What Is Ethernet | Tools You Need | Hardware and Software | NIC Installation | Choose Protocols | Address & TCP/IP

Pick An Address and Set Up TCP/IP

 Next, to use the TCP/IP protocol, you get to pick a numerical address (Internet Protocol or IP address) for your computer. 

1) You need to pick numbers that work.  You should start with either 192.168, 172.16. or 10.  Actually you can pick other numbers to start with, too.  But if you later want to connect your LAN to the Internet you will be in a world of hurt if you pick numbers other than those starting with 192.168.,   10. or 172.16. 

OK, I'm making this super easy.  Name the NIC of your computer that will have a modem to connect to the Internet 10.0.0.1.  Name the NIC on your second network computer 10.0.0.2.  Name your third one 10.0.0.3 and so on.  If you have more than one NIC on the same computer, give each one a different IP address.

2) All NICs on your LAN should have the same first nine numbers.  For now just trust me on this, you'll learn why when you read the upcoming chapter on routers.

3) Want to do this the hard way and not use 10.0.0.1, etc.?  To get numbers that will work, you will need to give each NIC a 12 digit number, for example 192.168.012.006.  (You can throw away the extra zeros and make that 192.168.12.6 if you want.) 

However, within those limits on the numbers you can choose are yet more limits!

In each field of three digits you must pick a number between 0 and 254.  Higher numbers wont work.  That is because computers only understand zeros and ones (binary numbers).  This is because they count using just two different voltages, and they use just eight zeros and/or ones to represent each field in an IP address.  (If you are on  a network where the sysadmin has applied a netmask of other than 255.255.255.0 it gets even more complicated.)

Note for flamers: If you can prove to me that you have built as many digital circuits gate by gate -- or transistor by transistor -- as I did as a young lady, then just MAYBE I just MIGHT listen to you making fun of this explanation of eight bit fields in IP addresses.  I got my sense of humor -- and temper -- from inhaling too much solder fumes.

When this IP address you choose is translated by the operating system into a form your computer understands, each three digit number will be represented as eight zeros and/or ones.  11111111 is the biggest number eight binary bits can represent.  This equals 255 in base ten numbers, which is what us humans use because we have ten fingers.

How do you know you aren't picking the same numbers for your NICs as someone else?  The IP addresses beginning with 10. and 192.168. are reserved for use on private local area networks only.  The router on your Internet Service provider should not let anyone on the outside connect to any computer with numbers beginning with 10 or 192.168.  So it doesn't matter how many people pick the same numbers as you pick, as long as they are in these number ranges.

Wizard tip:  Is someone's router misconfigured?  Try running an IP address scanner such as What's Up (http://www.ipswitch.com/) on 10. and 192.168. addresses on an Internet connection and see what you find.  I've found a few reachable through the Internet.  If you find one, you can do a good deed by letting its sysadmin know about it.