RFC 1002
Protocol standard for a NetBIOS service on a TCP/UDP transport: Detailed specifications
5.2. SESSION SERVICE PROTOCOLS The following are variables and should be configurable by the NetBIOS user. The default values of these variables is found in "Defined Constants and Variables" in the Detailed Specification.): - SSN_RETRY_COUNT - The maximum number TCP connection attempts allowable per a single NetBIOS call request. - SSN_CLOSE_TIMEOUT is the time period to wait when closing the NetBIOS session before killing the TCP connection if session sends are outstanding. The following are Defined Constants for the NetBIOS Session Service. (See "Defined Constants and Variables" in the Detailed Specification for the value of these constants): - SSN_SRVC_TCP_PORT - is the globally well-known TCP port allocated for the NetBIOS Session Service. The service accepts TCP connections on this port to establish NetBIOS Sessions. The TCP connection established to this port by the caller is initially used for the exchange of NetBIOS control information. The actual NetBIOS data connection may also pass through this port or, through the retargetting facility, through another port. 5.2.1. SESSION ESTABLISHMENT PROTOCOLS 5.2.1.1. USER REQUEST PROCESSING PROCEDURE listen(listening name, caller name) /* * User initiated processing for B, P and M nodes * * This procedure assumes that an incoming session will be * retargetted here by a session server. */ BEGIN Do TCP listen; /* Returns TCP port used */ Register listen with Session Service, give names and TCP port; Wait for TCP connection to open; /* Incoming call */ Read SESSION REQUEST packet from connection Process session request (see section on processing initiated by the reception of session service packets);
Inform Session Service that NetBIOS listen is complete;
IF session established THEN
return success and session information to user;
ELSE
return failure;
END /* procedure */
PROCEDURE call(calling name, called name)
/*
* user initiated processing for B, P and M nodes
*/
/*
* This algorithm assumes that the called name is a unique name.
* If the called name is a group name, the call() procedure
* needs to cycle through the members of the group
* until either (retry_count == SSN_RETRY_COUNT) or
* the list has been exhausted.
*/
BEGIN
retry_count = 0;
retarget = FALSE; /* TRUE: caller is being retargetted */
name_query = TRUE; /* TRUE: caller must begin again with */
/* name query. */
REPEAT
IF name_query THEN
BEGIN
do name discovery, returns IP address;
TCP port = SSN_SRVC_TCP_PORT;
IF name discovery fails THEN
return failure;
ELSE
name_query = FALSE;
END
/*
* now have IP address and TCP port of
* remote party.
*/
establish TCP connection with remote party, use an
ephemeral port as source TCP port;
IF connection refused THEN
BEGIN
IF retarget THEN
BEGIN
/* retry */
retarget = FALSE;
use original IP address and TCP port;
goto LOOP;
END
/* retry for just missed TCP listen */
pause(SESSION_RETRY_TIMER);
establish TCP connection, again use ephemeral
port as source TCP port;
IF connection refused OR
connection timed out THEN
return failure;
END
ELSE
IF connection timed out THEN
BEGIN
IF retarget THEN
BEGIN
/* retry */
retarget = FALSE;
use original IP address and TCP port;
goto LOOP;
END
ELSE
BEGIN
/*
* incorrect name discovery was done,
* try again
*/
inform name discovery process of
possible error;
name_query = TRUE;
goto LOOP;
END
END
/*
* TCP connection has been established
*/
wait for session response packet;
CASE packet type OF
POSITIVE SESSION RESPONSE:
return success and session established
information;
NEGATIVE SESSION RESPONSE:
BEGIN
CASE error OF
NOT LISTENING ON CALLED NAME:
NOT LISTENING FOR CALLING NAME:
BEGIN
kill TCP connection;
return failure;
END
CALLED NAME NOT PRESENT:
BEGIN
/*
* called name does not exist on
* remote node
*/
inform name discovery procedure
of possible error;
IF this is a P or M node THEN
BEGIN
/*
* Inform NetBIOS Name Server
* it has returned incorrect
* information.
*/
send NAME RELEASE REQUEST for called
name and IP address to
NetBIOS Name Server;
END
/* retry from beginning */
retarget = FALSE;
name_query = TRUE;
goto LOOP;
END /* called name not present */
END /* case */
END /* negative response */
RETARGET SESSION RESPONSE:
BEGIN
close TCP connection;
extract IP address and TCP port from
response;
retarget = TRUE;
END /* retarget response */
END /* case */
LOOP: retry_count = retry_count + 1;
UNTIL (retry_count > SSN_RETRY_COUNT);
return failure;
END /* procedure */
5.2.1.2. RECEIVED PACKET PROCESSING These are packets received on a TCP connection before a session has been established. The listen routines attached to a NetBIOS user process need not implement the RETARGET response section. The user process version, separate from a shared Session Service, need only accept (POSITIVE SESSION RESPONSE) or reject (NEGATIVE SESSION RESPONSE) a session request. PROCEDURE session_packet(packet) /* * processing initiated by receipt of a session service * packet for a session in the session establishment phase. * Assumes the TCP connection has been accepted. */ BEGIN CASE packet type SESSION REQUEST: BEGIN IF called name does not exist on node THEN BEGIN send NEGATIVE SESSION RESPONSE with CALLED NAME NOT PRESENT error code; close TCP connection; END Search for a listen with CALLING NAME for CALLED NAME; IF matching listen is found THEN BEGIN IF port of listener process is port TCP connection is on THEN BEGIN send POSITIVE SESSION RESPONSE; Hand off connection to client process and/or inform user session is established; END ELSE BEGIN send RETARGET SESSION RESPONSE with listener's IP address and TCP port; close TCP connection; END END ELSE BEGIN /* no matching listen pending */
send NEGATIVE SESSION RESPONSE with either
NOT LISTENING ON CALLED NAME or NOT
LISTENING FOR CALLING NAME error
code;
close TCP connection;
END
END /* session request */
END /* case */
END /* procedure */
5.2.2. SESSION DATA TRANSFER PROTOCOLS
5.2.2.1. USER REQUEST PROCESSING
PROCEDURE send_message(user_message)
BEGIN
build SESSION MESSAGE header;
send SESSION MESSAGE header;
send user_message;
reset and restart keep-alive timer;
IF send fails THEN
BEGIN
/*
* TCP connection has failed */
*/
close NetBIOS session;
inform user that session is lost;
return failure;
END
ELSE
return success;
END
5.2.2.2. RECEIVED PACKET PROCESSING
These are packets received after a session has been established.
PROCEDURE session_packet(packet)
/*
* processing initiated by receipt of a session service
* packet for a session in the data transfer phase.
*/
BEGIN
CASE packet type OF
SESSION MESSAGE:
BEGIN
process message header;
read in user data;
reset and restart keep-alive timer;
deliver data to user;
END /* session message */
SESSION KEEP ALIVE:
discard packet;
END /* case */
END /* procedure */
5.2.2.3. PROCESSING INITIATED BY TIMER
PROCEDURE session_ka_timer()
/*
* processing initiated when session keep alive timer expires
*/
BEGIN
send SESSION KEEP ALIVE, if configured;
IF send fails THEN
BEGIN
/* remote node, or path to it, is down */
abort TCP connection;
close NetBIOS session;
inform user that session is lost;
return;
END
END /* procedure */
5.2.3. SESSION TERMINATION PROTOCOLS
5.2.3.1. USER REQUEST PROCESSING
PROCEDURE close_session()
/* initiated by a user request to close a session */
BEGIN
close gracefully the TCP connection;
WAIT for the connection to close or SSN_CLOSE_TIMEOUT
to expire;
IF time out expired THEN
abort TCP connection;
END /* procedure */
5.2.3.2. RECEPTION INDICATION PROCESSING
PROCEDURE close_indication()
/*
* initiated by a TCP indication of a close request from
* the remote connection partner.
*/
BEGIN
close gracefully TCP connection;
close NetBIOS session;
inform user session closed by remote partner;
END /* procedure */
5.3. NetBIOS DATAGRAM SERVICE PROTOCOLS
The following are GLOBAL variables and should be NetBIOS user
configurable:
- SCOPE_ID: the non-leaf section of the domain name preceded by a
'.' which represents the domain of the NetBIOS scope for the
NetBIOS name. The following protocol description only supports
single scope operation.
- MAX_DATAGRAM_LENGTH: the maximum length of an IP datagram. The
minimal maximum length defined in for IP is 576 bytes. This
value is used when determining whether to fragment a NetBIOS
datagram. Implementations are expected to be capable of
receiving unfragmented NetBIOS datagrams up to their maximum
size.
- BROADCAST_ADDRESS: the IP address B-nodes use to send datagrams
with group name destinations and broadcast datagrams. The
default is the IP broadcast address for a single IP network.
The following are Defined Constants for the NetBIOS Datagram
Service:
- DGM_SRVC_UDP_PORT: the globally well-known UDP port allocated
where the NetBIOS Datagram Service receives UDP packets. See
section 6, "Defined Constants", for its value.
5.3.1. B NODE TRANSMISSION OF NetBIOS DATAGRAMS
PROCEDURE send_datagram(data, source, destination, broadcast)
/*
* user initiated processing on B node
*/
BEGIN
group = FALSE;
do name discovery on destination name, returns name type and
IP address;
IF name type is group name THEN
BEGIN
group = TRUE;
END
/*
* build datagram service UDP packet;
*/
convert source and destination NetBIOS names into
half-ASCII, biased encoded name;
SOURCE_NAME = cat(source, SCOPE_ID);
SOURCE_IP = this nodes IP address;
SOURCE_PORT = DGM_SRVC_UDP_PORT;
IF NetBIOS broadcast THEN
BEGIN
DESTINATION_NAME = cat("*", SCOPE_ID)
END
ELSE
BEGIN
DESTINATION_NAME = cat(destination, SCOPE_ID)
END
MSG_TYPE = select_one_from_set
{BROADCAST, DIRECT_UNIQUE, DIRECT_GROUP}
DGM_ID = next transaction id for Datagrams;
DGM_LENGTH = length of data + length of second level encoded
source and destination names;
IF (length of the NetBIOS Datagram, including UDP and
IP headers, > MAX_DATAGRAM_LENGTH) THEN
BEGIN
/*
* fragment NetBIOS datagram into 2 UDP packets
*/
Put names into 1st UDP packet and any data that fits
after names;
Set MORE and FIRST bits in 1st UDP packet's FLAGS;
OFFSET in 1st UDP = 0;
Replicate NetBIOS Datagram header from 1st UDP packet
into 2nd UDP packet;
Put rest of data in 2nd UDP packet;
Clear MORE and FIRST bits in 2nd UDP packet's FLAGS;
OFFSET in 2nd UDP = DGM_LENGTH - number of name and
data bytes in 1st UDP;
END
BEGIN
/*
* Only need one UDP packet
*/
USER_DATA = data;
Clear MORE bit and set FIRST bit in FLAGS;
OFFSET = 0;
END
IF (group == TRUE) OR (NetBIOS broadcast) THEN
BEGIN
send UDP packet(s) to BROADCAST_ADDRESS;
END
ELSE
BEGIN
send UDP packet(s) to IP address returned by name
discovery;
END
END /* procedure */
5.3.2. P AND M NODE TRANSMISSION OF NetBIOS DATAGRAMS
PROCEDURE send_datagram(data, source, destination, broadcast)
/*
* User initiated processing on P and M node.
*
* This processing is the same as for B nodes except for
* sending broadcast and multicast NetBIOS datagrams.
*/
BEGIN
group = FALSE;
do name discovery on destination name, returns name type
and IP address;
IF name type is group name THEN
BEGIN
group = TRUE;
END
/*
* build datagram service UDP packet;
*/
convert source and destination NetBIOS names into
half-ASCII, biased encoded name;
SOURCE_NAME = cat(source, SCOPE_ID);
SOURCE_IP = this nodes IP address;
SOURCE_PORT = DGM_SRVC_UDP_PORT;
IF NetBIOS broadcast THEN
BEGIN
DESTINATION_NAME = cat("*", SCOPE_ID)
END
ELSE
BEGIN
DESTINATION_NAME = cat(destination, SCOPE_ID)
END
MSG_TYPE = select_one_from_set
{BROADCAST, DIRECT_UNIQUE, DIRECT_GROUP}
DGM_ID = next transaction id for Datagrams;
DGM_LENGTH = length of data + length of second level encoded
source and destination names;
IF (length of the NetBIOS Datagram, including UDP and
IP headers, > MAX_DATAGRAM_LENGTH) THEN
BEGIN
/*
* fragment NetBIOS datagram into 2 UDP packets
*/
Put names into 1st UDP packet and any data that fits
after names;
Set MORE and FIRST bits in 1st UDP packet's FLAGS;
OFFSET in 1st UDP = 0;
Replicate NetBIOS Datagram header from 1st UDP packet
into 2nd UDP packet;
Put rest of data in 2nd UDP packet;
Clear MORE and FIRST bits in 2nd UDP packet's FLAGS;
OFFSET in 2nd UDP = DGM_LENGTH - number of name and
data bytes in 1st UDP;
END
BEGIN
/*
* Only need one UDP packet
*/
USER_DATA = data;
Clear MORE bit and set FIRST bit in FLAGS;
OFFSET = 0;
END
IF (group == TRUE) OR (NetBIOS broadcast) THEN
BEGIN
/*
* Sending of following query is optional.
* Node may send datagram to NBDD immediately
* but NBDD may discard the datagram.
*/
send DATAGRAM QUERY REQUEST to NBDD;
IF response is POSITIVE QUERY RESPONSE THEN
send UDP packet(s) to NBDD Server IP address;
ELSE
BEGIN
get list of destination nodes from NBNS;
FOR EACH node in list
BEGIN
send UDP packet(s) to this node's
IP address;
END
END
END
ELSE
BEGIN
send UDP packet(s) to IP address returned by name
discovery;
END /* procedure */
5.3.3. RECEPTION OF NetBIOS DATAGRAMS BY ALL NODES
The following algorithm discards out of order NetBIOS Datagram
fragments. An implementation which reassembles out of order
NetBIOS Datagram fragments conforms to this specification. The
fragment discard timer is initialized to the value FRAGMENT_TO.
This value should be user configurable. The default value is
given in Section 6, "Defined Constants and Variables".
PROCEDURE datagram_packet(packet)
/*
* processing initiated by datagram packet reception
* on B, P and M nodes
*/
BEGIN
/*
* if this node is a P node, ignore
* broadcast packets.
*/
IF this is a P node AND incoming packet is
a broadcast packet THEN
BEGIN
discard packet;
END
CASE packet type OF
DATAGRAM SERVICE:
BEGIN
IF FIRST bit in FLAGS is set THEN
BEGIN
IF MORE bit in FLAGS is set THEN
BEGIN
Save 1st UDP packet of the Datagram;
Set this Datagram's fragment discard
timer to FRAGMENT_TO;
return;
END
ELSE
Datagram is composed of a single
UDP packet;
END
ELSE
BEGIN
/* Have the second fragment of a Datagram */
Search for 1st fragment by source IP address
and DGM_ID;
IF found 1st fragment THEN
Process both UDP packets;
ELSE
BEGIN
discard 2nd fragment UDP packet;
return;
END
END
IF DESTINATION_NAME is '*' THEN
BEGIN
/* NetBIOS broadcast */
deliver USER_DATA from UDP packet(s) to all
outstanding receive broadcast
datagram requests;
return;
END
ELSE
BEGIN /* non-broadcast */
/* Datagram for Unique or Group Name */
IF DESTINATION_NAME is not present in the
local name table THEN
BEGIN
/* destination not present */
build DATAGRAM ERROR packet, clear
FIRST and MORE bit, put in
this nodes IP and PORT, set
ERROR_CODE;
send DATAGRAM ERROR packet to
source IP address and port
of UDP;
discard UDP packet(s);
return;
END
ELSE
BEGIN /* good */
/*
* Replicate received NetBIOS datagram for
* each recipient
*/
FOR EACH pending NetBIOS user's receive
datagram operation
BEGIN
IF source name of operation
matches destination name
of packet THEN
BEGIN
deliver USER_DATA from UDP
packet(s);
END
END /* for each */
return;
END /* good */
END /* non-broadcast */
END /* datagram service */
DATAGRAM ERROR:
BEGIN
/*
* name service returned incorrect information
*/
inform local name service that incorrect
information was provided;
IF this is a P or M node THEN
BEGIN
/*
* tell NetBIOS Name Server that it may
* have given incorrect information
*/
send NAME RELEASE REQUEST with name
and incorrect IP address to NetBIOS
Name Server;
END
END /* datagram error */
END /* case */
END
5.3.4. PROTOCOLS FOR THE NBDD
The key to NetBIOS Datagram forwarding service is the packet
delivered to the destination end node must have the same NetBIOS
header as if the source end node sent the packet directly to the
destination end node. Consequently, the NBDD does not reassemble
NetBIOS Datagrams. It forwards the UDP packet as is.
PROCEDURE datagram_packet(packet)
/*
* processing initiated by a incoming datagram service
* packet on a NBDD node.
*/
BEGIN
CASE packet type OF
DATAGRAM SERVICE:
BEGIN
IF packet was sent as a directed
NetBIOS datagram THEN
BEGIN
/*
* provide group forwarding service
*
* Forward datagram to each member of the
* group. Can forward via:
* 1) get list of group members and send
* the DATAGRAM SERVICE packet unicast
* to each
* 2) use Group Multicast, if available
* 3) combination of 1) and 2)
*/
...
END
ELSE
BEGIN
/*
* provide broadcast forwarding service
*
* Forward datagram to every node in the
* NetBIOS scope. Can forward via:
* 1) get list of group members and send
* the DATAGRAM SERVICE packet unicast
* to each
* 2) use Group Multicast, if available
* 3) combination of 1) and 2)
*/
...
END
END /* datagram service */
DATAGRAM ERROR:
BEGIN
/*
* Should never receive these because Datagrams
* forwarded have source end node IP address and
* port in NetBIOS header.
*/
send DELETE NAME REQUEST with incorrect name and
IP address to NetBIOS Name Server;
END /* datagram error */
DATAGRAM QUERY REQUEST:
BEGIN
IF can send packet to DESTINATION_NAME THEN
BEGIN
/*
* NBDD is able to relay Datagrams for
* this name
*/
send POSITIVE DATAGRAM QUERY RESPONSE to
REQUEST source IP address and UDP port
with request's DGM_ID;
END
ELSE
BEGIN
/*
* NBDD is NOT able to relay Datagrams for
* this name
*/
send NEGATIVE DATAGRAM QUERY RESPONSE to
REQUEST source IP address and UDP port
with request's DGM_ID;
END
END /* datagram query request */
END /* case */
END /* procedure */
6. DEFINED CONSTANTS AND VARIABLES GENERAL: SCOPE_ID The name of the NetBIOS scope. This is expressed as a character string meeting the requirements of the domain name system and without a leading or trailing "dot". An implementation may elect to make this a single global value for the node or allow it to be specified with each separate NetBIOS name (thus permitting cross-scope references.) BROADCAST_ADDRESS An IP address composed of the nodes's network and subnetwork numbers with all remaining bits set to one. I.e. "Specific subnet" broadcast addressing according to section 2.3 of RFC 950. BCAST_REQ_RETRY_TIMEOUT 250 milliseconds. An adaptive timer may be used. BCAST_REQ_RETRY_COUNT 3 UCAST_REQ_RETRY_TIMEOUT 5 seconds An adaptive timer may be used. UCAST_REQ_RETRY_COUNT 3 MAX_DATAGRAM_LENGTH 576 bytes (default) NAME SERVICE: REFRESH_TIMER Negotiated with NBNS for each name. CONFLICT_TIMER 1 second Implementations may chose a longer value. NAME_SERVICE_TCP_PORT 137 (decimal)
NAME_SERVICE_UDP_PORT 137 (decimal)
INFINITE_TTL 0
SESSION SERVICE:
SSN_SRVC_TCP_PORT 139 (decimal)
SSN_RETRY_COUNT 4 (default)
Re-configurable by user.
SSN_CLOSE_TIMEOUT 30 seconds (default)
Re-configurable by user.
SSN_KEEP_ALIVE_TIMEOUT 60 seconds, recommended, may be set to
a higher value.
(Session keep-alives are used only
if configured.)
DATAGRAM SERVICE:
DGM_SRVC_UDP_PORT 138 (decimal)
FRAGMENT_TO 2 seconds (default)