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Chapter 7. Name Resolution and Browsing

Name resolution is critical to Samba's operation because names are used to find the servers that share files or printers. Browsing takes the task of finding servers to a new level of sophistication by allowing a user to delve down into a hierarchy of networks, domains, hosts, and services offered by each server.

While name resolution and browsing are not difficult to configure, some complexity is introduced by the variety of available name-resolution systems. Historically, Unix and other TCP/IP users have moved from a flat hosts file to the Domain Name System, with the Network Information System being another popular choice. Meanwhile, Microsoft has moved from a broadcasting system to a simple, LAN-only name server called WINS and ultimately to DNS.

The reason for going over that history is that all previous systems of name resolution are still in use today! Finding a host is so crucial to networking that sites want robust (if limited) name-resolution systems to fall back on in case the main system fails. Browsing is also complicated by the frequent need to show hosts in other subnets. This chapter shows you how to configure your network to handle name resolution and browsing any way you want.

Some of the differences between Unix and Microsoft networking implementations are the result of fundamental design goals. Unix networking was originally designed largely to implement a relatively formal group of systems that were assumed to be small in number, well-maintained, and highly available, that have static IP addresses, and that wouldn't physically move around from place to place. Bringing a new server online was a labor-intensive task, but it did not have to be performed frequently. In contrast, Windows networking was originally developed as a peer-to-peer collection of small personal computers on a single subnet, having no centrally or hierarchically organized structure.

SMB networking is dynamic. Computers are allowed to leave the network at any time, sometimes without warning, and also to join or rejoin the network at any time. Furthermore, any user in a Windows network can add a new shared resource to the network or remove a resource that he had previously added. The change in the network's configuration is handled automatically by the rest of the network without requiring a system administrator to take any action.

Name Resolution

TCP/IP networks identify systems by IP addresses and always associate these addresses with more human-readable text names. In Microsoft's earliest networking implementations (for MS-DOS and Windows for Workgroups), the translation of names to network addresses was carried out in a manner that was very simple, yet very inefficient. When a system on the network needed an IP address corresponding to a name, it broadcasted the name to every other system on the network and waited for the system that owned the name to respond with its IP address.

The main problem with performing name resolution using broadcast packets is poor performance of the network as a whole, including CPU time consumed by each host on the network, which has to accept every broadcast packet and decide whether to respond to it. Also, broadcast packets usually aren't forwarded by routers, limiting name resolution to the local subnet. Microsoft's solution was to add WINS (Windows Internet Name Service) support to Windows NT so that the computers on the network can perform a direct query of the WINS server instead of using broadcast packets.

Modern Windows clients use a variety of methods for translating hostnames into IP addresses. The exact method varies depending on the version of Windows the client is running, how the client is configured (i.e., whether DNS server and/or WINS server IP addresses are provided), and whether the application software is accessing the network through Microsoft's Winsock or TCP/IP API. In general, Windows uses some combination of the following methods:

The first method is pretty much self-explanatory. A hostname is checked against a cache of hostnames that have been recently resolved to IP addresses. This helps to save time and network bandwidth for resolving names that are used frequently.

When a Windows system is configured with the IP address of at least one DNS server, it can use DNS to resolve fully qualified domain names, such as those for sites on the Internet. The DNS servers can be either Windows NT/2000 or Unix systems. You can learn more about DNS and DNS server configuration in the O'Reilly book DNS and BIND.

In this chapter, we focus mainly on name resolution using WINS, which is supported by Samba with the nmbd daemon.

WINS Clients and Server Interaction

There are two types of interaction between a WINS client and a server: the client keeps its own NetBIOS name[1] registered with the server and queries the server to get the IP address corresponding to the NetBIOS name of another system.

When a WINS client joins the network, it registers its NetBIOS name with the WINS server, which stores it along with the client's IP address in the WINS database. This entry is marked active. The client is then expected to renew the registration of its name periodically (typically, every four days) to inform the server that it is still using the name. This period is called the time to live, or TTL. When the client leaves the network by being shut down gracefully, it informs the server, and the server marks the client's entry in its database as released.

When a client leaves the network without telling the WINS server to release its name, the server waits until after it fails to receive the expected registration renewal from the client and then marks the entry as released.

In either case, the released name is available for use by other clients joining the network. It might persist in the released state in the WINS database, and if it is not reregistered, the entry will eventually be deleted.

More information on WINS can be found in the Microsoft white paper Windows Internet Naming Service (WINS) Architecture and Capacity Planning. It can be downloaded from the Microsoft web site at http://www.microsoft.com.

Setting Up Samba as a WINS Server

You can set up Samba as a WINS server by setting the wins support parameter in the configuration file, like this:

    wins support = yes

Believe it or not, that's all you need to do! The wins support option turns Samba into a WINS server. For most installations, Samba's default configuration is sufficient.


Remember, Samba cannot communicate with Windows WINS servers. If you are using Samba as your WINS server, you must make sure not to allow any Windows systems or other Samba servers on your network to be configured as WINS servers. If you do, their WINS databases will not synchronize, resulting in inconsistent name resolution.

Setting Up Samba to Use Another WINS Server

You can configure Samba to use a WINS server somewhere else on the network by simply providing it with the IP address of the WINS server. This is done with the global wins server configuration option, as shown here:

    wins server =

With this option enabled, Samba will direct all WINS requests to the server located at Note that because the request is directed at a single machine, we don't have to worry about any of the problems inherent in broadcasting. However, Samba will not necessarily use the WINS server before other forms of name resolution. The order in which Samba attempts various name-resolution techniques is given with the name resolve order configuration option, which we discussed earlier.

The wins support and the wins server parameters are mutually exclusive; you cannot simultaneously offer Samba as the WINS server and use another system as the server! Typically, one Samba server is set up as the WINS server using wins support, and all other Samba servers are configured with the wins server parameter pointing to the Samba WINS server.

Name-Resolution Configuration Options

Samba's name-resolution options are shown in Table 7-1.

Table 7-1. Name-resolution options






wins support


If set to yes, allows Samba to act as a WINS server



wins server

string (IP address or DNS name)

Identifies a WINS server for Samba to use for name registration and resolution



wins proxy


Allows Samba to act as a proxy to a WINS server on another subnet



wins hook


Command to run when the WINS database changes



dns proxy


If set to yes, allows a Samba WINS server to search DNS if it cannot find a name in WINS



name resolve order


The order of methods used to resolve NetBIOS names

lmhosts hosts wins bcast


max ttl


Maximum TTL in seconds for a requested NetBIOS name

259200 ( 3 days)


max wins ttl


Maximum TTL in seconds for NetBIOS names given out by Samba as a WINS server

518400 (6 days)


min wins ttl


Minimum TTL in seconds for NetBIOS names given out by Samba as a WINS server

21600 (6 hours)



Browsing was developed by Microsoft to help users find shared resources on the network. In a networked computing environment where users can add or remove shares at any time, it is important to have some automatic means of keeping track of the shared resources and allowing users to "browse" through them to find the ones they wish to use.

Before browsing was added to SMB networking, when anyone added a new share, the people with whom they wished to share the data or printer would have to be informed of the share's UNC, using some relatively low-tech method such as speaking to them in person or over the phone, or sending email. Already, this was very inconvenient in large organizations. To further complicate matters, the users working on client computers had to type in the share's UNC to connect to it. The only way to get around typing in the share's UNC every time it was used was to map a network drive to it, and with a large number of shares on the network, this could easily get out of hand.

Browsing in a Windows Network

To keep things simple, we will first describe network browsing in a network that contains only Windows systems and then show you how to add a Samba server.

The basic way browsing works is that one computer in the network takes on the role of the master browser (also called local master browser, browse master, or browse server) and keeps a list of all the computers on the local subnet that are acting as SMB servers. The list of computers is called the browse list and includes all Samba servers, Windows NT/2000/XP systems, and any Windows 95/98/Me systems that have the "File and printer sharing for Microsoft Networks" networking component installed. The browse list also contains the names of all workgroups and domains. At this level, browsing is limited to the local subnet because the browsing protocol depends on broadcast packets, which are typically not forwarded to other subnets by routers.

A user at any Windows system can view the browse list by opening up the Network Neighborhood (or My Network Places), as we showed you in Chapter 1. Or, the net view command can be used from a Windows command prompt:

C:\>net view
Server Name            Remark

\\MAYA                 Windows 98
\\MIXTEC               Samba 2.2.5
\\OLMEC                Windows XP Pro on Pentium/ASUS
\\TOLTEC               Samba 2.2.5
\\YAQUI                Windows 95 on mixtec/VMware
The command completed successfully.

Then, net view can be used with a computer name as an argument to contact a server directly and list the resources it is sharing:

C:\>net view \\maya
Shared resources at \\maya

Windows 98

Share name   Type         Used as  Comment

D            Disk
E            Disk
HP           Print
The command completed successfully.

The computers on the network involved in browsing are more than just the master browser and its clients. There are also backup browsers, which maintain copies of the browse list and respond to client requests for it. Backup browsers are therefore able to take over the role of master browser seamlessly in case it fails. The master browser usually doesn't serve the browse list directly to clients. Instead, its job is mainly to keep the master copy of the browse list up-to-date, and also periodically update the backup browsers. Clients are expected to get their copies of the browse list from backup browsers, selecting among them randomly to help to distribute the load on the backup browsers more evenly. Ideally, the interaction between any client and the master browser is limited to the client announcing when it joins or leaves the network (if it is a server) and requesting a list of backup browsers.

There can be more than one backup browser. A workgroup will have a backup browser if two or more computers are running Windows 95/98/Me or Windows NT Workstation (or another nonserver version of Windows NT/2000/XP) on the subnet. For every 32 additional computers, another backup browser is added.

In a Windows NT domain, the primary domain controller is always the local master browser, and if it fails, another Windows NT/2000 server (if one exists) will take over the role of local master browser. Other versions of Windows can function as backup browsers, but will never become a master browser if a Windows NT/2000 server is available.

In addition to acting as the local master browser, the primary domain controller also acts as the domain master browser, which ties subnets together and allows browse lists to be shared between master and backup browsers on separate subnets. This is how browsing is extended to function beyond the local subnet. Each subnet functions as a separate browsing entity, and the domain master browser synchronizes the master browsers of each subnet. In a Windows-only network, browsing cannot function across subnets unless a Windows NT/2000 PDC exists on the network. Samba can act as a domain master browser and can perform that task even in a workgroup network, which means that the Windows PDC is not required for this task. (It is also possible to use the remote browse sync parameter to configure a Samba server to synchronize its browse list with a Samba server on another subnet. In this case, each server must be acting as the local master browser of its subnet.)

Unless it is configured never to act as a browser, each computer on the subnet is considered a potential browser and can be ordered by the browse master to become a backup browser, or it can identify itself as a backup browser and accept the role on its own.

Browser Elections

When no master browser is running on the subnet, potential browsers choose a new master browser among themselves in a process called an election. An election is started by a computer in the subnet when it discovers that no master browser is currently running. If a master browser is shut down gracefully, it will broadcast an election request datagram, initiating an election by the remaining computers. If the master browser fails, the election can be started by a client computer that requests a list of backup browsers from the master browser or by a backup browser that requests to have its browse list updated from the master browser. In each case, the system fails to receive a reply from the master browser and initiates the election.

Browser elections are decided in multiple rounds of self-elimination. During each round, potential browsers broadcast election request datagrams containing their qualifications to notify other potential browsers that an election is happening and that if the recipient is more qualified, it should also broadcast a bid. When a potential browser receives an election request datagram from a more qualified opponent, it drops out, disqualifying itself from becoming the master browser. Otherwise, it responds with its own election request datagram. After a few rounds, only one potential browser is left in the election. After an additional four rounds of sending out an election request datagram and receiving no response, it becomes the master browser and sends a broadcast datagram announcing itself as the local master browser for the subnet. It then assigns runners-up in the election as backup browsers, as needed.

A potential browser's qualifications include the following:

If the potential browser has lost an election recently, it immediately disqualifies itself. The version of the election protocol it is running is checked, but so far, all Windows systems (and Samba) use the same election protocol, so the check is not very meaningful. The election criteria are usually what determine which computer becomes the local master browser. There are two parts to the election criteria, shown in Tables Table 7-2 and Table 7-3.

Table 7-2. Operating-system values in an election

Operating system


Windows NT/2000 Server, running as PDC


Windows NT/2000/XP, if not the PDC


Windows 95/98/Me


Windows for Workgroups


Table 7-3. Computer-role settings in an election



Domain master browser


WINS client


Preferred master


Running master


Recent backup browser


Backup browser


The operating-system type is compared first, and the system with the highest value wins. The values have been chosen to cause the primary domain controller, if there is one, to become the local master browser. Otherwise, a Windows NT/2000/XP system will win over a Windows for Workgroups or Windows 95/98/Me system.

When an operating-system type comparison results in a tie, the role of the computer is compared. A computer can have more than one of the values in Table 7-3, in which case the values are added.

A domain master browser has a role value of 128 to weight the election so heavily in its favor that it will also become the local master browser on its own subnet. Although the primary domain controller (which is always the domain master browser) will win the election based solely on its operating system value, sometimes there is no primary domain controller on the network, and the domain master browser would not otherwise be distinguished from other potential browsers.

Systems that are using a WINS server for name resolution are weighted heavily over ones that use broadcast name resolution with a role value of 32.

A preferred master is a computer that has been selected and configured manually by a system administrator to be favored as the choice master browser. When a preferred master starts up, it forces a browser election, even if an existing master browser is still active. A preferred master has a role value of 8, and the existing master browser gets a value of 4.

A backup browser that has recently been a master browser and still has an up-to-date browse list is given a role value of 2, and a potential browser that has been running as a backup browser gets a value of 1.

If comparing the operating-system type and role results in a tie, the computer that has been running the longest wins. In the unlikely event that the two have been up for the same amount of time, the computer that wins is the one with the NetBIOS name that sorts first alphabetically.

You can tell if a machine is a local master browser by using the Windows nbtstat command. Place the NetBIOS name of the machine you wish to check after the -a option:

C:\>nbtstat -a toltec

Local Area Connection:
Node IpAddress: [] Scope Id: []

           NetBIOS Remote Machine Name Table

       Name               Type         Status
    TOLTEC         <00>  UNIQUE      Registered
    TOLTEC         <03>  UNIQUE      Registered
    TOLTEC         <20>  UNIQUE      Registered
    ..__MSBROWSE__.<01>  GROUP       Registered
    METRAN         <00>  GROUP       Registered
    METRAN         <1B>  UNIQUE      Registered
    METRAN         <1C>  GROUP       Registered
    METRAN         <1D>  UNIQUE      Registered
    METRAN         <1E>  GROUP       Registered

    MAC Address = 00-00-00-00-00-00

The resource entry that you're looking for is .._ _MSBROWSE_ _.<01>. This indicates that the server is currently acting as the local master browser for the current subnet. If the machine is a Samba server, you can check the Samba nmbd log file for an entry such as:

Samba name server TOLTEC is now a local master browser for
workgroup METRAN on subnet

Or, you can use the nmblookup command with the -M option and the workgroup or domain name on any Samba server to find the IP address of the local master:

$ nmblookup -M metran
querying metran on metran<1d>

Configuring Samba for Browsing

Samba has full support for browsing and can participate as a master browser, a backup browser, a domain master browser, a potential browser, or just a server that doesn't participate in browsing elections. If you want to make sure your Samba server never becomes a master or backup browser, simply set:

    local master = no

Usually, you will want Samba to be available as a local master or at least a backup browser. In the simplest case, you don't need to do anything because Samba's default is to participate in browsing elections with its operating system value set to 20, which will beat any Windows system less than a Windows NT/2000 primary domain controller (see Table 7-2). The operating-system value Samba reports for itself in browser elections can be set using the os level parameter:

    os level = 33

The preceding value will allow Samba to beat even a Windows 2000 Advanced Server acting as a primary domain controller. As we show in the following section, though, forcing Samba to win this way is not recommended.

If you want to allow a Windows XP Professional system to be the master browser, you would need to set Samba lower:

    os level = 8

The maximum value for os level is 255 because it is handled as an 8-bit unsigned integer. Supposing we wanted to make absolutely sure our Samba server will be the local master browser at all times, we might say:

    local master = yes
    os level = 255
    preferred master = yes

The addition of the preferred master parameter causes Samba to start a browser election as soon as it starts up, and the os level of 255 allows it to beat any other system on the network. This includes other Samba servers, assuming they are configured properly! If another server is using a similar configuration file (with os level = 255 and preferred master = yes), the two will fight each other for the master browser role, winning elections based on minor criteria, such as uptime or their current role. To avoid this, other Samba servers should be set with a lower os level and not configured to be the preferred master.

Samba as the Domain Master Browser

Previously we mentioned that for a Windows workgroup or domain to extend into multiple subnets, one system would have to take the role of the domain master browser. The domain master browser propagates browse lists across each subnet in the workgroup. This works because each local master browser periodically synchronizes its browse list with the domain master browser. During this synchronization, the local master browser passes on the name of any server that the domain master browser does not have in its browse list, and vice versa. Each local master browser eventually holds the browse list for the entire domain.

There is no election to determine which machine assumes the role of the domain master browser. Instead, the administrator has to set it manually. By Microsoft design, however, the domain master browser and the PDC both register a resource type of <1B>, so the roles—and the machines—are inseparable.

If you have a Windows NT server on the network acting as a PDC, we recommend that you do not try to use Samba to become the domain master browser. The reverse is true as well: if Samba is taking on the responsibilities of a PDC, we recommend making it the domain master browser as well. Although it is possible to split the roles with Samba, this is not a good idea. Using two different machines to serve as the PDC and the domain master browser can cause random errors to occur in a Windows workgroup.

Samba can assume the role of a domain master browser for all subnets in the workgroup with the following options:

    domain master = yes
    preferred master = yes
    local master = yes
    os level = 255

The final three parameters ensure that the server is also the local master browser, which is vital for it to work properly as the domain master browser. You can verify that a Samba machine is in fact the domain master browser by checking the nmbd log file:

Samba name server TOLTEC is now a domain master browser for
workgroup METRAN on subnet

Or you can use the nmblookup command that comes with the Samba distribution to query for a unique <1B> resource type in the workgroup:

# nmblookup METRAN#1B
Sending queries to METRAN<1b>

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