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<?xml version="1.0" encoding="iso-8859-1"?>
<!DOCTYPE chapter PUBLIC "-//Samba-Team//DTD DocBook V4.2-Based Variant V1.0//EN" "http://www.samba.org/samba/DTD/samba-doc">
<chapter id="NetworkBrowsing">
<chapterinfo>
        &author.jht;
        &author.jelmer;
        <pubdate>July 5, 1998</pubdate>
        <pubdate>Updated: April 21, 2003</pubdate>
</chapterinfo>

<title>Network Browsing</title>

<para>
This document contains detailed information as well as a fast-track guide to
implementing browsing across subnets and/or across workgroups (or domains).
WINS is the best tool for resolution of NetBIOS names to IP addresses. WINS is
not involved in browse list handling except by way of name-to-address resolution.
</para>

<note><para>
MS Windows 2000 and later versions can be configured to operate with no NetBIOS 
over TCP/IP. Samba-3 and later versions also support this mode of operation.
When the use of NetBIOS over TCP/IP has been disabled, the primary
means for resolution of MS Windows machine names is via DNS and Active Directory.
The following information assumes that your site is running NetBIOS over TCP/IP.
</para></note>

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

<para>
Charles Dickens once referred to the past in these words: <quote><emphasis>It was the best of times,
it was the worst of times.</emphasis></quote> The more we look back, the more we long for what was and
hope it never returns.
</para>


<para>
<indexterm><primary>NetBIOS</primary></indexterm>
For many MS Windows network administrators, that statement sums up their feelings about
NetBIOS networking precisely. For those who mastered NetBIOS networking, its fickle
nature was just par for the course. For those who never quite managed to tame its
lusty features, NetBIOS is like Paterson's Curse.
</para>

<para>
For those not familiar with botanical problems in Australia, Paterson's Curse,
<emphasis>Echium plantagineum</emphasis>, was introduced to Australia from Europe during the mid-19th
century. Since then it has spread rapidly. The high seed production, with densities of
thousands of seeds per square meter, a seed longevity of more than 7 years, and an
ability to germinate at any time of year, given the right conditions, are some of the
features that make it such a persistent weed.
</para>

<para>
In this chapter we explore vital aspects of Server Message Block (SMB) networking with
a particular focus on SMB as implemented through running NetBIOS (Network Basic
Input/Output System) over TCP/IP. Since Samba does not implement SMB or NetBIOS over
any other protocols, we need to know how to configure our network environment and simply
remember to use nothing but TCP/IP on all our MS Windows network clients.
</para>

<para>
Samba provides the ability to implement a WINS (Windows Internetworking Name Server)
and implements extensions to Microsoft's implementation of WINS. These extensions
help Samba to effect stable WINS operations beyond the normal scope of MS WINS.
</para>

<para>
WINS is exclusively a service that applies only to those systems
that run NetBIOS over TCP/IP. MS Windows 200x/XP have the capacity to operate with
support for NetBIOS disabled, in which case WINS is of no relevance. Samba supports this also.
</para>

<para>
For those networks on which NetBIOS has been disabled (i.e., WINS is not required),
the use of DNS is necessary for hostname resolution.
</para>

</sect1>

<sect1>
<title>What Is Browsing?</title>

<para>
To most people, browsing means they can see the MS Windows and Samba servers
in the Network Neighborhood, and when the computer icon for a particular server is
clicked, it opens up and shows the shares and printers available on the target server.
</para>

<para>
What seems so simple is in fact a complex interaction of different technologies.
The technologies (or methods) employed in making all of this work include:
</para>

<itemizedlist>
        <listitem><para>MS Windows machines register their presence to the network.</para></listitem>
        <listitem><para>Machines announce themselves to other machines on the network.</para></listitem>
        <listitem><para>One or more machines on the network collate the local announcements.</para></listitem>
        <listitem><para>The client machine finds the machine that has the collated list of machines.</para></listitem>
        <listitem><para>The client machine is able to resolve the machine names to IP addresses.</para></listitem>
        <listitem><para>The client machine is able to connect to a target machine.</para></listitem>
</itemizedlist>

<para>
The Samba application that controls browse list management and name resolution is
called <filename>nmbd</filename>. The configuration parameters involved in nmbd's operation are:
</para>

<para>Browsing options:
        <smbconfoption name="os level"/>(*),
        <smbconfoption name="lm announce"/>,
        <smbconfoption name="lm interval"/>,
        <smbconfoption name="preferred master"/>(*),
        <smbconfoption name="local master"/>(*),
        <smbconfoption name="domain master"/>(*),
        <smbconfoption name="browse list"/>,
        <smbconfoption name="enhanced browsing"/>.
</para>

<para>Name Resolution Method:
        <smbconfoption name="name resolve order"/>(*).
</para>

<para>WINS options:
        <smbconfoption name="dns proxy"/>,
        <smbconfoption name="wins proxy"/>,
        <smbconfoption name="wins server"/>(*),
        <smbconfoption name="wins support"/>(*),
        <smbconfoption name="wins hook"/>.
</para>

<para>
<indexterm><primary>WINS</primary></indexterm>
For Samba, the WINS Server and WINS Support are mutually exclusive options. Those marked with
an (*) are the only options that commonly may need to be modified. Even if none of these
parameters is set, <filename>nmbd</filename> will still do its job.
</para>

</sect1>

<sect1 id="netdiscuss">
<title>Discussion</title>

<para>
<indexterm><primary>SMB-based messaging</primary></indexterm>
<indexterm><primary>NetBIOS</primary></indexterm>
All MS Windows networking uses SMB-based messaging.  SMB messaging may be implemented with or without NetBIOS.
MS Windows 200x supports NetBIOS over TCP/IP for backwards compatibility. Microsoft appears intent on phasing
out NetBIOS support.
</para>

<sect2>
<title>NetBIOS over TCP/IP</title>

<para>
<indexterm><primary>encapsulating</primary></indexterm>
<indexterm><primary>broadcast</primary></indexterm>
<indexterm><primary>unicast</primary></indexterm>
<indexterm><primary>UDP</primary></indexterm>
Samba implements NetBIOS, as does MS Windows NT/200x/XP, by encapsulating it over TCP/IP.
MS Windows products can do likewise. NetBIOS-based networking uses broadcast messaging to
effect browse list management. When running NetBIOS over TCP/IP, this uses UDP-based messaging.
UDP messages can be broadcast or unicast.
</para>

<para>
<indexterm><primary>UDP</primary></indexterm>
Normally, only unicast UDP messaging can be forwarded by routers. The
<smbconfoption name="remote announce"/> parameter to smb.conf helps to project browse announcements
to remote network segments via unicast UDP. Similarly, the 
<smbconfoption name="remote browse sync"/> parameter of &smb.conf;
implements browse list collation using unicast UDP.
</para>

<para>
The methods used by MS Windows to perform name lookup requests (name resolution) is determined by a 
configuration parameter called the netbios node-type. There are four basic NetBIOS node types:
</para>

<indexterm><primary>b-node</primary></indexterm>
<indexterm><primary>p-node</primary></indexterm>
<indexterm><primary>m-node</primary></indexterm>
<indexterm><primary>h-node</primary></indexterm>
<indexterm><primary>node-type</primary></indexterm>
<indexterm><primary>WINS</primary></indexterm>
<indexterm><primary>broadcast</primary></indexterm>
<indexterm><primary>unicast</primary></indexterm>
<itemizedlist>
        <listitem><para><emphasis>b-node (type 0x01):</emphasis> The Windows client will use only
        NetBIOS broadcast requests using UDP broadcast.</para></listitem>
        <listitem><para><emphasis>p-node (type 0x02):</emphasis> The Windows client will use point-to-point
        (NetBIOS unicast) requests using UDP unicast directed to a WINS server.</para></listitem>
        <listitem><para><emphasis>m-node (type 0x04):</emphasis> The Windows client will first use
        NetBIOS broadcast requests using UDP broadcast, then it will use (NetBIOS unicast) 
        requests using UDP unicast directed to a WINS server.</para></listitem>
        <listitem><para><emphasis>h-node (type 0x08):</emphasis> The Windows client will use 
        (NetBIOS unicast) requests using UDP unicast directed to a WINS server, then it will use 
        NetBIOS broadcast requests using UDP broadcast.</para></listitem>
</itemizedlist>

<para>
<indexterm><primary>Hybrid</primary></indexterm>
The default Windows network client (or server) network configuration enables NetBIOS over TCP/IP
and b-node configuration. The use of WINS makes most sense with h-node (hybrid mode) operation so that
in the event of a WINS breakdown or non-availability, the client can use broadcast-based name resolution.
</para>

<para>
<indexterm><primary>LMB</primary><see>Local Master Browser</see></indexterm>
<indexterm><primary>Local Master Browser</primary></indexterm>
In those networks where Samba is the only SMB server technology, wherever possible 
<filename>nmbd</filename> should be configured on one machine as the WINS
server. This makes it easy to manage the browsing environment. If each network
segment is configured with its own Samba WINS server, then the only way to
get cross-segment browsing to work is by using the 
<smbconfoption name="remote announce"/> and the 
<smbconfoption name="remote browse sync"/>
parameters to your &smb.conf; file.
</para>

<para>
<indexterm><primary>WINS</primary></indexterm>
If only one WINS server is used for an entire multisegment network, then
the use of the <smbconfoption name="remote announce"/> and the 
<smbconfoption name="remote browse sync"/> parameters should not be necessary.
</para>

<para>
<indexterm><primary>replication</primary><secondary>WINS</secondary></indexterm>
As of Samba-3 WINS replication is being worked on. The bulk of the code has
been committed, but it still needs maturation. This is not a supported feature
of the Samba-3.0.20 release. Hopefully, this will become a supported feature
of one of the Samba-3 release series.
</para>

<para>
Right now Samba WINS does not support MS-WINS replication. This means that
when setting up Samba as a WINS server, there must only be one <filename>nmbd</filename>
configured as a WINS server on the network. Some sites have used multiple Samba WINS
servers for redundancy (one server per subnet) and then used 
<smbconfoption name="remote browse sync"/> and <smbconfoption name="remote announce"/>
to effect browse list collation across all segments. Note that this means clients
will only resolve local names and must be configured to use DNS to resolve names
on other subnets in order to resolve the IP addresses of the servers they can see
on other subnets. This setup is not recommended but is mentioned as a practical
consideration (i.e., an <quote>if all else fails</quote> scenario).
</para>

<para>
Lastly, take note that browse lists are a collection of unreliable broadcast
messages that are repeated at intervals of not more than 15 minutes. This means
that it will take time to establish a browse list, and it can take up to 45
minutes to stabilize, particularly across network segments.
</para>

<para>
When an MS Windows 200x/XP system attempts to resolve a host name to an IP address,
it follows a defined path:
</para>

<orderedlist>
        <listitem><para>
        Checks the <filename>hosts</filename> file. It is located in
        <filename>%SystemRoot%\System32\Drivers\etc</filename>.
        </para></listitem>

        <listitem><para>
        Does a DNS lookup.
        </para></listitem>

        <listitem><para>
        Checks the NetBIOS name cache.
        </para></listitem>

        <listitem><para>
        Queries the WINS server.
        </para></listitem>

        <listitem><para>
        Does a broadcast name lookup over UDP.
        </para></listitem>

        <listitem><para>
        Looks up entries in LMHOSTS, located in
        <filename>%SystemRoot%\System32\Drivers\etc</filename>.
        </para></listitem>
</orderedlist>

</sect2>

<sect2>
<title>TCP/IP without NetBIOS</title>

<para>
<indexterm><primary>NetBIOS</primary></indexterm>
<indexterm><primary>NetBIOS-less</primary></indexterm>
<indexterm><primary>DNS</primary></indexterm>
All TCP/IP-enabled systems use various forms of hostname resolution. The primary
methods for TCP/IP hostname resolution involve either a static file (<filename>/etc/hosts</filename>)
or the Domain Name System (DNS). DNS is the technology that makes
the Internet usable. DNS-based hostname resolution is supported by nearly all
TCP/IP-enabled systems. Only a few embedded TCP/IP systems do not support DNS.
</para>

<para>
<indexterm><primary>DNS</primary></indexterm>
Windows 200x/XP can register its hostname with a dynamic DNS server. You can
force register with a dynamic DNS server in Windows 200x/XP using
<command>ipconfig /registerdns</command>.
</para>

<para>
With Active Directory, a correctly functioning DNS server is absolutely
essential. In the absence of a working DNS server that has been correctly configured,
MS Windows clients and servers will be unable to locate each other, so
network services consequently will be severely impaired.
</para>

<para>
The use of dynamic DNS is highly recommended with Active Directory, in which case
the use of BIND9 is preferred for its ability to adequately support the SRV (service)
records that are needed for Active Directory.
</para>

<para>
Use of raw SMB over TCP/IP (No NetBIOS layer) can be done only with Active
Directory domains. Samba is not an Active Directory domain controller: ergo,
it is not possible run Samba as a domain controller and at the same time <emphasis>not</emphasis> use
NetBIOS. Where Samba is used as an Active Directory domain member server (DMS)
it is possible to configure Samba to not use NetBIOS over TCP/IP. A Samba DMS
can integrate fully into an Active Directory domain.
</para>

</sect2>

<sect2 id="adsdnstech">
<title>DNS and Active Directory</title>


<para>
<indexterm><primary>DNS</primary><secondary>Active Directory</secondary></indexterm>
Occasionally we hear from UNIX network administrators who want to use a UNIX-based dynamic
DNS server in place of the Microsoft DNS server. While this might be desirable to some, the
MS Windows 200x DNS server is autoconfigured to work with Active Directory. It is possible
to use BIND version 8 or 9, but it will almost certainly be necessary to create service records
(SRV records) so MS Active Directory clients can resolve hostnames to locate essential network services.
The following are some of the default service records that Active Directory requires:
</para>

<variablelist>
<varlistentry>
        <term>_ldap._tcp.pdc._msdcs.<emphasis>Domain</emphasis></term>
        <listitem>
        <para>
        This provides the address of the Windows NT PDC for the domain.
        </para>
        </listitem>
</varlistentry>
<varlistentry>
        <term>_ldap._tcp.pdc._msdcs.<emphasis>DomainTree</emphasis></term>
        <listitem>
        <para>
        Resolves the addresses of global catalog servers in the domain.
        </para>
        </listitem>
</varlistentry>
<varlistentry>
        <term>_ldap._tcp.<emphasis>site</emphasis>.sites.writable._msdcs.<emphasis>Domain</emphasis></term>
        <listitem>
        <para>
        Provides list of domain controllers based on sites.
        </para>
        </listitem>
</varlistentry>
<varlistentry>
        <term>_ldap._tcp.writable._msdcs.<emphasis>Domain</emphasis></term>
        <listitem>
        <para>
        Enumerates list of domain controllers that have the writable copies of the Active Directory data store.
        </para>
        </listitem>
</varlistentry>
<varlistentry>
        <term>_ldap._tcp.<emphasis>GUID</emphasis>.domains._msdcs.<emphasis>DomainTree</emphasis></term>
        <listitem>
        <para>
        Entry used by MS Windows clients to locate machines using the global unique identifier.
        </para>
        </listitem>
</varlistentry>
<varlistentry>
        <term>_ldap._tcp.<emphasis>Site</emphasis>.gc._msdcs.<emphasis>DomainTree</emphasis></term>
        <listitem>
        <para>
        Used by MS Windows clients to locate site configuration-dependent global catalog server.
        </para>
        </listitem>
</varlistentry>
</variablelist>

        <para>
        Specific entries used by Microsoft clients to locate essential services for an example domain
        called <constant>quenya.org</constant> include:
        </para>

        <itemizedlist>
                <listitem><para>
                _kerberos._udp.quenya.org &smbmdash; Used to contact the KDC server via UDP.
                This entry must list port 88 for each KDC.
                </para></listitem>

                <listitem><para>
                _kpasswd._udp.quenya.org &smbmdash; Used to locate the <constant>kpasswd</constant> server
                when a user password change must be processed. This record must list port 464 on the
                master KDC.
                </para></listitem>

                <listitem><para>
                _kerberos._tcp.quenya.org &smbmdash; Used to locate the KDC server via TCP.
                This entry must list port 88 for each KDC.
                </para></listitem>

                <listitem><para>
                _ldap._tcp.quenya.org &smbmdash; Used to locate the LDAP service on the PDC.
                This record must list port 389 for the PDC.
                </para></listitem>

                <listitem><para>
                _kpasswd._tcp.quenya.org &smbmdash; Used to locate the <constant>kpasswd</constant> server
                to permit user password changes to be processed. This must list port 464.
                </para></listitem>

                <listitem><para>
                _gc._tcp.quenya.org &smbmdash; Used to locate the global catalog server  for the
                top of the domain. This must list port 3268.
                </para></listitem>
        </itemizedlist>
        
        <para>
        The following records are also used by the Windows domain member client to locate vital
        services on the Windows ADS domain controllers.
        </para>

        <itemizedlist>
                <listitem><para>
                _ldap._tcp.pdc._msdcs.quenya.org
                </para></listitem>

                <listitem><para>
                _ldap.gc._msdcs.quenya.org
                </para></listitem>

                <listitem><para>
                _ldap.default-first-site-name._sites.gc._msdcs.quenya.org
                </para></listitem>

                <listitem><para>
                _ldap.{SecID}.domains._msdcs.quenya.org
                </para></listitem>

                <listitem><para>
                _ldap._tcp.dc._msdcs.quenya.org
                </para></listitem>

                <listitem><para>
                _kerberos._tcp.dc._msdcs.quenya.org
                </para></listitem>

                <listitem><para>
                _ldap.default-first-site-name._sites.dc._msdcs.quenya.org
                </para></listitem>

                <listitem><para>
                _kerberos.default-first-site-name._sites.dc._msdcs.queyna.org
                </para></listitem>

                <listitem><para>
                SecID._msdcs.quenya.org
                </para></listitem>
        </itemizedlist>

        <para>
        Presence of the correct DNS entries can be validated by executing:
<screen>
&rootprompt; dig @frodo -t any _ldap._tcp.dc._msdcs.quenya.org

; &lt;lt;&gt;&gt; DiG 9.2.2 &lt;lt;&gt;&gt; @frodo -t any _ldap._tcp.dc._msdcs.quenya.org
;; global options:  printcmd
;; Got answer:
;; -&gt;&gt;HEADER&lt;&lt;- opcode: QUERY, status: NOERROR, id: 3072
;; flags: qr aa rd ra; QUERY: 1, ANSWER: 2, AUTHORITY: 0, ADDITIONAL: 2


;; QUESTION SECTION:
;_ldap._tcp.dc._msdcs.quenya.org. IN        ANY


;; ANSWER SECTION:
_ldap._tcp.dc._msdcs.quenya.org. 600 IN SRV 0 100 389 frodo.quenya.org.
_ldap._tcp.dc._msdcs.quenya.org. 600 IN SRV 0 100 389 noldor.quenya.org.


;; ADDITIONAL SECTION:
frodo.quenya.org.  3600  IN      A       10.1.1.16
noldor.quenya.org. 1200  IN      A       10.1.1.17


;; Query time: 0 msec
;; SERVER: frodo#53(10.1.1.16)
;; WHEN: Wed Oct  7 14:39:31 2004
;; MSG SIZE  rcvd: 171
</screen>
        </para>

</sect2>

</sect1>

<sect1>
<title>How Browsing Functions</title>

<para>
MS Windows machines register their NetBIOS names (i.e., the machine name for each service type in operation)
on startup.  The exact method by which this name registration takes place is determined by whether or not the
MS Windows client/server has been given a WINS server address, whether or not LMHOSTS lookup is enabled,
whether or not DNS for NetBIOS name resolution is enabled, and so on.
</para>

<para>
In the case where there is no WINS server, all name registrations as well as name lookups are done by UDP
broadcast. This isolates name resolution to the local subnet, unless LMHOSTS is used to list all names and IP
addresses. In such situations, Samba provides a means by which the Samba server name may be forcibly injected
into the browse list of a remote MS Windows network (using the <smbconfoption name="remote announce"/>
parameter).
</para>

<para>
Where a WINS server is used, the MS Windows client will use UDP unicast to register with the WINS server. Such
packets can be routed, and thus WINS allows name resolution to function across routed networks.
</para>

<para>
During the startup process, an election takes place to create a local master browser (LMB) if one does not
already exist. On each NetBIOS network one machine will be elected to function as the domain master browser
(DMB). This domain browsing has nothing to do with MS security Domain Control.  Instead, the DMB serves the
role of contacting each LMB (found by asking WINS or from LMHOSTS) and exchanging browse list contents. This
way every master browser will eventually obtain a complete list of all machines that are on the network. Every
11 to 15 minutes an election is held to determine which machine will be the master browser. By the nature of
the election criteria used, the machine with the highest uptime, or the most senior protocol version or other
criteria, will win the election as DMB.
</para>

<para>
Where a WINS server is used, the DMB registers its IP address with the WINS server using the name of the
domain and the NetBIOS name type #1B. e.g., DOMAIN&lt;1B&gt;. All LMBs register their IP address with the WINS
server, also with the name of the domain and the NetBIOS name type of #1D. The #1B name is unique to one
server within the domain security context, and only one #1D name is registered for each network segment.
Machines that have registered the #1D name will be authoritive browse list maintainers for the network segment
they are on. The DMB is responsible for synchronizing the browse lists it obtains from the LMBs.
</para>

<para>
Clients wishing to browse the network make use of this list but also depend on the availability of correct
name resolution to the respective IP address or addresses.
</para>

<para>
Any configuration that breaks name resolution and/or browsing intrinsics will annoy users because they will
have to put up with protracted inability to use the network services.
</para>

<para>
Samba supports a feature that allows forced synchronization of browse lists across routed networks using the
<smbconfoption name="remote browse sync"/> parameter in the &smb.conf; file. This causes Samba to contact the
LMB on a remote network and to request browse list synchronization. This effectively bridges two networks that
are separated by routers. The two remote networks may use either broadcast-based name resolution or WINS-based
name resolution, but it should be noted that the <smbconfoption name="remote browse sync"/> parameter provides
browse list synchronization &smbmdash; and that is distinct from name-to-address resolution. In other words,
for cross-subnet browsing to function correctly, it is essential that a name-to-address resolution mechanism
be provided. This mechanism could be via DNS, <filename>/etc/hosts</filename>, and so on.
</para>

<sect2 id="DMB">
<title>Configuring Workgroup Browsing</title>

<para>
To configure cross-subnet browsing on a network containing machines in a workgroup, not an NT domain, you need
to set up one Samba server to be the DMB (note that this is not the same as a Primary Domain Controller,
although in an NT domain the same machine plays both roles). The role of a DMB is to collate the browse lists
from LMB on all the subnets that have a machine participating in the workgroup. Without one machine configured
as a DMB, each subnet would be an isolated workgroup unable to see any machines on another subnet. It is the
presence of a DMB that makes cross-subnet browsing possible for a workgroup.
</para>

<para>
In a workgroup environment the DMB must be a Samba server, and there must only be one DMB per workgroup name.
To set up a Samba server as a DMB, set the following option in the <smbconfsection name="[global]"/> section
of the &smb.conf; file:
</para>

<para>
<smbconfblock>
<smbconfoption name="domain master">yes</smbconfoption>
</smbconfblock>
</para>

<para>
The DMB should preferably be the LMB for its own subnet. In order to achieve this, set the following options
in the <smbconfsection name="[global]"/> section of the &smb.conf; file as shown in <link
linkend="dmbexample">Domain Master Browser smb.conf</link>
</para>

<example id="dmbexample">
<title>Domain Master Browser smb.conf</title>
<smbconfblock>
<smbconfsection name="[global]"/>
<smbconfoption name="domain master">yes</smbconfoption>
<smbconfoption name="local master">yes</smbconfoption>
<smbconfoption name="preferred master">yes</smbconfoption>
<smbconfoption name="os level">65</smbconfoption>
</smbconfblock>
</example>

<para>
The DMB may be the same machine as the WINS server, if necessary.
</para>

<para>
Next, you should ensure that each of the subnets contains a machine that can act as an LMB for the workgroup.
Any MS Windows NT/200x/XP machine should be able to do this, as will Windows 9x/Me machines (although these
tend to get rebooted more often, so it is not such a good idea to use them). To make a Samba server an LMB,
set the following options in the <smbconfsection name="[global]"/> section of the &smb.conf; file as shown in
<link linkend="lmbexample">Local master browser smb.conf</link>
</para>

<example id="lmbexample">
<title>Local master browser smb.conf</title>
<smbconfblock>
<smbconfsection name="[global]"/>
<smbconfoption name="domain master">no</smbconfoption>
<smbconfoption name="local master">yes</smbconfoption>
<smbconfoption name="preferred master">yes</smbconfoption>
<smbconfoption name="os level">65</smbconfoption>
</smbconfblock>
</example>

<para>
Do not do this for more than one Samba server on each subnet, or they will war with
each other over which is to be the LMB.
</para>

<para>
The <smbconfoption name="local master"/> parameter allows Samba to act as a
LMB. The <smbconfoption name="preferred master"/> causes <command>nmbd</command>
to force a browser election on startup and the <smbconfoption name="os level"/>
parameter sets Samba high enough so it should win any browser elections.
</para>

<para>
If you have an NT machine on the subnet that you wish to be the LMB, you can disable Samba from
becoming an LMB by setting the following options in the <smbconfsection name="[global]"/> section of the 
&smb.conf; file as shown in <link linkend="nombexample">smb.conf for Not Being a Master Browser</link>.
</para>

<para>
<example id="nombexample">
<title>smb.conf for Not Being a Master Browser</title>
<smbconfblock>
<smbconfsection name="[global]"/>
<smbconfoption name="domain master">no</smbconfoption>
<smbconfoption name="local master">no</smbconfoption>
<smbconfoption name="preferred master">no</smbconfoption>
<smbconfoption name="os level">0</smbconfoption>
</smbconfblock>
</example>
</para>

</sect2>

<sect2>
<title>Domain Browsing Configuration</title>

<para>
If you are adding Samba servers to a Windows NT domain, then you must not set up a Samba server as a DMB.
By default, a Windows NT PDC for a domain is also the DMB for that domain. Network
browsing may break if a Samba server registers the DMB NetBIOS name (<replaceable>DOMAIN</replaceable>&lt;1B&gt;)
with WINS instead of the PDC.
</para>

<para>
For subnets other than the one containing the Windows NT PDC, you may set up Samba servers as LMBs as
described. To make a Samba server a Local Master Browser, set the following options in the <smbconfsection name="[global]"/> section 
of the &smb.conf; file as shown in <link linkend="remsmb">Local Master Browser smb.conf</link>
</para>

<example id="remsmb">
<title>Local Master Browser smb.conf</title>
<smbconfblock>
<smbconfsection name="[global]"/>
<smbconfoption name="domain master">no</smbconfoption>
<smbconfoption name="local master">yes</smbconfoption>
<smbconfoption name="preferred master">yes</smbconfoption>
<smbconfoption name="os level">65</smbconfoption>
</smbconfblock>
</example>

<para>
If you wish to have a Samba server fight the election with machines on the same subnet, you
may set the <smbconfoption name="os level"/> parameter to lower levels.
By doing this you can tune the order of machines that will become LMBs if
they are running. For more details on this, refer to Section 9.4.3, <link linkend="browse-force-master">Forcing Samba to Be the Master</link>.
</para>

<para>
If you have Windows NT machines that are members of the domain on all subnets and you are
sure they will always be running, you can disable Samba from taking part in browser elections
and ever becoming an LMB by setting the following options in the
<smbconfsection name="[global]"/> section of the &smb.conf; file as shown in <link linkend="xremmb">&smb.conf;
for Not Being a master browser</link>
</para>

<para>
<example id="xremmb">
<title>&smb.conf; for Not Being a master browser</title>
<smbconfsection name="[global]"/>
<smbconfoption name="domain master">no</smbconfoption>
<smbconfoption name="local master">no</smbconfoption>
<smbconfoption name="preferred master">no</smbconfoption>
<smbconfoption name="os level">0</smbconfoption>
</example>
</para>

</sect2>

<sect2 id="browse-force-master">
<title>Forcing Samba to Be the Master</title>

<para>
Who becomes the master browser is determined by an election process using broadcasts. Each election packet contains a number of parameters
that determine what precedence (bias) a host should have in the election. By default Samba uses a low precedence and thus loses
elections to just about every Windows network server or client.
</para>

<para>
If you want Samba to win elections, set the <smbconfoption name="os level"/>
global option in &smb.conf; to a higher number. It defaults to 20. Using 34 would make it win
all elections over every other system (except other Samba systems).
</para>

<para>
An <smbconfoption name="os level"/> of two would make it beat Windows for Workgroups and Windows 9x/Me, but not MS Windows
NT/200x Server. An MS Windows NT/200x Server domain controller uses level 32. The maximum os level is 255.
</para>

<para>
If you want Samba to force an election on startup, set the
<smbconfoption name="preferred master"/> global option in &smb.conf; to <constant>yes</constant>.
Samba will then have a slight advantage over other potential master browsers that are not preferred master browsers.
Use this parameter with care, because if you have two hosts (whether they are Windows 9x/Me or
NT/200x/XP or Samba) on the same local subnet both set with <smbconfoption name="preferred master"/>
to <constant>yes</constant>, then periodically and continually they will force an election in order
to become the LMB.
</para>

<para>
If you want Samba to be a <emphasis>DMB</emphasis>, then it is recommended that
you also set <smbconfoption name="preferred master"/> to <constant>yes</constant>, because
Samba will not become a DMB for the whole of your LAN or WAN if it is not also a
LMB on its own broadcast isolated subnet.
</para>

<para>
It is possible to configure two Samba servers to attempt to become the DMB for a domain. The first server that comes
up will be the DMB. All other Samba servers will attempt to become the DMB every 5 minutes. They
will find that another Samba server is already the DMB and will fail. This provides automatic redundancy should
the current DMB fail.
</para>

</sect2>

<sect2>
<title>Making Samba the Domain Master</title>

<para>
The domain master is responsible for collating the browse lists of multiple subnets so browsing can occur between subnets. You can
make Samba act as the domain master by setting <smbconfoption name="domain master">yes</smbconfoption>
in &smb.conf;. By default it will not be a domain master.
</para>

<para>
Do not set Samba to be the domain master for a workgroup that has the same name as an NT/200x domain.
If Samba is configured to be the domain master for a workgroup that is present on the same
network as a Windows NT/200x domain that has the same name, network browsing problems will
certainly be experienced.
</para>

<para>
When Samba is the domain master and the master browser, it will listen for master
announcements (made roughly every 12 minutes) from LMBs on
other subnets and then contact them to synchronize browse lists.
</para>

<para>
If you want Samba to be the domain master, you should also set the
<smbconfoption name="os level"/> high enough to make sure it wins elections, and
set <smbconfoption name="preferred master"/> to <constant>yes</constant>, to
get Samba to force an election on startup.
</para>

<para>
All servers (including Samba) and clients should be using a WINS server to resolve NetBIOS names. If your
clients are only using broadcasting to resolve NetBIOS names, then two things will occur:
</para>

<orderedlist>
<listitem>
        <para>
        LMBs will be unable to find a DMB because they will be looking only on the local subnet.
        </para>
</listitem>

<listitem>
        <para>
        If a client happens to get hold of a domain-wide browse list and a user attempts to access a
        host in that list, it will be unable to resolve the NetBIOS name of that host.
        </para>
</listitem>
</orderedlist>

<para>
If, however, both Samba and your clients are using a WINS server, then:
</para>

<orderedlist>
<listitem>
        <para>
        LMBs will contact the WINS server and, as long as Samba has registered that it is a DMB with the WINS
        server, the LMB will receive Samba's IP address as its DMB.
        </para>
</listitem>

<listitem>
        <para>
        When a client receives a domain-wide browse list and a user attempts to access a host in that list, it will contact the WINS server to
        resolve the NetBIOS name of that host. As long as that host has registered its NetBIOS name with the same WINS server, the user will
        be able to see that host. 
        </para>
</listitem>
</orderedlist>

</sect2>

<sect2>
<title>Note about Broadcast Addresses</title>

<para>
If your network uses a zero-based broadcast address (for example, if it ends in a 0), then you will strike problems. Windows for Workgroups
does not seem to support a zeros broadcast, and you will probably find that browsing and name lookups will not work.
</para>
</sect2>

<sect2>
<title>Multiple Interfaces</title>

<para>
Samba supports machines with multiple network interfaces. If you have multiple interfaces, you will
need to use the <smbconfoption name="interfaces"/> option in &smb.conf; to configure them. 
</para>
</sect2>
<sect2>
<title>Use of the Remote Announce Parameter</title>
<para>
The <smbconfoption name="remote announce"/> parameter of 
&smb.conf; can be used to forcibly ensure
that all the NetBIOS names on a network get announced to a remote network.
The syntax of the <smbconfoption name="remote announce"/> parameter is:
<smbconfblock>
<smbconfoption name="remote announce">a.b.c.d [e.f.g.h] ...</smbconfoption>
</smbconfblock>
<emphasis>or</emphasis>
<smbconfblock>
<smbconfoption name="remote announce">a.b.c.d/WORKGROUP [e.f.g.h/WORKGROUP] ...</smbconfoption>
</smbconfblock>

where:
<variablelist>
        <varlistentry><term><replaceable>a.b.c.d</replaceable> and <replaceable>e.f.g.h</replaceable></term>
                <listitem><para>
<indexterm><primary>LMB</primary><see>Local Master Browser</see></indexterm>
<indexterm><primary>Local Master Browser</primary></indexterm>
                is either the LMB IP address or the broadcast address of the remote network.
                That is, the LMB is at 192.168.1.10, or the address could be given as 192.168.1.255 where the netmask
                is assumed to be 24 bits (255.255.255.0). When the remote announcement is made to the broadcast
                address of the remote network, every host will receive our announcements. This is noisy and therefore
                undesirable but may be necessary if we do not know the IP address of the remote LMB.
                </para></listitem>
        </varlistentry>

        <varlistentry>
                <term><replaceable>WORKGROUP</replaceable></term>
                <listitem><para>is optional and can be either our own workgroup or that of the remote network. If you use the
                workgroup name of the remote network, our NetBIOS machine names will end up looking like
                they belong to that workgroup. This may cause name resolution problems and should be avoided.
                </para></listitem>
        </varlistentry>
</variablelist>
</para>

</sect2>

<sect2>
<title>Use of the Remote Browse Sync Parameter</title>

<para>
The <smbconfoption name="remote browse sync"/> parameter of 
&smb.conf; is used to announce to another LMB that it must synchronize its NetBIOS name list with our
Samba LMB. This works only if the Samba server that has this option is
simultaneously the LMB on its network segment.
</para>

<para>
The syntax of the <smbconfoption name="remote browse sync"/> parameter is:

<smbconfblock>
<smbconfoption name="remote browse sync"><replaceable>a.b.c.d</replaceable></smbconfoption>
</smbconfblock>

where <replaceable>a.b.c.d</replaceable> is either the IP address of the
remote LMB or the network broadcast address of the remote segment.
</para>

</sect2>

</sect1>

<sect1>
<title>WINS: The Windows Internetworking Name Server</title>

<para>
Use of WINS (either Samba WINS or MS Windows NT Server WINS) is highly
recommended. Every NetBIOS machine registers its name together with a
name_type value for each of several types of service it has available.
It registers its name directly as a unique (the type 0x03) name.
It also registers its name if it is running the LanManager-compatible
server service (used to make shares and printers available to other users)
by registering the server (the type 0x20) name.
</para>

<para>
All NetBIOS names are up to 15 characters in length. The name_type variable
is added to the end of the name, thus creating a 16 character name. Any
name that is shorter than 15 characters is padded with spaces to the 15th
character. Thus, all NetBIOS names are 16 characters long (including the
name_type information).
</para>

<para>
WINS can store these 16-character names as they get registered. A client
that wants to log onto the network can ask the WINS server for a list
of all names that have registered the NetLogon service name_type. This saves
broadcast traffic and greatly expedites logon processing. Since broadcast
name resolution cannot be used across network segments this type of
information can only be provided via WINS or via a statically configured
<filename>lmhosts</filename> file that must reside on all clients in the
absence of WINS.
</para>

<para>
WINS also forces browse list synchronization by all
LMBs. LMBs must synchronize their browse list with the DMB,
and WINS helps the LMB to identify its DMB. By definition this
will work only within a single workgroup. Note that the DMB
has nothing to do with what is referred to as an MS Windows NT domain. The
latter is a reference to a security environment, while the DMB refers to the
master controller for browse list information only.
</para>

<para>
WINS will work correctly only if every client TCP/IP protocol stack
is configured to use the WINS servers. Any client that is not
configured to use the WINS server will continue to use only broadcast-based
name registration, so WINS may never get to know about it. In any case,
machines that have not registered with a WINS server will fail name-to-address
lookup attempts by other clients and will therefore cause workstation access
errors.
</para>

<para>
To configure Samba as a WINS server, just add 
<smbconfoption name="wins support">yes</smbconfoption> to the &smb.conf;
file [global] section.
</para>

<para>
To configure Samba to register with a WINS server, just add
<smbconfoption name="wins server">a.b.c.d</smbconfoption>
to your &smb.conf; file <smbconfsection name="[global]"/> section.
</para>

<important><para>
Never use <smbconfoption name="wins support">yes</smbconfoption> together
with <smbconfoption name="wins server">a.b.c.d</smbconfoption>
particularly not using its own IP address. Specifying both will cause &nmbd; to refuse to start!
</para></important>

<sect2>
<title>WINS Server Configuration</title>

<para>
Either a Samba server or a Windows NT server machine may be set up
as a WINS server. To configure a Samba server to be a WINS server, you must
add to the &smb.conf; file on the selected Server the following line to
the <smbconfsection name="[global]"/> section:
</para>

<para>
<smbconfblock>
<smbconfoption name="wins support">yes</smbconfoption>
</smbconfblock>
</para>

<para>
Versions of Samba prior to 1.9.17 had this parameter default to
yes. If you have any older versions of Samba on your network, it is
strongly suggested you upgrade to a recent version, or at the very
least set the parameter to <quote>no</quote> on all these machines.
</para>

<para>
Machines configured with <smbconfoption name="wins support">yes</smbconfoption> will keep a list of 
all NetBIOS names registered with them, acting as a DNS for NetBIOS names.
</para>

<para>
It is strongly recommended to set up only one WINS server. Do not set the
<smbconfoption name="wins support">yes</smbconfoption> option on more than one Samba 
server.
</para>

<para>
<indexterm><primary>replication</primary><secondary>WINS</secondary></indexterm>
To configure Windows NT/200x Server as a WINS server, install and configure
the WINS service. See the Windows NT/200x documentation for details.
Windows NT/200x WINS servers can replicate to each other, allowing more
than one to be set up in a complex subnet environment. Because Microsoft
refuses to document the replication protocols, Samba cannot currently
participate in these replications. It is possible in the future that
a Samba-to-Samba WINS replication protocol may be defined, in which
case more than one Samba machine could be set up as a WINS server.
Currently only one Samba server should have the 
<smbconfoption name="wins support">yes</smbconfoption> parameter set.
</para>

<para>
After the WINS server has been configured, you must ensure that all
machines participating on the network are configured with the address
of this WINS server. If your WINS server is a Samba machine, fill in
the Samba machine IP address in the <guilabel>Primary WINS Server</guilabel> field of
the <guilabel>Control Panel->Network->Protocols->TCP->WINS Server</guilabel> dialogs
in Windows 9x/Me or Windows NT/200x. To tell a Samba server the IP address
of the WINS server, add the following line to the <smbconfsection name="[global]"/> section of
all &smb.conf; files:
</para>

<para>
<smbconfblock>
<smbconfoption name="wins server">&lt;name or IP address&gt;</smbconfoption>
</smbconfblock>
</para>

<para>
where &lt;name or IP address&gt; is either the DNS name of the WINS server
machine or its IP address.
</para>

<para>
This line must not be set in the &smb.conf; file of the Samba
server acting as the WINS server itself. If you set both the
<smbconfoption name="wins support">yes</smbconfoption> option and the 
<smbconfoption name="wins server">&lt;name&gt;</smbconfoption> option then
<command>nmbd</command> will fail to start.
</para>

<para>
There are two possible scenarios for setting up cross-subnet browsing.
The first details setting up cross-subnet browsing on a network containing
Windows 9x/Me, Samba, and Windows NT/200x machines that are not configured as
part of a Windows NT domain. The second details setting up cross-subnet
browsing on networks that contain NT domains.
</para>

</sect2>

<sect2>
<title>WINS Replication</title>

<para>
<indexterm><primary>replication</primary><secondary>WINS</secondary></indexterm>
Samba-3 permits WINS replication through the use of the <filename>wrepld</filename> utility.
This tool is not currently in use because it is still in active development.
As soon as this tool becomes moderately functional, we will prepare man pages and enhance this
section of the documentation to provide usage and technical details.
</para>

</sect2>
<sect2>
<title>Static WINS Entries</title>

<para>
Adding static entries to your Samba WINS server is actually fairly easy.
All you have to do is add a line to <filename>wins.dat</filename>, typically
located in <filename class="directory">/usr/local/samba/var/locks</filename> or
<filename>/var/run/samba</filename>.
</para>

<para>
Entries in <filename>wins.dat</filename> take the form of:

<programlisting>
"NAME#TYPE" TTL ADDRESS+ FLAGS
</programlisting>

where NAME is the NetBIOS name, TYPE is the NetBIOS type, TTL is the
time-to-live as an absolute time in seconds, ADDRESS+ is one or more
addresses corresponding to the registration, and FLAGS are the NetBIOS
flags for the registration.
</para>

<para>
A typical dynamic entry looks like this:
<programlisting>
"MADMAN#03" 1055298378 192.168.1.2 66R
</programlisting>

To make it static, simply set the TTL to 0, like this:

<programlisting>
"MADMAN#03" 0 192.168.1.2 66R
</programlisting>
</para>

<para>
Though this method works with early Samba-3 versions, there is a
possibility that it may change in future versions if WINS replication
is added.
</para>

</sect2>
</sect1>

<sect1>
<title>Helpful Hints</title>

<para>
The following hints should be carefully considered because they are stumbling points
for many new network administrators.
</para>

<sect2>
<title>Windows Networking Protocols</title>

<para>
A common cause of browsing problems results from installing more than
one protocol on an MS Windows machine.
</para>

<warning><para>
Do not use more than one protocol on MS Windows clients.
</para></warning>

<para>
Every NetBIOS machine takes part in a process of electing the LMB (and DMB)
every 15 minutes. A set of election criteria is used to determine the order
of precedence for winning this election process. A machine running Samba or
Windows NT will be biased, so the most suitable machine will predictably
win and thus retain its role.
</para>

<para>
The election process is fought out over every NetBIOS network
interface. In the case of a Windows 9x/Me machine that has both TCP/IP and IPX
installed and has NetBIOS enabled over both protocols, the election will be
decided over both protocols. As often happens, if the Windows 9x/Me machine is
the only one with both protocols, then the LMB may be won on the NetBIOS
interface over the IPX protocol. Samba will then lose the LMB role because Windows
9x/Me will insist it knows who the LMB is. Samba will then cease to function
as an LMB, and browse list operation on all TCP/IP-only machines will
therefore fail.
</para>

<para>
Windows 95, 98, 98se, and Me are referred to generically as Windows 9x/Me.
The Windows NT4, 200x, and XP use common protocols. These are roughly
referred to as the Windows NT family, but it should be recognized that 2000 and
XP/2003 introduce new protocol extensions that cause them to behave 
differently from MS Windows NT4. Generally, where a server does not support
the newer or extended protocol, these will fall back to the NT4 protocols.
</para>

<para>
The safest rule of all to follow is: Use only one protocol!
</para>

</sect2>

<sect2>
<title>Name Resolution Order</title>

<para>
Resolution of NetBIOS names to IP addresses can take place using a number
of methods. The only ones that can provide NetBIOS name_type information
are:
</para>

<itemizedlist>
        <listitem><para>WINS &smbmdash; the best tool.</para></listitem>
        <listitem><para>LMHOSTS &smbmdash; static and hard to maintain.</para></listitem>
        <listitem><para>Broadcast &smbmdash; uses UDP and cannot resolve names across remote segments.</para></listitem>
</itemizedlist>

<para>
Alternative means of name resolution include:
</para>
<itemizedlist>
<listitem><para>Static <filename>/etc/hosts</filename> &smbmdash;  hard to maintain and lacks name_type info.</para></listitem>
<listitem><para>DNS &smbmdash; is a good choice but lacks essential name_type info.</para></listitem>
</itemizedlist>

<para>
Many sites want to restrict DNS lookups and avoid broadcast name
resolution traffic. The <parameter>name resolve order</parameter> parameter is of great help here.
The syntax of the <parameter>name resolve order</parameter> parameter is:
<smbconfblock>
<smbconfoption name="name resolve order">wins lmhosts bcast host</smbconfoption>
</smbconfblock>
<emphasis>or</emphasis>
<smbconfblock>
<smbconfoption name="name resolve order">wins lmhosts   (eliminates bcast and host)</smbconfoption>
</smbconfblock>
The default is:
<smbconfblock>
<smbconfoption name="name resolve order">host lmhost wins bcast</smbconfoption>,
</smbconfblock>
where <quote>host</quote> refers to the native methods used by the UNIX system
to implement the gethostbyname() function call. This is normally
controlled by <filename>/etc/host.conf</filename>, <filename>/etc/nsswitch.conf</filename> and <filename>/etc/resolv.conf</filename>.
</para>
</sect2>
</sect1>

<sect1>
<title>Technical Overview of Browsing</title>

<para>
SMB networking provides a mechanism by which clients can access a list
of machines in a network called <smbconfoption name="browse list"/>. This list
contains machines that are ready to offer file and/or print services
to other machines within the network. It therefore does not include
machines that aren't currently able to do server tasks. The browse
list is heavily used by all SMB clients. Configuration of SMB
browsing has been problematic for some Samba users, hence this
document.
</para>

<para>
MS Windows 2000 and later versions, as with Samba-3 and later versions, can be
configured to not use NetBIOS over TCP/IP. When configured this way,
it is imperative that name resolution (using DNS/LDAP/ADS) be correctly
configured and operative. Browsing will not work if name resolution
from SMB machine names to IP addresses does not function correctly.
</para>

<para>
Where NetBIOS over TCP/IP is enabled, use of a WINS server is highly
recommended to aid the resolution of NetBIOS (SMB) names to IP addresses.
WINS allows remote segment clients to obtain NetBIOS name_type information
that cannot be provided by any other means of name resolution.
</para>

<sect2>
<title>Browsing Support in Samba</title>

<para>
Samba facilitates browsing. The browsing is supported by &nmbd;
and is also controlled by options in the &smb.conf; file.
Samba can act as an LMB for a workgroup, and the ability
to support domain logons and scripts is now available.
</para>

<para>
Samba can also act as a DMB for a workgroup. This
means that it will collate lists from LMBs into a
wide-area network server list. In order for browse clients to
resolve the names they may find in this list, it is recommended that
both Samba and your clients use a WINS server.
</para>

<para>
Do not set Samba to be the domain master for a workgroup that has the same
name as an NT Domain. On each wide-area network, you must only ever have one
DMB per workgroup, regardless of whether it is NT, Samba,
or any other type of domain master that is providing this service.
</para>

<note><para>
<command>nmbd</command> can be configured as a WINS server, but it is not
necessary to specifically use Samba as your WINS server. MS Windows
NT4, Server or Advanced Server 200x can be configured as
your WINS server. In a mixed NT/200x server and Samba environment on
a WAN, it is recommended that you use the Microsoft
WINS server capabilities. In a Samba-only environment, it is
recommended that you use one and only one Samba server as the WINS server.
</para></note>

<para>
To get browsing to work, you need to run nmbd as usual, but must
use the <smbconfoption name="workgroup"/> option in &smb.conf;
to control what workgroup Samba becomes a part of.
</para>

<para>
Samba also has a useful option for a Samba server to offer itself for
browsing on another subnet. It is recommended that this option is
used only for <quote>unusual</quote> purposes: announcements over the Internet, for
example. See <smbconfoption name="remote announce"/> in the 
&smb.conf; man page. 
</para>
</sect2>

<sect2>
<title>Problem Resolution</title>

<para>
If something does not work, the <filename>log.nmbd</filename> file will help
to track down the problem. Try a <smbconfoption name="log level"></smbconfoption> of 2 or 3 for finding
problems. Also note that the current browse list usually gets stored
in text form in a file called <filename>browse.dat</filename>.
</para>

<para>
If it does not work, you should still be able to
type the server name as <filename>\\SERVER</filename> in <command>filemanager</command>, then
press enter, and <command>filemanager</command> should display the list of available shares.
</para>

<para>
Some people find browsing fails because they do not have the global
<smbconfoption name="guest account"/> set to a valid account. Remember that the
IPC$ connection that lists the shares is done as guest and so you must have a valid guest account.
</para>

<para>
MS Windows 2000 and later (as with Samba) can be configured to disallow
anonymous (i.e., guest account) access to the IPC$ share. In that case, the
MS Windows 2000/XP/2003 machine acting as an SMB/CIFS client will use the
name of the currently logged-in user to query the IPC$ share. MS Windows
9x/Me clients are not able to do this and thus will not be able to browse
server resources.
</para>

<para>
The other big problem people have is that their broadcast address,
netmask, or IP address is wrong (specified with the <smbconfoption name="interfaces"></smbconfoption> option
in &smb.conf;)
</para>
</sect2>

<sect2>
<title>Cross-Subnet Browsing</title>

<para>
<indexterm><primary>replication</primary><secondary>browse lists</secondary></indexterm>
Since the release of Samba 1.9.17 (alpha1), Samba has supported the
replication of browse lists across subnet boundaries. This section
describes how to set this feature up in different settings.
</para>

<para>
To see browse lists that span TCP/IP subnets (i.e., networks separated
by routers that do not pass broadcast traffic), you must set up at least
one WINS server. The WINS server acts as a DNS for NetBIOS names. This will
allow NetBIOS name-to-IP address translation to be completed by a direct
query of the WINS server. This is done via a directed UDP packet on
port 137 to the WINS server machine. The WINS server avoids the necessity
of default NetBIOS name-to-IP address translation, which is done
using UDP broadcasts from the querying machine. This means that machines
on one subnet will not be able to resolve the names of machines on
another subnet without using a WINS server.
</para>

<para>
Remember, for browsing across subnets to work correctly, all machines,
be they Windows 95, Windows NT, or Samba servers, must have the IP address
of a WINS server given to them by a DHCP server or by manual configuration: 
for Windows 9x/Me and Windows NT/200x/XP, this is in the TCP/IP Properties, under Network 
settings; for Samba, this is in the &smb.conf; file.
</para>

<sect3>
<title>Behavior of Cross-Subnet Browsing</title>

<para>
Cross-subnet browsing is a complicated dance, containing multiple
moving parts. It has taken Microsoft several years to get the code
that correctly achieves this, and Samba lags behind in some areas.
Samba is capable of cross-subnet browsing when configured correctly.
</para>

<para>
Consider a network set up as in <link linkend="browsing1">Cross-Subnet Browsing Example</link>.
</para>

<figure id="browsing1">
        <title>Cross-Subnet Browsing Example.</title>
        <imagefile scale="40">browsing1</imagefile>
</figure>
        
<para>
This consists of three subnets (1, 2, 3) connected by two routers
(R1, R2), which do not pass broadcasts. Subnet 1 has five machines
on it, subnet 2 has four machines, and subnet 3 has four machines. Assume
for the moment that all machines are configured to be in the
same workgroup (for simplicity's sake). Machine N1_C on subnet 1
is configured as the DMB (i.e., it will collate the
browse lists for the workgroup). Machine N2_D is configured as
a WINS server, and all the other machines are configured to register
their NetBIOS names with it.
</para>

<para>
As these machines are booted up, elections for master browsers
take place on each of the three subnets. Assume that machine
N1_C wins on subnet 1, N2_B wins on subnet 2, and N3_D wins on
subnet 3. These machines are known as LMBs for
their particular subnet. N1_C has an advantage in winning as the
LMB on subnet 1 because it is set up as DMB.
</para>

<para>
On each of the three networks, machines that are configured to 
offer sharing services will broadcast that they are offering
these services. The LMB on each subnet will
receive these broadcasts and keep a record of the fact that
the machine is offering a service. This list of records is
the basis of the browse list. For this case, assume that
all the machines are configured to offer services, so all machines
will be on the browse list.
</para>

<para>
For each network, the LMB on that network is
considered <emphasis>authoritative</emphasis> for all the names it receives via
local broadcast. This is because a machine seen by the LMB
via a local broadcast must be on the same network as the
Local Master Browser and thus is a <emphasis>trusted</emphasis>
and <emphasis>verifiable</emphasis> resource. Machines on other networks that
the LMBs learn about when collating their
browse lists have not been directly seen. These records are
called <emphasis>non-authoritative.</emphasis>
</para>

<para>
At this point the browse lists appear as shown in <link linkend="browsubnet">Browse Subnet Example 1</link> (these are 
the machines you would see in your network neighborhood if you looked in it on a particular network right now).
</para>

<para>
<table frame="all" id="browsubnet">
        <title>Browse Subnet Example 1</title>          
        <tgroup align="left" cols="3">
        <thead>
                <row><entry>Subnet</entry><entry>Browse Master</entry><entry>List</entry></row>
        </thead>

        <tbody>
                <row><entry>Subnet1</entry><entry>N1_C</entry><entry>N1_A, N1_B, N1_C, N1_D, N1_E</entry></row>
                <row><entry>Subnet2</entry><entry>N2_B</entry><entry>N2_A, N2_B, N2_C, N2_D</entry></row>
                <row><entry>Subnet3</entry><entry>N3_D</entry><entry>N3_A, N3_B, N3_C, N3_D</entry></row>
        </tbody>
        </tgroup>
</table>
</para>

<para>
At this point all the subnets are separate, and no machine is seen across any of the subnets.
</para>

<para>
Now examine subnet 2 in <link linkend="brsbex">Browse Subnet Example 2</link>.
As soon as N2_B has become the LMB, it looks for a DMB with which to synchronize
its browse list. It does this by querying the WINS server
(N2_D) for the IP address associated with the NetBIOS name 
WORKGROUP&lt;1B&gt;. This name was registered by the DMB
(N1_C) with the WINS server as soon as it was started.
</para>

<para>
Once N2_B knows the address of the DMB, it
tells it that is the LMB for subnet 2 by
sending a <emphasis>MasterAnnouncement</emphasis> packet as a UDP port 138 packet.
It then synchronizes with it by doing a <emphasis>NetServerEnum2</emphasis> call. This
tells the DMB to send it all the server
names it knows about. Once the DMB receives
the <emphasis>MasterAnnouncement</emphasis> packet, it schedules a synchronization
request to the sender of that packet. After both synchronizations
are complete, the browse lists look like those in <link linkend="brsbex">Browse Subnet Example 2</link>
</para>

<table frame="all" id="brsbex">
        <title>Browse Subnet Example 2</title>          
        <tgroup cols="3">
                <colspec align="left"/>
                <colspec align="left"/>
                <colspec align="justify" colwidth="1*"/>
        <thead>
                <row><entry>Subnet</entry><entry>Browse Master</entry><entry>List</entry></row>
        </thead>

        <tbody>
                <row><entry>Subnet1</entry><entry>N1_C</entry><entry>N1_A, N1_B, N1_C, N1_D, N1_E,
N2_A(*), N2_B(*), N2_C(*), N2_D(*)</entry></row>
                <row><entry>Subnet2</entry><entry>N2_B</entry><entry>N2_A, N2_B, N2_C, N2_D, N1_A(*), 
N1_B(*), N1_C(*), N1_D(*), N1_E(*)</entry></row>
                <row><entry>Subnet3</entry><entry>N3_D</entry><entry>N3_A, N3_B, N3_C, N3_D</entry></row>
        </tbody>
        </tgroup>
</table>

<para>
Servers with an (*) after them are non-authoritative names.
</para>

<para>
At this point users looking in their Network Neighborhood on
subnets 1 or 2 will see all the servers on both; users on
subnet 3 will still see only the servers on their own subnet.
</para>

<para>
The same sequence of events that occurred for N2_B now occurs
for the LMB on subnet 3 (N3_D). When it
synchronizes browse lists with the DMB (N1_A)
it gets both the server entries on subnet 1 and those on
subnet 2. After N3_D has synchronized with N1_C and vica versa,
the browse lists will appear as shown in <link linkend="brsex2">Browse Subnet Example 3</link>
</para>

<table frame="all" id="brsex2">
        <title>Browse Subnet Example 3</title>          
        <tgroup cols="3" align="left">
                <colspec align="left"/>
                <colspec align="left"/>
                <colspec align="justify" colwidth="1*"/>

        <thead>
                <row><entry>Subnet</entry><entry>Browse Master</entry><entry>List</entry></row>
        </thead>

        <tbody>
                <row><entry>Subnet1</entry><entry>N1_C</entry><entry>N1_A, N1_B, N1_C, N1_D, N1_E, 
N2_A(*), N2_B(*), N2_C(*), N2_D(*), N3_A(*), N3_B(*), N3_C(*), N3_D(*)</entry></row>
                <row><entry>Subnet2</entry><entry>N2_B</entry><entry>N2_A, N2_B, N2_C, N2_D, N1_A(*), 
N1_B(*), N1_C(*), N1_D(*), N1_E(*)</entry></row>
                <row><entry>Subnet3</entry><entry>N3_D</entry><entry>N3_A, N3_B, N3_C, N3_D, N1_A(*), 
N1_B(*), N1_C(*), N1_D(*), N1_E(*), N2_A(*), N2_B(*), N2_C(*), N2_D(*)</entry></row>
        </tbody>
        </tgroup>
</table>

<para>
Servers with an (*) after them are non-authoritative names.
</para>

<para>
At this point, users looking in their Network Neighborhood on
subnets 1 or 3 will see all the servers on all subnets, while users on
subnet 2 will still see only the servers on subnets 1 and 2, but not 3.
</para>

<para>
Finally, the LMB for subnet 2 (N2_B) will sync again
with the DMB (N1_C) and will receive the missing
server entries. Finally, as when a steady state (if no machines
are removed or shut off) has been achieved, the browse lists will appear
as shown in <link linkend="brsex3">Browse Subnet Example 4</link>.
</para>

<table frame="all" id="brsex3">
        <title>Browse Subnet Example 4</title>          
        <tgroup cols="3" align="left">
                <colspec align="left"/>
                <colspec align="left"/>
                <colspec align="justify" colwidth="1*"/>

        <thead>
                <row><entry>Subnet</entry><entry>Browse Master</entry><entry>List</entry></row>
        </thead>

        <tbody>
                <row><entry>Subnet1</entry><entry>N1_C</entry><entry>N1_A, N1_B, N1_C, N1_D, N1_E,
N2_A(*), N2_B(*), N2_C(*), N2_D(*), N3_A(*), N3_B(*), 
N3_C(*), N3_D(*)</entry></row>
                <row><entry>Subnet2</entry><entry>N2_B</entry><entry>N2_A, N2_B, N2_C, N2_D, N1_A(*), 
N1_B(*), N1_C(*), N1_D(*), N1_E(*), N3_A(*), N3_B(*), 
N3_C(*), N3_D(*)</entry></row>
                <row><entry>Subnet3</entry><entry>N3_D</entry><entry>N3_A, N3_B, N3_C, N3_D, N1_A(*), 
N1_B(*), N1_C(*), N1_D(*), N1_E(*), N2_A(*), N2_B(*), 
N2_C(*), N2_D(*)</entry></row>
        </tbody>
        </tgroup>
</table>

<para>
Servers with an (*) after them are non-authoritative names.
</para>

<para>
Synchronizations between the DMB and LMBs
will continue to occur, but this should remain a
steady-state operation.
</para>

<para>
If either router R1 or R2 fails, the following will occur:
</para>

<orderedlist>
<listitem>
        <para>
        Names of computers on each side of the inaccessible network fragments
        will be maintained for as long as 36 minutes in the Network Neighborhood
        lists.
        </para>
</listitem>

<listitem>
        <para>
        Attempts to connect to these inaccessible computers will fail, but the
        names will not be removed from the Network Neighborhood lists.
        </para>
</listitem>

<listitem>
        <para>
        If one of the fragments is cut off from the WINS server, it will only
        be able to access servers on its local subnet using subnet-isolated
        broadcast NetBIOS name resolution. The effect is similar to that of
        losing access to a DNS server.
        </para>
</listitem>
</orderedlist>
</sect3>
</sect2>
</sect1>

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

<para>
Many questions are asked on the mailing lists regarding browsing. The majority of browsing
problems originate from incorrect configuration of NetBIOS name resolution. Some are of
particular note.
</para>

<sect2>
<title>How Can One Flush the Samba NetBIOS Name Cache without Restarting Samba?</title>

<para>
<indexterm><primary>flush name cache</primary></indexterm>
Samba's <command>nmbd</command> process controls all browse list handling. Under normal circumstances it is
safe to restart <command>nmbd</command>. This will effectively flush the Samba NetBIOS name cache and cause it
to be rebuilt. This does not make certain that a rogue machine name will not reappear
in the browse list. When <command>nmbd</command> is taken out of service, another machine on the network will
become the browse master. This new list may still have the rogue entry in it. If you really
want to clear a rogue machine from the list, every machine on the network must be
shut down and restarted after all machines are down. Failing a complete restart, the only
other thing you can do is wait until the entry times out and is then flushed from the list.
This may take a long time on some networks (perhaps months).
</para>

</sect2>
 
<sect2>
        <title>Server Resources Cannot Be Listed</title>

<para><quote>My Client Reports "<quote>This server is not configured to list shared resources."</quote></quote></para>

                
<para>
Your guest account is probably invalid for some reason. Samba uses the
guest account for browsing in <command>smbd</command>. Check that your guest account is
valid.
</para>

<para>Also see <smbconfoption name="guest account"/> in the &smb.conf; man page.</para>

</sect2>

<sect2>
        <title>I Get an "<errorname>Unable to browse the network</errorname>" Error</title>

        <para>This error can have multiple causes:
<indexterm><primary>browsing problems</primary></indexterm>
        </para>
        
        <itemizedlist>
                <listitem><para>There is no LMB. Configure &nmbd; 
                        or any other machine to serve as LMB.</para></listitem>
                <listitem><para>You cannot log onto the machine that is the LMB. 
                        Can you log on to it as a guest user? </para></listitem>
                <listitem><para>There is no IP connectivity to the LMB. 
                        Can you reach it by broadcast?</para></listitem>
</itemizedlist>
</sect2>

<sect2>
<title>Browsing of Shares and Directories is Very Slow</title>

<para><quote>
<indexterm><primary>slow browsing</primary></indexterm>
There are only two machines on a test network. One is a Samba server, the other a Windows XP machine.
Authentication and logons work perfectly, but when I try to explore shares on the Samba server, the
Windows XP client becomes unresponsive. Sometimes it does not respond for some minutes. Eventually,
Windows Explorer will respond and displays files and directories without problem.
</quote>
</para>

<para><quote>
But, the share is immediately available from a command shell (<command>cmd</command>, followed by 
exploration with DOS command. Is this a Samba problem, or is it a Windows problem? How can I solve this?
</quote></para>

<para>
Here are a few possibilities:
</para>

<variablelist>
        <varlistentry>
                <term>Bad Networking Hardware</term>
                <listitem><para>
<indexterm><primary>bad hardware</primary></indexterm>
<indexterm><primary>WebClient</primary></indexterm>
                Most common defective hardware problems center around low cost or defective hubs, routers,
                network interface controllers (NICs), and bad wiring. If one piece of hardware is defective,
                the whole network may suffer. Bad networking hardware can cause data corruption. Most bad
                networking hardware problems are accompanied by an increase in apparent network traffic,
                but not all.
                </para></listitem>
        </varlistentry>
        
        <varlistentry>
                <term>The Windows XP WebClient</term>
                <listitem><para>
                A number of sites have reported similar slow network browsing problems and found that when
                the WebClient service is turned off, the problem disappears. This is certainly something
                that should be explored because it is a simple solution &smbmdash; if it works.
                </para></listitem>
        </varlistentry>
        
        <varlistentry>
                <term>Inconsistent WINS Configuration</term>
                <listitem><para>
                This type of problem is common when one client is configured to use a WINS server (that is
                a TCP/IP configuration setting) and there is no WINS server on the network. Alternatively,
                this will happen if there is a WINS server and Samba is not configured to use it. The use of
                WINS is highly recommended if the network is using NetBIOS over TCP/IP protocols. If use
                of NetBIOS over TCP/IP is disabled on all clients, Samba should not be configured as a WINS
                server, nor should it be configured to use one.
                </para></listitem>
        </varlistentry>
        
        <varlistentry>
                <term>Incorrect DNS Configuration</term>
                <listitem><para>
                If use of NetBIOS over TCP/IP is disabled, Active Directory is in use and the DNS server
                has been incorrectly configured. For further information refer to
                <link linkend="adsdnstech">DNS and Active Directory</link>.
                </para></listitem>
        </varlistentry>
</variablelist>

</sect2>
</sect1>
</chapter>