So some people started to really bust loose with the out of the box thinking on this one. You know how you will hit some networks where you can only get DNS? like wifi spots? Guest networks NAC subnets? Here is a little trick to get access to resources by using UDP53 add that to your pentest. The first link has source step by step hosting service and video on how to work it, the other two are just followup info.

skript kiddy help for DNS tunnel

description with code sample for the dns tunnel

full how to dns tunnel