Gerald Combs wrote:

What happens when you run

ping 0x7f.1

and why?

I came in late and only guessed part of it myself. Here's the short summary of what's going on for those who didn't bother to follow the link...

You ping 127.0.0.1.

ping uses inet_aton from the standard c library to convert the string 0x7f.1 into a 32 bit integer value.

The string is assumed to be a series of numbers separated by .'s.

A number prefixed with 0x is assumed to be hexidecimal. Likewise, were it to be prefixed with only a 0 it would be assumed to be octal. This is standard practice for ascii to number conversions.

Each number is assumed to be an 8 bit value. However, the rightmost number in the series is as big as the remaining number of bits to be populated in the 32 bit value.

So...

127.1 = 01111111 000000000000000000000001 127.0.1 = 01111111 00000000 0000000000000001 127.0.0.1 = 01111111 00000000 00000000 00000000

I wonder how it works out under IPv6?

Garrett