Routing – How does a router learn about networks that can be reached from its interfaces

routerrouting

I was studying, and I got stuck in trying to find out the best way to answer this question:

explain how a router learns about networks that can be reached from its
interfaces and how it routes packets. You should assume that the
router has just been connected to the network.

So, am I correct in describing it in a simple way by saying that :

A router learns about networks that can be reached from its interface thanks to the switches, which themselves learn what computers are connected to each port. And once it learns, it uses the network layer to determine the best route to a destination by using IP.

I've been studying with the book Microsoft Networking Essentials, and I can't seem to find a detailed enough answer to this simple question. It is somewhat confusing because of the way the book is structured.

Best Answer

Your answer to the question is incorrect. There are multiple ways routers can learn which interfaces should be used for which network:

  • Routers implicitly know about directly connected networks when the interface is configured with an IP address and mask, either manually, or through DHCP.
  • Routers can be configured with static routes to specific networks, or even with a default route.
  • Routers can exchange route information with other routers through routing protocols.

Regardless of how a router learns a route to a network, it adds the route to its routing table, including the interface to which it should switch the traffic destined for that network.

This is a huge subject, and the details are far too broad to be discussed here in any more detail. You can ask specific questions on a subject to limit the answer(s) to acceptable size(s).

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