Alcatel Carrier Internetworking Solutions Switch/Router 用户手册

Page 26-11

The switch supports a 

UDP

 relay function that allows Network Basic Input/Output System 

(

NetBIOS

) messages to be sent across groups or 

VLANs

.

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.