IT Crate Tutorial, Tips, Technology NewsWebsite Design and Development Company

Testing the IP configuration

Before doing anything else, you are advised to check the computer’s IP configuration. Windows systems offer a command-line tool, called ipconfig, that lets you find out your computer’s IP configuration. The output of this command gives the IP configuration for each interface; a computer with two network cards and one wireless adapter has 3 interfaces each with its own configuration.

To view your computer’s IP configuration, simply enter the following command (Start/run):

cmd /k ipconfig /all

The output of such a command looks like this:

Windows IP Configuration
		Host name . . . . . . . . . . : CCM
		Primary DNS suffix . . . . . . :
		Node type . . . . . . . . . . : Broadcast
		IP routing enabled . . . . . . . . : No
		WINS proxy enabled . . . . . . . . : No
Ethernet adapter wireless network connection:
		Connection-specific DNS suffix:
		Description . . . . . . . . . . . : Intel(R) PRO/Wireless LAN
 2100 3A Mini PCI Adapter
		Physical address . . . . . . . . .: 00-0C-F1-54-D5-2C
		DHCP enabled. . . . . . . . . . . : No
		IP address. . . . . . . . . . . . : 192.168.1.3
		Subnet mask . . . . . . : 255.255.255.0
		Default gateway . . . . . . : 192.168.1.1
		DNS servers . . . . . . . . . .  : 193.19.219.210
						   193.19.219.211
Ethernet adapter local area connection:
		Media status . . . . . . . . . : Media disconnected
		Description . . . . . . . . . . . : Broadcom 570x Gigabit Integrated
Controller
		Physical address . . . . . . . . .: 0F-0F-1F-CB-99-87

The above report shows that the computer has two network interfaces, one of which is wireless. The name of the machine on the network is CCM.

The Ethernet interface connected to the local area network (network card) is not active since the cable is disconnected, but the wireless adapter is configured.

Machines on a same network must use a same address range (with different addresses) and a same subnet mask. In the case of a local network, connecting machines that do not have routable IP addresses, so-called private address ranges must be used.

The default gateway refers to, when applicable, the IP address of the machine offering internet access. DNS servers.

The DNS servers must correspond to the organization’s DNS servers; most of the time these are the service provider’s DNS servers.

Testing the connection

To test the proper functioning of a network, there is a highly practical utility provided as a standard feature with most operating systems; this is the ping utility. Ping lets you send a data packet to a network computer and lets you evaluate the response time. The ping command is explained in detail at the following address:

• Network tools – Ping command

To test the network thoroughly, simply open a command-line window, then successively carry out the following steps:

• ping the loopback address (127.0.0.1), representing your computer:

  ping -t 127.0.0.1

• ping the IP addresses of the network’s computers, for example:

  ping -t 192.168.0.3

• ping the computer names, for example:

  ping -t Mickey

• ping the computer used as gateway on the local area network, that is, the computer sharing its internet connection. It usually has the address 192.168.0.1:

  ping -t 192.168.0.1

• ping the service provider’s gateway. The address of the service provider’s gateway can be retrieved using the ipconfig command on the computer being used as gateway on the local area network;
• ping the service provider’s name servers . The address of the service provider’s DNS servers can be retrieved using the ipconfig command on the computer being used as gateway on the local area network;
• ping a machine on the internet network, for example:

  ping -t 193.19.219.210

• ping a domain name, for example:

  ping -t www.commentcamarche.net

If all this works, your network is ready to be used!

COLOR-CODE STANDARDS

Again, please bear with me… Let’s start with simple pin-out diagrams of the two types of UTP Ethernet cables and watch how committees can make a can of worms out of them. Here are the diagrams:

Note that the TX (transmitter) pins are connected to corresponding RX (receiver) pins, plus to plus and minus to minus.  And that  you must use a crossover cable to connect units with identical interfaces.  If you use a straight-through cable, one of the two units must, in effect, perform the cross-over function.

Two wire color-code standards apply: EIA/TIA 568A and EIA/TIA 568B. The codes are commonly depicted with RJ-45 jacks as follows (the view is from the front of the jacks):

If we apply the 568A color code and show all eight wires, our pin-out looks like this:

Note that pins 4, 5, 7, and 8 and the blue and brown pairs are not used in either standard.  Quite contrary to what you may read elsewhere, these pins and wires are not used or required to implement 100BASE-TX duplexing–they are just plain wasted.

However, the actual cables are not physically that simple.  In the diagrams, the orange pair of wires are not adjacent.  The blue pair is upside-down.  The right ends match RJ-45 jacks and the left ends do not.  If, for example, we invert the left side of the 568A “straight”-thru cable to match a 568A jack–put one 180° twist in the entire cable from end-to-end–and twist together and rearrange the appropriate pairs, we get the following can-of-worms:

This further emphasizes, I hope,  the importance of the word “twist” in making network cables which will work.  You cannot use an flat-untwisted telephone cable for a network cable.  Furthermore, you must use a pair of twisted wires to connect a set of transmitter pins to their corresponding receiver pins.  You cannot use a wire from one pair and another wire from a different pair.

Keeping the above principles in mind, we can simplify the diagram for a 568A straight-thru cable by untwisting  the wires, except the 180° twist in the entire cable, and bending the ends upward.  Likewise, if we exchange the green and orange pairs in the 568A diagram we will get a simplified diagram for a 568B straight-thru cable.  If we cross the green and orange pairs in the 568A diagram we will arrive at a simplified diagram for a crossover cable.  All three are shown below.