Different Representations of IPv4 Addresses

Localhost can be represented in a lot of different ways.

The last two of these are particularly interesting — IPv4 addresses can be represented as plain numbers!

Decimal/Hexidecimal conversion for IPv4 addresses is relatively simple if you remember that we break IPv4 addresses up into 4 octets, where each octet is 8 binary digits. Thus

127.0.0.1 = (127 × 2²⁴) + (0 × 2¹⁶) + (0 × 2⁸) + (1 × 2⁰)
          = 2130706432 + 0 + 0 + 1
          = 2130706433

Converting to hexadecimal is trivial using the excellent Qalculate tool.

2130706433 to hex = 0x7F000001

Common IP Addresses

169.254.169.254 is often used in to reference configuration data in cloud systems (just AWS?).

The nip.io service can be used to provide a domain name for an arbitrary IP address.