Computer Networks

A Computer Network is a set of nodes (computers and devices) interconnected by communication links that are wired or wireless. Nodes may be stationary or mobile. In many cases the network are pre-configured, and the topology (i.e., the layout of the network) may be fixed. In the case of ad-hoc networks, however, networks are formed automatically.

Network Types

Depending on the size and the geographical spread, networks can be classified into Local Area Networks (LAN), Metropolitan Area Networks (MAN) and Wide Area Networks (WAN). LANs are typically small. E.G., a home network or office network. A MAN is larger than LAN, and usually covers a big city or region. WANs are the largest, which normally span across states or even countries. Networks are usually interconnected forming a network of networks, called internet. The largest internet on planet is called Internet. Note that the first letter of Internet is capitalized, and this is the internet that normally people refer to when they say Internet. The set of rules by which computers and devices on a network can communicate each other is called a protocol. Internet Protocol is the protocol followed by computers connected to the Internet.

IP Address and Domain Name

Computers on the Internet are identified by IP addresses. IP address is usually four numbers separated by dots. For example, Numbers are hard to remember. So, there is another way of identification -- by using a domain name. A domain name is a group of words, separated by dots. For example, A domain name is can be translated to IP address and back by using a Domain Name System (DNS).


You can query the DNS using NSLookup utility. When NSLookup is started, default name server will be automatically set, which can be changed using the server directive. You can get the IP address for a domain name, or domain name for an IP address, by simply typing one to get the other. For more information on how to use NSLookup, please follow the appropriate link: (nslookup for for WindowsTM, for Linux®).


You can get basic information about your IP address, gateway, netmask etc. in WindowsTM, by running the utility ipconfig. A netmask is used to help the data packets to confine to an area within your sub-network (for efficiency, security and other reasons). A gateway will forward the data packets need to go out of the subnet to an outside destination. The all option of IPConfig (ipconfig /all) lists more information.


Ping is a tool that can be used to find out the round trip delay for a data packet to start from your computer, reach a destination and be back. It displays statistics such as minimum time, average time, maximum time, and error rate. Available under both WindowsTM and Unix®. Since ping is being misused by many hackers to launch Denial of Service (DoS) attacks, many system administrators disable ping.


Tracert displays the route from a particular computer to a given destination. This is similar to ping except that tracert displays the actual route information, not just the time delays. (In Unix® systems, the command name is traceroute.)

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