Configuring Remote Assistance to work across forests

Article ID: 2682075 - View products that this article applies to.
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SYMPTOMS

Scenario:

You have 2 forests

Resource.com – workstation forest
contoso.com – user forest

EMEA.contoso.com is a child domain in the user forest and contains user accounts.

There exists a Domain Local group in Resource.com – RESOURCE\R_remAssistAdmins

There exists a Global group in EMEA.contoso.com – EMEA\E_remAssistAdmins

EMEA\E_remAssistAdmins is a memberof RESOURCE\R_remAssistAdmins

The following configuration has been done:

1.     In Resource.com you have configure Remote assistance so that the local “Offer Remote Assistance Helpers” group contains RESOURCE\R_remAssistAdmins.

2.     Also the user rights policy to “access this computer from the network”  for the Workstations in Resource.com has been modified from the default and Everyone group has been removed. Instead RESOURCE\R_remAssistAdmins has been added.


Example users EMEA\expert and EMEA\novice log onto workstations Resource\W1 and Resource\W2 respectively.

EMEA\Expert  user wants to use Remote assistance to help the EMEA\novice user.

Expert runs msra /offerra from his workstation and receives the following error:

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On the Novice workstation (W2) the following event is logged in the security log:

Log Name:      Security
Source:        Microsoft-Windows-Security-Auditing
Date:          xx/xx/xxxx xx:xx:xx
Event ID:      4625
Task Category: Logon
Level:         Information
Keywords:      Audit Failure
User:          N/A
Computer:      W2.RESOURCE.com
Description:

An account failed to log on
Subject:

            Security ID:                   NULL SID
            Account Name:              -
            Account Domain:                        -
            Logon ID:                      0x0

Logon Type:                              3
Account For Which Logon Failed:

            Security ID:                   NULL SID
            Account Name:             
            Account Domain:                       

Failure Information:

            Failure Reason:              An Error occured during Logon.
            Status:                          0xc000006d
            Sub Status:                    0xc000015b

Process Information:
            Caller Process ID:          0x0
            Caller Process Name:     -

Network Information:

            Workstation Name:        -
            Source Network Address:           xxx.xx.xx.xx
            Source Port:                  xxxxx

Detailed Authentication Information:

            Logon Process:              Kerberos
            Authentication Package:  Kerberos
            Transited Services:        -
            Package Name (NTLM only):      -
            Key Length:                   0

This event is generated when a logon request fails. It is generated on the computer where access was attempted.

The Subject fields indicate the account on the local system which requested the logon. This is most commonly a service such as the Server service, or a local process such as Winlogon.exe or Services.exe.

The Logon Type field indicates the kind of logon that was requested. The most common types are 2 (interactive) and 3 (network).
The Process Information fields indicate which account and process on the system requested the logon.
The Network Information fields indicate where a remote logon request originated. Workstation name is not always available and may be left blank in some cases.

The authentication information fields provide detailed information about this specific logon request.

            - Transited services indicate which intermediate services have participated in this logon request.
            - Package name indicates which sub-protocol was used among the NTLM protocols.
            - Key length indicates the length of the generated session key. This will be 0 if no session key was requested.

A network trace of the connection shows the response from Novice workstatuion with RPC Fault Ox5 (Access Denied)
.

MSRPC MSRPC:c/o Fault: Call=0x2 Context=0x0 Status=0x5 Cancels=0x0 {MSRPC:89, TCP:87, IPv6:67}

CAUSE

The expert user token does not  contain sufficient rights to be able to Remote assist the novice user in this scenario.

This is due to the placement of the workstations into a separate forest from the users as well as the use of groups in the resource domain to permission the Remote Assistance and SeNetworkLogonRight.

RESOLUTION

1.     Configure RA such that the group EMEA\E_remAssistAdmins is a direct member of the “Offer Remote Assistance Helpers” local group on the workstations in the Resource.com domain.
AND
2.     Add Everyone or EMEA\E_remAssistAdmins directly to the User rights policy to “access this computer from the network” on the workstations in the Resource forest.

MORE INFORMATION

The msra.exe process on the Expert workstation runs under the logged on user EMEA\Expert .
On the novice workstation another process RAServer.exe starts (via remote DCOM call from msra.exe running on expert) under the credentials of the logged on user (EMEA\novice). 
MSRA.exe uses DCOM (over RPC) to make a connection to the RAServer.exe on the Novice workstation. 

msra.exe needs to authenticate to the RAserver.exe. Kerberos authentication is used. In this scenario EMEA\expert is the client and the EMEA\Novice is the service. As RAServer.exe runs under the EMEA\Novice credentials the EMEA\Expert user obtains a Kerberos ticket for the target of EMEA\Novice. As the target is a User account, Kerberos U2U authentication is used. Since the client (expert ) and the service (novice) are both in the EMEA domain the resulting service ticket contains the group membership of expert from EMEA. This works when the workstations are in the same domain as the users but it doesn’t work across forests/domains. 

Therefore EMEA groups need to be used to directly assign permissions for the Remote Assistance and accessing the computer from the network in the Resource forest.
Note This is a "FAST PUBLISH" article created directly from within the Microsoft support organization. The information contained herein is provided as-is in response to emerging issues. As a result of the speed in making it available, the materials may include typographical errors and may be revised at any time without notice. See Terms of Use for other considerations.

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Article ID: 2682075 - Last Review: March 14, 2012 - Revision: 2.0
APPLIES TO
  • Windows 7 Enterprise
  • Windows 7 Professional
  • Windows 7 Service Pack 1
Keywords: 
KB2682075

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