vpn_l2tp.php dns checks
recommend confirming that DNS servers l2tp_dns1 and l2tp_dns2
are IP addresses. Check this right in vpn_l2tp.php
since vpn_l2tp_configure silently checks it.
Also while there complain if l2tp_dns2 is set but l2tp_dns1
is not, since vpn_l2tp_configure won't use it if the first is not set.
(I noticed this while working on my book.
My list of bugs is at http://reedmedia.net/books/pfsense/bugs.html )