I am about to design/implement a customer network that has about 200 router neighbors on a flat vlan (all Cisco). Apart from trying to ascertain if OSPF is a better choice over EIGRP, I can't find any sizing documents on CCO about router spec/cpu/memory considerations. I've seen various threads where its stated these have to be taken into account, but not actually how I go about sizing those choices. A few questions I need to resolve:
1) OSPF or EIGRP. I prefer the latter, but appreciate OSPF has some scaling boundary advantages. But can't see how those would help on a flat network. Some of the downstream networks already have EIGRP implemented. If I went for an OSPF area topology, surely I'd have to create a number of vlans to segment various groups of stub sites into areas, I couldn't do that on a flat vlan could I?
2) The vast majority of these sites are stub and have no downstream neighbors and only about 2-3 subnets, hence I could implement EIGRP Stub in those. But they would still have 200 neighbors each. There are 2 "core" sites each that have other networks downstream.
3) How do I size minimum router spec for the stub and core sites? Would 2800/2900/3800/3900 be feasible or am I looking at higher spec routers?
so my guess was correct that your WAN is a VPLS.
Scenario1 puts high pressure on devices.
Scenario1: EIGRP all devices even if remote site routers are stub they see each other in the shared vlan and they build EIGRP neighborship with all the others. traffic between two remotes sites flow directly without going via HQ.
when a remote site losts connection to one of its internal subnets it sends out an EIGRP query on the WAN shared link.
All other devices have to reply within the expected time or a stucked in active SIA will happen. All other remote sites will answer restating they are stub routers and Hub routers can:
answer with a negative answer if appropriatate EIGRP summarization is in place that includes the IP subnet object of the query.
or they can propagate the query to the internals of HQ.
The risk is flapping of EIGRP neighborships on the VPLS WAN when a fault happens.
OSPF: OSPF neighbor stare machine is more complex but the DR and BDR concept helps. Only DR and BDR, the two hub routers with appropriate OSPF priority, have to build full adjacencies to all the remote routers. each remote router will have two adjacencies with DR and BDR and simple neighborship with all the others.
In case of a local subnet failure the remote router sends an updated LSA to all DR addresses 126.96.36.199. DR will resend it to all SPF routers 188.8.131.52.
what is important in the case of OSPF is to distinguish between number of routers in the same area and the number of devices in the same IP subnet.
Having 200 routers in the same area is not a problem nowdays, having 200 routers in the same IP subnet is not the same.
The load for DR and BDR is consistent.
The only advantage of this scenario is direct communication between remote sites, but usually traffic patterns involve remote site to HQ if all servers are in HQ (mail server, file servers, and so on).
here remote site to remote site communication can require to go through the HQ.
But it puts far less pressure on devices.
I would go for scenario2 putting remote devices in a few groups.
Using 802.1Q tags may be just a question of configuration, service provider can answer about this.
It may require configuration only in your side.
A flat network looks like attractive but when it comes to dynamic routing it is not a good thing with high number of devices.
Hope to help