InterdomainTrusts.xml [plain text]
<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>
<indexterm><primary>Interdomain Trusts</primary></indexterm>
<para>
Samba-3 supports NT4 style domain trust relationships. This is feature that many sites
will want to use if they migrate to Samba-3 from and NT4 style domain and do NOT want to
adopt Active Directory or an LDAP based authentication back end. 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 Samba3-to-Samba3
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 is possible 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 it's 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.x/4.0 type security domains employ a non-hierarchical security structure.
The limitations of this architecture as it affects the scalability of MS Windows networking
in large organisations is well known. Additionally, the flat namespace that results from
this design significantly impacts the delegation of administrative responsibilities in
large and diverse organisations.
</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 organisation is ready
or willing to embrace ADS. For small companies the older NT4 style domain security paradigm
is quite adequate, there thus remains an entrenched user base for whom there is no direct
desire to go through a disruptive change to adopt ADS.
</para>
<para>
Microsoft introduced with MS Windows NT the ability to allow differing security domains
to affect a mechanism so that 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 (2) 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 (3) 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. ie: Relationships are explicit and not
transitive.
</para>
<para>
<!-- FIXME: What are these colors doing here - I can't find them ... Jelmer -->
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 labelled
<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 Policies, then select Trust Relationships, then click on the
<guibutton>Add</guibutton> button that is next to the box that is labelled
<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>
<indexterm><primary>Interdomain Trusts</primary><secondary>Facilities</secondary></indexterm>
<para>
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><imagefile>trusts1</imagefile><imagedescription>Trusts overview</imagedescription></image>
<itemizedlist>
<listitem><para>
DomA (completes the trust connection) Trusts DomB
</para></listitem>
<listitem><para>
DomA is the Trusting domain
</para></listitem>
<listitem><para>
DomB is the Trusted domain (originates the trust account)
</para></listitem>
<listitem><para>
Users in DomB can access resources in DomA
</para></listitem>
<listitem><para>
Users in DomA can NOT 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 can NOT 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 can NOT 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 admininstrative 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 could participate in interdomain trust relationships. Trust relationship support in Samba
is in its early stage, so lot of things don't work yet.
</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 'smbpasswd' utility. Creating the trusted domain account is very
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 favourite 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: ''create this
account with the InterDomain trust flag''
</para>
<para>
The account name will be 'rumba$' (the name of the remote domain)
</para>
<para>
After issuing this command you'll be asked to enter the password for
the account. You can use any password you want, but be aware that Windows NT will
not change this password until 7 days following account creation.
After the command returns successfully, you can look at the entry for the new account
(in the standard way as appropriate for your configuration) and see that account's name is
really RUMBA$ and it has the 'I' flag set in the flags field. Now you're ready to confirm
the trust by establishing it from Windows NT Server.
</para>
<indexterm><primary>User Manager</primary></indexterm>
<para>
Open <application>User Manager for Domains</application> and from the
<guimenu>Policies</guimenu> menu, select <guimenuitem>Trust Relationships...</guimenuitem>.
Right beside the <guilabel>Trusted domains</guilabel> list box press 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.
Press OK and, if everything went without incident, you will see
<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 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>
<indexterm><primary>User Manager</primary></indexterm>
<para>
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 it's Samba's turn.
</para>
<para>
Using your favourite 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.
Do not worry if you see an error message that mentions a return code of
NT_STATUS_NOLOGON_INTERDOMAIN_TRUST_ACCOUNT. 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>
Note that 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
labelled <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 acess 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>
</sect1>
</chapter>