In case you have to hosted enterprise within your Peplink you need at least one valid fixed ip (public ip). In my tests when you use Peplink to authenticate (pppoe) is much better.
Some links that may help you:
http://www.peplink.com/index.php?view=faq&id=69&path=18
http://www.peplink.com/index.php?view=faq&id=55&path=18
http://www.peplink.com/index.php?view=faq&id=123&path=21
http://www.peplink.com/index.php?view=faq&id=162&path=21
http://www.peplink.com/index.php?view=faq&id=190&path=21
BR,
Andre