Help with OSPF!

suffah

I'm having some trouble getting OSPF going between two routers. Here's the relevant (?) output from running-config:

Router 1:
interface FastEthernet0/0
ip address 172.16.10.1 255.255.255.0
router ospf 100
log-adjacency-changes
network 172.16.10.0 0.0.0.255 area 1

Router 2:
interface FastEthernet0/0
ip address 172.16.20.1 255.255.255.0
router ospf 101
log-adjacency-changes
network 172.16.20.0 0.0.0.255 area 1

I'm at a loss here. show ip ospf neighbors shows nothing, and no routes in show ip route.

I'm sure I'm overlooking something real easy, any ideas?[/b]

nicklauscombs

are they connected between the fast ethernet ports?

suffah

Yes, they are. I actually tested that they could ping each other when on the same network.

nicklauscombs

put the interfaces in the same subnet

gojericho0

if these fast Ethernets are directly connected it will not work because they are in different networks. If they are not directly connected would you be able to post a network diagram?

mike3

Yes they'll have to be in the same subnet if they are directly connected.

aragoen_celtdra

I'm still new at OSPF, but i did create my own lab scenario last night very similar to this one. It worked for me.

The difference, configure a network command to advertise the serial int. Here's what mine looked like:

router ospf 1
log-adjacency-changes
network 10.1.5.2 0.0.0.0 area 0

---

> this is the serial interface on the router
network 172.16.10.10 0.0.0.0 area 0

---

> the Fa interface

The trick is you need to enable OSPF on each interfaces on the router. Hey don't ask me why! Wendell Odom said so.

remyforbes777

gojericho0 wrote:

if these fast Ethernets are directly connected it will not work because they are in different networks. If they are not directly connected would you be able to post a network diagram?

He is exactly right the connection you have between the two ports must reside in the same subnet. You can't have an interface in 10.0.0.1/24 and another 10.0.2.1/24 and have them communicate if they are on a point to point type link. Just because you enabled a routing protocol means nothing. They have to form an adjacency and if you remember reading, one of the criteria for forming that is the interfaces have to be in the same subnet.

suffah

Thanks guys, you hit the nail on the head. Once I put the interfaces the same subnet, my screen was spammed with ospf broadcast messages (I had debug on).

aragoen_celtdra

D'oh! Missed the part about the Fa interfaces being connected to each other. Here, I was thinking they're on their respective LANs.

But glad to see this has been great learning experience for all parties involved!

If you're interested, here's my topology (try to lab it up):

LAN1

---

(fa0/1)R1(s0/1)

---

(s0/1)R2(fa0/1)

---

LAN2.

R1 and R2 are connected on their serial interfaces, and I had a LAN segment on each routers connected through fa0/1 of each routers.

R1 Lan segment: 192.168.10.0/24
R2 LAN segment: 172.16.10.0/24
R1-R2 link: 10.1.5.0/30

With OSPF configured correctly, it's a thing of beauty.

suffah

Thanks Aragoen, I will try that out tonight.

I learned a lot more from my simple mistake than I could have from a sim.

marco71

In order to become neighbours, two OSPF routers have to match area, timers (hello and dead intervals), network type and subnet

netwayne

This is a perfect example of why a forum like like is so valuable. The benefits to both the poster (getting their question answered or getting a tip which spurs deeper thought) and the sharing of knowledge that a responder can impart is really beneficial to many.

Keep up the good work!!