htmldocs/using_samba/ch07.html

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<h1 class="head0">Chapter 7. Name Resolution and Browsing</h1>


<p><a name="INDEX-1"/><em class="firstterm">Name
resolution</em> is critical to Samba's
operation because names are used to find the servers that share files
or printers. <em class="firstterm">Browsing</em> takes the task of
finding servers to a new level of sophistication by allowing a user
to delve down into a hierarchy of networks, domains, hosts, and
services offered by each server.</p>

<p>While name resolution and
<a name="INDEX-2"/>browsing are not
difficult to configure, some complexity is introduced by the variety
of available name-resolution systems. Historically, Unix and other
TCP/IP users have moved from a flat hosts file to the Domain Name
System, with the Network Information System being another popular
choice. Meanwhile, Microsoft has moved from a broadcasting system to
a simple, LAN-only name server called WINS and ultimately to DNS.</p>

<p>The reason for going over that history is that all previous systems
of name resolution are still in use today! Finding a host is so
crucial to networking that sites want robust (if limited)
name-resolution systems to fall back on in case the main system
fails. Browsing is also complicated by the frequent need to show
hosts in other subnets. This chapter shows you how to configure your
network to handle name resolution and browsing any way you want.</p>

<p>Some of the differences between Unix and Microsoft networking
implementations are the result of fundamental design goals. Unix
networking was originally designed largely to implement a relatively
formal group of systems that were assumed to be small in number,
well-maintained, and highly available, that have static IP addresses,
and that wouldn't physically move around from place
to place. Bringing a new server online was a labor-intensive task,
but it did not have to be performed frequently. In contrast, Windows
networking was originally developed as a peer-to-peer collection of
small personal computers on a single subnet, having no centrally or
hierarchically organized structure.</p>

<p>SMB networking is dynamic. Computers are allowed to leave the network
at any time, sometimes without warning, and also to join or rejoin
the network at any time. Furthermore, any user in a Windows network
can add a new shared resource to the network or remove a resource
that he had previously added. The change in the
network's configuration is handled automatically by
the rest of the network without requiring a system administrator to
take any action.</p>


<div class="sect1"><a name="samba2-CHP-7-SECT-1"/>

<h2 class="head1">Name Resolution</h2>

<p>TCP/IP networks identify systems by IP addresses and always associate
these addresses with more human-readable text names. In
Microsoft's earliest networking implementations (for
MS-DOS and Windows for Workgroups), the translation of names to
network addresses was carried out in a manner that was very simple,
yet very inefficient. When a system on the network needed an IP
address corresponding to a name, it broadcasted the name to every
other system on the network and waited for the system that owned the
name to respond with its IP address.</p>

<p>The main problem with performing <a name="INDEX-3"/>name resolution using broadcast
packets is poor performance of the network as a whole, including CPU
time consumed by each host on the network, which has to accept every
broadcast packet and decide whether to respond to it. Also, broadcast
packets usually aren't forwarded by routers,
limiting name resolution to the local subnet.
Microsoft's solution was to add WINS (Windows
Internet Name Service) support to Windows NT so that the computers on
the network can perform a direct query of the WINS server instead of
using broadcast packets.</p>

<p>Modern Windows clients use a variety of methods for translating
hostnames into IP addresses. The exact method varies depending on the
version of Windows the client is running, how the client is
configured (i.e., whether DNS server and/or WINS server IP addresses
are provided), and whether the application software is accessing the
network through Microsoft's Winsock or TCP/IP API.
In general, Windows uses some combination of the following
methods:<a name="INDEX-4"/></p>

<ul><li>
<p>Looking up the name in its cache of recently resolved names</p>
</li><li>
<p>Querying DNS servers</p>
</li><li>
<p>Using the DNS <em class="filename">Hosts</em> file</p>
</li><li>
<p>Querying WINS servers</p>
</li><li>
<p>Using the WINS <em class="filename">LMHOSTS</em> file</p>
</li><li>
<p>Performing broadcast name resolution</p>
</li></ul>
<p>The first method is pretty much self-explanatory. A hostname is
checked against a cache of hostnames that have been recently resolved
to IP addresses. This helps to save time and network bandwidth for
resolving names that are used frequently.</p>

<p>When a Windows system is configured with the IP address of at least
one <a name="INDEX-5"/>DNS server, it can use DNS to
resolve fully qualified domain names, such as those for sites on the
Internet. The DNS servers can be either Windows NT/2000 or Unix
systems. You can learn more about DNS and DNS server configuration in
the O'Reilly book <em class="citetitle">DNS and
BIND</em>.</p>

<p>In this chapter, we focus mainly on name resolution using WINS, which
is supported by Samba with the <em class="emphasis">nmbd</em> daemon.</p>


<div class="sect2"><a name="samba2-CHP-7-SECT-1.1"/>

<h3 class="head2">WINS Clients and Server Interaction</h3>

<p>There are two types of interaction between a
<a name="INDEX-6"/>WINS client and a server: the
client keeps its own NetBIOS name<a name="FNPTR-1"/><a href="#FOOTNOTE-1">[1]</a> registered with the server and
queries the server to get the IP address corresponding to the NetBIOS
name of another system.</p>

<p>When a WINS client joins the network, it registers its NetBIOS name
with the WINS server, which stores it along with the
client's IP address in the WINS database. This entry
is marked <em class="firstterm">active</em>. The client is then expected
to renew the registration of its name periodically (typically, every
four days) to inform the server that it is still using the name. This
period is called the <em class="firstterm">time to live</em>, or TTL.
When the client leaves the network by being shut down gracefully, it
informs the server, and the server marks the
client's entry in its database as
<em class="firstterm">released</em>.</p>

<p>When a client leaves the network without telling the WINS server to
release its name, the server waits until after it fails to receive
the expected registration renewal from the client and then marks the
entry as released.</p>

<p>In either case, the released name is available for use by other
clients joining the network. It might persist in the released state
in the WINS database, and if it is not reregistered, the entry will
eventually be deleted.</p>

<p>More information on WINS can be found in the Microsoft white paper
<em class="citetitle">Windows Internet Naming Service (WINS) Architecture and
Capacity Planning</em><a name="INDEX-7"/>. It can be downloaded from the
Microsoft web site at <a href="http://www.microsoft.com">http://www.microsoft.com</a>.</p>


</div>


<div class="sect2"><a name="samba2-CHP-7-SECT-1.2"/>

<h3 class="head2">The lmhosts File</h3>

<p>In <a href="ch03.html">Chapter 3</a> we showed you how to configure
Windows systems to use the
<em class="filename">LMHOSTS</em><a name="INDEX-8"/>
file as an alternative to the WINS server for name resolution. Samba
also can use an <em class="filename">LMHOSTS</em> file, which by default
is <em class="filename">/usr/local/samba/lib/lmhosts</em>.
Samba's <em class="filename">lmhosts</em> is the same
format as the Windows version. A simple <em class="filename">lmhosts</em>
file might look like this:</p>

<blockquote><pre class="code">172.16.1.1    toltec
172.16.1.6    maya</pre></blockquote>

<p>The names on the right side of the entries are NetBIOS names, so you
can assign resource types to them and add additional entries for
computers:</p>

<blockquote><pre class="code">172.16.1.1    toltec#20
172.16.1.1    metran#1b
172.16.1.6    maya#20</pre></blockquote>

<p>Here, we've made <tt class="literal">toltec</tt> the
primary domain controller of the <tt class="literal">METRAN</tt> domain on
the second line. This line starts with
<tt class="literal">toltec</tt>'s IP address, followed by
the name metran and the resource type &lt;1B&gt;. The other lines are
entries for <tt class="literal">toltec</tt> and <tt class="literal">maya</tt> as
standard workstations.</p>

<p>If you wish to place an <em class="emphasis">lmhosts</em> file somewhere
other than the default location, you will need to notify the
<em class="emphasis">nmbd</em> process upon startup using the
<em class="emphasis">-H</em> option, followed by the name of your
<em class="filename">lmhosts</em> file, as follows:</p>

<blockquote><pre class="code"># <tt class="userinput"><b>nmbd -H /etc/samba/lmhosts -D</b></tt></pre></blockquote>


</div>


<div class="sect2"><a name="samba2-CHP-7-SECT-1.3"/>

<h3 class="head2">Configuring Name Resolution for the Samba Suite</h3>

<p>Various daemons and tools in the Samba suite need to perform
<a name="INDEX-9"/>name resolution. You can define the
order in which the programs try each name-resolution method through
the <tt class="literal">name</tt><a name="INDEX-10"/><a name="INDEX-11"/>
<tt class="literal">resolve</tt> <tt class="literal">order</tt> parameter, like
this:</p>

<blockquote><pre class="code">[global]
    name resolve order = wins lmhosts hosts bcast</pre></blockquote>

<p>The string used to define the parameter can take up to four values:</p>

<dl>
<dt><b>lmhosts</b></dt>
<dd>
<p>Uses the Samba server's local
<em class="filename">lmhosts</em> file</p>
</dd>


<dt><b>hosts</b></dt>
<dd>
<p>Uses the standard Unix name-resolution methods, which can be
<em class="emphasis">/etc/hosts</em>, DNS, NIS, or a combination,
depending on how the local system is configured</p>
</dd>


<dt><b>wins</b></dt>
<dd>
<p>Uses the WINS server</p>
</dd>


<dt><b>bcast</b></dt>
<dd>
<p>Uses the broadcast method</p>
</dd>

</dl>

<p>The order in which they are specified is the order in which name
resolution will be attempted. In our example, Samba will attempt to
use its WINS server first for name resolution, followed by the
<em class="emphasis">lmhosts</em> file on the local system. Next, the
<tt class="literal">hosts</tt> value tells it to use Unix name-resolution
methods. The word <tt class="literal">hosts</tt> can be misleading; it
covers not only the <em class="filename">/etc/hosts</em> file, but also
the use of DNS or NIS (as configured on the Unix host). Finally, if
those three do not work, it will perform a broadcast name resolution.</p>


</div>


<div class="sect2"><a name="samba2-CHP-7-SECT-1.4"/>

<h3 class="head2">Setting Up Samba as a WINS Server</h3>

<p>You can set up Samba as a <a name="INDEX-12"/>WINS server by setting the
<tt class="literal">wins</tt><a name="INDEX-13"/> <tt class="literal">support</tt>
parameter in the configuration file, like this:</p>

<blockquote><pre class="code">[global]
    wins support = yes</pre></blockquote>

<p>Believe it or not, that's all you need to do! The
<tt class="literal">wins</tt> <tt class="literal">support</tt> option turns Samba
into a WINS server. For most installations, Samba's
default configuration is sufficient.</p>
<a name="samba2-CHP-7-NOTE-137"/><blockquote class="note"><h4 class="objtitle">WARNING</h4>
<p>Remember, Samba cannot communicate with Windows WINS servers. If you
are using Samba as your WINS server, you must make sure not to allow
any Windows systems or other Samba servers on your network to be
configured as WINS servers. If you do, their WINS databases will not
synchronize, resulting in inconsistent name resolution.</p>
</blockquote>


<div class="sect3"><a name="samba2-CHP-7-SECT-1.4.1"/>

<h3 class="head3">Configuring a DNS proxy</h3>

<p>A Samba <a name="INDEX-14"/><a name="INDEX-15"/>WINS server can check with the
system's DNS server if a requested host cannot be
found in its WINS database. With a typical Linux system, for example,
you can find the IP address of the DNS server by searching the
<em class="filename">/etc/resolv.conf</em><a name="INDEX-16"/><a name="INDEX-17"/> file. In it, you might see an entry such
as the following:</p>

<blockquote><pre class="code">nameserver 127.0.0.1
nameserver 172.16.1.192</pre></blockquote>

<p>This tells us that the Linux system is configured to use a DNS server
located at 172.16.1.192. (The 127.0.0.1 is the
<tt class="literal">localhost</tt> address and is never a valid DNS server
address.)</p>

<p>Now it is a simple matter of using the
<tt class="literal">dns</tt><a name="INDEX-18"/> <tt class="literal">proxy</tt> option to tell
Samba to use the DNS server:</p>

<blockquote><pre class="code">[global]
    dns proxy = yes</pre></blockquote>

<a name="samba2-CHP-7-NOTE-138"/><blockquote class="note"><h4 class="objtitle">TIP</h4>
<p>Although this allows Windows clients to resolve fully qualified
Internet domain names through the Samba WINS server, it will work
only for domain names that fit within the 15-character limitation of
NetBIOS names. For this reason, we recommend you use <tt class="literal">dns
proxy</tt> only to act as a supplement to your WINS server,
rather than as a replacement for a DNS server.</p>
</blockquote>


</div>


</div>


<div class="sect2"><a name="samba2-CHP-7-SECT-1.5"/>

<h3 class="head2">Setting Up Samba to Use Another WINS Server</h3>

<p>You can configure Samba to use a <a name="INDEX-19"/>WINS server somewhere else on the
network by simply providing it with the IP address of the WINS
server. This is done with the global
<tt class="literal">wins</tt><a name="INDEX-20"/> <tt class="literal">server</tt>
configuration option, as shown here:</p>

<blockquote><pre class="code">[global]
    wins server = 172.16.1.1</pre></blockquote>

<p>With this option enabled, Samba will direct all WINS requests to the
server located at 172.16.1.1. Note that because the request is
directed at a single machine, we don't have to worry
about any of the problems inherent in broadcasting. However, Samba
will not necessarily use the WINS server before other forms of name
resolution. The order in which Samba attempts various name-resolution
techniques is given with the <tt class="literal">name</tt>
<tt class="literal">resolve</tt> <tt class="literal">order</tt> configuration
option, which we discussed earlier.</p>

<p>The <tt class="literal">wins</tt> <tt class="literal">support</tt> and the
<tt class="literal">wins</tt> <tt class="literal">server</tt> parameters are
mutually exclusive; you cannot simultaneously offer Samba as the WINS
server and use another system as the server! Typically, one Samba
server is set up as the WINS server using <tt class="literal">wins</tt>
<tt class="literal">support</tt>, and all other Samba servers are
configured with the <tt class="literal">wins</tt> <tt class="literal">server</tt>
parameter pointing to the Samba WINS server.</p>


<div class="sect3"><a name="samba2-CHP-7-SECT-1.5.1"/>

<h3 class="head3">Configuring a WINS proxy</h3>

<p><a name="INDEX-21"/>If you have a Samba server on a
subnet that doesn't have a WINS server, and the
Samba server has been configured with a WINS server on another
subnet, you can tell the Samba server to forward any name-resolution
requests with the <tt class="literal">wins</tt><a name="INDEX-22"/>
<tt class="literal">proxy</tt> option:</p>

<blockquote><pre class="code">[global]
    wins server = 172.16.200.12
    wins proxy = yes</pre></blockquote>

<p>Use this only in situations where the WINS server resides on another
subnet. Otherwise, the broadcast will reach the WINS server
regardless of any proxying.</p>


</div>


</div>


<div class="sect2"><a name="samba2-CHP-7-SECT-1.6"/>

<h3 class="head2">Name-Resolution Configuration Options</h3>

<p><a name="INDEX-23"/>Samba's <a name="INDEX-24"/>name-resolution options
are shown in <a href="ch07.html#samba2-CHP-7-TABLE-1">Table 7-1</a>.</p>

<a name="samba2-CHP-7-TABLE-1"/><h4 class="head4">Table 7-1. Name-resolution options</h4><table border="1">


<tr>
<th>
<p>Option</p>
</th>
<th>
<p>Parameters</p>
</th>
<th>
<p>Function</p>
</th>
<th>
<p>Default</p>
</th>
<th>
<p>Scope</p>
</th>
</tr>


<tr>
<td>
<p><tt class="literal">wins support</tt></p>
</td>
<td>
<p>boolean</p>
</td>
<td>
<p>If set to <tt class="literal">yes</tt>, allows Samba to act as a WINS server</p>
</td>
<td>
<p><tt class="literal">no</tt></p>
</td>
<td>
<p>Global</p>
</td>
</tr>
<tr>
<td>
<p><tt class="literal">wins server</tt></p>
</td>
<td>
<p>string (IP address or DNS name)</p>
</td>
<td>
<p>Identifies a WINS server for Samba to use for name registration and
resolution</p>
</td>
<td>
<p>None</p>
</td>
<td>
<p>Global</p>
</td>
</tr>
<tr>
<td>
<p><tt class="literal">wins proxy</tt></p>
</td>
<td>
<p>boolean</p>
</td>
<td>
<p>Allows Samba to act as a proxy to a WINS server on another subnet</p>
</td>
<td>
<p><tt class="literal">no</tt></p>
</td>
<td>
<p>Global</p>
</td>
</tr>
<tr>
<td>
<p><tt class="literal">wins hook</tt></p>
</td>
<td>
<p>string</p>
</td>
<td>
<p>Command to run when the WINS database changes</p>
</td>
<td>
<p>None</p>
</td>
<td>
<p>Global</p>
</td>
</tr>
<tr>
<td>
<p><tt class="literal">dns proxy</tt></p>
</td>
<td>
<p>boolean</p>
</td>
<td>
<p>If set to <tt class="literal">yes</tt>, allows a Samba WINS server to
search DNS if it cannot find a name in WINS</p>
</td>
<td>
<p><tt class="literal">no</tt></p>
</td>
<td>
<p>Global</p>
</td>
</tr>
<tr>
<td>
<p><tt class="literal">name resolve</tt> <tt class="literal">order</tt></p>
</td>
<td>
<p>string</p>
</td>
<td>
<p>The order of methods used to resolve NetBIOS names</p>
</td>
<td>
<p><tt class="literal">lmhosts</tt> <tt class="literal">hosts wins bcast</tt></p>
</td>
<td>
<p>Global</p>
</td>
</tr>
<tr>
<td>
<p><tt class="literal">max ttl</tt></p>
</td>
<td>
<p>numeric</p>
</td>
<td>
<p>Maximum TTL in seconds for a requested NetBIOS name</p>
</td>
<td>
<p><tt class="literal">259200</tt> ( 3 days)</p>
</td>
<td>
<p>Global</p>
</td>
</tr>
<tr>
<td>
<p><tt class="literal">max wins ttl</tt></p>
</td>
<td>
<p>numeric</p>
</td>
<td>
<p>Maximum TTL in seconds for NetBIOS names given out by Samba as a WINS
server</p>
</td>
<td>
<p><tt class="literal">518400</tt> (6 days)</p>
</td>
<td>
<p>Global</p>
</td>
</tr>
<tr>
<td>
<p><tt class="literal">min wins ttl</tt></p>
</td>
<td>
<p>numeric</p>
</td>
<td>
<p>Minimum TTL in seconds for NetBIOS names given out by Samba as a WINS
server</p>
</td>
<td>
<p><tt class="literal">21600</tt> (6 hours)</p>
</td>
<td>
<p>Global</p>
</td>
</tr>

</table>


<div class="sect3"><a name="samba2-CHP-7-SECT-1.6.1"/>

<a name="INDEX-25"/><h3 class="head3">wins support</h3>

<p>Samba will provide WINS name service to all machines in the network
if you set the following in the <tt class="literal">[global]</tt> section
of the <em class="filename">smb.conf</em> file:</p>

<blockquote><pre class="code">[global]
    wins support = yes</pre></blockquote>

<p>The default value is <tt class="literal">no</tt>, which is typically used
to allow a Windows NT/2000 server or another Samba server to be the
WINS server. If you enable this option, remember that a Samba WINS
server currently cannot exchange data with other WINS servers, so do
not allow any other WINS servers on the network. When set to
<tt class="literal">yes</tt>, this option is mutually exclusive with the
<tt class="literal">wins</tt> <tt class="literal">server</tt> parameter.</p>


</div>


<div class="sect3"><a name="samba2-CHP-7-SECT-1.6.2"/>

<a name="INDEX-26"/><h3 class="head3">wins server</h3>

<p>Samba will use an existing WINS server on the network if you specify
the <tt class="literal">wins</tt> <tt class="literal">server</tt> global option
in your configuration file. The value of this option is either the IP
address or DNS name (not NetBIOS name) of the WINS server. For
example:</p>

<blockquote><pre class="code">[global]
    wins server = 172.16.220.110</pre></blockquote>

<p>or:</p>

<blockquote><pre class="code">[global]
    wins server = wins.metran.cx</pre></blockquote>

<p>For this option to work, the <tt class="literal">wins</tt>
<tt class="literal">support</tt> option must be set to
<tt class="literal">no</tt> (the default). Otherwise, Samba will report an
error. You can specify only one WINS server using this option.</p>


</div>


<div class="sect3"><a name="samba2-CHP-7-SECT-1.6.3"/>

<a name="INDEX-27"/><h3 class="head3">wins proxy</h3>

<p>This option allows Samba to act as a proxy to another WINS server,
and thus relay name registration and resolution requests from itself
to the real WINS server, often outside the current subnet. The WINS
server can be indicated through the <tt class="literal">wins</tt>
<tt class="literal">server</tt> option. The proxy will then return the WINS
response back to the client. You can enable this option by specifying
the following in the <tt class="literal">[global]</tt> section:</p>

<blockquote><pre class="code">[global]
    wins proxy = yes</pre></blockquote>


</div>


<div class="sect3"><a name="samba2-CHP-7-SECT-1.6.4"/>

<a name="INDEX-28"/><h3 class="head3">wins hook</h3>

<p>This option allows you to run a script or other program whenever the
WINS database is modified. One application might be to set up another
Samba server to act as a backup for another Samba WINS server. This
is done by having the <tt class="literal">wins</tt> <tt class="literal">hook</tt>
script call <em class="emphasis">rsync</em> to synchronize the WINS
databases (<em class="filename">/usr/local/samba/var/locks/wins.dat</em>)
on the two systems whenever an entry is added or deleted. The script
would be specified in the Samba configuration file like this:</p>

<blockquote><pre class="code">[global]
    wins hook = /usr/local/bin/sync_wins</pre></blockquote>


</div>


<div class="sect3"><a name="samba2-CHP-7-SECT-1.6.5"/>

<a name="INDEX-29"/><h3 class="head3">dns proxy</h3>

<p>If you want the DNS to be used if a NetBIOS name
isn't found in WINS, you can set the following
option:</p>

<blockquote><pre class="code">[global]
    dns proxy = yes</pre></blockquote>

<p>This will permit <em class="filename">nmbd</em> to query the
server's standard DNS. You might wish to deactivate
this option if you do not have a permanent connection to your DNS
server. This option should not be used in place of a DNS server on
your network; it is intended for resolving NetBIOS names rather than
fully qualified Internet domain names.</p>


</div>


<div class="sect3"><a name="samba2-CHP-7-SECT-1.6.6"/>

<h3 class="head3">name resolve order</h3>

<p>The global <tt class="literal">name</tt><a name="INDEX-30"/>
<tt class="literal">resolve</tt> <tt class="literal">order</tt> option specifies
the order of services that Samba will use in performing name
resolution. The default order is to use the
<em class="emphasis">lmhosts</em> file, followed by standard Unix
name-resolution methods (some combination of
<em class="filename">/etc/hosts</em>, DNS, and NIS), then to query a WINS
server, and finally to use broadcasting to determine the address of a
NetBIOS name. You can override this option by specifying something
like the following:</p>

<blockquote><pre class="code">[global]
    name resolve order = lmhosts wins hosts bcast</pre></blockquote>

<p>This causes resolution to use the <em class="emphasis">lmhosts</em> file
first, followed by a query to a WINS server, the
<em class="filename">/etc/hosts</em> file, and finally broadcasting. You
need not use all four options. This option is covered in more detail
in <a href="ch07.html#samba2-CHP-7-SECT-1.4">Section 7.1.4</a>,
earlier in this chapter.</p>


</div>


<div class="sect3"><a name="samba2-CHP-7-SECT-1.6.7"/>

<a name="INDEX-31"/><h3 class="head3">max ttl</h3>

<p>This option is used when Samba is not acting as a WINS server but is
using another system on the network for its WINS server. It sets the
maximum T T L for NetBIOS names registered by the Samba server with
the WINS server. You should never need to alter this value.</p>


</div>


<div class="sect3"><a name="samba2-CHP-7-SECT-1.6.8"/>

<a name="INDEX-32"/><h3 class="head3">max wins ttl</h3>

<p>This option is used when Samba is providing WINS name service, and it
sets the maximum T T L for NetBIOS names registered with Samba. You
should never need to change this value from its default.</p>


</div>


<div class="sect3"><a name="samba2-CHP-7-SECT-1.6.9"/>

<a name="INDEX-33"/><h3 class="head3">min wins ttl</h3>

<p>This option is used when Samba is providing WINS name service, and it
sets the minimum T T L for NetBIOS names registered with Samba. You
should never need to alter this value from its default. <a name="INDEX-34"/> <a name="INDEX-35"/> <a name="INDEX-36"/></p>


</div>


</div>


</div>


<div class="sect1"><a name="samba2-CHP-7-SECT-2"/>

<h2 class="head1">Browsing</h2>

<p><a name="INDEX-37"/>Browsing
was developed by Microsoft to help users find shared resources on the
network. In a networked computing environment where users can add or
remove shares at any time, it is important to have some automatic
means of keeping track of the shared resources and allowing users to
&quot;browse&quot; through them to find the
ones they wish to use.</p>

<p>Before browsing was added to SMB networking, when anyone added a new
share, the people with whom they wished to share the data or printer
would have to be informed of the share's UNC, using
some relatively low-tech method such as speaking to them in person or
over the phone, or sending email. Already, this was very inconvenient
in large organizations. To further complicate matters, the users
working on client computers had to type in the
share's UNC to connect to it. The only way to get
around typing in the share's UNC every time it was
used was to map a network drive to it, and with a large number of
shares on the network, this could easily get out of hand.</p>


<div class="sect2"><a name="samba2-CHP-7-SECT-2.1"/>

<h3 class="head2">Browsing in a Windows Network</h3>

<p><a name="INDEX-38"/>To keep things simple, we will
first describe network browsing in a network that contains only
Windows systems and then show you how to add a Samba server.</p>

<p>The basic way browsing works is that one computer in the network
takes on the role of the <em class="firstterm">master
browser</em><a name="INDEX-39"/> (also
called <em class="firstterm">local master
browser</em><a name="INDEX-40"/>,<em class="firstterm"> browse
master</em><a name="INDEX-41"/>, or
<em class="firstterm">browse server</em><a name="INDEX-42"/>) and
keeps a list of all the computers on the local subnet that are acting
as SMB servers. The list of computers is called the <em class="firstterm">browse
list</em><a name="INDEX-43"/> and includes all Samba servers, Windows
NT/2000/XP systems, and any Windows 95/98/Me systems that have the
&quot;File and printer sharing for Microsoft
Networks&quot; networking component installed. The browse
list also contains the names of all workgroups and domains. At this
level, browsing is limited to the local subnet because the browsing
protocol depends on broadcast packets, which are typically not
forwarded to other subnets by routers.</p>

<p>A user at any Windows system can view the browse list by opening up
the Network Neighborhood (or My Network Places), as we showed you in
<a href="ch01.html">Chapter 1</a>. Or, the <em class="emphasis">net
view</em><a name="INDEX-44"/> command can be used from a Windows
command prompt:</p>

<blockquote><pre class="code">C:\&gt;<tt class="userinput"><b>net view</b></tt>
Server Name            Remark

-------------------------------------------------------------------------------
\\MAYA                 Windows 98
\\MIXTEC               Samba 2.2.5
\\OLMEC                Windows XP Pro on Pentium/ASUS
\\TOLTEC               Samba 2.2.5
\\YAQUI                Windows 95 on mixtec/VMware
\\ZAPOTEC
The command completed successfully.</pre></blockquote>

<p>Then, <em class="emphasis">net view</em> can be used with a computer name
as an argument to contact a server directly and list the resources it
is sharing:</p>

<blockquote><pre class="code">C:\&gt;<tt class="userinput"><b>net view \\maya</b></tt>
Shared resources at \\maya

Windows 98

Share name   Type         Used as  Comment

-------------------------------------------------------------------------------
D            Disk
E            Disk
HP           Print
The command completed successfully.</pre></blockquote>

<p>The computers on the network involved in browsing are more than just
the master browser and its clients. There are also backup browsers,
which maintain copies of the browse list and respond to client
requests for it. Backup browsers are therefore able to take over the
role of master browser seamlessly in case it fails. The master
browser usually doesn't serve the browse list
directly to clients. Instead, its job is mainly to keep the master
copy of the browse list up-to-date, and also periodically update the
backup browsers. Clients are expected to get their copies of the
browse list from backup browsers, selecting among them randomly to
help to distribute the load on the backup browsers more evenly.
Ideally, the interaction between any client and the master browser is
limited to the client announcing when it joins or leaves the network
(if it is a server) and requesting a list of backup browsers.</p>

<p>There can be more than one <a name="INDEX-45"/>backup browser. A workgroup will have a
backup browser if two or more computers are running Windows 95/98/Me
or Windows NT Workstation (or another nonserver version of Windows
NT/2000/XP) on the subnet. For every 32 additional computers, another
backup browser is added.</p>

<p>In a Windows NT domain, the <a name="INDEX-46"/>primary domain controller is
always the local master browser, and if it fails, another Windows
NT/2000 server (if one exists) will take over the role of local
master browser. Other versions of Windows can function as backup
browsers, but will never become a master browser if a Windows NT/2000
server is available.</p>

<p>In addition to acting as the local master browser, the primary domain
controller also acts as the <em class="firstterm">domain master
browser</em><a name="INDEX-47"/>, which ties subnets together and allows
browse lists to be shared between master and backup browsers on
separate subnets. This is how browsing is extended to function beyond
the local subnet. Each subnet functions as a separate browsing
entity, and the domain master browser synchronizes the master
browsers of each subnet. In a Windows-only network, browsing cannot
function across subnets unless a Windows NT/2000 PDC exists on the
network. Samba can act as a domain master browser and can perform
that task even in a workgroup network, which means that the Windows
PDC is not required for this task. (It is also possible to use the
<tt class="literal">remote</tt> <tt class="literal">browse</tt>
<tt class="literal">sync</tt> parameter to configure a Samba server to
synchronize its browse list with a Samba server on another subnet. In
this case, each server must be acting as the local master browser of
its subnet.)</p>

<p>Unless it is configured never to act as a browser, each computer on
the subnet is considered a <em class="firstterm">potential browser</em>
and can be ordered by the browse master to become a backup browser,
or it can identify itself as a backup browser and accept the role on
its own.</p>


</div>


<div class="sect2"><a name="samba2-CHP-7-SECT-2.2"/>

<h3 class="head2">Browser Elections</h3>

<p><a name="INDEX-48"/>When no master browser is running on
the subnet, potential browsers choose a new master browser among
themselves in a process called an <em class="firstterm">election</em>. An
election is started by a computer in the subnet when it discovers
that no master browser is currently running. If a master browser is
shut down gracefully, it will broadcast an election request datagram,
initiating an election by the remaining computers. If the master
browser fails, the election can be started by a client computer that
requests a list of backup browsers from the master browser or by a
backup browser that requests to have its browse list updated from the
master browser. In each case, the system fails to receive a reply
from the master browser and initiates the election.</p>

<p>Browser elections are decided in multiple rounds of self-elimination.
During each round, potential browsers broadcast election request
datagrams containing their qualifications to notify other potential
browsers that an election is happening and that if the recipient is
more qualified, it should also broadcast a bid. When a potential
browser receives an election request datagram from a more qualified
opponent, it drops out, disqualifying itself from becoming the master
browser. Otherwise, it responds with its own election request
datagram. After a few rounds, only one potential browser is left in
the election. After an additional four rounds of sending out an
election request datagram and receiving no response, it becomes the
master browser and sends a broadcast datagram announcing itself as
the local master browser for the subnet. It then assigns runners-up
in the election as backup browsers, as needed.</p>

<p>A potential browser's qualifications include the
following:</p>

<ul><li>
<p>Whether it has recently lost an election</p>
</li><li>
<p>The version of the election protocol it is running</p>
</li><li>
<p>Its election criteria</p>
</li><li>
<p>The amount of time the system has been up</p>
</li><li>
<p>The computer's NetBIOS name</p>
</li></ul>
<p>If the potential browser has lost an election recently, it
immediately disqualifies itself. The version of the election protocol
it is running is checked, but so far, all Windows systems (and Samba)
use the same election protocol, so the check is not very meaningful.
The election criteria are usually what determine which computer
becomes the local master browser. There are two parts to the election
criteria, shown in Tables <a href="ch07.html#samba2-CHP-7-TABLE-2">Table 7-2</a> and <a href="ch07.html#samba2-CHP-7-TABLE-3">Table 7-3</a>.</p>

<a name="samba2-CHP-7-TABLE-2"/><h4 class="head4">Table 7-2. Operating-system values in an election</h4><table border="1">


<tr>
<th>
<p>Operating system</p>
</th>
<th>
<p>Value</p>
</th>
</tr>


<tr>
<td>
<p>Windows NT/2000 Server, running as PDC</p>
</td>
<td>
<p>32</p>
</td>
</tr>
<tr>
<td>
<p>Windows NT/2000/XP, if not the PDC</p>
</td>
<td>
<p>16</p>
</td>
</tr>
<tr>
<td>
<p>Windows 95/98/Me</p>
</td>
<td>
<p>1</p>
</td>
</tr>
<tr>
<td>
<p>Windows for Workgroups</p>
</td>
<td>
<p>1</p>
</td>
</tr>

</table>

<a name="samba2-CHP-7-TABLE-3"/><h4 class="head4">Table 7-3. Computer-role settings in an election</h4><table border="1">


<tr>
<th>
<p>Role</p>
</th>
<th>
<p>Value</p>
</th>
</tr>


<tr>
<td>
<p>Domain master browser</p>
</td>
<td>
<p>128</p>
</td>
</tr>
<tr>
<td>
<p>WINS client</p>
</td>
<td>
<p>32</p>
</td>
</tr>
<tr>
<td>
<p>Preferred master</p>
</td>
<td>
<p>8</p>
</td>
</tr>
<tr>
<td>
<p>Running master</p>
</td>
<td>
<p>4</p>
</td>
</tr>
<tr>
<td>
<p>Recent backup browser</p>
</td>
<td>
<p>2</p>
</td>
</tr>
<tr>
<td>
<p>Backup browser</p>
</td>
<td>
<p>1</p>
</td>
</tr>

</table>

<p>The operating-system type is compared first, and the system with the
highest value wins. The values have been chosen to cause the primary
domain controller, if there is one, to become the local master
browser. Otherwise, a Windows NT/2000/XP system will win over a
Windows for Workgroups or Windows 95/98/Me system.</p>

<p>When an operating-system type comparison results in a tie, the role
of the computer is compared. A computer can have more than one of the
values in <a href="ch07.html#samba2-CHP-7-TABLE-3">Table 7-3</a>, in which case the values are
added.</p>

<p>A domain master browser has a role value of 128 to weight the
election so heavily in its favor that it will also become the local
master browser on its own subnet. Although the primary domain
controller (which is always the domain master browser) will win the
election based solely on its operating system value, sometimes there
is no primary domain controller on the network, and the domain master
browser would not otherwise be distinguished from other potential
browsers.</p>

<p>Systems that are using a WINS server for name resolution are weighted
heavily over ones that use broadcast name resolution with a role
value of 32.</p>

<p>A <em class="firstterm">preferred master</em> is a computer that has been
selected and configured manually by a system administrator to be
favored as the choice master browser. When a preferred master starts
up, it forces a browser election, even if an existing master browser
is still active. A preferred master has a role value of 8, and the
existing master browser gets a value of 4.</p>

<p>A backup browser that has recently been a master browser and still
has an up-to-date browse list is given a role value of 2, and a
potential browser that has been running as a backup browser gets a
value of 1.</p>

<p>If comparing the operating-system type and role results in a tie, the
computer that has been running the longest wins. In the unlikely
event that the two have been up for the same amount of time, the
computer that wins is the one with the NetBIOS name that sorts first
alphabetically.</p>

<p>You can tell if a machine is a local master browser by using the
Windows <em class="emphasis">nbtstat</em><a name="INDEX-49"/> command. Place the NetBIOS name of the
machine you wish to check after the <em class="emphasis">-a</em> option:</p>

<blockquote><pre class="code">C:\&gt;<tt class="userinput"><b>nbtstat -a toltec</b></tt>

Local Area Connection:
Node IpAddress: [172.16.1.4] Scope Id: []

           NetBIOS Remote Machine Name Table

       Name               Type         Status
    ---------------------------------------------
    TOLTEC         &lt;00&gt;  UNIQUE      Registered
    TOLTEC         &lt;03&gt;  UNIQUE      Registered
    TOLTEC         &lt;20&gt;  UNIQUE      Registered
    ..__MSBROWSE__.&lt;01&gt;  GROUP       Registered
    METRAN         &lt;00&gt;  GROUP       Registered
    METRAN         &lt;1B&gt;  UNIQUE      Registered
    METRAN         &lt;1C&gt;  GROUP       Registered
    METRAN         &lt;1D&gt;  UNIQUE      Registered
    METRAN         &lt;1E&gt;  GROUP       Registered

    MAC Address = 00-00-00-00-00-00</pre></blockquote>

<p>The resource entry that you're looking for is
<tt class="literal">.._ _MSBROWSE_ _.&lt;01&gt;</tt><a name="INDEX-50"/>. This indicates
that the server is currently acting as the local master browser for
the current subnet. If the machine is a Samba server, you can check
the Samba <em class="filename">nmbd</em> log file for an entry such as:</p>

<blockquote><pre class="code">nmbd/nmbd_become_lmb.c:become_local_master_stage2(406)
*****
Samba name server TOLTEC is now a local master browser for
workgroup METRAN on subnet 172.16.1.0</pre></blockquote>

<p>Or, you can use the
<em class="emphasis">nmblookup</em><a name="INDEX-51"/> command with the
<em class="emphasis">-M</em> option and the workgroup or domain name on
any Samba server to find the IP address of the local master:</p>

<a name="INDEX-52"/><blockquote><pre class="code">$ <tt class="userinput"><b>nmblookup -M metran</b></tt>
querying metran on 172.16.1.255
172.16.1.1 metran&lt;1d&gt;</pre></blockquote>


</div>


<div class="sect2"><a name="samba2-CHP-7-SECT-2.3"/>

<h3 class="head2">Server Announcements</h3>

<p><a name="INDEX-53"/>After
the master browser election is decided, each server on the network
announces itself to the network to allow the master and backup
browsers to build their browse lists. At first, the server
announcements happen every minute, but the interval is gradually
stretched out to every 12 minutes. When a server is shut down
gracefully, it sends an announcement that it is going offline to
allow the master and backup browsers to remove it from the browse
list. However, when a server goes offline by crashing or by some
other failure, the master browser notices its disappearance only
because it stops receiving server announcements. The master browser
waits for three of the server's announcement periods
before deciding that it is offline, which can take up to 36 minutes.
Because backup browsers have their browse lists updated from the
master browser once every 15 minutes, it can take up to 51 minutes
for clients to be informed of a failed server.</p>

<p>For more detailed information on Microsoft's
browsing protocols, consult the Microsoft documents
<em class="citetitle">Browsing and Windows 95
Networking</em><a name="INDEX-54"/> and
<em class="citetitle">CIFS/E Browser Protocol</em>. You can find these by
searching for the titles on the Microsoft web site at <a href="http://www.microsoft.com">http://www.microsoft.com</a>.</p>

<p>More information on configuring Samba for browsing can be found in
<em class="filename">BROWSING.txt</em><a name="INDEX-55"/> and
<em class="filename">BROWSING-Config.txt</em> in the Samba
distribution's <em class="filename">docs/textdocs</em>
directory. <a name="INDEX-56"/></p>


</div>


<div class="sect2"><a name="samba2-CHP-7-SECT-2.4"/>

<h3 class="head2">Configuring Samba for Browsing</h3>

<p><a name="INDEX-57"/><a name="INDEX-58"/><a name="INDEX-59"/>Samba has full support for browsing
and can participate as a master browser, a backup browser, a domain
master browser, a potential browser, or just a server that
doesn't participate in browsing elections. If you
want to make sure your Samba server never becomes a master or backup
browser, simply set:</p>

<a name="INDEX-60"/><blockquote><pre class="code">[global]
    local master = no</pre></blockquote>

<p>Usually, you will want Samba to be available as a local master or at
least a backup browser. In the simplest case, you
don't need to do anything because
Samba's default is to participate in browsing
elections with its operating system value set to 20, which will beat
any Windows system less than a Windows NT/2000 primary domain
controller (see <a href="ch07.html#samba2-CHP-7-TABLE-2">Table 7-2</a>). The operating-system
value Samba reports for itself in browser elections can be set using
the <tt class="literal">os</tt><a name="INDEX-61"/> <tt class="literal">level</tt>
parameter:</p>

<blockquote><pre class="code">[global]
    os level = 33</pre></blockquote>

<p>The preceding value will allow Samba to beat even a Windows 2000
Advanced Server acting as a primary domain controller. As we show in
the following section, though, forcing Samba to win this way is not
recommended.</p>

<p>If you want to allow a Windows XP Professional system to be the
master browser, you would need to set Samba lower:</p>

<blockquote><pre class="code">[global]
    os level = 8</pre></blockquote>

<p>The maximum value for <tt class="literal">os</tt> <tt class="literal">level</tt>
is 255 because it is handled as an 8-bit unsigned integer. Supposing
we wanted to make absolutely sure our Samba server will be the local
master browser at all times, we might say:</p>

<blockquote><pre class="code">[global]
    local master = yes
    os level = 255
    preferred master = yes</pre></blockquote>

<p>The addition of the
<tt class="literal">preferred</tt><a name="INDEX-62"/>
<tt class="literal">master</tt> parameter causes Samba to start a browser
election as soon as it starts up, and the <tt class="literal">os</tt>
<tt class="literal">level</tt> of 255 allows it to beat any other system on
the network. This includes other Samba servers, assuming they are
configured properly! If another server is using a similar
configuration file (with <tt class="literal">os</tt>
<tt class="literal">level</tt> <tt class="literal">=</tt> <tt class="literal">255</tt>
and <tt class="literal">preferred</tt> <tt class="literal">master</tt>
<tt class="literal">=</tt> <tt class="literal">yes</tt>), the two will fight each
other for the master browser role, winning elections based on minor
criteria, such as uptime or their current role. To avoid this, other
Samba servers should be set with a lower <tt class="literal">os</tt>
<tt class="literal">level</tt> and not configured to be the preferred
master.</p>


</div>


<div class="sect2"><a name="samba2-CHP-7-SECT-2.5"/>

<h3 class="head2">Samba as the Domain Master Browser</h3>

<p><a name="INDEX-63"/>Previously we mentioned that for a Windows
workgroup or domain to extend into multiple subnets, one system would
have to take the role of the domain master browser. The domain master
browser propagates browse lists across each subnet in the workgroup.
This works because each local master browser periodically
synchronizes its browse list with the domain master browser. During
this synchronization, the local master browser passes on the name of
any server that the domain master browser does not have in its browse
list, and vice versa. Each local master browser eventually holds the
browse list for the entire domain.</p>

<p>There is no election to determine which machine assumes the role of
the domain master browser. Instead, the administrator has to set it
manually. By Microsoft design, however, the domain master browser and
the PDC both register a resource type of &lt;1B&gt;, so the
roles&mdash;and the machines&mdash;are inseparable.</p>

<p>If you have a Windows NT server on the network acting as a PDC, we
recommend that you do not try to use Samba to become the domain
master browser. The reverse is true as well: if Samba is taking on
the responsibilities of a PDC, we recommend making it the domain
master browser as well. Although it is possible to split the roles
with Samba, this is not a good idea. Using two different machines to
serve as the PDC and the domain master browser can cause random
errors to occur in a Windows workgroup.</p>

<p>Samba can assume the role of a domain master browser for all subnets
in the workgroup with the following options:</p>

<blockquote><pre class="code">[global]
    domain master = yes
    preferred master = yes
    local master = yes
    os level = 255</pre></blockquote>

<p>The final three parameters ensure that the server is also the local
master browser, which is vital for it to work properly as the domain
master browser. You can verify that a Samba machine is in fact the
<a name="INDEX-64"/>domain master browser by checking the
<em class="emphasis">nmbd</em><a name="INDEX-65"/><a name="INDEX-66"/> log file:</p>

<blockquote><pre class="code">nmbd/nmbd_become_dmb.c:become_domain_master_stage2(118)
*****
Samba name server TOLTEC is now a domain master browser for
workgroup METRAN on subnet 172.16.1.0</pre></blockquote>

<p>Or you can use the
<em class="emphasis">nmblookup</em><a name="INDEX-67"/> command that comes with the Samba
distribution to query for a unique &lt;1B&gt; resource type in the
workgroup:</p>

<blockquote><pre class="code"># <tt class="userinput"><b>nmblookup METRAN#1B</b></tt>
Sending queries to 172.16.1.255
172.16.1.1 METRAN&lt;1b&gt;</pre></blockquote>


<div class="sect3"><a name="samba2-CHP-7-SECT-2.5.1"/>

<h3 class="head3">Multiple subnets</h3>

<p><a name="INDEX-68"/>You must
remember three rules when creating a
<a name="INDEX-69"/>workgroup/domain
that spans more than one subnet:</p>

<ul><li>
<p>You must have either a Windows NT/2000 or Samba server acting as a
local master browser on each subnet in the workgroup/domain.</p>
</li><li>
<p>You must have a Windows NT/2000 Server edition or a Samba server
acting as a domain master browser somewhere in the workgroup/domain.</p>
</li><li>
<p>A WINS server should be on the network, with each system on the
network configured to use it for name resolution.</p>
</li></ul>
<p>Samba has some additional features you can use if you
don't have or want a domain master browser on your
network and still need to have <a name="INDEX-70"/>cross-subnet browsing. Consider the
subnets shown in <a href="ch07.html#samba2-CHP-7-FIG-1">Figure 7-1</a>.</p>

<div class="figure"><a name="samba2-CHP-7-FIG-1"/><a name="INDEX-71"/><a name="INDEX-72"/><img src="figs/sam2_0701.gif"/></div><h4 class="head4">Figure 7-1. Multiple subnets with Samba servers</h4>

<p>First, a Samba server that is a local master browser can use the
<tt class="literal">remote</tt><a name="INDEX-73"/> <tt class="literal">announce</tt>
configuration option to make sure that computers in different subnets
are sent broadcast announcements about the server. This has the
effect of ensuring that the Samba server appears in the browse lists
of foreign subnets. To achieve this, however, the directed broadcasts
must reach the local master browser on the other subnet. Be aware
that many routers do not allow directed broadcasts by default; you
might have to change this setting on the router for the directed
broadcasts to get through to its subnet.</p>

<p>With the <tt class="literal">remote</tt> <tt class="literal">announce</tt>
option, list the subnets and the workgroup that should receive the
broadcast. For example, to ensure that machines in the 172.16.2 and
172.16.3 subnets and the METRAN workgroup are sent broadcast
information from our Samba server, we could specify the following:</p>

<blockquote><pre class="code">[global]
    remote announce = 172.16.2.255/METRAN \
        172.16.3.255/METRAN</pre></blockquote>

<p>Instead of supplying a broadcast address of the remote subnet, you
are allowed to specify the exact address where broadcasts should be
sent if the local master browser on the foreign subnet is guaranteed
to always have the same IP address.</p>

<p>A Samba local master browser can synchronize its browse list directly
with one or more Samba servers, each acting as a local master browser
on a different subnet. This is another way to implement browsing
across subnets. For example, let's assume that Samba
is configured as a local master browser, and Samba local master
browsers exist at 172.16.2.130 and 172.16.3.120. We can use the
<tt class="literal">remote</tt> <tt class="literal">browse</tt>
<tt class="literal">sync</tt> option to sync directly with the Samba
servers, as follows:</p>

<blockquote><pre class="code">[global]
    remote browse sync = 172.16.2.130 172.16.3.120</pre></blockquote>

<p>For this to work, the other Samba machines must also be local master
browsers. You can also use directed broadcasts with this option if
you do not know specific IP addresses of local master browsers.</p>


</div>


</div>


<div class="sect2"><a name="samba2-CHP-7-SECT-2.6"/>

<h3 class="head2">Making a Share Invisible</h3>

<p><a name="INDEX-74"/><a name="INDEX-75"/><a name="INDEX-76"/>You can keep a share from being in the
browse list by using the
<tt class="literal">browsable</tt><a name="INDEX-77"/> option. This Boolean option
prevents a share from being seen in the Network Neighborhood or My
Network Places. For example, to prevent the <tt class="literal">[data]</tt>
share from being visible, we could write:</p>

<blockquote><pre class="code">[data]
    path = /export/samba/userdata
    browsable = no</pre></blockquote>

<p>Although you typically don't want to do this to an
ordinary disk share, the <tt class="literal">browsable</tt> option is
useful in the event that you need to create a share with contents
that you do not want others to see, such as a
<tt class="literal">[netlogon]</tt><a name="INDEX-78"/> share for storing logon scripts
for Windows domain control (see <a href="ch04.html">Chapter 4</a> for more
information on logon scripts).</p>

<p>Another example is the
<tt class="literal">[homes]</tt><a name="INDEX-79"/> share. This share is often marked
nonbrowsable so that a share named <tt class="literal">[homes]</tt>
won't appear when its machine's
resources are browsed. However, if a user <tt class="literal">alice</tt>
logs on and looks at the machine's shares, an
<tt class="literal">[alice]</tt> share will appear under the machine.</p>

<p>What if we wanted to make sure
<tt class="literal">alice</tt>'s share appeared to
everyone before she logs on? This could be done with the global
<tt class="literal">auto</tt><a name="INDEX-80"/> <tt class="literal">services</tt>
option. This option preloads shares into the browse list to ensure
that they are always visible:</p>

<blockquote><pre class="code">[global]
    auto services = alice</pre></blockquote>


</div>


<div class="sect2"><a name="samba2-CHP-7-SECT-2.7"/>

<h3 class="head2">Browsing Options</h3>

<p><a href="ch07.html#samba2-CHP-7-TABLE-4">Table 7-4</a> <a name="INDEX-81"/><a name="INDEX-82"/>shows
options that define how Samba handles browsing tasks.</p>

<a name="samba2-CHP-7-TABLE-4"/><h4 class="head4">Table 7-4. Browsing configuration options</h4><table border="1">


<tr>
<th>
<p>Option</p>
</th>
<th>
<p>Parameters</p>
</th>
<th>
<p>Function</p>
</th>
<th>
<p>Default</p>
</th>
<th>
<p>Scope</p>
</th>
</tr>


<tr>
<td>
<p><tt class="literal">announce as</tt></p>
</td>
<td>
<p>string</p>
</td>
<td>
<p>Operating system that Samba will announce itself as.</p>
</td>
<td>
<p><tt class="literal">N T Server</tt></p>
</td>
<td>
<p>Global</p>
</td>
</tr>
<tr>
<td>
<p><tt class="literal">announce</tt> <tt class="literal">version</tt></p>
</td>
<td>
<p>numeric</p>
</td>
<td>
<p>Version of the operating system that Samba will announce itself as.</p>
</td>
<td>
<p><tt class="literal">4.5</tt></p>
</td>
<td>
<p>Global</p>
</td>
</tr>
<tr>
<td>
<p><tt class="literal">browsable</tt> <tt class="literal">(browseable)</tt></p>
</td>
<td>
<p>Boolean</p>
</td>
<td>
<p>Allows share to be displayed in list of machine resources.</p>
</td>
<td>
<p><tt class="literal">yes</tt></p>
</td>
<td>
<p>Share</p>
</td>
</tr>
<tr>
<td>
<p><tt class="literal">browse list</tt></p>
</td>
<td>
<p>Boolean</p>
</td>
<td>
<p>If <tt class="literal">yes</tt>, allows Samba to provide a browse list on
this server.</p>
</td>
<td>
<p><tt class="literal">yes</tt></p>
</td>
<td>
<p>Global</p>
</td>
</tr>
<tr>
<td>
<p><tt class="literal">auto services</tt> <tt class="literal">(preload)</tt></p>
</td>
<td>
<p>string (share list)</p>
</td>
<td>
<p>List of shares that will always appear in the browse list.</p>
</td>
<td>
<p>None</p>
</td>
<td>
<p>Global</p>
</td>
</tr>
<tr>
<td>
<p><tt class="literal">default</tt> <tt class="literal">service (default)</tt></p>
</td>
<td>
<p>string (share name)</p>
</td>
<td>
<p>Name of a share (service) that will be provided if the client
requests a share not listed in <em class="emphasis">smb.conf</em>.</p>
</td>
<td>
<p>None</p>
</td>
<td>
<p>Global</p>
</td>
</tr>
<tr>
<td>
<p><tt class="literal">local master</tt></p>
</td>
<td>
<p>Boolean</p>
</td>
<td>
<p>If <tt class="literal">yes</tt>, allows Samba to participate in browsing
elections.</p>
</td>
<td>
<p><tt class="literal">yes</tt></p>
</td>
<td>
<p>Global</p>
</td>
</tr>
<tr>
<td>
<p><tt class="literal">lm announce</tt></p>
</td>
<td>
<p><tt class="literal">yes</tt>, <tt class="literal">no</tt>, or
<tt class="literal">auto</tt></p>
</td>
<td>
<p>Enables or disables LAN Manager-style host announcements.</p>
</td>
<td>
<p><tt class="literal">auto</tt></p>
</td>
<td>
<p>Global</p>
</td>
</tr>
<tr>
<td>
<p><tt class="literal">lm interval</tt></p>
</td>
<td>
<p>numeric</p>
</td>
<td>
<p>Frequency in seconds that LAN Manager announcements will be made if
activated.</p>
</td>
<td>
<p><tt class="literal">60</tt></p>
</td>
<td>
<p>Global</p>
</td>
</tr>
<tr>
<td>
<p><tt class="literal">preferred</tt> <tt class="literal">master (prefered
master)</tt></p>
</td>
<td>
<p>Boolean</p>
</td>
<td>
<p>If <tt class="literal">yes</tt>, allows Samba to use the preferred master
browser bit to attempt to become the local master browser.</p>
</td>
<td>
<p><tt class="literal">no</tt></p>
</td>
<td>
<p>Global</p>
</td>
</tr>
<tr>
<td>
<p><tt class="literal">domain master</tt></p>
</td>
<td>
<p>Boolean</p>
</td>
<td>
<p>If <tt class="literal">yes</tt>, allows Samba to become the domain browser
master for the workgroup or domain.</p>
</td>
<td>
<p><tt class="literal">no</tt></p>
</td>
<td>
<p>Global</p>
</td>
</tr>
<tr>
<td>
<p><tt class="literal">os level</tt></p>
</td>
<td>
<p>numeric</p>
</td>
<td>
<p>Operating system level of Samba in an election for local master
browser.</p>
</td>
<td>
<p><tt class="literal">0</tt></p>
</td>
<td>
<p>Global</p>
</td>
</tr>
<tr>
<td>
<p><tt class="literal">remote browse</tt> <tt class="literal">sync</tt></p>
</td>
<td>
<p>string (list of IP addresses)</p>
</td>
<td>
<p>Samba servers to synchronize browse lists with.</p>
</td>
<td>
<p>None</p>
</td>
<td>
<p>Global</p>
</td>
</tr>
<tr>
<td>
<p><tt class="literal">remote</tt> <tt class="literal">announce</tt></p>
</td>
<td>
<p>string (IP address/workgroup pairs)</p>
</td>
<td>
<p>Subnets and workgroups to send directed broadcast packets to,
allowing Samba to appear in their browse lists.</p>
</td>
<td>
<p>None</p>
</td>
<td>
<p>Global</p>
</td>
</tr>

</table>


<div class="sect3"><a name="samba2-CHP-7-SECT-2.7.1"/>

<a name="INDEX-83"/><h3 class="head3">announce as</h3>

<p>This global configuration option specifies the type of operating
system that Samba announces to other machines on the network. The
default value for this option is <tt class="literal">N T</tt>
<tt class="literal">Server</tt>, which causes Samba to masquerade as a
Windows NT Server operating system. Other possible values are
<tt class="literal">NT</tt>, <tt class="literal">NT</tt>
<tt class="literal">Workstation</tt>, <tt class="literal">Win95</tt>, and
<tt class="literal">W f W</tt> for a Windows for Workgroup operating
system. You can override the default value with the following:</p>

<blockquote><pre class="code">[global]
    announce as = Win95</pre></blockquote>

<p>We recommend against changing the default value of this configuration
option.</p>


</div>


<div class="sect3"><a name="samba2-CHP-7-SECT-2.7.2"/>

<a name="INDEX-84"/><h3 class="head3">announce version</h3>

<p>This global option is frequently used with the
<tt class="literal">announce</tt> <tt class="literal">as</tt> configuration
option; it specifies the version of the operating system that Samba
announces to other machines on the network. The default value of this
option is 4.5, which places Samba above Windows NT Version 4.0, but
below Windows 2000. You can specify a new value with a global entry
such as the following:</p>

<blockquote><pre class="code">[global]
    announce version = 4.3</pre></blockquote>

<p>We recommend against changing the default value of this configuration
option.</p>


</div>


<div class="sect3"><a name="samba2-CHP-7-SECT-2.7.3"/>

<h3 class="head3">browsable</h3>

<p>The <tt class="literal">browsable</tt><a name="INDEX-85"/> option (also spelled
<tt class="literal">browseable</tt>) indicates whether the share referenced
should appear in the list of available resources for the system on
which it resides. This option is always set to <tt class="literal">yes</tt>
by default. If you wish to prevent the share from being seen in a
client's browser, you can reset this option to
<tt class="literal">no</tt>.</p>

<p>Note that this does not prevent someone from accessing the share
using other means, such as specifying a UNC location (e.g.,
<tt class="literal">\\server\accounting)</tt> in Windows Explorer. It only
prevents the share from being listed under the
system's resources when being browsed.</p>


</div>


<div class="sect3"><a name="samba2-CHP-7-SECT-2.7.4"/>

<a name="INDEX-86"/><h3 class="head3">browse list</h3>

<p>You should never need to change this parameter from its default value
of <tt class="literal">yes</tt>. If your Samba server is acting as a local
master browser (i.e., it has won the browsing election), you can use
the global <tt class="literal">browse</tt> <tt class="literal">list</tt> option
to instruct Samba to provide or withhold its browse list to all
clients. By default, Samba always provides a browse list. You can
withhold this information by specifying the following:</p>

<blockquote><pre class="code">[global]
    browse list = no</pre></blockquote>

<p>If you disable the browse list, clients cannot browse the names of
other machines, their services, and other domains currently available
on the network. Note that this won't make any
particular machine inaccessible; if someone knows a valid machine
name/address and a share on that machine, he can still connect to it
explicitly using the Windows <em class="emphasis">net use</em> command or
by mapping a drive letter to it using Windows Explorer. It simply
prevents information in the browse list from being retrieved by any
client that requests it.</p>


</div>


<div class="sect3"><a name="samba2-CHP-7-SECT-2.7.5"/>

<h3 class="head3">auto services</h3>

<p>The global <tt class="literal">auto</tt><a name="INDEX-87"/>
<tt class="literal">services</tt> option, which is also called
<tt class="literal">preload</tt> <a name="INDEX-88"/>, ensures that the specified
shares are always visible in the browse list. One common use for this
option is to advertise specific user or printer shares that are
created by the <tt class="literal">[homes]</tt> or
<tt class="literal">[printers]</tt> shares, but are not otherwise
browsable.</p>

<p>This option works best with disk shares. If you wish to force each of
your system printers (i.e., those listed in the printer capabilities
file) to appear in the browse list, we recommend using the
<tt class="literal">load</tt> <tt class="literal">printers</tt> option instead.</p>

<p>Shares listed with the <tt class="literal">auto</tt>
<tt class="literal">services</tt> option will not be displayed if the
<tt class="literal">browse</tt> <tt class="literal">list</tt> option is set to
<tt class="literal">no</tt>.</p>


</div>


<div class="sect3"><a name="samba2-CHP-7-SECT-2.7.6"/>

<h3 class="head3">default service</h3>

<p>The global <tt class="literal">default</tt><a name="INDEX-89"/>
<tt class="literal">service</tt> option (sometimes called
<tt class="literal">default</tt>) names a
&quot;last-ditch&quot; share. The value is
set to an existing share name without the enclosing brackets. When a
client requests a nonexistent disk or printer share, Samba will
attempt to connect the user to the share specified by this option
instead. The option is specified as follows:</p>

<blockquote><pre class="code">[global]
    default service = helpshare</pre></blockquote>

<p>When Samba redirects the requested, nonexistent service to the
service specified by <tt class="literal">default</tt>
<tt class="literal">service</tt>, the <tt class="literal">%S</tt> option takes on
the value of the requested service, with any underscores (
<tt class="literal">_</tt> ) in the requested service replaced by forward slashes
(<tt class="literal">/</tt>).</p>


</div>


<div class="sect3"><a name="samba2-CHP-7-SECT-2.7.7"/>

<a name="INDEX-90"/><h3 class="head3">local master</h3>

<p>This global option specifies whether Samba will attempt to become the
local master browser for the subnet when it starts up. If this option
is set to <tt class="literal">yes</tt>, Samba will participate in
elections. However, setting this option by itself does not guarantee
victory. (Other parameters, such as <tt class="literal">preferred</tt>
<tt class="literal">master</tt> and <tt class="literal">os</tt>
<tt class="literal">level</tt>, help Samba win browsing elections.) If this
option is set to <tt class="literal">no</tt>, Samba will lose all browsing
elections, regardless of which values are specified by the other
configuration options. The default value is <tt class="literal">yes</tt>.</p>


</div>


<div class="sect3"><a name="samba2-CHP-7-SECT-2.7.8"/>

<h3 class="head3">lm announce</h3>

<p>The global <tt class="literal">lm</tt><a name="INDEX-91"/>
<tt class="literal">announce</tt> option tells Samba's
<em class="emphasis">nmbd</em> whether to send <a name="INDEX-92"/>LAN Manager host
announcements on behalf of the server. These host announcements might
be required by older clients, such as IBM's OS/2
operating system. This announcement allows the server to be added to
the browse lists of the client. If activated, Samba will announce
itself repetitively at the number of seconds specified by the
<tt class="literal">lm</tt> <tt class="literal">interval</tt> option.</p>

<p>You can specify the option as follows:</p>

<blockquote><pre class="code">[global]
    lm announce = yes</pre></blockquote>

<p>This configuration option takes the standard Boolean values,
<tt class="literal">yes</tt> and <tt class="literal">no</tt>, which enable or
disable LAN Manager announcements, respectively. In addition, a third
option, <tt class="literal">auto</tt>, causes <em class="emphasis">nmbd</em> to
listen passively for LAN Manager announcements, but not to send any
of its own initially. If LAN Manager announcements are detected for
another machine on the network, <em class="emphasis">nmbd</em> will start
sending its own LAN Manager announcements to ensure that it is
visible. The default value is <tt class="literal">auto</tt>. You probably
won't need to change this value from its default.</p>


</div>


<div class="sect3"><a name="samba2-CHP-7-SECT-2.7.9"/>

<a name="INDEX-93"/><h3 class="head3">lm interval</h3>

<p>This option, which is used in conjunction with <tt class="literal">lm</tt>
<tt class="literal">announce</tt>, indicates the number of seconds
<em class="emphasis">nmbd</em> will wait before repeatedly broadcasting
LAN Manager-style announcements. LAN Manager announcements must be
enabled for this option to work. The default value is 60 seconds. If
you set this value to 0, Samba will not send any LAN Manager host
announcements, regardless of the value of the <tt class="literal">lm</tt>
<tt class="literal">announce</tt> option. You can reset the value of this
option as follows:</p>

<blockquote><pre class="code">[global]
    lm interval = 90</pre></blockquote>


</div>


<div class="sect3"><a name="samba2-CHP-7-SECT-2.7.10"/>

<h3 class="head3">preferred master</h3>

<p>The <tt class="literal">preferred</tt><a name="INDEX-94"/>
<tt class="literal">master</tt> option requests that Samba set the
preferred master bit when participating in an election. This gives
the server a higher preferred status in the workgroup than other
machines at the same operating-system level. If you are configuring
your Samba machine to become the local master browser, it is wise to
set the following value:</p>

<blockquote><pre class="code">[global]
    preferred master = yes</pre></blockquote>

<p>Otherwise, you should leave it set to its default,
<tt class="literal">no</tt>. If Samba is configured as a preferred master
browser, it will force an election when it first comes online.</p>


</div>


<div class="sect3"><a name="samba2-CHP-7-SECT-2.7.11"/>

<a name="INDEX-95"/><h3 class="head3">domain master</h3>

<p>If Samba is the primary domain controller for your workgroup or NT
domain, it should also be made the domain master browser. The domain
master browser is a special machine that has the NetBIOS resource
type &lt;1B&gt; and is used to propagate browse lists to and from
each local master browser in individual subnets across the domain. To
force Samba to become the <a name="INDEX-96"/>domain master browser, set the following in
the <tt class="literal">[global]</tt> section of the
<em class="filename">smb.conf</em>:</p>

<blockquote><pre class="code">[global]
    domain master = yes</pre></blockquote>

<p>If you have a Windows NT server on the network acting as a primary
domain controller (PDC), we recommend that you do not use Samba to
become the domain master browser. The reverse is true as well: if
Samba is taking on the responsibilities of a PDC, we recommend making
it the domain master browser. Splitting the PDC and the domain master
browser will cause unpredictable errors to occur on the network.</p>


</div>


<div class="sect3"><a name="samba2-CHP-7-SECT-2.7.12"/>

<h3 class="head3">os level</h3>

<p>The global <tt class="literal">os</tt><a name="INDEX-97"/> <tt class="literal">level</tt> option
defines the operating-system value with which Samba will masquerade
during a browser election. If you wish to have Samba win an election
and become the master browser, set the <tt class="literal">os</tt>
<tt class="literal">level</tt> higher than that of any other system on the
subnet. The values are shown in <a href="ch07.html#samba2-CHP-7-TABLE-2">Table 7-2</a>. The
default level is 20, which means that Samba will win elections
against all versions of Windows, except Windows NT/2000 if it is
operating as the PDC. If you wish Samba to win all elections, you can
set its operating system value as follows:</p>

<blockquote><pre class="code">[global]
    os level = 255</pre></blockquote>


</div>


<div class="sect3"><a name="samba2-CHP-7-SECT-2.7.13"/>

<h3 class="head3">remote browse sync</h3>

<p>The global <tt class="literal">remote</tt><a name="INDEX-98"/>
<tt class="literal">browse</tt> <tt class="literal">sync</tt> option specifies
that Samba should synchronize its browse lists with local master
browsers in other subnets. However, the synchronization can occur
only with other Samba servers and not with Windows computers. For
example, if your Samba server were a master browser on the subnet
172.16.235, and Samba local master browsers existed on other subnets
located at 172.16.234.92 and 172.16.236.2, you would specify the
following:</p>

<blockquote><pre class="code">[global]
    remote browse sync = 172.16.234.92 172.16.236.2</pre></blockquote>

<p>The Samba server would then directly contact the other machines on
the address list and synchronize browse lists. You can also say:</p>

<blockquote><pre class="code">[global]
    remote browse sync = 172.16.234.255 172.16.236.255</pre></blockquote>

<p>This forces Samba to broadcast queries to determine the IP addresses
of the local master browser on each subnet, with which it will then
synchronize browse lists. This works, however, only if your router
doesn't block directed broadcast requests ending in
255.</p>


</div>


<div class="sect3"><a name="samba2-CHP-7-SECT-2.7.14"/>

<h3 class="head3">remote announce</h3>

<p>Samba servers are capable of providing browse lists to foreign
subnets with the <tt class="literal">remote</tt><a name="INDEX-99"/>
<tt class="literal">announce</tt> option. This is typically sent to the
local master browser of the foreign subnet in question. However, if
you do not know the address of the local master browser, you can do
the following:</p>

<blockquote><pre class="code">[global]
    remote announce = 172.16.234.255/ACCOUNTING \
                        172.16.236.255/ACCOUNTING</pre></blockquote>

<p>With this, Samba will broadcast host announcements to all machines on
subnets 172.16.234 and 172.16.236, which will hopefully reach the
local master browser of the subnet.</p>

<p>You can also specify exact IP addresses, if they are known, but this
works only if the systems are guaranteed to maintain the role of
master browser on their subnets. By appending a workgroup or domain
name to the IP address, Samba announces that it is in that workgroup
or domain. If this is left out, the workgroup set by the
<tt class="literal">workgroup</tt> parameter is used. <a name="INDEX-100"/> <a name="INDEX-101"/><a name="INDEX-102"/></p>


</div>


</div>


</div>

<hr/><h4 class="head4">Footnotes</h4><blockquote><a name="FOOTNOTE-1"/> <p><a href="#FNPTR-1">[1]</a> As we explained in
<a href="ch01.html">Chapter 1</a>, a system can register under more than
one NetBIOS name. We use the singular here only to keep our
explanation simple.</p> </blockquote><hr/><h4 class="head4"><a href="toc.html">TOC</a></h4></body></html>