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Introduction to cyber security: stay safe online
Introduction to cyber security: stay safe online

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3.2 The internet protocol and IP addresses

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Figure 11

The Internet Protocol (known as IP) does the hard work of actually moving data across the internet. IP is only concerned with moving data, it doesn’t actually check that data actually arrives (that’s handled by TCP).

When IP receives data from TCP to be sent on to the internet it wraps the TCP datagram in its own IP datagram containing a sender’s and a receiver’s address as well as some other information.

When IP receives data from the internet, it removes the IP datagram information and passes it to TCP which will perform the checking of the contents and reordering of information before it can be passed through the appropriate port to an application.

IP addresses

The internet addresses used by humans (such as www.open.edu) are purely for our convenience, as computers use numeric addresses known as ‘Internet Protocol’ addresses (or IP addresses, or sometimes IP numbers) for communication. Every computer directly connected to the internet has a unique Internet Protocol (IP) address.

There are two major forms of IP address: IPv4 and IPv6.

IPv4 (Internet Protocol version 4)

This is the most familiar form of IP address consisting of four numbers, each ranging from 0 to 255, separated by full stops (periods) in the form 192.168.0.1. IPv4 has long underpinned the internet although it is now in urgent need of replacement (see below) because the number of devices connected to the internet has nearly exhausted the total number of available IPv4 addresses.

IPv6 (Internet Protocol version 6)

IPv6 is a a replacement for IPv4, originally outlined in 1998, to accommodate the increasing demand for IP numbers as more people and devices were connected to the internet. It can support a theoretical 3.4×1038 devices meaning it is suitable for any conceivable demand.

IPv6 is intended to replace IPv4; however this is an extremely complex process and it has taken a long time with even the most developed countries still far from completing the transition. A measure of compatibility exists in the form of IPv4-mapped IPv6 addresses where IPv4 addresses are stored in the IPv6 format.

Reserved IP numbers

Not all of the numbers in the IPv4 address range are actually available for use. As well as large blocks reserved for specific users in the early days of the internet, some are specifically used for ‘private’ networks outside of the internet.

  • 10.0.0.0 to 10.255.255.255
  • 169.254.0.0 to 169.254.255.255
  • 172.16.0.0 to 172.31.255.255
  • 192.168.0.0 to 192.168.255.255

Your computer will allocate itself an IP address beginning 169.254… if it is unable to connect to a local network. If you have a connection to the internet from your home your computer will almost certainly have an address beginning 192.168… In this case your network hub has a genuine IP address, your computer and other devices attached to the modem have private addresses. Your modem alters IP addresses on packets as they are sent to and from your home network and the internet.