KALOMBO NYEMBWE SERGE

L20192E060111

 

ROUTE PROTOCOL

• Classifying Routing Protocols

Routing protocols can be classified into different groups according to their characteristics. Specifically, routing protocols can be classified by their:

• Purpose: Interior Gateway Protocol (IGP) or Exterior Gateway Protocol (EGP)


• Operation: Distance vector protocol, link-state protocol, or path-vector protocol


• Behavior: Classful (legacy) or classless protocol

For example, IPv4 routing protocols are classified as follows:

• RIPv1 (legacy): IGP, distance vector, classful protocol


• IGRP (legacy): IGP, distance vector, classful protocol developed by Cisco (deprecated from 12.2 IOS and later)


• RIPv2: IGP, distance vector, classless protocol


• EIGRP: IGP, distance vector, classless protocol developed by Cisco


• OSPF: IGP, link-state, classless protocol


• IS-IS: IGP, link-state, classless protocol


• BGP: EGP, path-vector, classless protocol

The classful routing protocols, RIPv1 and IGRP, are legacy protocols and are only used in older networks. These routing protocols have evolved into the classless routing protocols, RIPv2 and EIGRP, respectively. Link-state routing protocols are classless by nature.

IGP and EGP Routing Protocols (3.1.4.2)

An autonomous system (AS) is a collection of routers under a common administration such as a company or an organization. An AS is also known as a routing domain. Typical examples of an AS are a company’s internal network and an ISP’s network.

The Internet is based on the AS concept; therefore, two types of routing protocols are required:

• Interior Gateway Protocols (IGP): Used for routing within an AS. It is also referred to as intra-AS routing. Companies, organizations, and even service providers use an IGP on their internal networks. IGPs include RIP, EIGRP, OSPF, and IS-IS.


• Exterior Gateway Protocols (EGP): Used for routing between autonomous systems. It is also referred to as inter-AS routing. Service providers and large companies may interconnect using an EGP. The Border Gateway Protocol (BGP) is the only currently viable EGP and is the official routing protocol used by the Internet.

• Distance Vector Routing Protocols

Distance vector means that routes are advertised by providing two characteristics:

• Distance: Identifies how far it is to the destination network and is based on a metric such as the hop count, cost, bandwidth, delay, and more


• Vector: Specifies the direction of the next-hop router or exit interface to reach the destination

A router using a distance vector routing protocol does not have the knowledge of the entire path to a destination network. Distance vector protocols use routers as sign posts along the path to the final destination. The only information a router knows about a remote network is the distance or metric to reach that network and which path or interface to use to get there. Distance vector routing protocols do not have an actual map of the network topology.

There are four distance vector IPv4 IGPs:

• RIPv1: First generation legacy protocol


• RIPv2: Simple distance vector routing protocol


• IGRP: First generation Cisco proprietary protocol (obsolete and replaced by EIGRP)


• EIGRP: Advanced version of distance vector routing

• Link-State Routing Protocols

In contrast to distance vector routing protocol operation, a router configured with a link-state routing protocol can create a complete view or topology of the network by gathering information from all of the other routers.

To continue our analogy of sign posts, using a link-state routing protocol is like having a complete map of the network topology. The sign posts along the way from source to destination are not necessary, because all link-state routers are using an identical map of the network. A link-state router uses the link-state information to create a topology map and to select the best path to all destination networks in the topology.