Is it safe to use a DHCP to assign the IP addresses to the servers

Discussion in 'Windows Networking' started by Giuseppe, Sep 30, 2008.

  1. Giuseppe

    Giuseppe Guest

    In my company we have at least 300 servers that are installed and managed by
    different people.

    Sometime It happens that the person that installs the server forgets
    something when configuring the TCP/IP section of the network card; some
    examples are:
    They forget to configure the wins
    They write a wrong wins address
    They assign to the server an IP address that is out of our standard range

    So I was thinking to use the DHCP to deploy the TCP/IP configuration (Using
    a reservation to make the IP address ever the same).

    I would like to know in your experience if this is a good way or if it is
    better to avoid this solution; what are the pros and the cons and if it is
    worth doing it.

    Some drowbacks I have been told are the following:
    1) if the DHCP fails we will not be able any more to access all the servers.
    A solution could be a redundant DHCP structure (2 or more DHCP servers) and
    to configure the "Alternate configuration" of the network card

    2) If we have two network cards in teaming and one of them fails the server
    will be no more work.
    In my knowkedge if we have a team the only mac address that cares is the
    Team mac address that is a software mac address so I should not have problems

    3) I could have problems with multihomed computers
    (I don't understand why; each computer should take its IP from the segment
    it is connected to)

    4) I can only assign one IP address
    This is true but It is not a common scenario (and we can configure taht
    machine manually)
    Giuseppe, Sep 30, 2008
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  2. Hello Giuseppe,

    See inline.

    For servers you should always use fixed ip's, so that the servername and
    ip address will not change.
    Depends on your configuration of the teaming, fault tolerance or load balancing.
    See my next posting about multihoming. It's big but informativ.
    Yes. And also with fixed ip's you should not multihome computers, especially
    Meinolf Weber, Sep 30, 2008
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  3. Hello Giuseppe,

    1. Domain Controllers should not be multi-homed
    2. Being a VPN Server and even simply running RRAS makes it multi-homed.
    3. DNS,..even just all by itself, is better on a single homed machine.
    4. Domain Controllers with the PDF Role are automatically Domain Master
    Browser. Master Browsers should not be multi-homed

    272294 - Active Directory Communication Fails on Multihomed Domain Controllers;en-us;272294

    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. -----------------------------------------------------

    See also:

    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 follow.

    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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    Meinolf Weber, Sep 30, 2008
  4. Giuseppe

    Giuseppe Guest

    Thanks Meinolf for your help but I have another question for you

    In your opinion are more the benefits or the disadvantages in deploying such
    a solution

    Thanks again and Regards
    Giuseppe, Oct 1, 2008
  5. Hello Giuseppe,

    Personally i see the biggest disadvantage with the DHCP server, you have
    allways to do some additional work if one of the servers fail, because the
    not avialable scopes has to be activated by hand.
    Meinolf Weber, Oct 1, 2008
  6. Giuseppe

    DevilsPGD Guest

    In message <> Giuseppe
    I realize it's the unpopular opinion, but we do this here without any
    noticeable downsides.

    At my main location, DCs, DNS servers and the default gateway are
    statically assigned, but everything else is dynamically assigned.

    We have two DHCP servers, both of which have a full copy of the
    reservations, so we have redundancy should one DHCP server fail.

    While it's true that if the DHCP servers both fail we lose connectivity
    with the servers, this hasn't been a big deal since the clients lose
    their IPs too, and as a result everyone is unable to communicate anyway.

    The advantage is as you noted, a consistent configuration across the
    board, plus the ability to centrally manage changes when needed.

    If you have well documented change policies, and through administration
    of each server, ensuring that admins always set up servers corrected
    then I wouldn't bother as DHCP adds additional complexity, but if you're
    more loosely managed, then I'd look at a competently managed DHCP
    environment to replace the mix-and-match of forgotten settings that can
    happen with multiple administrators.
    DevilsPGD, Oct 1, 2008
  7. Giuseppe

    Giuseppe Guest

    Thanks DevilsPGD

    I really needed someone that has tried it; because in theory I don't see
    many problems since we can use an internal A class so we can make the same
    reservation on each DHCP server and configure different ranges for each DHCP
    server so if one DHCP fails the other can bear all the load.
    Thanks again
    Giuseppe, Oct 2, 2008
  8. Giuseppe

    Giuseppe Guest


    if you configure the same reservation on each DHCP and use different scopes
    on both DHCPs (with each scope able to bear all the load); you can have both
    DHCPs on line having in this way load balancing and business continuity.

    Giuseppe, Oct 2, 2008
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