Facebook’s Custom IPv6 Range

I noticed an interesting thing with a certain visitor after posting a blog post to Facebook.

The IP address that the Facebook crawler uses to visit the site on callback to get meta-data has a custom IPv6 sub-range.

IPv6: 2a03:2880:ff:1a::face:b00c
Host: fwdproxy-prn-026.fbsv.net

Notice 2a03:2880:ff:1a::<strong>face:b00c</strong>

How this is done

The IPv4 addresses could only use regular integers (decimal); numbers between 0 and 9.

However, IPv6 can use any and all hexadecimal; 0-9 and a-f.

This means that when allocating a sub-range, they chose the face and b00c as they are all greater or equal to a and less than or equal to f.

Closing remarks

If you know about, or see other companies that are doing something similar, please tell me about it!