]

I see what is going on now. This prefix is connected to the loopback interface on NYcore. By default, OSPF will advertise this route as a /32. Do a "sh ip route 172.20.2.10" on newyork and corertr1 and you should see the route.

If you want to change the default OSPF behavior, configure "ip ospf network point-to-point" under the loopback interface on NYcore and you will start to see 172.20.2.0/24 advertised on the corertr1 and newyork.

Hope this helps,

[anthony.marsh]

Hi again,

I've done what you suggested but to no avail!

Can there be an issue with redistributing OSPF 200 area 0 networks into OSPF 1000 area 0 networks. I ask because newyork router connects to NYCore and both OSPF processes advertise them in area 1.

Corertr01 has all interfaces in area 0 (172.19.111.0 - 172.19.114.0/24)

NYCore has 10.0.6.0/28 and 172.20.2.0/24 in it's area 0 network and these two networks aren't being advertised to newyork and corertr01.

Thanks for you help, I really appreciate it.

[Harold Ritter]

Anthony,

I think we are dealing with multiple issues here. I'm looking at router newyork where you redistribute ospf 200 but there is no "router ospf 200" on that box. Could you please attach the config for NYcore as well so we can get a global view.

Thanks,

[Harold Ritter]

Also, can you check that the adjacency between newyork and NYcore is up and running.

On newyork, I see that the interface connected to NYcore is in area 1. Is the interface of NYcore connected to newyork in area 1 as well?

Thanks,

[Harold Ritter · Accepted solution]

I'm reading your reply again and can see that there is some mistakes in your topology. NYcore can't have interfaces in area 0 and area 1 since it is connected to newyork via area 1 and itself has interfaces in area 0 and 1 as well. This breaks area 0 contiguity.

Hope this helps,

[anthony.marsh]

Hi and thanks for your insight into my little dilemma!

I have corrected the area assignments on NYCore by advertising the networks via area 1 and I can now see them on newyork and corertr01.

So to clear up what I was trying to do with the original topology setup, the only way in which I could have two area 0 networks advertising routes to one another is if I used an EGP between NY and say Boston?

Thanks again for your replies as this is helping me to understand what I've not clearly understood from reading the book.