A machine can identify its own IP addresses. However, the mapping of DNS names both to and from IP addresses can actually be pretty complicated to get completely right. Multiple adapters per machine, virtual machines, Apache virtual hosts, load balancers, transparent proxies, multiple addresses per DNS entry, multiple DNS entries per address, ...

The header only needs to be "unique" to your script so that it can identify its own requests, e.g. X-dbooth-Loop-Prevention: foo. Or you could set a custom User-Agent like tobyink suggested, except that you could check for the presence of this header in your script instead of letting the webserver do it. The only case where this scheme could go wrong is if there is a transparent proxy in the path which modifies or removes headers.

In reply to Re^3: How can I determine whether a URI, hostname or IP address is to the local host machine? by Anonymous Monk
in thread How can I determine whether a URI, hostname or IP address is to the local host machine? by dbooth

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.