I am not sure why you would need a DHCP server in perl? One easy way to determine the interface of an incoming packet is to use iptables with the LOG target. A rule similar to the following (untested) should log udp packets coming through eth0 to your /var/log/messages 
iptables -I INPUT -p udp --dport 67 -i eth0 -j LOG \
--log-prefix \
"broadcast on eth0"

[download]
I do not know if what you want can be done using existing perl modules. Your problem requires querying kernel info, and am not sure if there are perl modules for that.

In reply to Re: Figuring out which network interface a broadcast packet came in on? by linuxfan
in thread Figuring out which network interface a broadcast packet came in on? by lyeoh

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.