Samba Part 3
Each NetBIOS name is a communications end-point, representing an application or daemon that is waiting to hear from other applications or daemons across the virtual wire. The Name Service keeps track of which names are in use at which IP addresses, thus allowing the underlying IP network to find the nodes and transport NetBIOS messages between them. The Name Service runs on UDP port 137.
There are two kinds of names -- group and unique. Group names can be shared so that datagrams can be multicast to all members of the group. In contrast, only one instance of a unique name may be registered at a time within a virtual PC-Network LAN.
The Name Service has two modes of operation -- broadcast and point-to-point. In broadcast mode, names are registered, queried, and eventually released by sending UDP broadcasts to port 137. It's sort of like calling out, "Yo! Anybody here named RUGRAT?" in a crowded room. If there is a RUGRAT in the room, you would expect an answer like, "Yeah, here I am."
Point-to-point mode is used to cross IP subnet boundaries. Since IP broadcasts are typically limited to local IP subnets, a special server called the NetBIOS Name Server (NBNS) must be used to coordinate and manage the names in use on a given NBT virtual LAN. All registrations, queries, and releases are sent directly to the NBNS, which keeps the name-to-IP mappings in a database. Microsoft's NBNS implementation is called WINS (Windows Internet Name Service). The term WINS is now commonly used instead of NBNS, but we will be pedantic and stick with the latter.
It is possible, and even common, to combine broadcast and point-to-point name management. The RFCs describe "Mixed mode," and Microsoft later added "Hybrid mode." These two modes differ only in the order in which the broadcast and point-to-point mechanisms are applied.
The following is a list of acronyms relevant to the Microsoft Networking Protocols: