Maintained by: NLnet Labs

[Unbound-users] Unbound vs MS Resolver

Chris Smith
Wed Jun 4 00:03:20 CEST 2014


On Tue, Jun 3, 2014 at 1:57 PM, Dave Warren <davew at hireahit.com> wrote:
> In general, I agree that it makes sense to split authoritative and resolver
> roles. However, in the case of Windows and Active Directory, Active
> Directory is built under the assumption that your DNS servers accept AD
> authenticated dynamic updates, both from AD itself and from clients, so it's
> best practice to only specify Microsoft DNS servers for Active Directory
> domain controllers, member servers and workstations when possible.

First a caveat - all of my clients and experience (after my big iron
days that is) are small businesses. Most are non-AD but a couple of
them do have AD domains running on Microsoft servers (no giant
Forests, one domain). One is an inherited account and the other needed
to run software that required an AD. Not my preference (which is
Linux/BSD servers), but they work.

So file this under some guys opinion and probably not applicable to
your environment.

First, unless a box is a server there's no pressing need for it to
have DNS entry. Nice, can be helpful, but not absolutely needed in
most cases.

> My theory is that each site (physical location as well as Active Directory
> site/subnet) would have one unbound server that performs internet
> resolution, with multiple AD servers that forward to the unbound server.

At one site I run the Unbound resolver/cache on an OpenBSD box
configured with stub-zones for the AD domain (forward and reverse).
All clients are configured to query this Unbound box. The AD server
forwards to Unbound anything it is not authoritative for.

The important thing this accomplishes (at least in my paranoid mind)
is that it removes the AD from direct Internet access for DNS purposes
(admittedly I have some trust issues with MS systems and Internet
access). With a side benefit that the AD does not supply DNS answers
directly to the clients - it's DNS workload is very low, as it is a
server with little to no need to resolve outside its authoritative
domain (just the occasional update, new software download, etc.).
Also, and maybe a bit unexpectedly the clients still update their DNS
entries (although as I mentioned earlier I don't find this all that
necessary) on the AD as even though their resolvers point to Unbound
the SRV records (cached by Unbound for all clients) are what allow
them to locate the AD and update.

At any rate the performance is quite good, and (if anecdotal
"evidence" can be offered) improved (I ran no performance tests). But
more importantly I have piece of mind that the AD has very limited
Internet exposure.

I have also run with all clients pointing to the AD with a forward to
the Unbound server (no stub-zone to the AD), which does limit the AD's
Internet footprint, but I like the setup using the stub-zone, reducing
the DNS workload on the AD and even possibly preventing some DNS
nonsense from internal systems.

Chris