Multiple Routers in the Company

[ankitohc]

My company uses a single Cisco router at each location. Since routers are used to connect different networks, I'm curious as to why there are many routers at a single location communicating to one another using OSPF.

I apologies for the ridiculous question, but since I am self-studying, I post whatever questions comes in my mind.

I want to know the examples or reason having multiple router at one site

Ankit

[Kasun Bandara]

@ankitohc to answer this, we need to know your architecture. how many locations in your company, are the near by or distant, how you connected locations (MPLS, IPsec, etc) if your all locations in same building, then you can try to re architect your network. 

but need more information.  

[ankitohc]

@Kasun Bandara thank you for the reply. my question is not specific to my company. It is just a general question about multiple routers in the company.

I want to know the examples or reasons for having multiple routers at one site

[ammahend]

As you said "routers are used to connect different networks", a single site can have different network in different segment of site, for e.g. Wireless can have its own set of network, so can LAN, so can data center, so can DMZ etc .. and sometimes you may not accommodate all network into a single router for security reasons or resource reasons or connectivity limitations etc. And in order for some of the network to talk to each other you will need some sort of routing protocol like OSPF, this is not a perfect answer, but I hope it helps.

[Kasun Bandara]

@ankitohc ok. if you means for general use case, most companies uses routers to terminate WAN connections. This can be MPLS, internet, etc. mostly, L3 Switch can do routing also. but in designs that using only for VLAN routing in same location and if you need sperate traffic filtering between VLANS, best place to do that in firewall. 

If your location only in 1 building with few floors, internal traffic routing can do using 3 tire architecture and if you have different geographical locations, routers need to terminate WAN links. check below links to understand differentiates between L3 switch and routers.

https://blog.router-switch.com/2021/07/layer-3-switch-vs-router-can-layer-3-switch-replace-router/

one site may have different WAN links (many internet or inter site connections). To terminate that we can use 1 router, but that is lack of reliability of network. of when we design WAN side, we may include number of Routers to cater the redundancy requirement. if you have multiple routers, need to configure routing protocol to maintain reliable/redundant traffic flow. 

Also latest L3 switches have many features which router can do. so when you design network you can select L3 switch if your expected features are covered by L3 switch. also switches using different traffic handling mechanism than router, so need to be aware on those differences too.

[Joseph W. Doherty]

As you note, routers (or L3 switches) are used to tie together networks.  Assuming all networks can be attached to one router, why not do that?

Basically for 3 reasons.

First, the physical performance limits of a device.

Second, for device redundancy.

Third, to (hopefully) minimize the impact of a "berserk" device.

Aside from the above you often see more routers being used for legacy topology issues or "slavish" adherence to the classical three tier network topology model.

Regarding using OSPF, it's chosen because it's non-propritaty, can handle many networks fairly well, is classless, and is offered by many vendors.  For the prior criteria, basically it's the only choice.