1 <html><head><meta http-equiv="Content-Type" content="text/html; charset=ISO-8859-1"><title>Chapter 3. Server Types and Security Modes</title><link rel="stylesheet" href="samba.css" type="text/css"><meta name="generator" content="DocBook XSL Stylesheets V1.68.1"><link rel="start" href="index.html" title="The Official Samba-3 HOWTO and Reference Guide"><link rel="up" href="type.html" title="Part II. Server Configuration Basics"><link rel="prev" href="type.html" title="Part II. Server Configuration Basics"><link rel="next" href="samba-pdc.html" title="Chapter 4. Domain Control"></head><body bgcolor="white" text="black" link="#0000FF" vlink="#840084" alink="#0000FF"><div class="navheader"><table width="100%" summary="Navigation header"><tr><th colspan="3" align="center">Chapter 3. Server Types and Security Modes</th></tr><tr><td width="20%" align="left"><a accesskey="p" href="type.html">Prev</a> </td><th width="60%" align="center">Part II. Server Configuration Basics</th><td width="20%" align="right"> <a accesskey="n" href="samba-pdc.html">Next</a></td></tr></table><hr></div><div class="chapter" lang="en"><div class="titlepage"><div><div><h2 class="title"><a name="ServerType"></a>Chapter 3. Server Types and Security Modes</h2></div><div><div class="author"><h3 class="author"><span class="firstname">Andrew</span> <span class="surname">Tridgell</span></h3><div class="affiliation"><span class="orgname">Samba Team<br></span><div class="address"><p><code class="email"><<a href="mailto:tridge@samba.org">tridge@samba.org</a>></code></p></div></div></div></div><div><div class="author"><h3 class="author"><span class="firstname">Jelmer</span> <span class="othername">R.</span> <span class="surname">Vernooij</span></h3><div class="affiliation"><span class="orgname">The Samba Team<br></span><div class="address"><p><code class="email"><<a href="mailto:jelmer@samba.org">jelmer@samba.org</a>></code></p></div></div></div></div><div><div class="author"><h3 class="author"><span class="firstname">John</span> <span class="othername">H.</span> <span class="surname">Terpstra</span></h3><div class="affiliation"><span class="orgname">Samba Team<br></span><div class="address"><p><code class="email"><<a href="mailto:jht@samba.org">jht@samba.org</a>></code></p></div></div></div></div></div></div><div class="toc"><p><b>Table of Contents</b></p><dl><dt><span class="sect1"><a href="ServerType.html#id2526556">Features and Benefits</a></span></dt><dt><span class="sect1"><a href="ServerType.html#id2526724">Server Types</a></span></dt><dt><span class="sect1"><a href="ServerType.html#id2526884">Samba Security Modes</a></span></dt><dd><dl><dt><span class="sect2"><a href="ServerType.html#id2527047">User Level Security</a></span></dt><dt><span class="sect2"><a href="ServerType.html#id2527223">Share-Level Security</a></span></dt><dt><span class="sect2"><a href="ServerType.html#id2527414">Domain Security Mode (User-Level Security)</a></span></dt><dt><span class="sect2"><a href="ServerType.html#id2527936">ADS Security Mode (User-Level Security)</a></span></dt><dt><span class="sect2"><a href="ServerType.html#id2528097">Server Security (User Level Security)</a></span></dt></dl></dd><dt><span class="sect1"><a href="ServerType.html#id2528382">Password Checking</a></span></dt><dt><span class="sect1"><a href="ServerType.html#id2528582">Common Errors</a></span></dt><dd><dl><dt><span class="sect2"><a href="ServerType.html#id2528605">What Makes Samba a Server?</a></span></dt><dt><span class="sect2"><a href="ServerType.html#id2528638">What Makes Samba a Domain Controller?</a></span></dt><dt><span class="sect2"><a href="ServerType.html#id2528678">What Makes Samba a Domain Member?</a></span></dt><dt><span class="sect2"><a href="ServerType.html#id2528706">Constantly Losing Connections to Password Server</a></span></dt></dl></dd></dl></div><p>
2 <a class="indexterm" name="id2526516"></a>
3 <a class="indexterm" name="id2526523"></a>
4 This chapter provides information regarding the types of server that Samba may be configured to be. A
5 Microsoft network administrator who wishes to migrate to or use Samba will want to know the meaning, within a
6 Samba context, of terms familiar to the MS Windows administrator. This means that it is essential also to
7 define how critical security modes function before we get into the details of how to configure the server
10 This chapter provides an overview of the security modes of which Samba is capable and how they relate to MS
11 Windows servers and clients.
13 A question often asked is, “<span class="quote">Why would I want to use Samba?</span>” Most chapters contain a section that
14 highlights features and benefits. We hope that the information provided will help to answer this question. Be
15 warned though, we want to be fair and reasonable, so not all features are positive toward Samba. The benefit
16 may be on the side of our competition.
17 </p><div class="sect1" lang="en"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a name="id2526556"></a>Features and Benefits</h2></div></div></div><p>
18 Two men were walking down a dusty road, when one suddenly kicked up a small red stone. It
19 hurt his toe and lodged in his sandal. He took the stone out and cursed it with a passion
20 and fury befitting his anguish. The other looked at the stone and said, “<span class="quote">This is a garnet.
21 I can turn that into a precious gem and some day it will make a princess very happy!</span>”
23 The moral of this tale: Two men, two very different perspectives regarding the same stone.
24 Like it or not, Samba is like that stone. Treat it the right way and it can bring great
25 pleasure, but if you are forced to use it and have no time for its secrets, then it can be
26 a source of discomfort.
28 <a class="indexterm" name="id2526585"></a>
29 <a class="indexterm" name="id2526594"></a>
30 Samba started out as a project that sought to provide interoperability for MS Windows 3.x
31 clients with a UNIX server. It has grown up a lot since its humble beginnings and now provides
32 features and functionality fit for large-scale deployment. It also has some warts. In sections
33 like this one, we tell of both.
35 So, what are the benefits of the features mentioned in this chapter?
36 </p><div class="itemizedlist"><ul type="disc"><li><p>
37 <a class="indexterm" name="id2526618"></a>
38 Samba-3 can replace an MS Windows NT4 domain controller.
40 <a class="indexterm" name="id2526632"></a>
41 Samba-3 offers excellent interoperability with MS Windows NT4-style
42 domains as well as natively with Microsoft Active Directory domains.
44 <a class="indexterm" name="id2526646"></a>
45 Samba-3 permits full NT4-style interdomain trusts.
47 <a class="indexterm" name="id2526661"></a>
48 <a class="indexterm" name="id2526668"></a>
49 Samba has security modes that permit more flexible authentication
50 than is possible with MS Windows NT4 domain controllers.
52 <a class="indexterm" name="id2526683"></a>
53 <a class="indexterm" name="id2526695"></a>
54 Samba-3 permits use of multiple concurrent account database backends.
55 (Encrypted passwords that are stored in the account database are in
56 formats that are unique to Windows networking).
58 <a class="indexterm" name="id2526709"></a>
59 The account database backends can be distributed
60 and replicated using multiple methods. This gives Samba-3
61 greater flexibility than MS Windows NT4 and in many cases a
62 significantly higher utility than Active Directory domains
64 </p></li></ul></div></div><div class="sect1" lang="en"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a name="id2526724"></a>Server Types</h2></div></div></div><p>
65 <a class="indexterm" name="id2526732"></a>
66 Administrators of Microsoft networks often refer to three different types of servers:
67 </p><div class="itemizedlist"><ul type="disc"><li><p>Domain Controller</p><div class="itemizedlist"><ul type="circle"><li><p>Primary Domain Controller (PDC)</p></li><li><p>Backup Domain Controller (BDC)</p></li><li><p>ADS Domain Controller</p></li></ul></div></li><li><p>Domain Member Server</p><div class="itemizedlist"><ul type="circle"><li><p>Active Directory Domain Server</p></li><li><p>NT4 Style Domain Domain Server</p></li></ul></div></li><li><p>Standalone Server</p></li></ul></div><p>
68 <a class="indexterm" name="id2526794"></a>
69 <a class="indexterm" name="id2526803"></a>
70 <a class="indexterm" name="id2526812"></a>
71 <a class="indexterm" name="id2526821"></a>
72 The chapters covering domain control (<a href="samba-pdc.html" title="Chapter 4. Domain Control">Domain Control</a>),
73 backup domain control (<a href="samba-bdc.html" title="Chapter 5. Backup Domain Control">Backup Domain Control</a>), and
74 domain membership (<a href="domain-member.html" title="Chapter 6. Domain Membership">Domain Membership</a>) provide
75 pertinent information regarding Samba configuration for each of these server roles.
76 You are strongly encouraged to become intimately familiar with these chapters because
77 they lay the foundation for deployment of Samba domain security.
79 <a class="indexterm" name="id2526861"></a>
80 A Standalone server is autonomous in respect of the source of its account backend.
81 Refer to <a href="StandAloneServer.html" title="Chapter 7. Standalone Servers">Standalone Servers</a> to gain a wider appreciation
82 of what is meant by a server being configured as a <span class="emphasis"><em>standalone</em></span> server.
83 </p></div><div class="sect1" lang="en"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a name="id2526884"></a>Samba Security Modes</h2></div></div></div><p>
84 <a class="indexterm" name="id2526892"></a>
85 <a class="indexterm" name="id2526899"></a>
86 In this section, the function and purpose of Samba's security modes are described. An accurate understanding of
87 how Samba implements each security mode as well as how to configure MS Windows clients for each mode will
88 significantly reduce user complaints and administrator heartache.
90 <a class="indexterm" name="id2526914"></a>
91 <a class="indexterm" name="id2526923"></a>
92 Microsoft Windows networking uses a protocol that was originally called the Server Message Block (SMB)
93 protocol. Since some time around 1996 the protocol has been better known as the Common Internet Filesystem
96 <a class="indexterm" name="id2526939"></a>
97 <a class="indexterm" name="id2526946"></a>
98 <a class="indexterm" name="id2526953"></a>
99 <a class="indexterm" name="id2526960"></a>
100 In the SMB/CIFS networking world, there are only two types of security: <span class="emphasis"><em>user-level</em></span> and
101 <span class="emphasis"><em>share level</em></span>. We refer to these collectively as <span class="emphasis"><em>security levels</em></span>. In
102 implementing these two security levels, Samba provides flexibilities that are not available with MS Windows
103 NT4/200x servers. In fact, Samba implements <span class="emphasis"><em>share-level</em></span> security only one way, but has
104 four ways of implementing <span class="emphasis"><em>user-level</em></span> security. Collectively, we call the Samba
105 implementations of the security levels <span class="emphasis"><em>security modes</em></span>. They are known as
106 <span class="emphasis"><em>share</em></span>, <span class="emphasis"><em>user</em></span>, <span class="emphasis"><em>domain</em></span>, <span class="emphasis"><em>ADS</em></span>,
107 and <span class="emphasis"><em>server</em></span> modes. They are documented in this chapter.
109 An SMB server informs the client, at the time of a session setup, the security level the server is running.
110 There are two options: share-level and user-level. Which of these two the client receives affects the way the
111 client then tries to authenticate itself. It does not directly affect (to any great extent) the way the Samba
112 server does security. This may sound strange, but it fits in with the client/server approach of SMB. In SMB
113 everything is initiated and controlled by the client, and the server can only tell the client what is
114 available and whether an action is allowed.
116 The term <code class="literal">client</code> refers to all agents whether it is a Windows workstation, a Windows server,
117 another Samba server, or any vanilla SMB or CIFS client application (e.g., <span><strong class="command">smbclient</strong></span>) that
118 make use of services provided by an SMB/CIFS server.
119 </p><div class="sect2" lang="en"><div class="titlepage"><div><div><h3 class="title"><a name="id2527047"></a>User Level Security</h3></div></div></div><p>
120 <a class="indexterm" name="id2527055"></a>
121 We describe user-level security first because its simpler. In user-level security, the client sends a session
122 setup request directly following protocol negotiation. This request provides a username and password. The
123 server can either accept or reject that username/password combination. At this stage the server has no idea
124 what share the client will eventually try to connect to, so it can't base the
125 <span class="emphasis"><em>accept/reject</em></span> on anything other than:
126 </p><div class="orderedlist"><ol type="1"><li><p>the username/password.</p></li><li><p>the name of the client machine.</p></li></ol></div><p>
127 <a class="indexterm" name="id2527094"></a>
128 If the server accepts the username/password credentials, the client expects to be able to mount shares (using
129 a <span class="emphasis"><em>tree connection</em></span>) without further specifying a password. It expects that all access
130 rights will be as the username/password credentials set that was specified in the initial <span class="emphasis"><em>session
133 <a class="indexterm" name="id2527116"></a>
134 It is also possible for a client to send multiple <span class="emphasis"><em>session setup</em></span>
135 requests. When the server responds, it gives the client a <span class="emphasis"><em>uid</em></span> to use
136 as an authentication tag for that username/password. The client can maintain multiple
137 authentication contexts in this way (WinDD is an example of an application that does this).
139 <a class="indexterm" name="id2527138"></a>
140 <a class="indexterm" name="id2527145"></a>
141 <a class="indexterm" name="id2527152"></a>
142 <a class="indexterm" name="id2527159"></a>
143 <a class="indexterm" name="id2527166"></a>
144 Windows networking user account names are case-insensitive, meaning that upper-case and lower-case characters
145 in the account name are considered equivalent. They are said to be case-preserving, but not case significant.
146 Windows and LanManager systems previous to Windows NT version 3.10 have case-insensitive passwords that were
147 not necessarilty case-preserving. All Windows NT family systems treat passwords as case-preserving and
149 </p><div class="sect3" lang="en"><div class="titlepage"><div><div><h4 class="title"><a name="id2527181"></a>Example Configuration</h4></div></div></div><p>
150 The <code class="filename">smb.conf</code> parameter that sets user-level security is:
151 </p><table class="simplelist" border="0" summary="Simple list"><tr><td><a class="indexterm" name="id2527204"></a><em class="parameter"><code>security = user</code></em></td></tr></table><p>
152 This is the default setting since Samba-2.2.x.
153 </p></div></div><div class="sect2" lang="en"><div class="titlepage"><div><div><h3 class="title"><a name="id2527223"></a>Share-Level Security</h3></div></div></div><p>
154 <a class="indexterm" name="id2527231"></a>
155 <a class="indexterm" name="id2527238"></a>
156 In share-level security, the client authenticates itself separately for each share. It sends a password along
157 with each tree connection request (share mount), but it does not explicitly send a username with this
158 operation. The client expects a password to be associated with each share, independent of the user. This means
159 that Samba has to work out what username the client probably wants to use, the SMB server is not explicitly
160 sent the username. Some commercial SMB servers such as NT actually associate passwords directly with shares
161 in share-level security, but Samba always uses the UNIX authentication scheme where it is a username/password
162 pair that is authenticated, not a share/password pair.
164 To understand the MS Windows networking parallels, think in terms of MS Windows 9x/Me where you can create a
165 shared folder that provides read-only or full access, with or without a password.
167 Many clients send a session setup request even if the server is in share-level security. They normally send a valid
168 username but no password. Samba records this username in a list of possible usernames. When the client then
169 issues a tree connection request, it also adds to this list the name of the share they try to connect to (useful for
170 home directories) and any users listed in the <a class="indexterm" name="id2527273"></a>user parameter in the <code class="filename">smb.conf</code> file.
171 The password is then checked in turn against these possible usernames. If a match is found, then the client is
172 authenticated as that user.
174 <a class="indexterm" name="id2527291"></a>
175 <a class="indexterm" name="id2527300"></a>
176 <a class="indexterm" name="id2527307"></a>
177 Where the list of possible user names is not provided, Samba makes a UNIX system call to find the user
178 account that has a password that matches the one provided from the standard account database. On a system that
179 has no name service switch (NSS) facility, such lookups will be from the <code class="filename">/etc/passwd</code>
180 database. On NSS enabled systems, the lookup will go to the libraries that have been specified in the
181 <code class="filename">nsswitch.conf</code> file. The entries in that file in which the libraries are specified are:
182 </p><pre class="screen">
183 passwd: files nis ldap
184 shadow: files nis ldap
185 group: files nis ldap
187 <a class="indexterm" name="id2527341"></a>
188 <a class="indexterm" name="id2527348"></a>
189 <a class="indexterm" name="id2527354"></a>
190 In the example shown here (not likely to be used in practice) the lookup will check
191 <code class="filename">/etc/passwd</code> and <code class="filename">/etc/group</code>, if not found it will check NIS, then
193 </p><div class="sect3" lang="en"><div class="titlepage"><div><div><h4 class="title"><a name="id2527377"></a>Example Configuration</h4></div></div></div><p>
194 The <code class="filename">smb.conf</code> parameter that sets share-level security is:
195 </p><table class="simplelist" border="0" summary="Simple list"><tr><td><a class="indexterm" name="id2527399"></a><em class="parameter"><code>security = share</code></em></td></tr></table></div></div><div class="sect2" lang="en"><div class="titlepage"><div><div><h3 class="title"><a name="id2527414"></a>Domain Security Mode (User-Level Security)</h3></div></div></div><p>
196 <a class="indexterm" name="id2527422"></a>
197 <a class="indexterm" name="id2527432"></a>
198 <a class="indexterm" name="id2527441"></a>
199 <a class="indexterm" name="id2527447"></a>
200 <a class="indexterm" name="id2527454"></a>
201 <a class="indexterm" name="id2527461"></a>
202 Domain security provides a mechanism for storing all user and group accounts in a central, shared, account
203 repository. The centralized account repository is shared between domain (security) controllers. Servers that
204 act as domain controllers provide authentication and validation services to all machines that participate in
205 the security context for the domain. A primary domain controller (PDC) is a server that is responsible for
206 maintaining the integrity of the security account database. Backup domain controllers (BDCs) provide only domain
207 logon and authentication services. Usually, BDCs will answer network logon requests more responsively than
210 <a class="indexterm" name="id2527482"></a>
211 <a class="indexterm" name="id2527489"></a>
212 <a class="indexterm" name="id2527496"></a>
213 <a class="indexterm" name="id2527505"></a>
214 <a class="indexterm" name="id2527514"></a>
215 When Samba is operating in <a class="indexterm" name="id2527524"></a>security = domain mode, the Samba server has a
216 domain security trust account (a machine account) and causes all authentication requests to be passed through
217 to the domain controllers. In other words, this configuration makes the Samba server a domain member server,
218 even when it is in fact acting as a domain controller. All machines that participate in domain security must
219 have a machine account in the security database.
221 <a class="indexterm" name="id2527541"></a>
222 <a class="indexterm" name="id2527550"></a>
223 <a class="indexterm" name="id2527560"></a>
224 <a class="indexterm" name="id2527569"></a>
225 Within the domain security environment, the underlying security architecture uses user-level security. Even
226 machines that are domain members must authenticate on startup. The machine account consists of an account
227 entry in the accounts database, the name of which is the NetBIOS name of the machine and of which the password
228 is randomly generated and known to both the domain controllers and the member machine. If the machine account
229 cannot be validated during startup, users will not be able to log on to the domain using this machine because
230 it cannot be trusted. The machine account is referred to as a machine trust account.
232 There are three possible domain member configurations:
233 </p><div class="orderedlist"><ol type="1"><li><p>Primary domain controller (PDC) - of which there is one per domain.</p></li><li><p>Backup domain controller (BDC) - of which there can be any number per domain.</p></li><li><p>Domain member server (DMS) - of which there can be any number per domain.</p></li></ol></div><p>
234 <a class="indexterm" name="id2527618"></a>
235 We will discuss each of these in separate chapters. For now, we are most interested in basic DMS
237 </p><div class="sect3" lang="en"><div class="titlepage"><div><div><h4 class="title"><a name="id2527628"></a>Example Configuration</h4></div></div></div><p><span class="emphasis"><em>
238 Samba as a Domain Member Server
240 <a class="indexterm" name="id2527641"></a>
241 This method involves addition of the following parameters in the <code class="filename">smb.conf</code> file:
242 </p><table class="simplelist" border="0" summary="Simple list"><tr><td><a class="indexterm" name="id2527663"></a><em class="parameter"><code>security = domain</code></em></td></tr><tr><td><a class="indexterm" name="id2527676"></a><em class="parameter"><code>workgroup = MIDEARTH</code></em></td></tr></table><p>
244 In order for this method to work, the Samba server needs to join the MS Windows NT
245 security domain. This is done as follows:
246 <a class="indexterm" name="id2527694"></a>
247 <a class="indexterm" name="id2527702"></a>
248 </p><div class="procedure"><ol type="1"><li><p>On the MS Windows NT domain controller, using
249 the Server Manager, add a machine account for the Samba server.
250 </p></li><li><p>On the UNIX/Linux system execute:</p><pre class="screen"><code class="prompt">root# </code><strong class="userinput"><code>net rpc join -U administrator%password</code></strong></pre></li></ol></div><div class="note" style="margin-left: 0.5in; margin-right: 0.5in;"><h3 class="title">Note</h3><p>
251 <a class="indexterm" name="id2527752"></a>
252 Samba-2.2.4 and later Samba 2.2.x series releases can autojoin a Windows NT4-style domain just by executing:
253 </p><pre class="screen">
254 <code class="prompt">root# </code><strong class="userinput"><code>smbpasswd -j <em class="replaceable"><code>DOMAIN_NAME</code></em> -r <em class="replaceable"><code>PDC_NAME</code></em> \
255 -U Administrator%<em class="replaceable"><code>password</code></em></code></strong>
257 <a class="indexterm" name="id2527787"></a>
258 Samba-3 can do the same by executing:
259 </p><pre class="screen">
260 <code class="prompt">root# </code><strong class="userinput"><code>net rpc join -U Administrator%<em class="replaceable"><code>password</code></em></code></strong>
262 It is not necessary with Samba-3 to specify the <em class="replaceable"><code>DOMAIN_NAME</code></em> or the
263 <em class="replaceable"><code>PDC_NAME</code></em>, as it figures this out from the <code class="filename">smb.conf</code> file settings.
265 <a class="indexterm" name="id2527836"></a>
266 <a class="indexterm" name="id2527843"></a>
267 <a class="indexterm" name="id2527850"></a>
268 Use of this mode of authentication requires there to be a standard UNIX account for each user in order to
269 assign a UID once the account has been authenticated by the Windows domain controller. This account can be
270 blocked to prevent logons by clients other than MS Windows through means such as setting an invalid shell in
271 the <code class="filename">/etc/passwd</code> entry. The best way to allocate an invalid shell to a user account is to
272 set the shell to the file <code class="filename">/bin/false</code>.
274 <a class="indexterm" name="id2527879"></a>
275 <a class="indexterm" name="id2527885"></a>
276 Domain controllers can be located anywhere that is convenient. The best advice is to have a BDC on every
277 physical network segment, and if the PDC is on a remote network segment the use of WINS (see <a href="NetworkBrowsing.html" title="Chapter 9. Network Browsing">Network Browsing</a> for more information) is almost essential.
279 An alternative to assigning UIDs to Windows users on a Samba member server is presented in <a href="winbind.html" title="Chapter 23. Winbind: Use of Domain Accounts">Winbind</a>, <a href="winbind.html" title="Chapter 23. Winbind: Use of Domain Accounts">Winbind: Use of Domain Accounts</a>.
281 For more information regarding domain membership, <a href="domain-member.html" title="Chapter 6. Domain Membership">Domain Membership</a>.
282 </p></div></div><div class="sect2" lang="en"><div class="titlepage"><div><div><h3 class="title"><a name="id2527936"></a>ADS Security Mode (User-Level Security)</h3></div></div></div><p>
283 <a class="indexterm" name="id2527945"></a>
284 <a class="indexterm" name="id2527951"></a>
285 Both Samba-2.2, and Samba-3 can join an Active Directory domain using NT4 style RPC based security. This is
286 possible if the domain is run in native mode. Active Directory in native mode perfectly allows NT4-style
287 domain members. This is contrary to popular belief.
289 If you are using Active Directory, starting with Samba-3 you can join as a native AD member. Why would you
290 want to do that? Your security policy might prohibit the use of NT-compatible authentication protocols. All
291 your machines are running Windows 2000 and above and all use Kerberos. In this case, Samba, as an NT4-style
292 domain, would still require NT-compatible authentication data. Samba in AD-member mode can accept Kerberos
295 <a class="indexterm" name="id2527976"></a>
296 <a class="indexterm" name="id2527983"></a>
297 Sites that use Microsoft Windows active directory services (ADS) should be aware of the significance of the
298 terms: <code class="literal">native mode</code> and <code class="literal">mixed mode</code> ADS operation. The term
299 <code class="literal">realm</code> is used to describe a Kerberos-based security architecture (such as is used by
301 </p><div class="sect3" lang="en"><div class="titlepage"><div><div><h4 class="title"><a name="id2528013"></a>Example Configuration</h4></div></div></div><table class="simplelist" border="0" summary="Simple list"><tr><td><a class="indexterm" name="id2528025"></a><em class="parameter"><code>realm = your.kerberos.REALM</code></em></td></tr><tr><td><a class="indexterm" name="id2528038"></a><em class="parameter"><code>security = ADS</code></em></td></tr></table><p>
302 The following parameter may be required:
303 </p><table class="simplelist" border="0" summary="Simple list"><tr><td><a class="indexterm" name="id2528061"></a><em class="parameter"><code>password server = your.kerberos.server</code></em></td></tr></table><p>
304 Please refer to <a href="domain-member.html" title="Chapter 6. Domain Membership">Domain Membership</a>, and <a href="domain-member.html#ads-member" title="Samba ADS Domain Membership">Samba
305 ADS Domain Membership</a> for more information regarding this configuration option.
306 </p></div></div><div class="sect2" lang="en"><div class="titlepage"><div><div><h3 class="title"><a name="id2528097"></a>Server Security (User Level Security)</h3></div></div></div><p>
307 Server security mode is left over from the time when Samba was not capable of acting
308 as a domain member server. It is highly recommended not to use this feature. Server
309 security mode has many drawbacks that include:
310 </p><div class="itemizedlist"><ul type="disc"><li><p>Potential account lockout on MS Windows NT4/200x password servers.</p></li><li><p>Lack of assurance that the password server is the one specified.</p></li><li><p>Does not work with Winbind, which is particularly needed when storing profiles remotely.</p></li><li><p>This mode may open connections to the password server and keep them open for extended periods.</p></li><li><p>Security on the Samba server breaks badly when the remote password server suddenly shuts down.</p></li><li><p>With this mode there is NO security account in the domain that the password server belongs to for the Samba server.</p></li></ul></div><p>
311 <a class="indexterm" name="id2528150"></a>
312 <a class="indexterm" name="id2528157"></a>
313 In server security mode the Samba server reports to the client that it is in user-level security. The client
314 then does a session setup as described earlier. The Samba server takes the username/password that the client
315 sends and attempts to log into the <a class="indexterm" name="id2528168"></a>password server by sending exactly the same
316 username/password that it got from the client. If that server is in user-level security and accepts the
317 password, then Samba accepts the client's connection. This parameter allows the Samba server to use another
318 SMB server as the <a class="indexterm" name="id2528179"></a>password server.
320 <a class="indexterm" name="id2528190"></a>
321 <a class="indexterm" name="id2528197"></a>
322 You should also note that at the start of all this, when the server tells the client
323 what security level it is in, it also tells the client if it supports encryption. If it
324 does, it supplies the client with a random cryptkey. The client will then send all
325 passwords in encrypted form. Samba supports this type of encryption by default.
327 The parameter <a class="indexterm" name="id2528213"></a>security = server means that Samba reports to clients that
328 it is running in <span class="emphasis"><em>user mode</em></span> but actually passes off all authentication requests to another
329 user mode server. This requires an additional parameter <a class="indexterm" name="id2528227"></a>password server that points to
330 the real authentication server. The real authentication server can be another Samba server, or it can be a
331 Windows NT server, the latter being natively capable of encrypted password support.
332 </p><div class="note" style="margin-left: 0.5in; margin-right: 0.5in;"><h3 class="title">Note</h3><p>
333 <a class="indexterm" name="id2528242"></a>
334 <a class="indexterm" name="id2528249"></a>
335 When Samba is running in <span class="emphasis"><em>server security mode</em></span>, it is essential that the parameter
336 <span class="emphasis"><em>password server</em></span> is set to the precise NetBIOS machine name of the target authentication
337 server. Samba cannot determine this from NetBIOS name lookups because the choice of the target authentication
338 server is arbitrary and cannot be determined from a domain name. In essence, a Samba server that is in
339 <span class="emphasis"><em>server security mode</em></span> is operating in what used to be known as workgroup mode.
340 </p></div><div class="sect3" lang="en"><div class="titlepage"><div><div><h4 class="title"><a name="id2528275"></a>Example Configuration</h4></div></div></div><p><span class="emphasis"><em>
341 Using MS Windows NT as an Authentication Server
343 This method involves the additions of the following parameters in the <code class="filename">smb.conf</code> file:
344 </p><table class="simplelist" border="0" summary="Simple list"><tr><td><a class="indexterm" name="id2528303"></a><em class="parameter"><code>encrypt passwords = Yes</code></em></td></tr><tr><td><a class="indexterm" name="id2528316"></a><em class="parameter"><code>security = server</code></em></td></tr><tr><td><a class="indexterm" name="id2528329"></a><em class="parameter"><code>password server = "NetBIOS_name_of_a_DC"</code></em></td></tr></table><p>
345 There are two ways of identifying whether or not a username and password pair is valid.
346 One uses the reply information provided as part of the authentication messaging
347 process, the other uses just an error code.
349 <a class="indexterm" name="id2528351"></a>
350 <a class="indexterm" name="id2528358"></a>
351 The downside of this mode of configuration is that for security reasons Samba
352 will send the password server a bogus username and a bogus password, and if the remote
353 server fails to reject the bogus username and password pair, then an alternative mode of
354 identification or validation is used. Where a site uses password lockout, after a
355 certain number of failed authentication attempts, this will result in user lockouts.
357 Use of this mode of authentication requires a standard UNIX account for the user.
358 This account can be blocked to prevent logons by non-SMB/CIFS clients.
359 </p></div></div></div><div class="sect1" lang="en"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a name="id2528382"></a>Password Checking</h2></div></div></div><p>
360 MS Windows clients may use encrypted passwords as part of a challenge/response
361 authentication model (a.k.a. NTLMv1 and NTLMv2) or alone, or clear-text strings for simple
362 password-based authentication. It should be realized that with the SMB protocol,
363 the password is passed over the network either in plaintext or encrypted, but
364 not both in the same authentication request.
366 <a class="indexterm" name="id2528400"></a>
367 <a class="indexterm" name="id2528406"></a>
368 When encrypted passwords are used, a password that has been entered by the user
369 is encrypted in two ways:
370 </p><div class="itemizedlist"><ul type="disc"><li><p>An MD4 hash of the unicode of the password
371 string. This is known as the NT hash.
372 </p></li><li><p>The password is converted to uppercase,
373 and then padded or truncated to 14 bytes. This string is
374 then appended with 5 bytes of NULL characters and split to
375 form two 56-bit DES keys to encrypt a "magic" 8-byte value.
376 The resulting 16 bytes form the LanMan hash.
377 </p></li></ul></div><p>
378 <a class="indexterm" name="id2528437"></a>
379 MS Windows 95 pre-service pack 1 and MS Windows NT versions 3.x and version 4.0 pre-service pack 3 will use
380 either mode of password authentication. All versions of MS Windows that follow these versions no longer
381 support plain-text passwords by default.
383 <a class="indexterm" name="id2528454"></a>
384 MS Windows clients have a habit of dropping network mappings that have been idle
385 for 10 minutes or longer. When the user attempts to use the mapped drive
386 connection that has been dropped, the client re-establishes the connection using
387 a cached copy of the password.
389 When Microsoft changed the default password mode, support was dropped for caching
390 of the plaintext password. This means that when the registry parameter is changed
391 to re-enable use of plaintext passwords, it appears to work, but when a dropped
392 service connection mapping attempts to revalidate, this will fail if the remote
393 authentication server does not support encrypted passwords. It is definitely not
394 a good idea to re-enable plaintext password support in such clients.
396 The following parameters can be used to work around the issue of Windows 9x/Me clients
397 uppercasing usernames and passwords before transmitting them to the SMB server
398 when using clear-text authentication:
399 </p><table class="simplelist" border="0" summary="Simple list"><tr><td><a class="indexterm" name="id2528495"></a><em class="parameter"><code>password level</code></em></td></tr><tr><td><a class="indexterm" name="id2528507"></a><em class="parameter"><code>username level</code></em></td></tr></table><p>
400 By default Samba will convert to lowercase the username before attempting to lookup the user
401 in the database of local system accounts. Because UNIX usernames conventionally
402 only contain lowercase characters, the <a class="indexterm" name="id2528526"></a>username-level parameter
405 <a class="indexterm" name="id2528537"></a>
406 However, passwords on UNIX systems often make use of mixed-case characters. This means that in order for a
407 user on a Windows 9x/Me client to connect to a Samba server using clear-text authentication, the
408 <a class="indexterm" name="id2528547"></a>password level must be set to the maximum number of uppercase letters that
409 <span class="emphasis"><em>could</em></span> appear in a password. Note that if the Server OS uses the traditional DES version
410 of crypt(), a <a class="indexterm" name="id2528561"></a>password level of 8 will result in case-insensitive passwords as seen
411 from Windows users. This will also result in longer login times because Samba has to compute the permutations
412 of the password string and try them one by one until a match is located (or all combinations fail).
414 The best option to adopt is to enable support for encrypted passwords wherever
415 Samba is used. Most attempts to apply the registry change to re-enable plaintext
416 passwords will eventually lead to user complaints and unhappiness.
417 </p></div><div class="sect1" lang="en"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a name="id2528582"></a>Common Errors</h2></div></div></div><p>
418 We all make mistakes. It is okay to make mistakes, as long as they are made in the right places
419 and at the right time. A mistake that causes lost productivity is seldom tolerated; however, a mistake
420 made in a developmental test lab is expected.
422 Here we look at common mistakes and misapprehensions that have been the subject of discussions
423 on the Samba mailing lists. Many of these are avoidable by doing your homework before attempting
424 a Samba implementation. Some are the result of a misunderstanding of the English language,
425 which has many phrases that are potentially vague and may be highly confusing
426 to those for whom English is not their native tongue.
427 </p><div class="sect2" lang="en"><div class="titlepage"><div><div><h3 class="title"><a name="id2528605"></a>What Makes Samba a Server?</h3></div></div></div><p>
428 To some, the nature of the Samba security mode is obvious, but entirely
429 wrong all the same. It is assumed that <a class="indexterm" name="id2528615"></a>security = server means that Samba
430 will act as a server. Not so! This setting means that Samba will <span class="emphasis"><em>try</em></span>
431 to use another SMB server as its source for user authentication alone.
433 Samba is a server regardless of which security mode is chosen. When Samba is used outside of a domain security
434 context, it is best to leave the security mode at the default setting. By default Samba-3 uses user-mode
436 </p></div><div class="sect2" lang="en"><div class="titlepage"><div><div><h3 class="title"><a name="id2528638"></a>What Makes Samba a Domain Controller?</h3></div></div></div><p>
437 <a class="indexterm" name="id2528646"></a>
438 The <code class="filename">smb.conf</code> parameter <a class="indexterm" name="id2528660"></a>security = domain does not really make Samba behave
439 as a domain controller. This setting means we want Samba to be a domain member. See <a href="samba-pdc.html" title="Chapter 4. Domain Control">Samba as a PDC</a> for more information.
440 </p></div><div class="sect2" lang="en"><div class="titlepage"><div><div><h3 class="title"><a name="id2528678"></a>What Makes Samba a Domain Member?</h3></div></div></div><p>
441 Guess! So many others do. But whatever you do, do not think that <a class="indexterm" name="id2528688"></a>security = user
442 makes Samba act as a domain member. Read the manufacturer's manual before the warranty expires. See
443 <a href="domain-member.html" title="Chapter 6. Domain Membership">Domain Membership</a>, for more information.
444 </p></div><div class="sect2" lang="en"><div class="titlepage"><div><div><h3 class="title"><a name="id2528706"></a>Constantly Losing Connections to Password Server</h3></div></div></div><p>
445 “<span class="quote">
446 Why does server_validate() simply give up rather than re-establish its connection to the
447 password server? Though I am not fluent in the SMB protocol, perhaps the cluster server
448 process passes along to its client workstation the session key it receives from the password
449 server, which means the password hashes submitted by the client would not work on a subsequent
450 connection whose session key would be different. So server_validate() must give up.</span>”
452 Indeed. That's why <a class="indexterm" name="id2528729"></a>security = server
453 is at best a nasty hack. Please use <a class="indexterm" name="id2528737"></a>security = domain;
454 <a class="indexterm" name="id2528744"></a>security = server mode is also known as pass-through authentication.
455 </p></div></div></div><div class="navfooter"><hr><table width="100%" summary="Navigation footer"><tr><td width="40%" align="left"><a accesskey="p" href="type.html">Prev</a> </td><td width="20%" align="center"><a accesskey="u" href="type.html">Up</a></td><td width="40%" align="right"> <a accesskey="n" href="samba-pdc.html">Next</a></td></tr><tr><td width="40%" align="left" valign="top">Part II. Server Configuration Basics </td><td width="20%" align="center"><a accesskey="h" href="index.html">Home</a></td><td width="40%" align="right" valign="top"> Chapter 4. Domain Control</td></tr></table></div></body></html>
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