Improved browsing in samba

SAMBA Project Documentation
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# Chapter 2. Improved browsing in samba

# 2.1. 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.

# 2.2. 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.

# 2.3. 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)

# 2.4. 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.

## 2.4.1. 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:

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.

# 2.5. 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.

# 2.6. 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

# 2.7. 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

# 2.8. 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.

# 2.9. 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:

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

2. 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:

1. 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.

2. 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.

# 2.10. 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.

# 2.11. 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.

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