TCP/IP for Beginners - Breaking Down an IP Address

TCP/IP is actually a suite of protocols. TCP or Transmission Control Protocol ensures your data will get to and from its destination. IP or Internet protocol ensures the proper fastest route will be taken. So how do computers communicate?

Computers can only talk with computers that are on the same network. In order to talk with computers outside of their network, computers have to rely on routers. Routers are gateways to other networks. These devices connect dissimilar (not similar) networks.

In order to break down IP, you have to understand the different classes of IP addresses (also known as subnets).

From the first part of this series, the first octet (the octet is the first numbers of an IP address) determines the subnet your computer is on. This determination gives you information about how many computers can be on a network. To break down the first octet, let's look at the chart below.

Class A 1-126

Class B 128-191

Class C 192-223

As you can see from this chart, an IP address of 192.168.0.1 is on a Class C. To find out which network the computer is on, A is the 1st letter of the Alphabet, B is the 2nd and C is the 3rd. Now since the aforesaid number is on a class C (the third letter of the alphabet). The network is the first three octets or 192.168.0. The remaining number is the host. So your breakdown is this:

192.168.0 = Network and 1 = Host This computer is computer 1 on the 192.168.0 network.

Let's look at a few more examples.

IP Address Subnet Network Host

10.0.0.3 A 10 0.0.3 (or basically the 3rd computer on this network)

10.0.1.1 A 10 0.1.1 (or basically the 255th comuter on this network)

• Each Octet (2nd, 3rd and 4th) can go up to 254. Like an odometer after the last octet hits 254, the third octet goes to one and the last octet starts over at 1. Confused? On the class A above, the numbering began at 10.0.0.1 then 10.0.0.2 until it reached 10.0.0.254. The numbering then rolled over and went to 10.0.1.1.

IP Address Subnet Network Host

172.16.0.56 B 172.16 0.56 (or basically the 56th computer in this network)

192.168.1.1 C 192.168.1 .1 (or basically the first computer in this sequence of IP addresses)

So can these two IP addresses talk on the same LAN? 192.168.0.1 and 192.168.1.1

No, not without a router (or gateway) of some sort. IP address one has a network of 192.168.0 and the second one is 192.168.1 . The networks portion of an IP address has to match in order to talk. Because these two are different, they can't talk without a router.

TCP/IP is necessary for the Internet. TCP/IP is more complex than what is shown in these articles. Although other protocols such as http, ftp, udp, smtp, snmp, pop3 and others exsist, it is this understanding and foundation of TCP/IP that is necessary for computers to communicate.