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Samba HowTo Guide
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How Browsing Functions

MS Windows machines register their NetBIOS names (i.e., the machine name for each service type in operation) on startup. 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, whether or not DNS for NetBIOS name resolution is enabled, and so on.

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 takes place to create a local master browser (LMB) if one does not already exist. On each NetBIOS network one machine will be elected to function as the domain master browser (DMB). This domain browsing has nothing to do with MS security Domain Control. Instead, the DMB serves the role of contacting each LMB (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 DMB.

Where a WINS server is used, the DMB registers its IP address with the WINS server using the name of the domain and the NetBIOS name type 1B (e.g., DOMAIN<1B>). All LMBs register their IP addresses with the WINS server, also with the name of the domain and the NetBIOS name type of 1D. The 1B name is unique to one server within the domain security context, and only one 1D name is registered for each network segment. Machines that have registered the 1D name will be authoritive browse list maintainers for the network segment they are on. The DMB is responsible for synchronizing the browse lists it obtains from the LMBs.

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 or 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 LMB 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.

Samba HowTo Guide
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