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March 2011The monthly newsletter by Felgall Pty Ltd

My Word

How IP Addresses Work

A lot of people do not seem to know exactly how IP addresses are allocated. There seem to be a lot of people who appear to consider that a specific IP address will belong to a particular person or to a particular web site.

There are in fact two different sorts of IP addresses which are known as IPv4 and IPv6. IPv4 were the original type of IP addresses allocated and there are approximately 4,000,000,000 addresses available using that system. IPv6 is a more recent system that is gradually being introduced as a replacement for IPV4.The IPv6 system will allow every atom in the universe to have its own IP address and so there is no danger that the newer addressing system will ever run out of addresses.

There is one central authority that is responsible for allocating blocks of IP addresses to the various countries. The appropriate authority in that country then allocates those in smaller blocks to ISPs and web hosting providers that are located in that country. It is the ISPs and hosting providers who then allocate the IP addresses to their customers.

The central authority has already allcated all of the available IPv4 addresses to various countries and so once a country runs out of IPv4 addresses. Over the next few years we can therefore expect to see a gradual conversion of sectuions of the internet to use IPv6 addressing.

With the older address system there are already far more devices attached to the internet than there are addresses to go around. That they can all be connected is because some address ranges have been predefined as belonging to private networks and these private networks can be connected to the internet using just the one public address to represent all of the devices on the private network. For this reason everyone employed at a company may be using the same IP address at the same time when accessing the internet. You can't distinguish individual people or even individual computers by the IP address.

ISPs can also swap IP addresses around so that the IP address you use to connect to the internet today is not the same address you used yesterday. They will be related addresses since they will each come from the same block of addresses that the ISP was allocated. There are a couple of reasons that they do this. One reason is that the number of IP addresses that they may have can be less than the number of customers that they have and so the IP addresses that they have get allocated to those who are actually using them at the time and if you stop using the address it gets allocated to someone else and when you next need an address you get allocated one from those currently not in use. Another reason they swap addresses around is to prevent people from using their connection for purposes that the ISP does not intend that it be used for. There are many reasons for not hosting your own web site on your own computer and by swapping your IP address every so often the ISPs discourage you from doing so. That IP addresses get swapped around means that the person using a given IP address today need not be the same person who is using it tomorrow.

With web sites too, a particular site does not necessarily have its own IP address. While the bigger site will likely have their own IP address, smaller sites often use shared hosting and in many instances the many sites using shared hosting that are all sharing the same web server will also be sharing the same IP address. Only where the site needs a security certificate or where the site uses software that requires access that doesn't go via the web server does a site actually need its own IP address and so most of the sites that do not require this will not be paying the extra to get their own IP address. This means that while a given web site will usually be on the same IP address for a long period, it will not necessarily be the only web site using that IP address.

These limitations on what you can tell from an IP address apply to IPv4 addresses due to the limited number of such addresses and that we now have far more devices in use than there are addresses. These reasons don't apply to IPv6 addresses and so the relationship between web sites, computers, and people to their associated IP addresses may be completely different once IPv6 addressing becomes common. Perhaps the allocation of blocks of addresses will go one step further with specific blocks of IP addresses being allocated by hosting providers and ISPs to each of their customers. If that happens then and only then will it be possible to associate a specific IP address with a specific person and then the person will not have just the one IP address available for their personal use but may be allocated a block that includes millions of separate IP addresses.

On Site

I am still pushing ahead with more and more JavaScript example pages for and not making too many changes to This should change before too much longer as I have now got most of the way through creating all of the example pages and the huge changes I made to my own site at the start of the year seem to have had little adverse effect (other than a few minor issues in sending out the last couple of newsletters). This means that I should soon be able to move on to phase two of the major upgrade to my site within the next copuple of months. I should also be able to return to the PHP Security and SQL series soon to add more articles to those sections.

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