You probably want to check both the relevant RFCs and books on how to implement network software. There are also several DNS modules on the CPAN. Net::DNS::ToolKit even provides tools for working directly with DNS packets. If there's a particular motive for reinventing this particular wheel, that's cool. If not, the modules are probably a better use of your time.

ISBN 9780201615715, ISBN 9780131411555 (I actually have the older version of this ISBN 9780134900124 that still has XTI information as well), ISBN 9780201633467, and ISBN 9781565925724 are the books to which I refer most for networking topics.