Route Protocol

 

A routing protocol specifies how routers communicate with each other, distributing information that enables them to select routes between any two nodes on a computer network. A routing protocol can be analyzed as a process. A protocol is formalized through the Request for Comments (RFC) process. This process involves open written commentary on a proposed technology in an effort to bring about standardization of that technology.

Although there are many types of routing protocols, three major classes are in widespread use on IP networks:

• Interior gateway protocols type 1, link-state routing protocols, such as OSPF and IS-IS


• Interior gateway protocols type 2, distance-vector routing protocols, such as Routing Information Protocol, RIPv2, IGRP.


• Exterior gateway protocols are routing protocols used on the Internet for exchanging routing information between Autonomous Systems, such as Border Gateway Protocol (BGP), Path Vector Routing Protocol. Exterior gateway protocols should not be confused with Exterior Gateway Protocol (EGP), an obsolete routing protocol.

The basic reason you are studying this topic is to understand how, through the use of OSPF, you can get packets from one host to another over a network. This process can be summarized, from a router's perspective, as consisting of two steps, forwarding and routing:

Forwarding-Refers to the process of a router receiving a packet on an interface and then knowing which interface to retransmit that packet out of so that the packet can continue to its destination. However, forwarding is entirely dependent on the router knowing where to send the packet; if it does not know this, it just discards the packet.

Routing-For the router to know in which direction to forward packets, it requires a route or road map that illustrates the path from source to destination. This route can be generated by either a static or dynamic configuration; at this point, you need to be concerned with only the dynamic aspect of routing. OSPF is a dynamic routing protocol, and when a router is running OSPF, it dynamically develops routes to all destinations within a network. You can view these routes when you view a router's routing table.

A routed protocol such as IP is used as the method of communication between devices on a network. Using a selected routing protocol, such as OSPF, which is supported by the routed protocol, such as IP, you can build the network so that every device can communicate. For example, as previously mentioned, IP is a routed protocol that can use either OSPF or RIP as its routing protocol.

 

In summary, a dynamic routing protocol is a set of standardized rules that allow routers to determine routes. The routing protocol builds routing tables that tell the router the optimal path to a destination. Routing protocols compare numeric values known as metrics to determine the optimal route (sometimes referred to as path). Metrics are numeric values that represent route path characteristics. Metrics can be thought of as costs; therefore, the numeric value is explained as the cost of transiting a link. This information is then stored in the routing table to be used by the router when determining the best route to a destination network.