Chapter 1: Introduction to Networking

The Ipconfig Command

These notes guide you through the understanding of the ipconfig command .

Introduction
The ipconfig Command
The ipconfig /all Command
Summary

Introduction

The ipconfig command is used for displaying the TCP/IP network configuration values of an adapter. Adapters can represent physical interfaces, such as installed network cards, or other interfaces, such as dial-up connections. Settings such as the computers IP address, subnet mask, and default gateway for all network adapters can be viewed.

The ipconfig command is useful on computers that are configured manually. It is even more useful on computers configured to obtain their settings automatically.

The ipconfig Command

The ipconfig command must be run at the Command Prompt. The command prompt should be found in the Windows menu - usually in All Programs > Accessories.

To view the configuration of a network adapter at the command prompt, all you need to do is type in ipconfig. This displays the IP address of the host, the subnet mask and the default gateway.

The IP address of the host is extremely important. Without an IP address the host would not be able to connect to other hosts on the network or connect to the Internet.

As shown in the picture above, my computer's IP address is 10.0.0.14. Other computer's on my home network also have IP addresses, but each computers IP address is unique. Two computers on the same network cannot have the same IP address. This would be comparable to two houses on the same street having the same house number.

A computer must also have a subnet mask. Using the comparison that an IP addresses is like a house number, then a subnet mask would be like a street name. All computers on the same network segment must have the same subnet mask. In other words, they must have different IP addresses but the same subnet mask. My computer's subnet mask is 255.0.0.0

For a computer to be able to connect to the Internet, it must know the IP address of the default gateway. The default gateway is usually a device called a router. The router is the way out onto the Internet. You can imagine the gateway as being positioned in between all PCs on a network segment and the Internet. The IP address of the gateway on this network is 10.0.0.2

The ipconfig /all Command

If I wish for more in-depth information about the configuration of a network card I can use the command ipconfig /all.

The ipconfig /all command gives a lot more information about the network adapter settings, although the IP address, subnet mask and default gateway are still shown. Other useful settings are discussed below:-
 

Host Name

The computers name (host name) is displayed by ipconfig /all..

Host Name ...: by_i004_01

All computers must have a name. A name identifies your computer on the network. To participate in the network, each computer must have a unique name. If two computers have the same name it creates a conflict and communication between computers becomes difficult.
 

Adapter - Network Card

Information about the adapter is also displayed. The network adapter card in this example has a Realtek chipset.

Description ...: Realtek RTL8139 Family PCI Fast Ethernet

The Fast Ethernet part means it can transfer data at a rate of 100 Mbps.
 

Physical Address

Another important piece of information is the physical address. The physical address of a network card is different to its IP address. The physical address is also known as the MAC address. This is an address that is burned into the network card by the manufacturer. Every network card has a unique MAC address.

Physical Address ...: 00-40-F4-2C-4C-9C

The example shows that a MAC address is a series of 6 pairs of HEX numbers.
 

DHCP

Another setting is the DHCP setting. DHCP stands for dynamic host configuration protocol and the job of a DHCP server is to tell the computer the network settings it should have.

If DHCP is enabled, this means that the computers settings have been configured dynamically by the DHCP server. This network does have a DHCP server, so DHCP is shown as enabled.

Dhcp Enabled ....: Yes

A DHCP server assigns an IP address and subnet mask to a computer and tells it the address of the gateway. If a network does not have a DHCP server then the network settings have to be configured manually.
 

DNS

Another important server is the DNS server. DNS stands for Domain Name Server. This server is responsible for finding an IP address given a name. On this network, the DNS server's address is...

DNS Servers ....: 10.0.0.2

To explain the function of a DNS server, consider what happens when you fetch a web page from the Internet. Suppose I wanted to display Google in my web browser I would type in www.google.com. However, to go and fetch the Google page, what the browser really needs is the IP address of Google. The DNS server carries out the function of finding Google's IP address and telling the browser. Once it has the address it can fetch the web page from that address.

Of course, we do not notice any of this happening.

It is convenient for us to use domain names and web URL's like www.google.com because we can remember them, whereas we find it much more difficult to remember IP addresses. However, a web browser cannot find any web page using a web URL. For a computer to contact any other computer on the Internet it needs an IP address.

If I wanted to, I could also ask a DNS server to find an IP address for me given a name.

All I have to do is use the nslookup command at the Command Prompt. The instruction nslookup www.google.com asks the DNS server for Google's IP address.

You can see from the figure below that the DNS server find two IP addresses for Google.

I could just as well use Googles IP address in a web browser instead of the URL.

Using the IP address of a web page is actually faster than using the URL because the browser does not have to ask the DNS server to find an IP address for it.

Summary

A wealth of information about the configuration of a network card can be obtained from the ipconfig /all command .

After configuring a network card manually, or setting it up to be configured by a DHCP server instead, it is a good idea to check the settings using ipconfig. Moreover, ipconfig is one of the first step in troubleshooting a network connection when a problems occurs.