When a user first makes a request to access a network disk or send a print job to a remote printer, NetBIOS takes care of making a connection at the session layer. The result is a bidirectional virtual channel between the client and server. In reality, there are only two messages that the client and server need to establish this connection. This is shown in the following example session request and response, as captured by
tcpdump :
>>> NBT Packet
NBT Session Request
Flags=0x81000044
Destination=ESCRIME NameType=0x20 (Server)
Source=WIZZIN NameType=0x00 (Workstation)
>>> NBT Packet
NBT Session Granted
Flags=0x82000000
