Re: Default-First-Site-Name

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From: Ulf B. Simon-Weidner [MVP] (nospam2-ulf_at_usw-consulting.com)
Date: 02/11/05 

Date: Fri, 11 Feb 2005 23:37:46 +0000

Hi Paul,

"ptwilliams" <ptw2001@hotmail.com> wrote in message
news:ptw2001@hotmail.com:
> GUYS: Would you mind pointing me at the documentation that states that the
> default-first-site-name is special, and clients will go to it if they
> cannot
> find the site. That is not how I understood the DNS locator process to
> work.

I haven't seen that documentation about the default-first-site-name as
well - unfortunately. The behavior described by me and Doug was tested
extensively by someone in one of the communities. The client was always
falling back into the default-first-site-name, even after it got
renamed, when it was unable to get a subnet.

> I'm under the impression that the DNS locator, if it has not already found
> a site, queries DNS for a DC and then netlogon 'pings' (sends a datagram -
> either an LDAP UDP search or a NetBT mailslot) all DCs that DNS returned
> (based on net mask ordering and round-robin balancing).

This might be the behavior if the client is locating the DC the first
time, however usually a client stores the last DC it was using (if that
DC is not available same behavior you stated). To be correct - in those
cases it ".., queries DNS for _any_ DC" (the client has no clue about
anything at this point). The DC the client is contacting is comparing
the clients IP with the subnet and site-infos stored in AD, and
returned a list of DCs in the clients site to the client. Then the
client is LDAP-UDP-pinging again.

Main discussion point was that every Site has a DC assigned - there are
no sites without DCs.

This is stated in the link you provided - look for "Automatic Site
Coverage" and the following chapters.

> When a client's address cannot be found in the subnet-to-site mappings,
> the DC returns a NULL and then that DC issued. This, in a typical hub and
> spoke
> environment, will usually be the default-first-site-name; but this is not
> a final ruling.

This is stated in the reskit - however the testing Doug and I remember
showed that the client was falling back into the
default-first-site-name (or whatever it was renamed to)

> True, the DC chooses who's closer -the client simply caches this info- the
> clients don't calculate closest. That is, the DCs decide which sites they
> cover. And this decision *is* based on site link cost.

Right.

> I don't know of any query for default-first-site-link. Sure, the
> dsGetDcName call can vary depending on the nature of the call - whether
> the PDCe is required, a GC call, etc.

Don't get what you mean here. However a client can not query in which
site it is in. The site and subnet mapping is not in DNS (as you know),
and the client is usually using it's last DC which queries AD. Or it
queries any DC, which will return the infos for him.

> I've never read of a reason to not rename or delete the
> default-first-site-name.

As I said - no docs available that I know of, but tests have proved
that the client was falling back. I have not done the tests myself, but
I know this has been discussed and tested in a community with a lot of
bright people.

However - don't get this wrong - if the default-first-site-name is
renamed than the testing proved that the clients not associated to a
subnet were still using the renamed one. If it would be deleted the
clients will still be able to log on, however they will fall back to
any DC. 

-- 
Gruesse - Sincerely,
Ulf B. Simon-Weidner
  MVP-Book "Windows XP - Die Expertentipps":  http://tinyurl.com/44zcz
  Weblog: http://msmvps.org/UlfBSimonWeidner
  WebSite: http://www.windowsserverfaq.org

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