OSPF network type

This morning I was playing around with the Brocade vRouter (Brocade’s vyatta acquisition) and setting up an adjacency with a cisco 3750 L3 switch. The vRouter is a guest OS in my VMware lab server where I have several of these virtual instances. I had configured the ip ospf network point-to-point network type on the SVI interface on the c3750, however somewhere along the lines I decided I would configure all my VM’s management IP’s on the same Ethernet segment (rather than put all devices on their own separate segments) so I removed the point-to-point command from the vRouter but not the switch.

Here is where things started getting weird. The adjacencies came up, both routers were in the FULL state and everything looked fine however the vRouter was not learning any routes from the 3750 (at this point the vRouter was not advertising any routes). I spent some time troubleshooting, first confirming that the switch was correctly learning routes from another physical router on my network. I checked debugs like the ospf packet and events etc but I could not find any errors or any indication that anything was wrong.

After some research I found that using different network types on each device will cause this kind of problem, I checked the vRouter’s config and there was no network type command in place, however on the c3750 I had the ip ospf network point-to-point command configured, once I removed this from the SVI I checked the route table on the vRouter and low and behold it started learning routes.

At first the reason for this did not occur to me and it is the first time I have seen it in practice. I am sure that this would have been something mentioned in the CCNP Cisco press exam guides but it just goes to show that hands on experience is vital to reinforcing concepts. I know that, now that I have seen this and resolved this in on actual gear I am going to be less likely to forget this in the future.

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