Chapter 10. Network Browsing
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## Chapter 10. Network Browsing

### John H. Terpstra

Samba Team

`<jht@samba.org>`

### Jelmer R. Vernooij

The Samba Team

`<jelmer@samba.org>`

July 5, 1998

Updated: April 21, 2003

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

### Note

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

## Features and Benefits

Someone once referred to the past in these words “It was the best of times, it was the worst of times.” The more we look back, the more we long for what was and hope it never returns.

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

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

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

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

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

For those networks on which NetBIOS has been disabled (i.e., WINS is not required) the use of DNS is necessary for host name resolution.

## What Is Browsing?

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

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

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

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

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`.

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

## Discussion

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

### NetBIOS over TCP/IP

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

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

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

If only one WINS server is used for an entire multi-segment network, then the use of the `remote announce` and the `remote browse sync` parameters should not be necessary.

As of Samba-3 WINS replication is being worked on. The bulk of the code has been committed, but it still needs maturation. This is not a supported feature of the Samba-3.0.0 release. Hopefully, this will become a supported feature of one of the Samba-3 release series.

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 `nmbd` 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 `remote browse sync` and `remote announce` to effect browse list collation across all segments. Note that this means clients will only resolve local names, and must be configured to use DNS to resolve names on other subnets in order to resolve the IP addresses of the servers they can see on other subnets. This setup is not recommended, but is mentioned as a practical consideration (i.e., an “if all else fails” scenario).

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

### TCP/IP without NetBIOS

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

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

1. Checks the `hosts` file. It is located in `C:\Windows NT\System32\Drivers\etc`.

2. Does a DNS lookup.

3. Checks the NetBIOS name cache.

4. Queries the WINS server.

5. Does a broadcast name lookup over UDP.

6. Looks up entries in LMHOSTS. It is located in `C:\Windows NT\System32\Drivers\etc`.

Windows 200x/XP can register its host name with a Dynamic DNS server. You can force register with a Dynamic DNS server in Windows 200x/XP using: ipconfig /registerdns.

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

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

### DNS and Active Directory

Occasionally we hear from UNIX network administrators who want to use a UNIX-based Dynamic DNS server in place of the Microsoft DNS server. While this might be desirable to some, the MS Windows 200x DNS server is auto-configured to work with Active Directory. It is possible to use BIND version 8 or 9, but it will almost certainly be necessary to create service records so MS Active Directory clients can resolve host names to locate essential network services. The following are some of the default service records that Active Directory requires:

_ldap._tcp.pdc.ms-dcs.Domain

  This provides the address of the Windows NT PDC for the Domain.

_ldap._tcp.pdc.ms-dcs.DomainTree

  Resolves the addresses of Global Catalog servers in the domain.

_ldap._tcp.site.sites.writable.ms-dcs.Domain

  Provides list of Domain Controllers based on sites.

_ldap._tcp.writable.ms-dcs.Domain

  Enumerates list of Domain Controllers that have the writable copies of the Active Directory datastore.

_ldap._tcp.GUID.domains.ms-dcs.DomainTree

  Entry used by MS Windows clients to locate machines using the Global Unique Identifier.

_ldap._tcp.Site.gc.ms-dcs.DomainTree

  Used by MS Windows clients to locate site configuration dependent Global Catalog server.

## How Browsing Functions

MS Windows machines register their NetBIOS names (i.e., the machine name for each service type in operation) on start-up. 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.

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 `remote announce` parameter).

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.

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 to 15 minutes an election is held to determine which machine will be the master browser. By the nature of the election criteria used, the machine with the highest uptime, or the most senior protocol version or other criteria, will win the election as Domain Master Browser.

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.

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.

Samba supports a feature that allows forced synchronization of browse lists across routed networks using the `remote browse sync` parameter in the `smb.conf` file. This causes Samba to contact the local master browser on a remote network and to request browse list synchronization. This effectively bridges two networks that are separated by routers. The two remote networks may use either broadcast-based name resolution or WINS-based name resolution, but it should be noted that the `remote browse sync` parameter provides browse list synchronization 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, `/etc/hosts`, and so on.

### Configuring WORKGROUP Browsing

To configure cross-subnet browsing on a network containing machines in a WORKGROUP, not an NT Domain, you need to set up one Samba server to be the 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 another subnet. It is the presence of a Domain Master Browser that makes cross-subnet browsing possible for a workgroup.

In a 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 preferably 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 as shown in .

Example 10.1. Domain Master Browser smb.conf

`[global]`
`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 necessary.

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/200x/XP machine should be able to do this, as will Windows 9x/Me machines (although these tend to get rebooted more often, so it is not such a good idea to use these). To make a Samba server a Local Master Browser set the following options in the `[global]` section of the `smb.conf` file as shown in :

Example 10.2. Local master browser smb.conf

`[global]`
`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 it should win any browser elections.

If you have an NT machine on the subnet that you wish to be the Local Master Browser, you can disable Samba from becoming a Local Master Browser by setting the following options in the `[global]` section of the `smb.conf` file as shown in :

Example 10.3. smb.conf for not being a Master Browser

`[global]`
`domain master = no`
`local master = no`
`preferred master = no`
`os level = 0`

### DOMAIN Browsing Configuration

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 is also the Domain Master Browser for that domain. Network browsing may 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 as shown in :

Example 10.4. Local Master Browser smb.conf

`[global]`
`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 refer to .

If you have Windows NT machines that are members of the domain on all subnets and you are sure they will always be running, you can disable Samba from taking part in browser elections and ever becoming a Local Master Browser by setting the following options in the `[global]` section of the `smb.conf` file as shown in :

Example 10.5. smb.conf for not being a master browser

`[global]`
`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 that determine what precedence (bias) a host should have in the election. By default Samba uses a low precedence and thus loses elections to just about every Windows network server or client.

If you want Samba to win elections, set the `os level` global option in `smb.conf` to a higher number. It defaults to zero. Using 34 would make it win all elections every other system (except other samba systems).

An `os level` of two would make it beat Windows for Workgroups and Windows 9x/Me, but not MS Windows NT/200x Server. An MS Windows NT/200x Server Domain Controller uses level 32. The maximum os level is 255.

If you want Samba to force an election on startup, 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 Perferred Master Browsers. Use this parameter with care, as if you have two hosts (whether they are Windows 9x/Me or NT/200x/XP or Samba) on the same local subnet both set with `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 five 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 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.

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

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 synchronize browse lists.

If you want Samba to be the domain master, you should 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.

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

1. Local Master Browsers will be unable to find a Domain Master Browser, as they will be looking only 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. 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, the 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.

### 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 zeros broadcast and you will probably find that browsing and name lookups will not work.

### Multiple Interfaces

Samba supports machines with multiple network interfaces. If you have multiple interfaces, you will need to use the `interfaces` option in `smb.conf` to configure them.

### Use of the Remote Announce Parameter

The `remote announce` parameter of `smb.conf` can be used to forcibly ensure that all the NetBIOS names on a network get announced to a remote network. The syntax of the `remote announce` parameter is:

`remote announce = a.b.c.d [e.f.g.h] ...`

or

`remote announce = a.b.c.d/WORKGROUP [e.f.g.h/WORKGROUP] ...`

where:

`a.b.c.d` and `e.f.g.h`

  is either the LMB (Local Master Browser) IP address or the broadcast address of the remote network. i.e., 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.

`WORKGROUP`

  is optional and can be either our own workgroup or that of the remote network. If you use the workgroup name of the remote network, our NetBIOS machine names will end up looking like they belong to that workgroup. This may cause name resolution problems and should be avoided.

### Use of the Remote Browse Sync Parameter

The `remote browse sync` parameter of `smb.conf` is used to announce to another LMB that it must synchronize its NetBIOS name list with our Samba LMB. This works only if the Samba server that has this option is simultaneously the LMB on its network segment.

The syntax of the `remote browse sync` parameter is:

`remote browse sync = a.b.c.d`

where `a.b.c.d` is either the IP address of the remote LMB or else is the network broadcast address of the remote segment.

## WINS The Windows Internetworking Name Server

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

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

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

WINS also serves the purpose of forcing browse list synchronization by all LMBs. LMBs must synchronize their browse list with the DMB (Domain Master Browser) and WINS helps the LMB to identify its 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.

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

To configure Samba as a WINS server just add `wins support` = yes to the `smb.conf` file [global] section.

To configure Samba to register with a WINS server just add `wins server` = a.b.c.d to your `smb.conf` file `[global]` section.

### Important

Never use both `wins support` = yes together with `wins server` = a.b.c.d particularly not using its own IP address. Specifying both will cause nmbd to refuse to start!

### WINS Server Configuration

Either a Samba Server or a Windows NT Server machine may be set up as a WINS server. To configure a Samba Server to be a WINS server you must add to the `smb.conf` file on the selected Server the following line to the `[global]` section:

`wins support = yes`

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.

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

It is strongly recommended to set up only one WINS server. Do not set the `wins support` = yes option on more than one Samba server.

To configure Windows NT/200x Server as a WINS server, install and configure the WINS service. See the Windows NT/200x documentation for details. Windows NT/200x WINS servers can replicate to each other, allowing more than one to be set up in a complex subnet environment. As Microsoft refuses to document the replication protocols, Samba cannot currently participate in these replications. It is possible in the future that a Samba-to-Samba WINS replication protocol may be defined, in which case more than one Samba machine could be set up as a WINS server. Currently only one Samba server should have the `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 9x/Me or Windows NT/200x. 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.

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 9x/Me, Samba and Windows NT/200x machines that are not configured as part of a Windows NT Domain. The second details setting up cross-subnet browsing on networks that contain NT Domains.

### WINS Replication

Samba-3 permits WINS replication through the use of the `wrepld` 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.

### Static WINS Entries

Adding static entries to your Samba WINS server is actually fairly easy. All you have to do is add a line to `wins.dat`, typically located in `/usr/local/samba/var/locks`.

Entries in `wins.dat` take the form of:

    "NAME#TYPE" TTL ADDRESS+ FLAGS

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

A typical dynamic entry looks like this:

    "MADMAN#03" 1055298378 192.168.1.2 66R

To make it static, all that has to be done is set the TTL to 0, like this:

    "MADMAN#03" 0 192.168.1.2 66R

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

## Helpful Hints

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

### Windows Networking Protocols

### Warning

Do not use more than one protocol on MS Windows machines.

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

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

The election process is “fought out” so to speak over every NetBIOS network interface. In the case of a Windows 9x/Me machine that has both TCP/IP and IPX installed and has NetBIOS enabled over both protocols, the election will be decided over both protocols. As often happens, if the Windows 9x/Me machine is the only one with both protocols then the LMB may be won on the NetBIOS interface over the IPX protocol. Samba will then lose the LMB role as Windows 9x/Me 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.

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

The safest rule of all to follow is: use only one protocol!

### Name Resolution Order

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:

- WINS the best tool.
- LMHOSTS static and hard to maintain.
- Broadcast uses UDP and cannot resolve names across remote segments.

Alternative means of name resolution include:

- Static `/etc/hosts` hard to maintain, and lacks name_type info.
- DNS is a good choice but lacks essential name_type info.

Many sites want to restrict DNS lookups and avoid broadcast name resolution traffic. The `name resolve order` parameter is of great help here. The syntax of the `name resolve order` parameter is:

`name resolve order = wins lmhosts bcast host`

or

`name resolve order = wins lmhosts (eliminates bcast and host)`

The default is:

`name resolve order = host lmhost wins bcast`

where “host” refers to the native methods used by the UNIX system to implement the gethostbyname() function call. This is normally controlled by `/etc/host.conf`, `/etc/nsswitch.conf` and `/etc/resolv.conf`.

## Technical 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 that aren't currently able to do server tasks. The browse list is heavily used by all SMB clients. Configuration of SMB browsing has been problematic for some Samba users, hence this document.

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

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

### Browsing Support in Samba

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.

Samba can also act as a Domain Master Browser for a workgroup. This means that it will collate lists from Local Master Browsers 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.

Do not set Samba to be the Domain Master for a workgroup that has the same name as an NT Domain. On each wide area network, you must only ever have one 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

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 200x can be configured as your WINS server. In a mixed NT/200x 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 the 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 does not work, the `log.nmbd` file will help to track down the problem. Try a `log 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`.

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

Some people find browsing fails because they do not 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.

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

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`)

### Cross-Subnet Browsing

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

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

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

#### Behavior of Cross-Subnet Browsing

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.

Consider a network set up as .

Figure 10.1. Cross-Subnet Browsing Example.

This consists of 3 subnets (1, 2, 3) connected by two routers (R1, R2) which do not pass broadcasts. Subnet 1 has five machines on it, subnet 2 has four machines, subnet 3 has four machines. Assume for the moment that all machines are configured to be in the same workgroup (for simplicity's sake). Machine N1_C on subnet 1 is configured as Domain Master Browser (i.e., 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 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 appear as shown in (these are the machines you would see in your network neighborhood if you looked in it on a particular network right now).

Table 10.1. Browse Subnet Example 1

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

At this point all the subnets are separate, and 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 with which to synchronize its browse list. It does this by querying the WINS server (N2_D) for the IP address associated with the NetBIOS name WORKGROUP<1B>. This name was registered by the Domain Master Browser (N1_C) with the WINS server as soon as it was started.

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 complete the browse lists look as shown in :

Table 10.2. Browse Subnet Example 2

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 an (*) 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 occurred 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 will appear as shown in .

Table 10.3. Browse Subnet Example 3

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 an (*) 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 subnets, while 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 receive the missing server entries. Finally, as when a steady state (if no machines are removed or shut off) has been achieved, the browse lists will appear as shown in .

Table 10.4. Browse Subnet Example 4

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 an (*) after them are non-authoritative names.

Synchronizations between the Domain Master Browser and Local Master Browsers will continue to occur, but this should remain a steady state operation.

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 neighborhood lists.

2. Attempts to connect to these inaccessible computers will fail, but the names will not be removed from the network neighborhood 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 using subnet-isolated broadcast NetBIOS name resolution. The effects are similar to that of losing access to a DNS server.

## Common Errors

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

### How Can One Flush the Samba NetBIOS Name Cache without Restarting Samba?

Samba's 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. 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, every machine on the network will need to be shut down and restarted after all machines are down. Failing a complete restart, the only other thing you can do is wait until the entry times out and is then flushed from the list. This may take a long time on some networks (perhaps months).

### Server Resources Can Not Be Listed

“My Client Reports ‘This server is not configured to list shared resources’”

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

Also see `guest account` in the `smb.conf` man page.

### I get an `Unable to browse the network' error

This error can have multiple causes:

- There is no Local Master Browser. Configure nmbd or any other machine to serve as Local Master Browser.

- You cannot log onto the machine that is the local master browser. Can you logon to it as a guest user?

- There is no IP connectivity to the Local Master Browser. Can you reach it by broadcast?

### Browsing of Shares and Directories is Very Slow

“ There are only two machines on a test network. One a Samba server, the other a Windows XP machine. Authentication and logons work perfectly, but when I try to explore shares on the Samba server, the Windows XP client becomes unrespsonsive. Sometimes it does not respond for some minutes. Eventually, Windows Explorer will respond and displays files and directories without problem. display file and directory.”

“ But, the share is immediately available from a command shell (cmd, followed by exploration with dos command. Is this a Samba problem or is it a Windows problem? How can I solve this? ”

Here are a few possibilities:

Bad Networking Hardware

  Most common defective hardware problems center around low cost or defective HUBs, routers, Network Interface Controllers (NICs) and bad wiring. If one piece of hardware is defective the whole network may suffer. Bad networking hardware can cause data corruption. Most bad networking hardware problems are accompanied by an increase in apparent network traffic, but not all.

The Windows XP WebClient

  A number of sites have reported similar slow network browsing problems and found that when the WebClient service is turned off, the problem dissapears. This is certainly something that should be explored as it is a simple solution if it works.

Inconsistent WINS Configuration

  This type of problem is common when one client is configured to use a WINS server (that is a TCP/IP configuration setting) and there is no WINS server on the network. Alternately, this will happen is there is a WINS server and Samba is not configured to use it. The use of WINS is highly recommended if the network is using NetBIOS over TCP/IP protocols. If use of NetBIOS over TCP/IP is disabled on all clients, Samba should not be configured as a WINS server neither should it be configured to use one.

Incorrect DNS Configuration

  If use of NetBIOS over TCP/IP is disabled, Active Directory is in use and the DNS server has been incorrectly configured. Refer for more information.

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