The Peplink Balance DHCP server will not accept anything but an IP address when configuring DHCP extended option 17: root-path. This field needs to accept all valid path characters, not IP addresses, as stated in the description for this field and copied below.
Please fix. Thanks.
This option specifies the path of the client’s root disk. The path value is formatted as ASCII text. The length of the value field depends on the number of characters used in the root path specified. For example, if the root path entered has 20 characters, the value field for this option is 20 octets in length.
Peplink Balance 30
Firmware: 5.4.9 build 1732
Good catch 
thanks Nic.
This will be addressed in firmware 6.1. We are wrapping this up in beta. If you want to sneak a peep, please signup to the beta program at http://www.peplink.com/beta/ and you will be notified when a beta is available.
After further investigation, apparently (have not checked the spec.) an IP address is actually valid in this field, as long as it is also followed by a path (again, can’t remember syntax but probably something like “10.11.11.11:/path/to/root”).
This then allows (from memory) the root FS to reside on a different host to the boot file while requiring one less DHCP option and necessary (again, from memory) in certain circumstances when net booting nano/FreeBSD…
Will post links re: above paragraph if I have time although I doubt it as baby no. 1 is due in a few days…
n.
Thanks for update Nic. Your feedback is appreciated. Good luck with baby #1!
Mike
thanks Nic.