path: root/docs/textdocs/BROWSING.txt

Author/s:	Many (Thanks to Luke, Jeremy, Andrew, etc.)
Updated:	June 29, 1997
Status:		Current - For VERY Advanced Users ONLY

Summary: This describes how to configure Samba for improved browsing.
=====================================================================

OVERVIEW:
=========
SMB networking provides a mechanism by which clients can access a list
of machines that are available within the network. This list is called
the browse list and is heavily used by all SMB clients. Configuration
of SMB browsing has been problematic for some Samba users, hence this
document.

=====================================================================

BROWSING
========
Samba now fully supports browsing. The browsing is supported by nmbd
and is also controlled by options in the smb.conf file (see smb.conf(5)).

Samba can act as a local browse master for a workgroup and the ability
for samba to support domain logons and scripts is now available.  See
DOMAIN.txt for more information on domain logons.

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

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

[Note that nmbd can be configured as a WINS server, but it is not
necessary to specifically use samba as your WINS server.  NTAS can
be configured as your WINS server.  In a mixed NT server and
samba environment on a Wide Area Network, it is recommended that
you use the NT server's WINS server capabilities.  In a samba-only
environment, it is recommended that you use one and only one nmbd
as your WINS server].

To get browsing to work you need to run nmbd as usual, but will need
to use the "workgroup" option in smb.conf to control what workgroup
Samba becomes a part of.

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 "remote announce" in the smb.conf man page. 

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.

Note that if it doesn't work for you, then you should still be able to
type the server name as \\SERVER in filemanager then hit enter and
filemanager should display the list of available shares.

Some people find browsing fails because they don't have the global
"guest account" 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.

Also, a lot of people are getting bitten by the problem of too many
parameters on the command line of nmbd in inetd.conf. This trick is to
not use spaces between the option and the parameter (eg: -d2 instead
of -d 2), and to not use the -B and -N options. New versions of nmbd
are now far more likely to correctly find your broadcast and network
addess, so in most cases these aren't needed.

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)

BROWSING ACROSS SUBNETS
=======================

With the release of Samba 1.9.17(alpha1 and above) 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.

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.

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.

How does cross subnet browsing work ?
=====================================

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.
However, with the 1.9.17 release, Samba is capable of cross subnet
browsing when configured correctly.

Consider a network set up as follows :

                                   (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)

Consisting of 3 subnets (1, 2, 3) conneted 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.

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.

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.

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'.

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).

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

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

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<1B>. This name was registerd by the Domain master
browser (N1_C) with the WINS server as soon as it was booted.

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 :

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.

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.

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.

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.

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.

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 :

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.

Synchronizations between the domain master browser and local
master browsers will continue to occur, but this should be a
steady state situation.

If either router R1 or R2 fails the following will occur:

1) 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.

2) Attempts to connect to these inaccessible computers will fail, but the
names will not be removed from the network neighbourhood lists.

3) 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.

Setting up a WINS server
========================

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 

        wins support = yes

Versions of Samba previous 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 1.9.17 or above, or at the very
least set the parameter to 'no' on all these machines.

Machines with "wins support = yes" will keep a list of all NetBIOS
names registered with them, acting as a DNS for NetBIOS names.

You should set up only ONE wins server. Do NOT set the
"wins support = yes" option on more than one Samba server.

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 "wins support = yes"
parameter set.

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 :

        wins server = <name or IP address>

where <name or IP address> is either the DNS name of the WINS server
machine or it's IP address.

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
"wins support = yes" option and the "wins server = <name>" option then
nmbd will fail to start.

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.

Setting up Browsing in a WORKGROUP
==================================

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.

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 (although the same Samba server can act as Domain
master browser for multiple workgroup names). To set up a Samba
server as a domain master browser set the following option in the
[global] section of the smb.conf file :

        domain master = yes

The domain master browser should also preferrably be the local master
browser for it's own subnet. In order to achieve this set the following
options in the [global] section of the smb.conf file :

        domain master = yes
        local master = yes
        preferred master = yes
        os level = 65

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

Next, you should ensure that each of the subnets contains a
machine that can act as a local master browser for the
workgroup. Any NT machine should be able to do this, as will
Windows 95 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 :

        domain master = no
        local master = yes
        preferred master = yes
        os level = 65

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.

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

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 [global] section of the smb.conf file :

        domain master = no
        local master = no
        preferred master = no
        os level = 0

Setting up Browsing in a DOMAIN
===============================

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 (DOMAIN<1B>) with WINS instead of the PDC.

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 [global] section of the smb.conf 
file :

        domain master = no
        local master = yes
        preferred master = yes
        os level = 65

If you wish to have a Samba server fight the election with machines
on the same subnet you may set the "os level" 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 "FORCING SAMBA TO BE THE MASTER"
below.

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 [global] section of the smb.conf file :
 
        domain master = no
        local master = no
        preferred master = no
        os level = 0

FORCING SAMBA TO BE THE MASTER
==============================

Who becomes the "master browser" 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.

If you want Samba to win elections then just set the "os level" 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!)

A "os level" of 2 would make it beat WfWg and Win95, but not NTAS. A
NTAS domain controller uses level 32.

The maximum os level is 255

If you want samba to force an election on startup, then set the
"preferred master" 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 "preferred master" to
"yes", then periodically and continually they will force an election
in order to become the local master browser.

If you want samba to be a "domain master browser", then it is
recommended that you also set "preferred master" 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.

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.
 

MAKING SAMBA THE DOMAIN MASTER
==============================

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 "domain master = yes"
in smb.conf. By default it will not be a domain master.

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

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.

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

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:

a) your local master browsers will be unable to find a domain master
   browser, as it will only be looking on the local subnet.

b) 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.

If, however, both samba and your clients are using a WINS server, then:

a) 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.

b) 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. 

NOTE ABOUT BROADCAST ADDRESSES
==============================

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.


MULTIPLE INTERFACES
===================

Samba now supports machines with multiple network interfaces. If you
have multiple interfaces then you will need to use the "interfaces"
option in smb.conf to configure them. See smb.conf(5) for details.