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Getting a Public IP Address

Nowadays, it is no longer possible to purchase class IP addresses. Instead ICANN (the Internet Corporation for Assigned Names and Numbers) issues classless addresses. These allow ICANN to issue a specific number of addresses rather than a set range.

CIDR (Classless Internetwork Domain Routing) addressing uses a slash notation where the number after the slash represents the number of bits that ICANN controls.


In a slash 28 network ICANN controls the leftmost 28 bits with 4 bits under the control of the organisation issued to. This would effectively give the organisation 16 IP addresses.

The Future - Internet Protocol Version 6 (IPv6)

IPv6 uses 128 bit addresses rather than the 32 bit addresses used in Ipv4 - this should help solve some of the problems with the current standard including,

  • Limited address space (v6 will support slightly over 4.2 billion address assignments)
  • Lack of security (v4 does not support native encryption)
  • Speed problems (v6 requires less work from routers and hence is faster)
  • Configuration problems (v6 supports more configuration parameters)

Next: Static versus Dynamic Addressing