Saturday, December 30, 2006

Intranet Routers II

Today, we see the way a router handles traffic. This is applicable to both, Intranet and the Internet.

Packets are sent to a router's input port faster than it can process them. When this happens, the packets are sent to a special holding area called an input queue, an area of RAM on the router. That specific input queue is associated with a specific input port. A router can have more than one input queue, if several input ports are being sent packets faster than the router can process them. Each input port will process packets from the queue in the order in which they were received.

If the traffic through the router is very heavy, the number of packets in the queue can be greater than the capacity of the queue. (The capacity of the queue is called the queue's length.) When this happens, there is a possibility that packets may be dropped and so will not be processed by the router, and won't be sent to their destination. This doesn't mean, though, that the information has be to lost. The TCP protocol was designed to take into account that packets can be lost en route to their final destination. If not all the packets are sent to the receiving end, TCP at the receiving computer recognizes that and asks that the missing packets be re-sent. It will keep requesting that the packets be re-sent until they are all received. Sophisticated routers can be managed and problems diagnosed and resolved using special software. TCP can tell what actions to take because there are various flags in the packet, like the hop count in IP, that tell TCP what it needs to know to act.

A wide variety of routing hardware and software is available. In some cases, a variety of different kinds of routing software can be run on a given piece of hardware. For example, Novell's Multi Protocol Router is routing software that runs on router hardware. In other instances-and particularly when routers are high-performance routers-the routing software is built directly into a router's hardware or firmware.

There are several kinds of tables used in routing. In the simplest kind of intranet, an exceedingly simple routing table can be used, called a minimal routing table. When an intranet is composed of a single TCP/IP network, and when that network is not connected to any other TCP/IP network or to the Internet, minimal routing can be used. In minimal routing, a program called ifconfig automatically creates the table, which contains only a few basic entries. Since there are very few places that data can be sent, only a minimal number of routes need to be configured.

Next article will deal with types of routing table allocation. Don't miss it.