Sub domain name registration in custom DynDNS

Hello,

I have few questions about sub domain name registration in "DynDNS Custom" services.

I set up a remote desktop host on Windows Server 2008R2 must be accessible from outside. The fully qualified domain name (FQDN) that I need is "my-host.my-domain.net".

DynDNS says "We do not currently support domain registration for the requested TLD" when I try to register "my-host.my-domain.net" in DynDNS Custom, but it seems to be right when I try to register "my-domain.net".

1) How can I buy a sub domain name in "DynDNS Custom" services ? Should I buy "my-domain.net" and then change some DynDNS parameters to manage "my-host.my-domain.net" ? If yes, which ones ? Should I register the domain before registering the sub domain ?

2) Is sub domain compatible with Dynamic IP of my host (via DynDNS client) ?

Thanks for replies. Best regards.

Eric FAYET