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IP addresses

Since the Internet is just one massive network, each connection on the Internet also needs a unique address. This is an Internet Protocol (IP) address. IP addresses consist of 4 'octets' of numbers e.g. 10.77.91.19 or 209.112.113.56 where each number between the dots can be from 0 to 255.

Long binary numbers are very hard to remember and not practical for a human interface (imagine 32 bit phone numbers with only the digits 0 and 1 on the handset. Ouch!). Computer words were broken down into 8 bit bytes (and sometimes 4 bit nibbles!) and these were represented as hexadecimal pairs. Numeral characters 0-9 were used, plus the alphabetic characters A-F, to represent the full 16 numeric characters required to cover 4 bits, so that the full 8 bits can be shown as pairs of hexadecimal. However if you are feeling uncomfortable with this leap into numerical systems, so too were many others and the decimal representation of the 8 bit bytes, from 0 - 255 decimal, became popular. Unlike a hexadecimal system in which numeric characters can be placed beside each other and not lose their value, decimals could not. Consequently the full stop was needed to split the decimal numbers into their 8 bit sections. These became known as the quad-dot format. For example -

Notice how the . is needed to identify which sequences of the decimal characters belong to which numbers; after all, 21623910344 in decimals could mean anything depending how it was broken up.

Network experts also reasoned that if a mask (see Subnet Masks) was provided to identify the network component of the address (which all local segment computers would recognise) then the identification of the rest of the address, which indicated the machine in that segment would be easy to identify as well. This could then be used to identify traffic that needed to be routed out of the local segment or kept local. Now if the NIC electronics is working back from the decimal versions of the IP address to the binary and applying some logic to the mask and the numbers, the network address and host address will be shown. The network component can be found between the address bits and the mask bits.

Dynamic IP addresses are granted just for the duration of a connection to the Internet ( or as determined by the server). Typically, an Internet Service Provider has reserved a big enough pool of IP addresses to allocate one address to each of their modems. When users dial up the ISP, they are each assigned an IP address for the duration of their calls. This means that every time you connect to the Internet by dialup modem, you will probably get a different IP address.

Other devices, such as web servers and cable modems, are connected to the Internet permanently. These devices are allocated a static IP address, which usually does not change. Because hackers can easily target computers with permanent IP addresses, it is important that cable modem users install a firewall.

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