Two Methods to Conserve IP Addresses
The Internet Protocol, or "IP," system is a way of negotiating traffic on the Internet by linking every web server and computer with a unique identifying address, or "IP address." Because the number of IP addresses is subject to certain rules, it's a limited resource, and several steps have been taken to prevent the exhaustion of addresses -- two of these focus on conserving existing addresses, and one involves increasing the available number of IP addresses to allocate.
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IP Version 4
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The fourth version of the Internet Protocol system has been in place for as long as most people have been using the Internet. Each domain name ("www.example.com") resolves to a unique IP address, and when you connect to another computer by browsing to a website, your computer's IP address is connected to the IP of that website. An IP v4 address consists of a string of four numbers, each between 0 and 255 (for example, "192.168.0.255"), so in principle there are 256*256*256*256, or about 4.3 billion IP v4 addresses. In practice, many of these addresses are "reserved," so there are many fewer available -- but even if all 4 billion were accessible, the rising number of websites, computers and Internet-enabled phones puts a heavy strain on the supply of addresses.
Dynamic Host Configuration Protocol
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One way to conserve IP addresses is at the side of your Internet Service Provider, or ISP. To connect you to the Internet, your computer must have an IP address (so the Internet knows where to send you traffic). If you have a "static IP," this address never changes. Many ISPs, however, use something called "Dynamic Host Configuration Protocol," or "DHCP." In this case, when you want to connect to the ISP, your computer requests an IP address and it is assigned from a pool the ISP owns. Because not everyone is using the Internet at every second, this allows the ISP to use fewer IP addresses -- they can reuse addresses that aren't currently active.
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Network Address Translation
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If you have multiple computers connected to a home network, the IP system says that each of them should have a unique IP address. And, in fact, they do -- but it's not one that the Internet as a whole knows about. Most home routers employ something called "Network Address Translation," or "NAT," so that the router has the IP address assigned by the ISP, and each individual computer on the network has an IP address that's internal to your home, selected from a pool of reserved numbers generally between 192.168.0.0 and 192.168.255.255. When traffic reaches your router, it uses NAT to send the traffic to the right computer, but because the numbers are internal, many different people can use the same "192.168.x.x" number, so long as they're not on the same internal network.
IP Version 6
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Conserving IP addresses is only a short-term solution, however. Because more and more people are using the Internet, there simply aren't enough IP addresses available under the current system. In the future, IP version 4 will be replaced by IP version 6, which has many more numbers available -- an IP version 6 address has 128 bits. There are so many possible IP version 6 addresses that it would be possible, via math done based on Jefferson Lab conclusions, to assign one to every atom in every human being on the planet -- making it much less likely that they'll have to be conserved.
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