Introducing Routing And Packet Forwading

Today's networks have a significant impact on our lives - changing the way we live, work, and play. Computer networks - and in a larger context the Internet - allow people to communicate, collaborate, and interact in ways they never did before. We use the network in a variety of ways, including web applications, IP telephony, video conferencing, interactive gaming, electronic commerce, education, and more.

At the center of the network is the router. Stated simply, a router connects one network to another network. Therefore, the router is responsible for the delivery of packets across different networks. The destination of the IP packet might be a web server in another country or an e-mail server on the local area network. It is the responsibility of the routers to deliver those packets in a timely manner. The effectiveness of internetwork communications depends, to a large degree, on the ability of routers to forward packets in the most efficient way possible.

Routers are now being added to satellites in space. These routers will have the ability to route IP traffic between satellites in space in much the same way that packets are moved on Earth, thereby reducing delays and offering greater networking flexibility.

In addition to packet forwarding, a router provides other services as well. To meet the demands on today's networks, routers are also used to:
Ensure 24x7 (24 hours a day, 7 days a week) availability. To help guarantee network reachability, routers use alternate paths in case the primary path fails.
Provide integrated services of data, video, and voice over wired and wireless networks. Routers use Quality of service (QoS) prioritization of IP packets to ensure that real-time traffic, such as voice, video and critical data are not dropped or delayed.
Mitigate the impact of worms, viruses, and other attacks on the network by permitting or denying the forwarding of packets.

All of these services are built around the router and its primary responsibility of forwarding packets from one network to the next. It is only because of the router's ability to route packets between networks that devices on different networks can communicate. This chapter will introduce you to the router, its role in the networks, its main hardware and software components, and the routing process itself.