OSPF on 40 routers

[azi123]

Hi guys,

Do you run OSFP on 40 routers which are connected to each other in a ring topology? Is there any better solution?

And if OSPF is ok, how can I configure these routers for faster convergence? Do I need to define more than one area? (Multiple areas make convergence faster? ). Do I need to define virtual links?

Best, Amir

[Deepak Kumar · Accepted solution]

Hi,

As this is very little information for designing a network or routing protocol. 

It will work fine but it again depends on the router hardware. If all routers are a higher model then it is ok. As higher models are costly so I am not sure which router has chosen. If those are SMB routers then you must go with areas.

OSPF having some rules as All areas must be connected to the area 0 (Backbone Area) and Virtual Link will not work on the stub areas. We need to consider all the things in the design. 

For fast conversation, you can enable fast reroute mechanisms on the OSPF.  

[Joseph W. Doherty]

I cannot say whether another routing protocol would be better, but for 40 routers, a single OSPF area would likely be just fine.

The OSPF iSPF feature might be of benefit. The dampening feature would be useful to avoid link flaps (which are bad for OSPF, although Cisco's implementation has features to deal with them).

To speed convergence, you probably want to tune hello timers and other timers (Cisco, I recall has a whitepaper on that [for EIGRP too]).

You may be able to configure for sub second convergence.

[Richard Burts]

I agree with Deepak that we do not have much information. But believe that what we know may be sufficient to ask the simple question given in the original post. And I agree with Joseph that 40 routers is not a large number of routers to run OSPF. It seems to me that the most significant aspect of the original question is that all 40 routers are in a ring. For 40 routers each connected to 2 neighbors in a ring topology running OSPF it pretty much means that all routers need to be in the same area. As a technical point it could be any area not necessarily area 0 if all routers are in the same area. But for simplicity I would suggest that it should be area 0.

The ring topology means that for any router to communicate with a router on the opposite side of the ring it must send its message many hops. I would suggest a different topology. Perhaps a topology such as an Ethernet segment as the backbone with 5 routers connected to it. That backbone Ethernet could be the OSPF area 0 backbone. Each of the 5 backbone routers could be connected (probably by Ethernet but some other media is possible) to 7 other routers. Thus all 40 routers are accommodated but each router is probably a maximum of 3 hops away from any other router. Also this topology would allow each backbone router to configure a separate OSPF area for its 7 connected non-backbone routers. With multiple areas you can use some of the techniques that help OSPF to scale to be more efficient.

HTH

Rick