samba-mirror/source/nameservreply.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: nameservreply.doc

   Revision History:

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

/*************************************************************************
  reply_name_query()
  *************************************************************************/

this function is responsible for replying to a NetBIOS name query.

there are two kinds of name queries: directed, and broadcast. directed
queries are usually sent to samba in its WINS capacity. such hosts are
termed 'point-to-point' hosts. broadcast queries are usually sent from
'broadcast' or 'mixed' hosts.

broadcasting is used by either older NetBIOS hosts, new NetBIOS hosts that
have not had WINS capabilities added and new NetBIOS hosts that think the
WINS server has died.

the samba NetBIOS name database is divided into sections, on a
per-subnet basis. there is also a WINS NetBIOS name database, and for
convenience this is added as a pseudo-subnet with the ip address of
255.255.255.255.

the local subnet NetBIOS name databases only contain samba's names.
the reason for this is that if a broadcast query is received, a NetBIOS
hosts is only expected to respond if that query is for one of its own
names (the exception to this is if a host is configured as a 'proxy'
server, in which case, samba should redirect the query to another WINS
server).

the WINS pseudo-subnet NetBIOS database contains all NetBIOS names
that are not 'special browser' type names (regarding this i am a
_bit_ confused :-). names of type 0x01, 0x1d and 0x1e i consider to
be 'special browser' names. at the moment. maybe.

the type of search to be initiated is determined. if the NetBIOS name
type is a non-special-browser name, then the WINS database is included
in the search.

if the name is not a special browser name, then we need to find the
right subnet that the query came from. this is done using
find_req_subnet(). this also has the benefit of stopping any queries
from subnets that samba does not know about.

if the query is a broadcast query, then the database of the local subnet
is included in the search.

the name is then searched for in the appropriate NetBIOS data structures.
if it is found, then we need to check whether it is appropriate for us
to reply to such a query.

we will only reply if the query is a directed query, the name belongs to
samba on that subnet, or the name is a domain master browser type,
or we're doing replies on behalf of hosts on subnets not known to the
host issuing the query. in the latter instance, it would be appropriate
if samba is using a WINS server for it to forward the name query on to
this WINS server.

reply_name_query() then takes note of all the information that is
needed to construct a reply to the caller. a negative reply (if the
name is unknown to samba) or a positive reply (the name is known to
samba) is then issued.


/*************************************************************************
  reply_name_status()
  *************************************************************************/

this function is responsible for constructing a reply to a NetBIOS
name status query. this response contains all samba's NetBIOS names
on the subnet that the query came in from.

a reply will only be made if the NetBIOS name being queried exists.

see rfc1001.txt and rfc1002.txt for details of the name status reply.


/*************************************************************************
  reply_name_reg()
  *************************************************************************/

this function is responsible for updating the NetBIOS name database
from registration packets sent out by hosts wishing to register a
name, and for informing them, if necessary, if this is acceptable
or not.

name registration can be done by broadcast or by point-to-point,
i.e the registration is sent directly to samba in its capacity as
a WINS server.

if the name registration is done by broadcast (see rfc1001.txt 15.2.1),
then samba's involvement in replying is limited to whether that name
is owned by samba or not, on the relevant subnet.

if the name registration is done point-to-point (see rfc1001.txt 15.2.2)
then samba will first need to check its WINS name database records and
proceed accordingly.

samba looks for the appropriate subnet record that the registration
should be added to / checked against, using find_req_subnet().

next, the name is searched for in the local database or the WINS
database as appropriate.

if the name is not found, then it is added to the NetBIOS name database,
using add_netbios_entry(), which may choose not to add the name (not
that this affects the registration of the name on the network in any way).
it will only add names to the WINS database, and even then it will only
add non-special-browser type names.

if the name is found, then samba must decide whether to accept the name
or not. a group name is always added. for unique names, further checks
need to be carried out.

firstly, if the name in the database is one of samba's names, or if the
name in the database is a group name, then it cannot be added as a unique
name belonging to someone else. it is therefore rejected.

secondly, if the ip address of the name being registered does not match
against the ip in the database, then the unique name may belong to
someone else. a check needs to be carried out with the owner in case
they still wish to keep this name. a detailed discussion of what action
to take is in rfc1001.txt 15.2.2.2 and 15.2.2.3.

samba currently implements non-secured WINS, whereupon the responsibility
for checking the name is passed on to the host doing the registration.
rfc1001.txt refers to this as an END-NODE CHALLENGE REGISTRATION RESPONSE.
(samba itself cannot yet cope with receiving such responses if it
registers its names with another WINS server). 

having decided what kind of response to send (if any - acceptance of
name registrations by broadcast is implicit), samba will send either a
positive or negative NAME REGISTRATION RESPONSE, or an END-NODE CHALLENGE
REGISTRATION RESPONSE to the host that initially sent the registration.

whew.


/*************************************************************************
  reply_name_release()
  *************************************************************************/

this function is responsible for removing a NetBIOS name from the
database when a server sends a release packet.

samba looks for the appropriate subnet record that the release should
be removed from, using find_req_subnet(). next, the name is searched
for in the local database or the WINS database as appropriate.

if the name is found, it is removed from the database and a
positive reply is sent confirming this. if the name is not
found, a negative reply is sent.

a reply is _not_ sent if the release was done by broadcast: the
release is implicit, and we should be grateful that they bothered
to tell us. if the release was done by directed packet, then
we deal with it as a WINS server and must reply (pos / neg).

at present, the criteria for removing a name have yet to be
developed / experimented with. at present, the only flags that
are checked are the NetBIOS flags.


/*************************************************************************
  send_name_response()
  *************************************************************************/

this function is a wrap around reply_netbios_packet(). it sends
a response to a name registration or release packet, minimising
the function parameters needed to do this.

if the function is called with the parameter 'success' set to
True, then a positive response (to the registration or release)
is made (see rfc1002.txt 4.2.5 and 4.2.10). if this parameter
is False, then a negative response is issued (see rfc1002.txt
4.2.6 and 4.2.11)

if the function is called with a registration code, and the
parameter 'recurse' is False, then an End-Node Challenge
Registration response is issued (see rfc1002.txt 4.2.7)

note: this function could also easily be used for name conflict
demand (see rfc1002.txt 4.2.8).

note: End-Node Challenge Registration response is only sent in
non-secured NetBIOS Name Server implementations. samba now
implements secured NetBIOS Name Server functionality (see
rfc1001.txt 15.1.6).