This document should be read in conjunction with Browsing and may be taken as the 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 addesses. WINS is NOT involved in browse list handling except by way of name to address mapping.
Note: MS Windows 2000 and later can be configured to operate with NO NetBIOS over TCP/IP. Samba-3 and later also supports this mode of operation.
Firstly, all MS Windows networking is based on SMB (Server Message Block) based messaging. SMB messaging may be implemented using NetBIOS or without NetBIOS. Samba implements NetBIOS by encapsulating it over TCP/IP. MS Windows products can do likewise. NetBIOS based networking uses broadcast messaging to affect 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 (1) machine as the WINS server. This makes it easy to manage the browsing environment. If each network segment is configured with it's 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.
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 affect 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 (ie: 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 stabilise, particularly across network segments.
As stated above, MS Windows machines register their NetBIOS names (i.e.: the machine name for each service type in operation) on start up. Also, as stated above, 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 11-15 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 synchonisation 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 synchronisation. 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 synchronisation - 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.
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:
is either the LMB (Local Master Browser) IP address or the broadcst address of the remote network. ie: 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.
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 then our NetBIOS machine names will end up looking like they belong to that workgroup, this may cause name resolution problems and should be avoided.
The "remote browse sync" parameter of smb.conf is used to announce to another LMB that it must synchronise it's NetBIOS name list with our Samba LMB. It works ONLY if the Samba server that has this option is simultaneously the LMB on it's network segment.
The syntax of the "remote browse sync" parameter is:
remote browse sync = a.b.c.dwhere a.b.c.d is either the IP address of the remote LMB or else is the network broadcast address of the remote segment.
Use of WINS (either Samba WINS _or_ MS Windows NT Server WINS) is highly recommended. Every NetBIOS machine registers it's name together with a name_type value for each of of several types of service it has available. eg: It registers it's name directly as a unique (the type 0x03) name. It also registers it's 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. ie: 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 can not be used across network segments this type of information can only be provided via WINS _or_ via statically configured "lmhosts" files that must reside on all clients in the absence of WINS.
WINS also serves the purpose of forcing browse list synchronisation by all LMB's. LMB's must synchronise their browse list with the DMB (domain master browser) and WINS helps the LMB to identify it's 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.
Use of WINS will work correctly only if EVERY client TCP/IP protocol stack has been configured to use the WINS server/s. Any client that has not been configured to use the WINS server will continue to use only broadcast based name registration so that 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 [globals] section.
To configure Samba to register with a WINS server just add "wins server = a.b.c.d" to your smb.conf file [globals] section.
DO NOT EVER use both "wins support = yes" together with "wins server = a.b.c.d" particularly not using it's own IP address. Specifying both will cause nmbd to refuse to start!
A very 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 precidence for winning this election process. A machine running Samba or Windows NT will be biased so that the most suitable machine will predictably win and thus retain it's role.
The election process is "fought out" so to speak over every NetBIOS network interface. In the case of a Windows 9x 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 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 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, Me are referred to generically as Windows 9x. The Windows NT4, 2000, XP and 2003 use common protocols. These are roughly referred to as the WinNT family, but it should be recognised 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 it this - USE ONLY ONE PROTOCOL!
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: is static and hard to maintain. |
| Broadcast: uses UDP and can not resolve names across remote segments. |
Alternative means of name resolution includes:
| /etc/hosts: is static, 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 want to 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 the 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.