Saturday, September 18, 2010

NetBIOS Datagram Service

The Datagram Distribution Service is the NBT service that handles NetBIOS datagram transport. It runs on UDP 138 and handles unicast, multicast and broadcast NetBIOS datagrams.

For unicast, the IP address is obtained from Name Services and the NetBIOS packet is encapsulated in a UDP packet for the target IP.

for multicast and broadcast delivery, a B node encapsulate NetBIOS packet and send over the IP broadcast address. The packet would picked up by all nodes on the IP segment (138/UDP). In case of multicast, nodes which are not member of the group will discard the packet. For P, M or H nodes, the WINS database must be consulted to determine the distribution.

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