Improved browsing in samba

Overview of browsing

SMB networking provides a mechanism by which clients can access a list -of machines in a network, a so-called "browse list". 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.

Browsing will NOT work if name resolution from NetBIOS names to IP -addresses does not function correctly. 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.

Browsing support in samba

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: 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.

[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.

Problem resolution

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 browse.dat.

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 -address, 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) 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.

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:

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

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

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. -
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.