Seeking info about 'best practice' for multihomed (or not) DCs

Discussion in 'Windows Networking' started by Eggy, Sep 11, 2007.

  1. Eggy

    Eggy Guest

    After encountering a problem that occurred when I introduced a multihomed DC
    into my network I learned that it is, apparently, not advisable to use
    multihoming on a DC. Can you refer me to any 'official' documentation on
    this practice?


    PS - The problem that popped-up regards the 'net view' command. After
    installing a new DC things worked fine until I enabled it's second NIC.
    Afterward, on certain machines, 'net view' broke, complaining that a "System
    error 6118 has occurred". It might be relevent that the system on which net
    view failed is a Windows 2000 DC (the new DC is Win 2003). I resolved the
    problem by disabling NetBIOS over TCP/IP on the second NIC.
    Eggy, Sep 11, 2007
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  2. 157025 - Default Gateway Configuration for Multihomed Computers;en-us;157025&Product=win2000

    159168 - Multiple Default Gateways Can Cause Connectivity Problems

    272294 - Active Directory Communication Fails on Multihomed Domain

    191611 - Symptoms of Multihomed Browsers;EN-US;191611

    Phillip Windell

    The views expressed, are my own and not those of my employer, or Microsoft,
    or anyone else associated with me, including my cats.
    Phillip Windell, Sep 11, 2007
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  3. Eggy

    Eggy Guest

    Phillip (and All),

    Thanks. The KB's you cited are helpful. Part of my trouble is that many of
    the issues with multihoming are due to limitations of NT & 2000. I plan to
    be rid of all 2000 and earlier servers soon, and am trying to develop a clear
    understanding of multihoming in 2003-only environment.

    Sorry to belabor the point, but please let me inquire further. KB 191611
    states "The domain master browser service properly binds to only one network
    interface. The PDC serves the role of the domain master browser. We suggest
    that your PDC is not multihomed." Can you help me determine if this advice
    is applicable to a 2003-only environment? When I attain 2003-only status
    will I be OK with a multihomed PDC?

    BTW, in my case, multihoming is only for redundancy; it is not used for
    RRAS, and RRAS is not active on any server.

    Thanks Again!
    Eggy, Sep 11, 2007
  4. It will not change with 2003 or R2 or anything in the near future that I
    have ever heard about.
    Multi-Homing does NOT provide proper redundancy, only screws things up.
    Redundancy at that level is done with "Nic Teaming". With "Nic Teaming" the
    two Nics behave as a single virtual interface so it is therefore
    single-homed and not multi-homed. Nic Teaming requires the Nics and the
    software designed with this abilty.

    Phillip Windell

    The views expressed, are my own and not those of my employer, or Microsoft,
    or anyone else associated with me, including my cats.
    Phillip Windell, Sep 11, 2007
  5. Eggy

    Eggy Guest


    Thanks again! I appreciate the clarification.

    Eggy, Sep 11, 2007
  6. No problem.
    Although I haven't bothered to mess with it myself,..I think a lot of the
    news nic in the new servers can do Teaming if you want to look into that.

    Phillip Windell

    The views expressed, are my own and not those of my employer, or Microsoft,
    or anyone else associated with me, including my cats.
    Phillip Windell, Sep 11, 2007
  7. Eggy

    Bill Grant Guest

    No, going all server 2003 will not mean that the problem goes away. If you
    use Netbios over TCP/IP (with or without WINS) you still have the problems
    which you had in NT. Even if yo get rid of Netbt, you still strike similar
    problems because of dynamic DNS.

    The basic problem is that, it a server has more than one interface, you
    end up with two IP addresses (linked to two different interfaces) which are
    associated with the same computer name. If a machine tries to access the
    server by name and gets the "wrong" IP you can get strange things happening.
    That is basically what causes the browser problems with Netbt, and why
    disabling Netbios over TCP/IP on one NIC solves the problem.
    Bill Grant, Sep 12, 2007
  8. In
    Phillip and Bill provided some good suggestions and documentation. I would
    like to reiterate that a multihomed DC is not advisable unless the NICs are
    teamed. Unteamed NICs in a DC is inviting trouble, whether with RRAS or not.

    However, if YOU insist on using a multhomed DC, below is a re-print of my
    notes on how to PROPERLY configure a mutlihomed DC. Please read each step
    carefully to understand why the settings are being made. AThere are also
    registry entries to be modified. Prior to making any registry modification,
    make sure you back up the registry first.

    Honestly, in my opinion, it rally is NOT worth altering a DC's default
    functionality to force mutlihoming to work, for whatever reason. - Good

    Multihomed DCs, DNS, RRAS servers.
    Below are the manual steps in more detail, which I had outlined in the above

    Honestly, multi-homed DCs are not recommended because of the associated
    issues that can occur, as you've encountered. We usually recommend
    purchasing an inexpensive Linksys, DLink, etc, Cable/DSL router to perform
    NAT for you, take out the extra NIC off the DC, but still let the DC handle
    DHCP (and not the router).

    Little background on AD and DNS:
    First, just to get this out of the way, if you have your ISP's DNS addresses
    in your IP configuration (DCs and clients), they need to be REMOVED.

    If the ISP's DNS is in there, this will cause additional problems.

    Also, AD registers certain records in DNS in the form of SRV records that
    signify AD's resource and service locations. When there are multiple NICs,
    each NIC registers. IF a client, or another DC queries DNS for this DC, it
    may get the wrong record. One factor controlling this is Round Robin. If a
    DC or client on another subnet that the DC is not configured on queries for
    it, Round Robin will kick in offering one or the other. If the wrong one
    gets offered, it may not have a route to it. On the other hand, Subnetmask
    Priortization will ensure a querying client will get an IP that corresponds
    to the subnet it's on, which will work. To insure everything works, stick
    with one NIC.

    Since this DC is multi-homed, it requires additional configuration to
    prevent the public interface addresses from being registered in DNS. This
    creates a problem for internal clients locating AD to authenticate and find
    other services and resources such as the Global Catalog, file sharing and
    the SYSVOL DFS share and can cause GPO errors with Userenv 1000 events to be
    logged, authenticating to shares and printers, logging on takes forever,
    among numerous other issues.

    But if you like, there are some registry changes to eliminate the
    registration of the external NIC. Here's the whole list of manual steps to

    But believe me, it's much easier to just get a separate NAT device or
    multihome a non-DC then having to alter the DC. - Good luck!

    1. Insure that all the NICS only point to your internal DNS server(s) only
    and none others, such as your ISP's DNS servers' IP addresses.

    2. In Network & Dialup properties, Advanced Menu item, Advanced Settings,
    move the internal NIC (the network that AD is on) to the top of the binding
    order (top of the list).

    3. Disable the ability for the outer NIC to register. The procedure, as
    mentioned, involves identifying the outer NIC's GUID number. This link will
    show you how:
    246804 - How to Enable-Disable Windows 2000 Dynamic DNS Registrations (per
    NIC too):

    4. Disable NetBIOS on the outside NIC. That is performed by choosing to
    disable NetBIOS in IP Properties, Advanced, and you will find that under the
    "WINS" tab. You may want to look at step #3 in the article to show you how
    to disable NetBIOS on the RRAS interfaces if this is a RRAS server.
    296379 - How to Disable NetBIOS on an Incoming Remote Access Interface
    [Registry Entry]:

    Note: A standard Windows service, called the "Browser service", provides the
    list of machines, workgroup and domain names that you see in "My Network
    Places" (or the legacy term "Network Neighborhood"). The Browser service
    relies on the NetBIOS service. One major requirement of NetBIOS service is a
    machine can only have one name to one IP address. It's sort of a
    fingerprint. You can't have two brothers named Darrell. A multihomed machine
    will cause duplicate name errors on itself because Windows sees itself with
    the same name in the Browse List (My Network Places), but with different
    IPs. You can only have one, hence the error generated.

    5. Disable the "File and Print Service" and disable the "MS Client Service"
    on the outer NIC. That is done in NIC properties by unchecking the
    respective service under the general properties page. If you need these
    services on the outside NIC (which is unlikely), which allow other machines
    to connect to your machine for accessing resource on your machine (shared
    folders, printers, etc.), then you will probably need to keep them enabled.

    6. Uncheck "Register this connection" under IP properties, Advanced
    settings, "DNS" tab.

    7. Delete the outer NIC IP address, disable Netlogon registration, and
    manually create the required records

    a. In DNS under the zone name, (your DNS domain name), delete the outer
    NIC's IP references for the "LdapIpAddress". If this is a GC, you will need
    to delete the GC IP record as well (the "GcIpAddress"). To do that, in the
    DNS console, under the zone name, you will see the _msdcs folder. Under
    that, you will see the _gc folder. To the right, you will see the IP address
    referencing the GC address. That is called the GcIpAddress. Delete the IP
    addresses referencing the outer NIC.

    i. To stop these two records from registering that information,
    use the steps provided in the links below:
    Private Network Interfaces on a Domain Controller Are Registered in

    ii. The one section of the article that disables these records is
    done with this registry entry:

    (Create this Multi-String Value under it):
    Registry value: DnsAvoidRegisterRecords
    Data type: REG_MULTI_SZ
    Values: LdapIpAddress

    iii. Here is more information on these and other Netlogon Service records:
    Restrict the DNS SRV resource records updated by the Netlogon service
    [including GC]:

    b. Then you will need to manually create these two records in DNS with
    the IP addresses that you need for the DC. To create the

    LdapIpAddress, create a new host under the domain, but leave the "hostname"
    field blank, and provide the internal IP of the DC, which results in a
    record that looks like:
    (same as parent) A ( is used for illustrative

    i. You need to also manually create the GcIpAddress as well, if
    this is a GC. That would be under the _msdcs._gc SRV record under the zone.
    It is created in the same fashion as the LdapIpAddress mentioned above.

    8. In the DNS console, right click the server name, choose properties, then
    under the "Interfaces" tab, force it only to listen to the internal NIC's IP
    address, and not the IP address of the outer NIC.

    9. Since this is also a DNS server, the IPs from all NICs will register,
    even if you tell it not to in the NIC properties. See this to show you how
    to stop that behavior (this procedure is for Windows 2000, but will also
    work for Windows 2003):
    275554 - The Host's A Record Is Registered in DNS After You Choose Not to
    Register the Connection's Address:

    10. If you haven't done so, configure a forwarder. You can use if
    not sure which DNS to forward to until you've got the DNS address of your
    How to set a forwarder? Good question. Depending on your operating
    system,choose one of the following articles:

    300202 - HOW TO: Configure DNS for Internet Access in Windows 2000

    323380 - HOW TO: Configure DNS for Internet Access in Windows Server 2003
    (How to configure a forwarder):

    Active Directory communication fails on multihomed domain controllers

    <==*** Some additional reading ***==>
    More links to read up and understand what is going on:

    292822 - Name Resolution and Connectivity Issues on Windows 2000 Domain
    Controller with Routing and Remote Access and DNS Insta {DNS and RRAS and
    unwanted IPs registering]:

    Active Directory communication fails on multihomed domain controllers

    246804 - How to enable or disable DNS updates in Windows 2000 and in Windows
    Server 2003

    295328 - Private Network Interfaces on a Domain Controller Are Registered in
    [also shows DnsAvoidRegisterRecords LdapIpAddress to avoid reg sameasparent
    private IP]:

    306602 - How to Optimize the Location of a DC or GC That Resides Outside of
    a Client's
    Site [Includes info LdapIpAddress and GcIpAddress information and the SRV
    mnemonic values]:

    825036 - Best practices for DNS client settings in Windows 2000 Server and
    in Windows Server 2003 (including how-to configure a forwarder):;en-us;825036

    291382 - Frequently asked questions about Windows 2000 DNS and Windows
    Server 2003 DNS

    296379 - How to Disable NetBIOS on an Incoming Remote Access Interface
    [Registry Entry]:

    Rid Pool Errors and other mutlhomed DC errors, and how to configure a
    multihomed DC, Ace Fekay, 24 Feb 2006



    This posting is provided "AS-IS" with no warranties or guarantees and
    confers no rights.

    Ace Fekay, MCSE 2003 & 2000, MCSA 2003 & 2000, MCSE+I, MCT,
    MVP Microsoft MVP - Directory Services
    Microsoft Certified Trainer

    Infinite Diversities in Infinite Combinations

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    Ace Fekay [MVP], Sep 12, 2007
  9. Eggy

    Eggy Guest

    Phillip, Bill and Ace,

    Thank you so much for providing this info. It is exactly what I was
    seeking. And exactly what I suspected! -- thanks for the confirmation.

    I'll modify my system until I have a chance to investigate teaming.

    Thanks Again!

    Eggy, Sep 25, 2007
  10. Ok, good luck with it!

    Phillip Windell

    The views expressed, are my own and not those of my employer, or Microsoft,
    or anyone else associated with me, including my cats.

    Phillip Windell, Sep 25, 2007
  11. In
    Yes, good luck too!

    Ace Fekay [MVP], Sep 26, 2007
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