We have been having DMVPN issues since we started implementing it. The build was originally set up with EIGRP. We were having alot of problems - missing routes, neighbors going up and down and we thought it might be easier to change all the remote routers and the headends to ospf - just like the rest of the network. We thought that this would simplify our issues and enable us to narrow it down. Come to find out, an upgarde of the headends was needed because of a bug. The DMVPN is not working perfectly but, it is better. My question is this: We are planning on rolling out 250, 881s to remote workers. With OSPF, do think this might become a problem? At this point we are including them in the same area as the rest of our netwok, 0. Might it be better for us to create a new area for these remote workers? Or, maybe go back to EIGRP for the remote workers?
I've used OSPF extensively in my previous job, but never in a DMVPN configuration. In my current job I use DMVPN a lot but only with EIGRP I decided to look around a bit and came across this which would be applicable to you:
As far as Cisco recommends for OSPF, no more than 50 routers per area and no more than 3 areas per router (that would be your ABR in this case). Also the areas would have to be stubby or totally stubby. Not so sure about those router / area limits. What I would do is SNMP graph the cpu / memory utilization of the ABR and watch how it rises the more you put on it. Obviously a 6500 would handle more adjacencies than a 2900 or than a 1900 series router.
Another thing to potentially consider is the encrypted throughput capabilities of your hub router in question assuming you will be encrypting the traffic. Those limits are not published by Cisco and I had to contact my Cisco SE to get that information from him. Unfortunately I won't be back at work for a few days and don't have some of those limits in front of me and Im not even sure where I wrote them down to be honest. If I come across them I can email them to you or something. I believe 881's can do around 8 Mbps of encrypted throughput which is pretty decent for such a small router.
The official documentation says you need to configure all OSPF routers as a broadcast network type and also force the hub to be the only one allowed to become the DR for that broadcast segment.
All those types of issues are avoided in EIGRP and you don't have to worry about them. As an example, if you forget to set the OSPF priority on one of your spokes and your hub fails, that spoke will become the BDR which will cause a lot of problems for you and could be tricky to troubleshoot. For EIGRP, configure all spokes as stubs and advertise a summary route (either a default route or an aggregate of your corporate IP structure) on your hub's dmvpn interface and you're done.
I hope all that makes sense!