Different IPv4 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)
• 017700000001 (IPv4 in octal)
• 0x7f000001 (IPv4 in hexadecimal)

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

Tip

Many parsing libraries will also accept mixed formats, such as 0x7f.1 (first octet in hexadecimal, remaining octets as decimal), though this behavior is less standardized.

Decimal/Hexadecimal 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

Converting to hexadecimal is trivial using the excellent Qalculate! tool.

2130706433 to hex = 0x7F000001

Common addresses

localhost

localhost → 127.0.0.1 → 0x7f000001 → 2130706433

Server metadata

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

169.254.169.254 → 0xa9fea9fe → 2852039166