Another set of updates.

[sfrench/samba-autobuild/.git] / docs / docbook / projdoc / NetworkBrowsing.xml

<chapter id="NetworkBrowsing">
<chapterinfo>
        &author.jht;
        <pubdate>July 5, 1998</pubdate>
        <pubdate>Updated: April 21, 2003</pubdate>
</chapterinfo>

<title>Samba / MS Windows Network Browsing Guide</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 addesses. WINS is
NOT involved in browse list handling except by way of name to address resolution.
</para>

<note><para>
MS Windows 2000 and later can be configured to operate with NO NetBIOS 
over TCP/IP. Samba-3 and later also supports this mode of operation.
When the use of NetBIOS over TCP/IP has been disabled then 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>What is Browsing?</title>

<para>
To most people browsing means that 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 very complex interaction of different technologies.
The technologies (or methods) employed in making all of this work includes:
</para>

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

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

<para><programlisting>
        Browsing options:
        -----------------
                * os level
                  lm announce
                  lm interval
                * preferred master
                * local master
                * domain master
                  browse list
                  enhanced browsing

        Name Resolution Method:
        -----------------------
                * name resolve order

        WINS options:
        -------------
                  dns proxy
                  wins proxy
                * wins server
                * wins support
                  wins hook
</programlisting></para>

<para>
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 not one of these parameters
is set nmbd will still do it's job.
</para>
</sect1>

<sect1>
<title>Discussion</title>

<para>
Firstly, all MS Windows networking is based on SMB (Server Message
Block) based messaging. SMB messaging may be implemented using NetBIOS or 
without NetBIOS. Samba implements NetBIOS by encapsulating it over TCP/IP.
MS Windows products can do likewise. NetBIOS based networking uses broadcast
messaging to affect browse list management. When running NetBIOS over
TCP/IP this uses UDP based messaging. UDP messages can be broadcast or unicast.
</para>

<para>
Normally, only unicast UDP messaging can be forwarded by routers. The
<command>remote announce</command>
parameter to smb.conf helps to project browse announcements
to remote network segments via unicast UDP. Similarly, the 
<command>remote browse sync</command> parameter of <filename>smb.conf</filename>
implements browse list collation using unicast UDP.
</para>

<para>
Secondly, in those networks where Samba is the only SMB server technology
wherever possible <filename>nmbd</filename> should be configured on one (1) machine as the WINS
server. This makes it easy to manage the browsing environment. If each network
segment is configured with it's own Samba WINS server, then the only way to
get cross segment browsing to work is by using the 
<command>remote announce</command> and the <command>remote browse sync</command>
parameters to your <filename>smb.conf</filename> file.
</para>

<para>
If only one WINS server is used for an entire multi-segment network then
the use of the <command>remote announce</command> and the 
<command>remote browse sync</command> parameters should NOT be necessary.
</para>

<para>
As of Samba 3 WINS replication is being worked on. The bulk of the code has
been committed, but it still needs maturation.
</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 
<command>remote browse sync</command> and <command>remote announce</command>
to affect 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 (ie: an 'if all else fails' 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 stabilise, particularly across network segments.
</para>

</sect1>

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

<para>
As stated above, MS Windows machines register their NetBIOS names 
(ie: the machine name for each service type in operation) on start 
up. Also, as stated above, 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, or if DNS for NetBIOS name resolution is enabled, etc.
</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 
<command>remote announce</command> 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 will take place to create a 
local master browser if one does not already exist. On each NetBIOS network 
one machine will be elected to function as the domain master browser. This 
domain browsing has nothing to do with MS security domain control. 
Instead, the domain master browser serves the role of contacting each local 
master browser (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 11-15 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 domain master browser.
</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/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 synchonisation 
of browse lists across routed networks using the <command>remote 
browse sync</command> parameter in the <filename>smb.conf</filename> file. 
This causes Samba to contact the local master browser on a remote network and 
to request browse list synchronisation. 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 <command>remote 
browse sync</command> parameter provides browse list synchronisation - 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>
<title>Setting up WORKGROUP Browsing</title>

<para>
To set up cross subnet browsing on a network containing machines
in up to be in a WORKGROUP, not an NT Domain you need to set up one
Samba server to be the Domain Master Browser (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 Domain master browser is
to collate the browse lists from local master browsers on all the
subnets that have a machine participating in the workgroup.  Without
one machine configured as a domain master browser each subnet would
be an isolated workgroup, unable to see any machines on any other
subnet.  It is the presense of a domain master browser that makes
cross subnet browsing possible for a workgroup.
</para>

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

<para>
<programlisting>
        domain master = yes
</programlisting>
</para>

<para>
The domain master browser should also preferrably be the local master
browser for its own subnet.  In order to achieve this set the following
options in the [global] section of the &smb.conf; file :
</para>

<para>
<programlisting>
        domain master = yes
        local master = yes
        preferred master = yes
        os level = 65
</programlisting>
</para>

<para>
The domain master browser may be the same machine as the WINS
server, if you require.
</para>

<para>
Next, you should ensure that each of the subnets contains a
machine that can act as a local master browser for the
workgroup.  Any MS Windows NT/2K/XP/2003  machine should be
able to do this, as will Windows 9x machines (although these
tend to get rebooted more often, so it's not such a good idea
to use these).  To make a Samba server a local master browser
set the following options in the [global] section of the
&smb.conf; file :
</para>

<para>
<programlisting>
        domain master = no
        local master = yes
        preferred master = yes
        os level = 65
</programlisting>
</para>

<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 local
master browser.
</para>

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

<para>
If you have an NT machine on the subnet that you wish to
be the local master browser then you can disable Samba from
becoming a local master browser by setting the following
options in the <command>[global]</command> section of the 
&smb.conf; file :
</para>

<para>
<programlisting>
        domain master = no
        local master = no
        preferred master = no
        os level = 0
</programlisting>
</para>

</sect2>

<sect2>
<title>Setting up DOMAIN Browsing</title>

<para>
If you are adding Samba servers to a Windows NT Domain then
you must not set up a Samba server as a domain master browser.
By default, a Windows NT Primary Domain Controller for a Domain
name is also the Domain master browser for that name, and many
things will break if a Samba server registers the Domain master
browser 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 local master browsers as
described.  To make a Samba server a local master browser set 
the following options in the <command>[global]</command> section 
of the &smb.conf; file :
</para>

<para>
<programlisting>
        domain master = no
        local master = yes
        preferred master = yes
        os level = 65
</programlisting>
</para>

<para>
If you wish to have a Samba server fight the election with machines
on the same subnet you may set the <command>os level</command> parameter
to lower levels.  By doing this you can tune the order of machines that
will become local master browsers if they are running.  For
more details on this see the section <link linkend="browse-force-master">
Forcing samba to be the master browser</link>
below.
</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 then
you can disable Samba from taking part in browser elections and
ever becoming a local master browser by setting following options 
in the <command>[global]</command> section of the &smb.conf;
file :
</para>

<para>
<programlisting>
        domain master = no
        local master = no
        preferred master = no
        os level = 0
</programlisting>
</para>

</sect2>

<sect2 id="browse-force-master">
<title>Forcing samba to be the master</title>

<para>
Who becomes the <command>master browser</command> is determined by an election
process using broadcasts.  Each election packet contains a number of parameters
which determine what precedence (bias) a host should have in the
election.  By default Samba uses a very low precedence and thus loses
elections to just about anyone else.
</para>

<para>
If you want Samba to win elections then just set the <command>os level</command> global
option in &smb.conf; to a higher number.  It defaults to 0.  Using 34
would make it win all elections over every other system (except other
samba systems!)
</para>

<para>
A <command>os level</command> of 2 would make it beat WfWg and Win95, but not MS Windows
NT/2K Server.  A MS Windows NT/2K Server domain controller uses level 32.
</para>

<para>The maximum os level is 255</para>

<para>
If you want samba to force an election on startup, then set the
<command>preferred master</command> global option in &smb.conf; to "yes".  Samba will
then have a slight advantage over other potential master browsers
that are not preferred master browsers.  Use this parameter with
care, as if you have two hosts (whether they are windows 95 or NT or
samba) on the same local subnet both set with <command>preferred master</command> to
"yes", then periodically and continually they will force an election
in order to become the local master browser.
</para>

<para>
If you want samba to be a <command>domain master browser</command>, then it is
recommended that you also set <command>preferred master</command> to "yes", because
samba will not become a domain master browser for the whole of your
LAN or WAN if it is not also a local master browser on its own
broadcast isolated subnet.
</para>

<para>
It is possible to configure two samba servers to attempt to become
the domain master browser for a domain.  The first server that comes
up will be the domain master browser.  All other samba servers will
attempt to become the domain master browser every 5 minutes.  They
will find that another samba server is already the domain master
browser and will fail.  This provides automatic redundancy, should
the current domain master browser 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 that browsing can occur between subnets.  You can
make samba act as the domain master by setting <command>domain master = yes</command>
in &smb.conf;.  By default it will not be a domain master.
</para>

<para>
Note that you should NOT set Samba to be the domain master for a
workgroup that has the same name as an NT Domain.
</para>

<para>
When samba is the domain master and the master browser it will listen
for master announcements (made roughly every twelve minutes) from local
master browsers on other subnets and then contact them to synchronise
browse lists.
</para>

<para>
If you want samba to be the domain master then I suggest you also set
the <command>os level</command> high enough to make sure it wins elections, and set
<command>preferred master</command> to "yes", to get samba to force an election on
startup.
</para>

<para>
Note that all your 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>
        your local master browsers will be unable to find a domain master
        browser, as it will only be looking 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>
        your local master browsers will contact the WINS server and, as long as
        samba has registered that it is a domain master browser with the WINS
        server, your local master browser will receive samba's ip address
        as its domain master browser.
        </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 "0" 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 0's broadcast and you will probably find
that browsing and name lookups won't work.
</para>
</sect2>

<sect2>
<title>Multiple interfaces</title>

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

where:
<variablelist>
<varlistentry><term><replaceable>a.b.c.d</replaceable> and 
<replaceable>e.f.g.h</replaceable></term>
<listitem><para>is either the LMB (Local Master Browser) IP address
or the broadcst address of the remote network.
ie: 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 then 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 <command>Remote Browse Sync</command> parameter</title>

<para>
The <command>remote browse sync</command> parameter of 
<filename>smb.conf</filename> is used to announce to
another LMB that it must synchronise it's NetBIOS name list with our
Samba LMB. It works ONLY if the Samba server that has this option is
simultaneously the LMB on it's network segment.
</para>

<para>
The syntax of the <command>remote browse sync</command> parameter is:

<programlisting>
remote browse sync = <replaceable>a.b.c.d</replaceable>
</programlisting>

where <replaceable>a.b.c.d</replaceable> is either the IP address of the
remote LMB or else is 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 it's name together with a
name_type value for each of of several types of service it has available.
eg: It registers it's name directly as a unique (the type 0x03) name.
It also registers it's 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. ie: 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 can not be used across network segments this type of
information can only be provided via WINS _or_ via statically configured
<filename>lmhosts</filename> files that must reside on all clients in the
absence of WINS.
</para>

<para>
WINS also serves the purpose of forcing browse list synchronisation by all
LMB's. LMB's must synchronise their browse list with the DMB (domain master
browser) and WINS helps the LMB to identify it's DMB. By definition this
will work only within a single workgroup. Note that the domain master browser
has NOTHING to do with what is referred to as an MS Windows NT Domain. The
later is a reference to a security environment while the DMB refers to the
master controller for browse list information only.
</para>

<para>
Use of WINS will work correctly only if EVERY client TCP/IP protocol stack
has been configured to use the WINS server/s. Any client that has not been
configured to use the WINS server will continue to use only broadcast based
name registration so that 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 
<command>wins support = yes</command> to the <filename>smb.conf</filename>
file [globals] section.
</para>

<para>
To configure Samba to register with a WINS server just add
"wins server = a.b.c.d" to your smb.conf file [globals] section.
</para>

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

<sect2>
<title>Setting up a WINS server</title>

<para>
Either a Samba machine or a Windows NT Server machine may be set up
as a WINS server.  To set a Samba machine to be a WINS server you must
add the following option to the &smb.conf; file on the selected machine :
in the [globals] section add the line 
</para>

<para>
<programlisting>
        wins support = yes
</programlisting>
</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 'no' on all these machines.
</para>

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

<para>
You should set up only ONE wins server.  Do NOT set the
<command>wins support = yes</command> option on more than one Samba 
server.
</para>

<para>
To set up a Windows NT Server as a WINS server you need to set up
the WINS service - see your NT documentation for details.  Note that
Windows NT WINS Servers can replicate to each other, allowing more
than one to be set up in a complex subnet environment.  As Microsoft
refuse to document these replication protocols Samba cannot currently
participate in these replications.  It is possible in the future that
a Samba->Samba WINS replication protocol may be defined, in which
case more than one Samba machine could be set up as a WINS server
but currently only one Samba server should have the 
<command>wins support = yes</command> 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 "Primary WINS Server" field of
the "Control Panel->Network->Protocols->TCP->WINS Server" dialogs
in Windows 95 or Windows NT.  To tell a Samba server the IP address
of the WINS server add the following line to the [global] section of
all &smb.conf; files :
</para>

<para>
<programlisting>
        wins server = &lt;name or IP address&gt;
</programlisting>
</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>
Note that 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
<command>wins support = yes</command> option and the 
<command>wins server = &lt;name&gt;</command> option then
nmbd 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 95, Samba and Windows NT 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>
Samba-3 permits WINS replication through the use of the <filename>wrepld</filename> utility.
This tool is not currently capable of being used as 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>
New to Samba-3 is a tool called <filename>winsedit</filename> that may be used to add
static WINS entries to the WINS database. This tool can be used also to modify entries
existing in the WINS database.
</para>

<para>
The development of the winsedit tool was made necessary due to the migration
of the older style wins.dat file into a new tdb binary backend data store.
</para>

</sect2>
</sect1>

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

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

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

<warning><para>
Do NOT use more than one (1) protocol on MS Windows machines
</para></warning>

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

<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 precidence for winning this election process. A machine running Samba or
Windows NT will be biased so that the most suitable machine will predictably
win and thus retain it's role.
</para>

<para>
The election process is "fought out" so to speak over every NetBIOS network
interface. In the case of a Windows 9x 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 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 as Windows
9x will insist it knows who the LMB is. Samba will then cease to function
as an LMB and thus browse list operation on all TCP/IP only machines will
fail.
</para>

<para><emphasis>
Windows 95, 98, 98se, Me are referred to generically as Windows 9x.
The Windows NT4, 2000, XP and 2003 use common protocols. These are roughly
referred to as the WinNT family, but it should be recognised 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.
</emphasis></para>

<para>
The safest rule of all to follow it this - 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>

<simplelist>
        <member>WINS: the best tool!</member>
        <member>LMHOSTS: is static and hard to maintain.</member>
        <member>Broadcast: uses UDP and can not resolve names across remote segments.</member>
</simplelist>

<para>
Alternative means of name resolution includes:</para>
<simplelist>
<member>/etc/hosts: is static, hard to maintain, and lacks name_type info</member>
<member>DNS: is a good choice but lacks essential name_type info.</member>
</simplelist>

<para>
Many sites want to restrict DNS lookups and want to avoid broadcast name
resolution traffic. The "name resolve order" parameter is of great help here.
The syntax of the "name resolve order" parameter is:
<programlisting>
name resolve order = wins lmhosts bcast host
</programlisting>
_or_
<programlisting>
name resolve order = wins lmhosts       (eliminates bcast and host)
</programlisting>
The default is:
<programlisting>
name  resolve order = host lmhost wins bcast
</programlisting>
where "host" refers the 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, a so-called <command>browse list</command>.  This list
contains machines that are ready to offer file and/or print services
to other machines within the network. Thus it does not include
machines which 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, as with Samba 3 and later, 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 can NOT 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 a local browse master for a workgroup and the ability
to support domain logons and scripts is now available.
</para>

<para>
Samba can also act as a domain master browser for a workgroup.  This
means that it will collate lists from local browse masters 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>
Note that you should 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 domain master browser per workgroup,
regardless of whether it is NT, Samba or any other type of domain master
that is providing this service.
</para>

<note><para>
Nmbd 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 2000 or 2003 can be configured as
your WINS server.  In a mixed NT/2000/2003 server and samba environment on
a Wide Area Network, 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 your WINS server.
</para></note>

<para>
To get browsing to work you need to run nmbd as usual, but will need
to use the <command>workgroup</command> 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 only
used for 'unusual' purposes: announcements over the internet, for
example.  See <command>remote announce</command> in the 
&smb.conf; man page.  
</para>
</sect2>

<sect2>
<title>Problem resolution</title>

<para>
If something doesn't work then hopefully the log.nmb file will help
you track down the problem.  Try a debug level 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>
Note that if it doesn't work for you, then you should still be able to
type the server name as <filename>\\SERVER</filename> in filemanager then
hit enter and filemanager should display the list of available shares.
</para>

<para>
Some people find browsing fails because they don't have the global
<command>guest account</command> set to a valid account.  Remember that the
IPC$ connection that lists the shares is done as guest, and thus you must
have a valid guest account.
</para>

<para><emphasis>
MS Windows 2000 and upwards (as with Samba) can be configured to disallow
anonymous (ie: 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 clients are not able to do this and thus will NOT be able to browse
server resources.
</emphasis></para>

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

<sect2>
<title>Browsing across subnets</title>
<para>
Since the release of Samba 1.9.17(alpha1) Samba has been
updated to enable it to support the replication of browse lists
across subnet boundaries.  New code and options have been added to
achieve this.  This section describes how to set this feature up
in different settings.
</para>

<para>
To see browse lists that span TCP/IP subnets (ie.  networks separated
by routers that don't pass broadcast traffic) you must set up at least
one WINS server.  The WINS server acts as a DNS for NetBIOS names, allowing
NetBIOS name to IP address translation to be done by doing a direct
query of the WINS server.  This is done via a directed UDP packet on
port 137 to the WINS server machine.  The reason for a WINS server is
that by default, all NetBIOS name to IP address translation is done
by 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 Win95 and WinNT, this is in the TCP/IP Properties, under Network 
settings) for Samba this is in the &smb.conf; file.
</para>

<sect3>
<title>How does cross subnet browsing work ?</title>

<para>
Cross subnet browsing is a complicated dance, containing multiple
moving parts.  It has taken Microsoft several years to get the code
that achieves this correct, 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 follows :
</para>

<para>
<programlisting>
                                   (DMB)
             N1_A      N1_B        N1_C       N1_D        N1_E
              |          |           |          |           |
          -------------------------------------------------------
            |          subnet 1                       |
          +---+                                      +---+
          |R1 | Router 1                  Router 2   |R2 |
          +---+                                      +---+
            |                                          |
            |  subnet 2              subnet 3          |
  --------------------------       ------------------------------------
  |     |     |      |               |        |         |           |
 N2_A  N2_B  N2_C   N2_D           N3_A     N3_B      N3_C        N3_D 
                    (WINS)
</programlisting>
</para>
        
<para>
Consisting of 3 subnets (1, 2, 3) connected by two routers
(R1, R2) - these do not pass broadcasts.  Subnet 1 has 5 machines
on it, subnet 2 has 4 machines, subnet 3 has 4 machines.  Assume
for the moment that all these machines are configured to be in the
same workgroup (for simplicities sake).  Machine N1_C on subnet 1
is configured as Domain Master Browser (ie.  it will collate the
browse lists for the workgroup).  Machine N2_D is configured as
WINS server and all the other machines are configured to register
their NetBIOS names with it.
</para>

<para>
As all these machines are booted up, elections for master browsers
will 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 local master browsers for
their particular subnet.  N1_C has an advantage in winning as the
local master browser on subnet 1 as it is set up as Domain Master
Browser.
</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 local master browser 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 local master browser on that network is
considered 'authoritative' for all the names it receives via
local broadcast.  This is because a machine seen by the local
master browser via a local broadcast must be on the same 
network as the local master browser and thus is a 'trusted'
and 'verifiable' resource.  Machines on other networks that
the local master browsers learn about when collating their
browse lists have not been directly seen - these records are
called 'non-authoritative'.
</para>

<para>
At this point the browse lists look as follows (these are 
the machines you would see in your network neighborhood if
you looked in it on a particular network right now).
</para>

<para>
<programlisting>
Subnet           Browse Master   List
------           -------------   ----
Subnet1          N1_C            N1_A, N1_B, N1_C, N1_D, N1_E

Subnet2          N2_B            N2_A, N2_B, N2_C, N2_D

Subnet3          N3_D            N3_A, N3_B, N3_C, N3_D
</programlisting>
</para>

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

<para>
Now examine subnet 2.  As soon as N2_B has become the local
master browser it looks for a Domain master browser to synchronize
its browse list with.  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 registerd by the Domain master
browser (N1_C) with the WINS server as soon as it was booted.
</para>

<para>
Once N2_B knows the address of the Domain master browser it
tells it that is the local master browser for subnet 2 by
sending a MasterAnnouncement packet as a UDP port 138 packet.
It then synchronizes with it by doing a NetServerEnum2 call.  This
tells the Domain Master Browser to send it all the server
names it knows about.  Once the domain master browser receives
the MasterAnnouncement packet it schedules a synchronization
request to the sender of that packet.  After both synchronizations
are done the browse lists look like :
</para>

<para>
<programlisting>
Subnet           Browse Master   List
------           -------------   ----
Subnet1          N1_C            N1_A, N1_B, N1_C, N1_D, N1_E, 
                                 N2_A(*), N2_B(*), N2_C(*), N2_D(*)

Subnet2          N2_B            N2_A, N2_B, N2_C, N2_D
                                 N1_A(*), N1_B(*), N1_C(*), N1_D(*), N1_E(*)

Subnet3          N3_D            N3_A, N3_B, N3_C, N3_D

Servers with a (*) after them are non-authoritative names.
</programlisting>
</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 only see the servers on their own subnet.
</para>

<para>
The same sequence of events that occured for N2_B now occurs
for the local master browser on subnet 3 (N3_D).  When it
synchronizes browse lists with the domain master browser (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 look like.
</para>

<para>
<programlisting>
Subnet           Browse Master   List
------           -------------   ----
Subnet1          N1_C            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(*)

Subnet2          N2_B            N2_A, N2_B, N2_C, N2_D
                                 N1_A(*), N1_B(*), N1_C(*), N1_D(*), N1_E(*)

Subnet3          N3_D            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(*)

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

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

<para>
Finally, the local master browser for subnet 2 (N2_B) will sync again
with the domain master browser (N1_C) and will recieve the missing
server entries.  Finally - and as a steady state (if no machines
are removed or shut off) the browse lists will look like :
</para>

<para>
<programlisting>
Subnet           Browse Master   List
------           -------------   ----
Subnet1          N1_C            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(*)

Subnet2          N2_B            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(*)

Subnet3          N3_D            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(*)
        
Servers with a (*) after them are non-authoritative names.
</programlisting>
</para>

<para>
Synchronizations between the domain master browser and local
master browsers will continue to occur, but this should be a
steady state situation.
</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 neighbourhood
        lists.
        </para>
</listitem>

<listitem>
        <para>
        Attempts to connect to these inaccessible computers will fail, but the
        names will not be removed from the network neighbourhood 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, by using subnet-isolated
        broadcast NetBIOS name resolution.  The effects are 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 sked on the mailing lists regarding browsing. The majority of browsing
problems originate out of 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>
Sambas' nmbd process controls all browse list handling. Under normal circumstances it is
safe to restart nmbd. This will effectively flush the samba NetBIOS name cache and cause it
to be rebuilt. Note that this does NOT make certain that a rogue machine name will not re-appear
in the browse list. When nmbd 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 then every machine on the network will need to be
shut down and restarted at 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 (months).
</para>

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