What does an actual router do?

This is mostly curiosity, what does a router actually do, and how is it connected to a network.

I'm not talking about residential internet gateways, which act as a router, DNS, DHCP, and network switch.

I'm talking about honest-to-goodness real routers, they kind you would find in a mid to large business, or a school or something.

Where do they exactly connect to a network, and what do they do in terms of services?

I mean physically - where does it go. In just about every home network (and a number of small business networks) , the gateway will sit at the very front of the network, on one side is the internet, on the other site is the LAN.

Since most high-end routers only have one or two network interfaces, I doubt they act as a gateway, therefore, I doubt they do not sit between the internet and the LAN.

routers break up networks. for example,
1.1.1.0/24----R1----2.2.2.0/24----R2--...


Routers use routing protocols to find or rather converge on networks

for more info see this link:

http://www.cisco.com/en/US/tech/tk365/te...

Routers usually are racked in 8 foot tall racks located in data centers or wiring closets called IDF or BDF or telco room.

Also, routers do sit between a company's Internet connection and their LAN. Networks are designed in a hierarchical fashion. switches will be at the access layer, this is where PC and IP phones would plug into. Upstream from the access layer switches would be the distribution layer and this is where routers come into play. As a PC on the access switches are in vlans or seperate broadcast domains. A LAN is a broadcast domain. Vlans are LANS broken up into smaller LANS and the only way for a PC in one vlan, say vlan 5 to communicate to a PC in another vlan, say vlan 10, the router will have to route between the two vlans. It's the routers job to pass the traffic from one vlan to another vlan.

hope this helps

Most "internet gateways" are routers anymore, not just modems. They do exactly that, DNS (if the first router after the internet connection). Could be a DHCP server. They route traffic. They look at the packets and decide where they should go.

EDIT: They physically go where they are necessary. Lets say a small business has 10 PC's and are in a simple workgroup. Lets just say they have a basic Cable internet modem. It would go cable modem - To a Router (yes, it is a real router) that uses NAT to go from WAN to LAN. Now after that router. It could go to switches, it could go to more routers.

Lets say they wanted two different subnets 192.168.2.X and 3.x, you could put those two routers after the first router and run the respective PC's off of those. A router can go anywhere in a network after the internet connection.

Routers connect two or more different networks together and they block broadcast traffic, which is important.
They make their routing decisions based on the IP address.