NetBIOS Relays
Page 26-11

NetBIOS Relays

The switch supports a UDP relay function that allows Network Basic Input/Output System
(NetBIOS) messages to be sent across groups or VLANs.

Overview of NetBIOS

NetBIOS is an applications interface that allows computers on Ethernet or token ring LANs to
communicate with one another. An enhanced version of the protocol is used by networking
operating systems such as LAN Manager and Windows NT.
With NetBIOS, each client and host in the LAN has a unique NetBIOS name. Stations in a
NetBIOS network broadcast queries to verify that their names are unique on the LAN. Names
may be verified by using the NetBIOS Name Server (NBNS) protocol, which sends messages to
a well-known UDP port (137). Name requests are sent to an IP subnet broadcast address or
the unicast address of the server.
The NetBIOS protocol also has a datagram service that allows an application to exchange data-
grams with a specific application or to broadcast and receive datagrams on a VLAN. A NetBIOS
Datagram Distribution (NBDD) server may be installed in the network to provide this service,
which uses a well-known UDP port number (138).
NetBIOS may be configured to run over TCP/IP using the various modes defined in RFC_1001
and RFC_1002. These modes are defined in terms of nodes and determine how NetBIOS
stations (or nodes) in the network register their NetBIOS names and resolve (or map) these
names to IP addresses. Each NetBIOS PC has a node type. The nodes are defined as follows:
• Broadcast node (b-node)—These nodes use broadcast for name registration and resolu-
tion. Since routers do not forward broadcast traffic, b-node clients in different networks
will not be able to communicate
• Point-to-point node (p-node)—In this environment, each station knows the address of the
server. Unicast queries are sent directly to the name and datagram servers. This method
does not use broadcast.
• Mixed-mode node (m-node)—This mode uses a combination of b-node and p-node.