Routing

Once you create an internetwork by connecting your WANs and LANs to a router, you’ll need to configure logical network addresses, such as IP addresses, to all hosts on the internetwork so that they can communicate across that internetwork.

   The term routing is used when you take a packet from one device and sending it through the network to another device on a different network. Routers don’t really care about hosts – they only care about networks and the best path to each network. The logical network address of the destination host is used to get packets to a network through a routed network, and then the hardware address (MAC address) of the host is used to deliver the packet from a router to the correct destination host.

  If your network has no routers, then it should be apparent that you are not routing. Routers route traffic to all networks in your internetwork. To be able to route packets, a router must know, at least, the following:

·         Destination address

·         Neighbor routers from which it can learn about remote networks

·         Possible routes to all remote network

·         The best route to each remote network

·         How to maintain and verify routing information.

The router learns about remote networks from neighbor routers or from an administrator. The router then builds a routing table (a map of the internetwork) that describes how to find the remote networks. If a network is directly connected, then the router already knows how to get to it.

    If a network isn’t directly connected to the router, the router must use one of two ways to learn how to get to the remote network: static routing, meaning someone must hand-type all network location into the routing table, or something called dynamic routing.