Kerberos logon to Terminal Server prevents folder redirection

Discussion in 'Server Security' started by McDavid, May 26, 2009.

  1. McDavid

    McDavid Guest

    Environment:
    - Terminal Server
    - Windows 2008 x64 Server Standard
    - Kerberos Token Size set to maximum
    - Profile and Folder Redirection hosts
    - Windows 2003 x64 Server Standard
    - Kerberos Token Size set to maximum

    Issue:
    When our users logon to our Terminal Servers using kerberos, they receive a
    temporary profile and none of the Folder Redirection policies are applied.
    The event log reports both processing failing with "Logon failure: unknown
    user name or bad password.". However the user is successfully logged onto
    the server using kerberos. The server hosting the profiles also reports
    "unknown user name or bad password" in the security log and the
    authentication package as NTLM. The users can navigate to the network
    locations of their roaming profiles and redirected folders just fine without
    any errors.

    If the users logon to our Terminal Servers using NTLM, their roaming profile
    is loaded and folder redirection policies applied successfully.

    Kerberos is the required authentication method for logging into our Terminal
    Servers. We are using Citrix Web Interface and single signon leverages
    kerberos.

    Initial Troubleshooting:
    I turned on Kerberos logging on the Terminal Server. When the user logs into
    the Terminal Server using kerberos, the logon process attempts to load their
    profile and redirect their profiles using kerberos. This is failing because
    we don't have SPNs registered for these resources. I'm guessing the logon
    process then attempts NTLM and that is failing because they didn't login with
    NTLM.

    Is there any way to get the fallback to NTLM to function? If not, how does
    one go about registering SPNs for file-shares that are cluster resources
    (virtual IPs and computer names that aren't regisered in Active Directory).
    In addition, how does one go about registering SPNs for DFS roots?

    Any/all help is appreciated.

    Thanks.
     
    McDavid, May 26, 2009
    #1
    1. Advertisements

  2. McDavid

    McDavid Guest

    Found that we don't have kerberos enabled on our clustered file shares.
    Would still like to know if there is a way to have the logon process revert
    to NTLM if kerberos authentication fails (because the user logged onto the
    Terminal Server with kerberos and the file share doesn't currently support
    kerberos).
     
    McDavid, May 27, 2009
    #2
    1. Advertisements

  3. McDavid,
    I am not an expert in Kerberos, so you may get a more expert answer from
    someone else, but:
    - we run Citrix with Web Interface and single sign-on, and you don't need to
    do anything special to do it.
    - when you sign on to the WI server, it authenticates you to other servers
    in the farm: I don't think this is AD Kerberos, although it is
    Kerberos-like. You get a ticket from a Citrix Secure Ticket Authority (STA)
    and present this to other servers in the farm
    - I suspect the problem lies with the cluster resources and delegated
    authentication. What cluster is this?
    - You can use the SetSPN utility to create additional SPN's:
    http://technet.microsoft.com/en-us/library/cc773257.aspx
    Hope that helps,
    Anthony
    http://www.airdesk.com
     
    Anthony [MVP], May 27, 2009
    #3
  4. McDavid

    McDavid Guest

    Kerberos (and possibly ADFS) is the only supported single sign-on protocol
    when authenticating to a Web Interface (or PN Agent site) from a XenApp
    Server. I believe the XenApp Client readme states this limitation. When
    running the XenApp client from a XenApp server, the ssonsvr.exe process is
    not available to perform the sign-on.

    Kerberos authentication is working fine for us to the Web Interface server.
    And the Web Interface is passing kerberos just fine, logging the users into
    the Terminal Servers. The logon process is attempting to use kerberos to
    load the roaming profile and perform folder redirection. That is failing
    because we have kerberos disabled on the cluster resources. I'm going to
    enable kerberos on the cluster resources during our next maintenance window.
    However, I would still like to figure out an interim solution. Is there a
    way to force the logon process to use NTLM even though the user logged on
    with kerberos?

    Our file shares are hosted on a Windows 2003 x64 cluster.
     
    McDavid, May 27, 2009
    #4
  5. I have been puzzling over this.
    As you say, you can enable Kerberos authentication on the cluster:
    http://support.microsoft.com/kb/302389
    But I am curious what it is about the logon process that makes the profile
    load fail.
    As you are already aware, there are numerous authentication processes in
    Citrix. Can you tell us how people authenticate initially from their client
    to the Web Interface? Are you using Pass-through authentication with
    Kerberos enabled?
    Anthony
    http://www.airdesk.com
     
    Anthony [MVP], May 29, 2009
    #5
  6. McDavid

    McDavid Guest

    Client-to-WebInterface authentication = kerberos using passthrough. This is
    the authentication method that results in profile/FolderRedirecton failure
    (since kerberos is not enabled on the file-share cluster).

    When the users choose explicit logon at the Web Interface (which I believe
    results in the Web Interface passing the users credentials to the XenApp
    Server using NTLM), their profiles load just fine.
     
    McDavid, May 29, 2009
    #6
  7. Pass-through refers to the client browser passing through credentials to the
    Web Interface server; so you can still use Pass-through without enabling the
    option "Use Kerberos authentication to connect to servers".
    Likewise with the PNAgent you can enable Pass-through using the
    single-signon service without enabling the option "Use Kerberos only".

    I know there is a problem if you try to daisy-chain Citrix servers (i.e log
    on to Web Interface, connect to a published desktop on a Citrix server, and
    from there connect to a published app on another Citrix server).

    "Pass-through authentication is not available when accessing a published
    application from within a published desktop on XenApp 5.0 servers. Instead,
    the user must provide valid credentials to launch a session within a desktop
    session even when pass-through authentication is enabled in the plugin. To
    resolve this issue, you must install a server-side hotfix that contains Fix
    #194894. [#194894]"

    So it looks to me as though you either need to enable Kerberos on the
    cluster; or disable Kerberos options in the Pass-through,
    Anthony
    http://www.airdesk.com
     
    Anthony [MVP], May 29, 2009
    #7
  8. McDavid

    McDavid Guest

    Originally the README had said that single sign-on was not available from a
    published desktop unless you used kerberos. So, we configured our Web
    Interface site to use kerberos (as opposed to spinning off and managing
    another site that doesn't use kerberos... one for the clients and one for the
    XenApp desktop).

    I didn't realize they had published a hotfix for this issue. Might resolve
    our issue if cranking up kerberos on the file shares doesn't work.

     
    McDavid, May 29, 2009
    #8
  9. OK, good luck. It sounds as thought there isn't any reason for the cluster
    not to use Kerberos anyway,
    Anthony,
    http://www.airdesk.com


     
    Anthony [MVP], May 30, 2009
    #9
    1. Advertisements

Ask a Question

Want to reply to this thread or ask your own question?

You'll need to choose a username for the site, which only take a couple of moments (here). After that, you can post your question and our members will help you out.