samba-mirror/source/nameresp.doc

/* 
   Unix SMB/Netbios documentation.
   Version 0.0
   Copyright (C) Luke Leighton  Andrew Tridgell  1996
   
   This program is free software; you can redistribute it and/or modify
   it under the terms of the GNU General Public License as published by
   the Free Software Foundation; either version 2 of the License, or
   (at your option) any later version.
   
   This program is distributed in the hope that it will be useful,
   but WITHOUT ANY WARRANTY; without even the implied warranty of
   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
   GNU General Public License for more details.
   
   You should have received a copy of the GNU General Public License
   along with this program; if not, write to the Free Software
   Foundation, Inc., 675 Mass Ave, Cambridge, MA 02139, USA.
   
   Document name: nameresp.doc

   Revision History:

   0.0 - 02jul96 : lkcl@pires.co.uk
   created
*/

the netbios expected response code is a key part of samba's NetBIOS
handling capabilities. it allows samba to carry on dealing with
other things while expecting a response from one or more hosts.

this allows samba to simultaneously deal with registering its names
with another WINS server, register its names on its local subnets,
query any hosts that have registered with samba in its capacity as
a WINS server, and at a later date it will be also be able handle
END-NODE CHALLENGES (see rfc1001.txt 15.2.2.2 and 15.2.2.3 - secured
NBNS functionality).

all at once!

when a netbios packet is sent out by samba and it expects a response,
a record of all the relevant information is kept (most importantly,
the unique transaction id associated which will come back to us in
a response packet is recorded, and also recorded is the reason that
the original packet was sent out by samba in the first place!).

if a response is received, then the unique transaction identifier 
returned in the response packet is searched for in the expected
response records. the record indicates why the initial request was
made (and therefore the type of response can be verified) and
appropriate action can be taken.

when no responses, after a number of retries, are not received, then
samba may take appropriate action. this is a crucial part of samba's
operation: for a key number of NetBIOS operations, no response is an
implicit positive response.

module nameresp deals with the initial transmission, re-transmission
and time-out of netbios response records.

module namedbresp deals with the maintenance of the list of expected
responses - creation, finding and removal.


/*************************************************************************
  queue_netbios_packet()
  *************************************************************************/

this function is responsible for sending out a netbios packet, and then
making a record of the information that was sent out. a response will
be expected later (or not, as the case may be).

if a response is received, response_netbios_packet() will deal with it.
otherwise, it will be dealt with in expire_netbios_response_entries().


/*************************************************************************
  queue_netbios_pkt_wins()
  *************************************************************************/

this function is a wrapper around queue_netbios_packet(). there is
some confusion about B, M and P nodes (see rfc1001.txt section 10) -
confusion introduced by luke :-) - which needs sorting out.

for example, rfc1001.txt 15.2.3 - an M node must attempt to register a
name first as a B node, then attempt to register as an M node. negative
responses on either of these attempts is a failure to register the
name.

this is NOT the case with a P node.


/*************************************************************************
  expire_netbios_response_entries()
  *************************************************************************/

this function is responsible for dealing with queued response records
that have not received a response packet matching their unique
transaction id.

if the retry count for any record is non-zero, and its time-out period
has expired, the retry count is reduced, the time-out period is stepped
forward and the packet is re-transmitted (from the information stored
in the queued response record) with the same unique transaction id of
the initial attempt at soliciting a response.

if the retry count is zero, then the packet is assumed to have expired.
dead_netbios_entry() is called to deal with the possibility of an error
or a problem (or in certain instances, no answer is an implicit
positive response!).

the expected response record is then deleted, and the number of expected
responses reduced. when this count gets to zero, listen_for_packets()
will no longer time-out for 1 second on account of expecting response
packets.


/*************************************************************************
  dead_netbios_entry()
  *************************************************************************/

this function is responsible for dealing with the case when a NetBIOS
response to a packet sent out by samba was not received. for certain
transactions, this may be normal. for others, under certain conditions
it may constitute either an error or a problem with or failure of one
or more hosts.

- NAME_QUERY_CONFIRM

when a samba 'state' of type NAME_QUERY_CONFIRM is sent, a response
may or may not be forthcoming. if no response is received to a unique
name, then the record is removed from samba's WINS database. non-unique
names are simply expected to die off on a time-to-live basis (see
rfc1001.txt 15.1.3.4)

query_refresh_names() issues this samba 'state'
response_name_query_sync() deals with responses to NAME_QUERY_CONFIRM.

- NAME_QUERY_MST_CHK

when a samba 'state' of type NAME_QUERY_MST_CHK is sent, and a response
is not received, this implies that a master browser will have failed.
remedial action may need to be taken, for example if samba is a member
of that workgroup and it is also a potential master browser it could
force an election.

check_master_browser() issues this samba 'state'.
response_process() does nothing if a response is received. this is normal.

- NAME_RELEASE

when a samba 'state' of type NAME_RELEASE is sent, and a response is
not received, it is assumed to be acceptable to release the name. if the
original response was sent to another WINS server, then that WINS server
may be inaccessible or may have failed. if so, then at a later date
samba should take this into account (see rfc1001.txt 10.3).

remove_name_entry() issues this samba 'state'
response_name_rel() deals with responses to NAME_RELEASE.

- NAME_REGISTER

when a samba 'state' of type NAME_REGISTER is sent, and a response is
not received, if the registration was done by broadcast, it is assumed
that there are no objections to the registration of this name, and samba
adds the name to the appropriate subnet record name database. if the
registration was point-to-point (i.e with another WINS server) then that
WINS server may be inaccessible or may have failed. if so, then at a later
date samba should take this into account (see rfc1001.txt 10.3).

add_my_name_entry() issues this samba 'state'
response_name_reg() deals with responses to NAME_REGISTER.

no action is taken for any other kinds of samba 'states' if a response
is not received. this is not to say that action may not be appropriate,
just that it's not been looked at yet :-)