DNS on DC's

If a DC can't find a DNS server, it won't even be able to authenticate users logging on locally. I always put in 127.0.0.1 as a secondary just in case somebody accidentally messes up a DNS IP, or changes the server IP, that way it can always find itself. I had that happen before, it sucks, you pretty much get to rebuild the DC.

Pointing to another DC makes sure that your DC can always find the rest of the Active Directory and not get orphaned with no clue how to find the rest of your network when something gets change.

I would point to whatever DC is going to give you the fastest response. If they are all in the same site with no real difference in ping times, it shouldn't matter much.

To be technical for a minute >> what's the rule for setting primary and secondary <<
There is no such rule as primary and secondary DNS servers are something different all together

No is what you really mean is preferred and alternate DNS servers that's a different matter

Put simply the jury is out. Some prefer to point each server at itself as the preferred sever as lookups are faster and more reliable.
However, pointing them at each other prevents an issue called 'racing' that can occasionally occur.

I prefer to point them at themselves and have never found 'racing' to be an issue

KCTS, presumably then your DNS servers are not AD integrated?

Otherwise you would see the race condition quite often because DNS is required for AD but it can't start because AD isn't yet.

Racing is not always an issue but I've seen it happen a handful of times at major agencies.  At this point I'd argue that the jury is not really out.  Microsoft support and the AD team see a lot of tickets and that is why they made the recommendations they did.

Thanks

Mike

Thanks all
excellent answers and a great debate!
so I conclude primary = another DC and secondary = loopback 127.0.0.1

Many Thanks

>> NO  so I conclude primary = another DC and secondary = loopback 127.0.0.1<<

I won't argue if you say PREFERRED = another DC and ALTERNATE = loopback, but please don't use the terms primary and secondary - as I said they refer to something totally different.

That said I have never had any issues with it the other way around - and yes most of my servers a AD Integrated.

KCTS, I am amused that you keep bringing this up.  It may not be technically correct but you are the only one I know that keeps pointing it out.

I think it's human nature to refer to something that comes first to be called primary and some thing that comes second to be called secondary.

Call me pedantic if you like but I think that it is important to use the correct terminology to avoid confusion

As I'm sure you are aware in DNS terms PRIMARY refers to an updateable zone file and SECONDARY to a zone file which is transferred from the PRIMARY and has nothing to do with the client DNS settings

The terms PREFERRED and ALTERNATE are also more descriptive of the actual process that is involved in DNS lookups, the alternate only being used if there is no timely response from the client.

Anyway that's my view :-)