Ok here we go
Borrowed from
this page
a) Generate an MD5 key, which will be used as a shared secret. The "dnssec-keygen" tool is used. The key is written to a file.
dnssec-keygen -a HMAC-MD5 -b 128 -n HOST updater
Which creates files like: Kupdater.+157+08531.key and Kupdater.+157+08531.private. What interests us is the 'Key' entry in the private file, which looks something like k2Pb7gEcbXg6ZosOqAbV8A==.
So we add the following to /dns/etc/named.conf:
key updater { algorithm hmac-md5; secret "k2Pb7gEcbXg6ZosOqAbV8A=="; };
And in the zone definition for yourdomain.com:
allow-update { key updater; };
b) Download and Install DynSite
The "Account Assistant" screen should appear on the first run.
1) Click Next
2) In the Dialog Box click DNS Servers
3) CLick the Configure New DNS Server option, type in a name, and click next
4) In DNS Server put either IP or FQDN of your DNS server, ie: ns1.yourdomain.com
5) Leave port @ 53
6) Under Method Change to Transaction Signature (hmac-md5)
7) Under keyname type in updater

Under keyvalue type in what you got for the Key entry earlier, and click next
9) Give the hostname you want to update a 'screen name'
10) under the Zone, put in the name of the zone you want to update, ie: yourdomain.com
11) Under host names, type in the subdomain you wish to update, ie home/box1/something/cheese
12) Check Update Zone as well
13) Click Next>Next>Finish