IP Routing Basics

The term routing refers to taking 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 of the host is used to deliver the packet from a router to the correct destination host.

A router must have the following information to route the packets:

• Destination address.
• Neighbor router (where it can learn about remote networks).
• Possible routes to all remote networks.
• The best route to each remote network.
• How to maintain and verify routing information.

Routers learn about remote networks from neighboring routers or from administrator defined static routes. The router then builds a table  which is known as routing table or  routing information base (RIB).

 Difference between a Routing Protocol and Routed Protocol

A routing protocol is used by routers to dynamically find all the networks in the network and to ensure that all routers have the same routing table. Basically, a routing
protocol determines the path of a packet through an network. Examples: RIP, EIGRP, and OSPF.
A routed protocol can be used to send user data (packets) through the established enterprise. Routed protocols are assigned to an interface and determine the method of packet delivery. Examples: IP, IPv6, AppleTalk and IPX.

There are three ways for a router to learn the routes:

Static Routing

Static routing is a form of routing that occurs when a router uses a manually-configured routing entry, rather than information from a dynamic routing protocol to forward traffic. Static routes are manually configured by a network administrator by adding in entries into a routing table.

Dynamic Routing

Dynamic routing is a form of routing in which routing protocols operating on the routers are responsible for the creation, maintenance and updating of the routing table. The routes thus learned are dynamic and keeps changing as there is any change in network. Dynamic routing is easy to configure on large networks and is more intuitive at selecting the best route, detecting route changes and discovering remote networks. However, because routers share updates, they consume more bandwidth than in static routing.

Default Routing

In this method the router is configured to send all packets towards a single router.  This is a very useful method of routing for small networks or for stub networks with a single entry and exit point.

Back