Routing

ROUTING

Routing is the process of moving a packet of data from one network to another network based on the destination IP address.

The Internet uses routing to move data from your computer, across several networks, to reach a final destination, like a website.

Specialized computer devices that perform this routing function are referred to as routers.

Routers use the information contained in a route to make decisions about which network interface to forward a packet through in order to reach the destination address in the packet. Routers maintain a list of routes which is often referred to as a routing table.

Routers look up routes in the routing table to figure out how to move data from one network to another network. Routes are simply the signposts that tell a router which network interface to forward a packet through in order to reach the packet's intended destination.

Types of Routes

Static Routes

Routes can be entered into a router by a person who administrates the network (the network administrator). Since these routes are entered by the administrator, and these routes don't change until the administrator changes them, they are referred to as static routes.

Example:

Cisco devices (and several other routing devices) use the following command to configure a static route:

ip route

Example: ip route 192.168.1.0 255.255.255.0 192.168.1.1

NULL ROUTES

A static route which points to the null 0 interface on a Cisco router is called a null route. Null routes are used to cause packets that have been sent to an unreachable network to be dropped from the network thereby preventing those packets from consuming bandwidth.

DEFAULT ROUTES

A default route is also referred to as the 'route of last resort'. This is the route a router uses when all other routes have been examined and none seem to be the right route to use.

2. Dynamic Routes

If the routes are learned on-the-fly from other routers, it is called a dynamically-learned route, or a...