Different IP address representations

Localhost can be represented in a lot of different ways.

• localhost
• 127.0.0.1 (IPv4 address)
• [::] or :: (IPv6 address)
• 2130706433 (IPv4 in decimal)
• 0x7f000001 (IPv4 in hexadecimal)

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