IPv4 Addresses

The IPv4 addressing scheme is the “original” IP numbering method employed in the public Internet (and still in use today), which is the scheme most people are passingly familiar with. If someone asks you for the IP address of your desktop computer, server or other device, they invariable are asking for the IPv4 address.

IPv4 uses a string of four numbers, each ranging from 0 to 255, joined by dots, i.e. The chart below shows a typical range of IPv4 subnet sizes – a “class C” is another name for a /24, which contains 256 unique addresses. Note that ‘hosts’ indicates how many of the IPs in the range would be usable by you once the reserved addresses (mentioned in previous topic) are taken away. This count includes the gateway address, which is technically assigned to you, but cannot be used as a host in its gateway role – so subtract one from hosts to get the true minimum number of usable addresses:

 NET Addresses Hosts Netmask Amount of a Class C
/30 4 2 1/64
/29 8 6 1/32
/28 16 14 1/16
/27 32 30 1/8
/26 64 62 1/4
/25 128 126 1/2
/24 256 254 1
/23 512 510 2
/22 1024 1022 4
/21 2048 2046 8
/20 4096 4094 16
/19 8192 8190 32
/18 16384 16382 64
/17 32768 32766 128
/16 65536 65534 256

This system allows a maximum of 4,294,967,296 possible unique addresses – and 20+ years ago it was generally believed that the world would never need anywhere near that many IP addresses.

Fast-forward to today – as of mid-summer of 2015, ARIN (a governing body tasked with handing out IP addresses to carriers, ISPs and large end-users) has less than 50,000 IPv4 addresses left, and has entered the 4th and final phase of their IPv4 depletion countdown plan. Clearly the hunger for IP address space far exceeded the expectations of those early pioneers.

What does this mean to the prospective colocation client? IPv4 is still the de facto standard addressing scheme on the Internet, and will be used and supported for years to come, but IPv6 – the successor scheme which we will discuss next – will need to be an active part of your colocation strategy. Be prepared to support and implement IPv6 in your colocation setup. Furthermore, don’t expect your provider to be particularly generous with IPv4 space. You may find that they offer you a very minimal amount of v4 space, with any additional space requiring written justification and an additional monthly fee.

Finally, if you are considering a provider who is (still!) not running a production v6 network, move on. They are not worth your time.