It is a historical standard because it was implemented in the BSD inet_ntoa and copied into other implementation. It may even be standardized in POSIX.

No RFC describes the long form IP address. The RFCs I know that describe grammars for IPv4 addresses only support dotted quad form. This includes URLs.

You can see a few places where differences between expectations create problems. For example, most web browsers parse out the host portion of the http URL and pass it to inet_aton. So they accept "long form" address even when the RFCs say they shouldn't. This is seen with scammers writing URLs like: http://www.example.com@0x7F000001/. They use the username and unexpected IP address syntax to hide the destination.

Including the long form IP addresses in a regular expression makes them much more complicated. The regex has to match one to three components that could be decimal, hex, or octal numbers. Just to accept a format that is only used by a few people.

In reply to Re: Re: Re: Re: Untaint IP address/hostname question by iburrell
in thread Untaint IP address/hostname question by jcpunk

Title:
Use:  <p> text here (a paragraph) </p>
and:  <code> code here </code>
to format your post, it's "PerlMonks-approved HTML":


  • Posts are HTML formatted. Put <p> </p> tags around your paragraphs. Put <code> </code> tags around your code and data!
  • Titles consisting of a single word are discouraged, and in most cases are disallowed outright.
  • Read Where should I post X? if you're not absolutely sure you're posting in the right place.
  • Please read these before you post! —
  • Posts may use any of the Perl Monks Approved HTML tags:
    a, abbr, b, big, blockquote, br, caption, center, col, colgroup, dd, del, details, div, dl, dt, em, font, h1, h2, h3, h4, h5, h6, hr, i, ins, li, ol, p, pre, readmore, small, span, spoiler, strike, strong, sub, summary, sup, table, tbody, td, tfoot, th, thead, tr, tt, u, ul, wbr
  • You may need to use entities for some characters, as follows. (Exception: Within code tags, you can put the characters literally.)
            For:     Use:
    & &amp;
    < &lt;
    > &gt;
    [ &#91;
    ] &#93;
  • Link using PerlMonks shortcuts! What shortcuts can I use for linking?
  • See Writeup Formatting Tips and other pages linked from there for more info.