How to Change DHCP/DNS Hostname in Windows Server 2008

I believe what you are wanting to do is simply tell all your DHCP clients to not register their own DNS records in AD. The dynamic update GPO controls this behaviour on a per-computer basis; when it is disabled, the per-connection "register this connection's address in DNS" option has no effect and dynamic registration does not occur, leaving the DHCP server to take care of it without interference. You should set this GPO only on computers which should be DHCP clients.

If you find it useful, here is a reference for GPOs which apply to the Windows DNS client.

You will find this specific GPO at computer scope, under administrative templates and network, in DNS settings. Set the dynamic update policy to disabled, wait for the GPO to be applied, and the behaviour should stop.

Is there a downside to selecting Always dynamically update DNS A and PTR records?

It depends on what you want to do.

By default, a Windows machine will speak directly to DNS and update its own A record, and it will ask DHCP to update the PTR record.

By enabling Always dynamically update DNS A and PTR records you are telling DHCP to update both records even if the client only asks it to update the PTR.

What's the difference between that and "...for DHCP clients that do not request updates..."

The NT 4.0 example isn't so relevant these days, so consider a mixed environment where you have Windows and Mac (or Linux) clients.

The Windows machines handle their dynamic DNS updates (or they ask DHCP to do so).

But the Mac/Linux clients do not. This option allows DHCP to create records for these machines which do not or cannot request dynamic DNS updates.

Some things to consider:

• You should create a dedicated, non-privileged AD user account for DHCP to use for dynamic DNS updates, and add it to the DnsUpdateProxy group (this is especially important if DHCP runs on a domain controller).
• DHCP always registers the name reported by the client, even if you set up a reservation. If the client reports a name different than the one you set in the reservation, the reservation's name will be overwritten.
• Dynamic DNS records set via DHCP will have a timestamp set on them. You should properly set up DNS scavenging to delete these records, even if you have DHCP set to remove records when the lease expires (it's good to have that on, but there are many cases where this just doesn't happen).