DNS _sites and empty site

Discussion in 'Active Directory' started by Ondrej Sevecek, Nov 8, 2004.

  1. Hello,

    I have 3 sites + DefaultFirstSiteName. My domain controlers (10 distinct
    computers) reside only in 2 sites (and no one in the DFSN). So 1 site + DFSN
    is empty. In DNS, those empty (meaning _sites SRV domain) are filled with
    one selected DC not really placed in that site (but in different,
    certainly). I understand there must be such an assignement for client
    computers from the "empty" site. But what determines the one DC used as
    "stub" for the empty sites?

    Ondrej Sevecek, Nov 8, 2004
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  2. .... now, I suppose the empty sites are served with DCs in the site the first
    one alphabically among others, right?

    Ondrej Sevecek, Nov 8, 2004
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  3. Hello Ondrej,

    The DCs are determining if there are sites without DCs assigned to it.
    Then DCs of a site which is according to the site and site-link
    structure close to that site will advertise itself in DNS for that
    site. Therefore clients will be able to find a DC which is not in the
    same site, but in one of the sites which are better connected than
    other sites.

    If the clients would not be able to find a DC in the site they are
    trying to connect to they will try any dc of any site, which is quite
    bad because it might go over multiple wan-links. That's the reason for
    the advertising mechanism.

    I hope that answers your question.

    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
    Ulf B. Simon-Weidner [MVP], Nov 8, 2004
  4. many thanks. But what is the "closest site link" determination procedure
    like, exactly? Some KB links etc.?

    Ondrej Sevecek, Nov 8, 2004
  5. Ondrej Sevecek

    ptwilliams Guest

    It's worked out on cost. If you have three sites A, B and C, with site
    links AB and AC with costs of 100 and 125 respectively, the AB link is used
    for the site without DCs. So, in the case of this example, if there are DCs
    in B and C, the DCs in B will be the closest to A and are thus used.

    If there are multiple sites with the same cost, the first site
    alphabetically is used.

    Once this happens, the clients cache this info. in the registry. At
    startup, if a DC doesn't respond to the locator's 'ping', the locator
    process will start again.

    For documented info. on this, checkout chapter three (I think) Name
    Resolution in AD, in the Windows 2000 Server Resource Kit, Distributed
    Systems Guide - a truly awesome resource.

    This is a simplistic answer; the RK guide goes into a lot more info.

    If you want even more detail, you'll need to look at the Windows SDK - and
    the dsGetDcName, dsGetSiteName, etc. methods. (I think that's what they're
    called and are ;-)


    Paul Williams


    "Ondrej Sevecek" <ondra_at_sevecek_dt_com> wrote in message
    many thanks. But what is the "closest site link" determination procedure
    like, exactly? Some KB links etc.?

    ptwilliams, Nov 8, 2004
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