Routers

[gurwinkle]

If I have 50 routers in the Core Layer,Distribution Layer and Access Layers. They all are running their summary addresses. The virtual links are avoided.The branches are connected with the two distribution routers.

What can be the arrangement or how routers can be placed in the Core Layer?

The maximum routers can be 4 or 8?

What can be the arrangement?

Could I ask this question? Please delete if you did not like the question.

I will appreciate your answer.

[Joseph W. Doherty]

Could you further describe the actual devices being used, the current topology and the IGP being used.

As to maximum number of core routers, no fixed maximum although more than two probably leans toward being unusual.

[Richard Burts]

I agree with Joseph that if we knew more about the environment we would be able to give better advice. The OP indicates that there are branches. How are the branches connected to the main site? Are they on dedicated private links? Are they on some type of provider link? And if on a provider link, is the provider doing the routing over those links or are you?

You tell us "They all are running their summary addresses" which implies some sort of routing protocol. Can you tell us more about this?

[gurwinkle]

OSPF is implemented. 50 Routers will not connect many branches at the Access Layer. I am looking for the composition of the routers in the Core Layer. The correct term is aggregation for the OSPF. The ABRs will connect the branches. You can connect the branches with IPSec. I have not considered DMVPN. IP Prefix List must be used by the service provider. Routing can be done on the private link. SD-WAN can be used also. 

[Joseph W. Doherty]

Unfortunately, your latest reply helps, at least for me, little in understanding your situation or what you're trying to solve as an issue.  In fact, that reply, again, at least for me, creates many more questions.  For example, you seem you may have an overly complex OSPF design for a 50 router network.  It's unclear, what is currently running vs. possibly technology changes, such as your mention of SD-WAN.

In general, a core is often two physical devices to provide full device redundancy.  However, as physical network devices can have pretty good redundancy features, sometimes there's only one core device.  As I mentioned in an earlier reply, it's rather unusual to need four or eight core devices, unless, perhaps, we're discussing a spine/leaf architecture, and the spine is your core.