path: root/docs/howto/InterdomainTrusts.xml

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<chapter id="InterdomainTrusts">
<chapterinfo>
	&author.jht;
	&author.mimir;
	<author>&person.jelmer;<contrib>drawing</contrib></author>
        <author>
                <firstname>Stephen</firstname><surname>Langasek</surname>
                <affiliation>
                        <address><email>vorlon@netexpress.net</email></address>
                </affiliation>
        </author>
	<pubdate>April 3, 2003</pubdate>
</chapterinfo>

<title>Interdomain Trust Relationships</title>


<para>
<indexterm><primary>Interdomain Trusts</primary></indexterm>
Samba-3 supports NT4-style domain trust relationships. This is a feature that many sites
will want to use if they migrate to Samba-3 from an NT4-style domain and do not want to
adopt Active Directory or an LDAP-based authentication backend. This section explains
some background information regarding trust relationships and how to create them. It is now
possible for Samba-3 to trust NT4 (and vice versa), as well as to create Samba-to-Samba 
trusts.
</para>

<sect1>
<title>Features and Benefits</title>

<para>
Samba-3 can participate in Samba-to-Samba as well as in Samba-to-MS Windows NT4-style
trust relationships. This imparts to Samba similar scalability as with MS Windows NT4.
</para>

<para>
Given that Samba-3 has the capability to function with a scalable backend authentication
database such as LDAP, and given its ability to run in Primary as well as Backup Domain Control
modes, the administrator would be well advised to consider alternatives to the use of
Interdomain trusts simply because by the very nature of how this works it is fragile.
That was, after all, a key reason for the development and adoption of Microsoft Active Directory.
</para>

</sect1>

<sect1>
<title>Trust Relationship Background</title>

<para>
MS Windows NT3/4 type security domains employ a non-hierarchical security structure.
The limitations of this architecture as it effects the scalability of MS Windows networking
in large organizations is well known. Additionally, the flat namespace that results from
this design significantly impacts the delegation of administrative responsibilities in
large and diverse organizations.
</para>

<para>
Microsoft developed Active Directory Service (ADS), based on Kerberos and LDAP, as a means
of circumventing the limitations of the older technologies. Not every organization is ready
or willing to embrace ADS. For small companies the older NT4-style domain security paradigm
is quite adequate, there remains an entrenched user base for whom there is no direct
desire to go through a disruptive change to adopt ADS.
</para>

<para>
With MS Windows NT, Microsoft introduced the ability to allow differing security domains
to effect a mechanism so users from one domain may be given access rights and privileges
in another domain. The language that describes this capability is couched in terms of
<emphasis>Trusts</emphasis>. Specifically, one domain will <emphasis>trust</emphasis> the users
from another domain. The domain from which users are available to another security domain is
said to be a trusted domain. The domain in which those users have assigned rights and privileges
is the trusting domain. With NT3.x/4.0 all trust relationships are always in one direction only,
thus if users in both domains are to have privileges and rights in each others' domain, then it is
necessary to establish two relationships, one in each direction.
</para>

<para>
In an NT4-style MS security domain, all trusts are non-transitive. This means that if there
are three domains (let's call them RED, WHITE and BLUE) where RED and WHITE have a trust
relationship, and WHITE and BLUE have a trust relationship, then it holds that there is no
implied trust between the RED and BLUE domains. Relationships are explicit and not
transitive.
</para>

<para>
New to MS Windows 2000 ADS security contexts is the fact that trust relationships are two-way
by default. Also, all inter-ADS domain trusts are transitive. In the case of the RED, WHITE and BLUE
domains above, with Windows 2000 and ADS the RED and BLUE domains can trust each other. This is
an inherent feature of ADS domains. Samba-3 implements MS Windows NT4-style Interdomain trusts
and interoperates with MS Windows 200x ADS security domains in similar manner to MS Windows NT4-style domains.
</para>

</sect1>

<sect1>
<title>Native MS Windows NT4 Trusts Configuration</title>

<para>
There are two steps to creating an interdomain trust relationship. To effect a two-way trust
relationship, it is necessary for each domain administrator to create a trust account for the 
other domain to use in verifying security credentials.
<indexterm><primary>Interdomain Trusts</primary><secondary>creating</secondary></indexterm>
</para>


<sect2>
<title>Creating an NT4 Domain Trust</title>

<para>
For MS Windows NT4, all domain trust relationships are configured using the 
<application>Domain User Manager</application>. This is done from the Domain User Manager Policies
entry on the menu bar. From the <guimenu>Policy</guimenu> menu, select
<guimenuitem>Trust Relationships</guimenuitem>. Next to the lower box labeled
<guilabel>Permitted to Trust this Domain</guilabel> are two buttons, <guibutton>Add</guibutton>
and <guibutton>Remove</guibutton>. The <guibutton>Add</guibutton> button will open a panel in which
to enter the name of the remote domain that will be able to assign access rights to users in 
your domain. You will also need to enter a password for this trust relationship, which the 
trusting domain will use when authenticating users from the trusted domain.
The password needs to be typed twice (for standard confirmation).
</para>

</sect2>


<sect2>
<title>Completing an NT4 Domain Trust</title>

<para>
<indexterm><primary>Interdomain Trusts</primary><secondary>Completing</secondary></indexterm>
A trust relationship will work only when the other (trusting) domain makes the appropriate connections
with the trusted domain. To consummate the trust relationship, the administrator will launch the
Domain User Manager from the menu select <guilabel>Policies</guilabel>, then select
<guilabel>Trust Relationships</guilabel>, click on the <guibutton>Add</guibutton> button
next to the box that is labeled <guilabel>Trusted Domains</guilabel>. A panel will open in which
must be entered the name of the remote domain as well as the password assigned to that trust.
</para>

</sect2>

<sect2>
<title>Inter-Domain Trust Facilities</title>


<para>
<indexterm><primary>Interdomain Trusts</primary><secondary>Facilities</secondary></indexterm>
A two-way trust relationship is created when two one-way trusts are created, one in each direction.
Where a one-way trust has been established between two MS Windows NT4 domains (let's call them
DomA and DomB), the following facilities are created:
</para>

<image id="trusts1"><imagefile>trusts1</imagefile><imagedescription>Trusts overview.</imagedescription></image>

<itemizedlist>
	<listitem><para>
	DomA (completes the trust connection) <parameter>Trusts</parameter> DomB.
	</para></listitem>

	<listitem><para>
	DomA is the <parameter>Trusting</parameter> domain.
	</para></listitem>

	<listitem><para>
	DomB is the <parameter>Trusted</parameter> domain (originates the trust account).
	</para></listitem>

	<listitem><para>
	Users in DomB can access resources in DomA.
	</para></listitem>

	<listitem><para>
	Users in DomA cannot access resources in DomB.
	</para></listitem>

	<listitem><para>
	Global groups from DomB can be used in DomA.
	</para></listitem>

	<listitem><para>
	Global groups from DomA cannot be used in DomB.
	</para></listitem>

	<listitem><para>
	DomB does appear in the logon dialog box on client workstations in DomA.
	</para></listitem>

	<listitem><para>
	DomA does not appear in the logon dialog box on client workstations in DomB.
	</para></listitem>
</itemizedlist>

<itemizedlist>
	<listitem><para>
	Users/Groups in a trusting domain cannot be granted rights, permissions or access
	to a trusted domain.
	</para></listitem>

	<listitem><para>
	The trusting domain can access and use accounts (Users/Global Groups) in the
	trusted domain.
	</para></listitem>

	<listitem><para>
	Administrators of the trusted domain can be granted administrative rights in the 
	trusting domain.
	</para></listitem>

	<listitem><para>
	Users in a trusted domain can be given rights and privileges in the trusting
	domain.
	</para></listitem>

	<listitem><para>
	Trusted domain Global Groups can be given rights and permissions in the trusting
	domain.
	</para></listitem>

	<listitem><para>
	Global Groups from the trusted domain can be made members in Local Groups on
	MS Windows Domain Member machines.
	</para></listitem>
</itemizedlist>

</sect2>

</sect1>

<sect1>
<title>Configuring Samba NT-Style Domain Trusts</title>

<para>
This description is meant to be a fairly short introduction about how to set up a Samba server so
that it can participate in interdomain trust relationships. Trust relationship support in Samba
is at an early stage, so do not be surprised if something does not function as it should.
</para>

<para>
Each of the procedures described below assumes the peer domain in the trust relationship is 
controlled by a Windows NT4 server. However, the remote end could just as well be another 
Samba-3  domain. It can be clearly seen, after reading this document, that combining 
Samba-specific parts of what's written below leads to trust between domains in a purely Samba 
environment.
</para>

<sect2 id="samba-trusted-domain">
<title>Samba as the Trusted Domain</title>

<para>
In order to set the Samba PDC to be the trusted party of the relationship, you first need
to create a special account for the domain that will be the trusting party. To do that,
you can use the <command>smbpasswd</command> utility. Creating the trusted domain account is 
similar to creating a trusted machine account. Suppose, your domain is
called SAMBA, and the remote domain is called RUMBA. The first step
will be to issue this command from your favorite shell:
</para>

<para>
<screen>
&rootprompt; <userinput>smbpasswd -a -i rumba</userinput>
New SMB password: <userinput>XXXXXXXX</userinput>
Retype SMB password: <userinput>XXXXXXXX</userinput>
Added user rumba$
</screen>

where <option>-a</option> means to add a new account into the
passdb database and <option>-i</option> means: <quote>create this
account with the Inter-Domain trust flag</quote>.
</para>

<para>
The account name will be <quote>rumba$</quote> (the name of the remote domain).
If this fails, you should check that the trust account has been added to the system
password database (<filename>/etc/passwd</filename>). If it has not been added, you
can add it manually and then repeat the step above.
</para>

<para>
After issuing this command, you will be asked to enter the password for
the account. You can use any password you want, but be aware that Windows NT will
not change this password until seven days following account creation.
After the command returns successfully, you can look at the entry for the new account
(in the standard way as appropriate for your configuration) and see that accounts name is
really RUMBA$ and it has the <quote>I</quote> flag set in the flags field. Now you are ready to confirm
the trust by establishing it from Windows NT Server.
</para>


<para>
<indexterm><primary>User Manager</primary></indexterm>
Open <application>User Manager for Domains</application> and from the
<guimenu>Policies</guimenu> menu, select <guimenuitem>Trust Relationships...</guimenuitem>.
Beside the <guilabel>Trusted domains</guilabel> list box click the
<guimenu>Add...</guimenu> button. You will be prompted for
the trusted domain name and the relationship password. Type in SAMBA, as this is
the name of the remote domain and the password used at the time of account creation.
Click on <guibutton>OK</guibutton> and, if everything went without incident, you will see 
the <computeroutput>Trusted domain relationship successfully 
established</computeroutput> message.
</para>

</sect2>
<sect2>
<title>Samba as the Trusting Domain</title>

<para>
This time activities are somewhat reversed. Again, we'll assume that your domain
controlled by the Samba PDC is called SAMBA and the NT-controlled domain is called RUMBA.
</para>

<para>
The very first step is to add an account for the SAMBA domain on RUMBA's PDC.
</para>


<para>
<indexterm><primary>User Manager</primary></indexterm>
Launch the <application>Domain User Manager</application>, then from the menu select
<guimenu>Policies</guimenu>, <guimenuitem>Trust Relationships</guimenuitem>.
Now, next to the <guilabel>Trusted Domains</guilabel> box press the <guibutton>Add</guibutton>
button and type in the name of the trusted domain (SAMBA) and the password to use in securing
the relationship.
</para>

<para>
The password can be arbitrarily chosen. It is easy to change the password
from the Samba server whenever you want. After confirming the password your account is
ready for use. Now its Samba's turn.
</para>

<para>
Using your favorite shell while being logged in as root, issue this command:
</para>

<para>
&rootprompt;<userinput>net rpc trustdom establish rumba</userinput>
</para>

<para>
You will be prompted for the password you just typed on your Windows NT4 Server box.
An error message <errorname>`NT_STATUS_NOLOGON_INTERDOMAIN_TRUST_ACCOUNT'</errorname>
that may be reported periodically is of no concern and may safely be ignored.
It means the password you gave is correct and the NT4 Server says the account is ready for
interdomain connection and not for ordinary connection.  After that, be patient;
it can take a while (especially in large networks), but eventually you should see
the <computeroutput>Success</computeroutput> message. Congratulations! Your trust
relationship has just been established.
</para>

<note><para>
You have to run this command as root because you must have write access to
the <filename>secrets.tdb</filename> file.
</para></note>

</sect2>
</sect1>

<sect1>
<title>NT4-Style Domain Trusts with Windows 2000</title>
<para>
Although <application>Domain User Manager</application> is not present in Windows 2000, it is 
also possible to establish an NT4-style trust relationship with a Windows 2000 domain 
controller running in mixed mode as the trusting server. It should also be possible for 
Samba to trust a Windows 2000 server, however, more testing is still needed in this area.
</para>

<para>
After <link linkend="samba-trusted-domain">creating the interdomain trust account on the 
Samba server</link> as described above, open <application>Active Directory Domains and 
Trusts</application> on the AD controller of the domain whose resources you wish Samba users 
to have access to. Remember that since NT4-style trusts are not transitive, if you want 
your users to have access to multiple mixed-mode domains in your AD forest, you will need to 
repeat this process for each of those domains. With <application>Active Directory Domains 
and Trusts</application> open, right-click on the name of the Active Directory domain that 
will trust our Samba domain and choose <guimenuitem>Properties</guimenuitem>, then click on
the <guilabel>Trusts</guilabel> tab. In the upper part of the panel, you will see a list box 
labeled <guilabel>Domains trusted by this domain:</guilabel>, and an 
<guilabel>Add...</guilabel> button next to it. Press this button and just as with NT4, you 
will be prompted for the trusted domain name and the relationship password. Press OK and 
after a moment, Active Directory will respond with <computeroutput>The trusted domain has 
been added and the trust has been verified.</computeroutput>  Your Samba users can now be 
granted access to resources in the AD domain.
</para>
</sect1>

<sect1>
<title>Common Errors</title>

<para>
Interdomain trust relationships should not be attempted on networks that are unstable
or that suffer regular outages. Network stability and integrity are key concerns with
distributed trusted domains.
</para>

<sect2>
<title>Browsing of Trusted Domain Fails</title>

<para>
Browsing from a machine in a trusted Windows 200x Domain to a Windows 200x member of
a trusting samba domain, I get the following error:
</para>

<formalpara><emphasis>
The system detected a possible attempt to compromise security. Please ensure that
you can contact the server that authenticated you.</emphasis>
</formalpara>

<para>
The event logs on the box I'm trying to connect to have entries regarding group
policy not being applied because it is a member of a down-level domain.
</para>

<para><emphasis>Answer: </emphasis> If there is a computer account in the Windows
200x Domain for the machine in question, and it is disabled, this problem can
occur.  If there is no computer account (removed or never existed), or if that 
account is still intact (i.e.: you just joined it to another domain) everything 
seems to be fine. By default, when you un-join a domain (the Windows 200x 
Domain), the computer tries to automatically disable the computer account in 
the domain.  If you are running as an account which has privileges to do this 
when you un-join the machine, it is done, otherwise it is not done.
</para>

</sect2>

<sect2>
<title>Problems With LDAP ldapsam And The smbldap-tools</title>

<para>
If you use the <command>smbldap-useradd.pl</command> script to create a trust
account to set up Interdomain trusts the process of setting up the trust will
fail. The account that was created in the LDAP database will have an account
flags field that has <constant>[W          ]</constant>, when it must have
<constant>[I          ]</constant> for Interdomain trusts to work.
</para>

<para><emphasis>Answer: </emphasis>Here is a simple solution.
Create a machine account as follows:
<screen>
&rootprompt; smbldap-useradd.pl -w domain_name
</screen>
Then set the desired trust account password as shown here:
<screen>
&rootprompt; smbldap-passwd.pl domain_name\$
</screen>
Using a text editor, create the following file:
<screen>
dn: uid=domain_name$,ou=People,dc={your-domain},dc={your-top-level-domain}
changetype: modify
sambaAcctFlags: [I         ]
</screen>
Then apply the text file to the LDAP database as follows:
<screen>
&rootprompt; ldapmodify -x -h localhost \
 -D "cn=Manager,dc={your-domain},dc={your-top-level-domain}" \
 -W -f /path-to/foobar
</screen>
Create a single-sided trust under the NT4 Domain User Manager, then execute:
<screen>
&rootprompt; net rpc trustdom establish domain_name
</screen>
</para>

<para>
It works with Samba-3  and NT4 Domains, and also with Samba-3 and Windows 200x ADS in mixed mode.
Both DC's, samba and NT, must have the same WINS server otherwise
the trust will never work. 
</para>

</sect2>

</sect1>

</chapter>