Intra- and Interdomain Routing 

Today, an internet can be so large that one routing protocol cannot handle the task of updating the routing tables of all routers. For this reason, an internet is divided into autonomous systems. An autonomous system (AS) is a group of networks and routers under the authority of a single administration. Routing inside an autonomous system is referred to as intradomain routing. Routing between autonomous systems is referred to as interdomain routing. Each autonomous system can choose one or more intra domain routing protocols to handle routing inside the autonomous system. However, only one interdomain routing protocol handles routing between autonomous systems.

 Several intradomain and interdomain routing protocols are in use. In this section, we cover only the most popular ones. We discuss two intradomain routing protocols: distance vector and link state. We also introduce one interdomain routing protocol: path vector. Routing Information Protocol (RIP) is an implementation of the distance vector protocol. Open Shortest Path First (OSPF) is an implementation of the link state proto col. Border Gateway Protocol (BGP) is an implementation of the path vector protocol.



Distance Vector Routing -

In distance vector routing, the least-cost route between any two nodes is the route with minimum distance. In this protocol, as the name implies, each node maintains a vector (table) of minimum distances to every node. The table at each node also guides the packets to the desired node by showing the next stop in the route (next-hop routing). We can think of nodes as the cities in an area and the lines as the roads connecting them. A table can show a tourist the minimum distance between cities.




 Initialization 

 The tables in Figure 22.14 are stable; each node knows how to reach any other node and the cost. At the beginning, however, this is not the case. Each node can know only the distance between itself and its immediate neighbors, those directly connected to it. So for the moment, we assume that each node can send a message to the immediate neighbors and find the distance between itself and these neighbors. Figure 22.15 shows the initial tables for each node. The distance for any entry that is not a neighbor is marked as infinite (unreachable).



 Sharing

Updating
RIP Routing Information Protocol

The Routing Information Protocol (RIP) is an intradomain routing protocol used inside an autonomous system. It is a very simple protocol based on distance vector routing. RIP implements distance vector routing directly with some considerations: 
1. In an autonomous system, we are dealing with routers and networks (links). The routers have routing tables; networks do not. 
2. The destination in a routing table is a network, which means the first column defines a network address. 
3. The metric used by RIP is very simple; the distance is defined as the number of links (networks) to reach the destination. For this reason, the metric in RIP is called a hop count. 
4. Infinity is defined as 16, which means that any route in an autonomous system using RIP cannot have more than 15 hops. 
5. The next-node column defines the address of the router to which the packet is to be sent to reach its destination.

Comments

Post a Comment

Popular posts from this blog

Image
  OSI ·          OSI stands for Open Systems Interconnection ·          Created by International Standards Organization (ISO) ·          Was created as a framework and reference model to explain how different networking technologies work together and interact ·           Each layer has specific functions it is responsible for ·          All layers work together in the correct order to move data around a network  Physical Layer  The physical layer coordinates the functions required to carry a bit stream over a physical medium. It deals with the mechanical and electrical specifications of the interface and transmission medium. It also defines the procedures and functions that physical devices and interfaces have to perform for transmission to Occur.  The physical layer is al...
Read more

Data communications system components

Image
  A data communications system has five components 1      Message . The message is the information (data) to be communicated. Popular forms of information include text, numbers, pictures, audio, and video. 2      Sender . The sender is the device that sends the data message. It can be a computer, workstation, telephone handset, video camera, and so on. 3      Receiver . The receiver is the device that receives the message. It can be a computer, workstation, telephone handset, television, and so on. 4          Transmission medium . The transmission medium is the physical path by which a message travels from sender to receiver. Some examples of transmission media include twisted-pair wire, coaxial cable, fiber-optic cable, and radio waves. 5        Protocol . A protocol is a set of rules that govern data communications. It represents an agreement betw...
Read more

Introduction

  NETWORK- A network is a set of devices (often referred to as nodes) connected by communication links. A node can be a computer, printer, or any other device capable of sending and/or receiving data generated by other nodes on the network.   Computer network mean a collection of autonomous computers interconnected by a single technology. Two computers are said to be interconnected if they are able to exchange information.   The connection need not be via a copper wire; fiber optics, microwaves, infrared, and communication satellites can also be used. USES OF COMPUTER NETWORKS Business Applications   1.       To distribute information throughout the company ( resource sharing ). sharing physical resources such as printers, and tape backup systems, is sharing information 2.       Client-server model . It is widely used and forms the basis of much network usage.   3.       C...
Read more