samba-mirror/source3/nameannounce.doc

/* 
   Unix SMB/Netbios documentation.
   Version 0.2
   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: nameannounce.doc

   Revision History:

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

   0.1 - 22jul96 : Andrew.Tridgell@anu.edu.au
   tridge's comments on first revision

   0.2 - 05aug96 : lkcl@pires.co.uk
   actioned tridge comments about pdc -> domain master
   documented NAME_QUERY_ANNOUNCE_HOST

*/


this module deals with announcements: the sending of announcement requests
and the sending of announcements either to refresh other servers' records
or as a response to announcement requests.


/*************************************************************************
  announce_master()
  *************************************************************************/

this function is responsible for announcing samba as a master browser
to all known domain masters.

this announcement is sent out at CHECK_TIME_MST_ANNOUNCE minute
intervals, only if samba is a master browser on one or more of
its local interfaces.

if no domain controller has been specified (lp_domain_controller())
samba goes through its list of servers looking for domain master
browsers. when it finds one (other than itself) it will either
initiate a NAME_QUERY_PDC_SRV_CHK by broadcast or with a WINS
server. this will result in a NAME_STATUS_PDC_SRV_CHK, which
will result in a sync browse list and an announcement
ANN_MasterAnnounce being sent (see sync_server()).

if a domain controller has been specified, samba will search for
a domain master browser for its workgroup (either by directed
packet or by broadcast if it cannot resolve the domain controller
name using DNS), which results in the same action as listed above.

------------
NOTE FROM TRIDGE: 

PDC in the above should really be DMB (domain master browser). They
might be separate entities.

I also propose a simpler scheme :-)

If a DMB is not configured with lp_domain_controller() (perhaps
renamed to lp_domain_master()?) then just don't do master
announcements. Remember that most peoples networks are very simple and
don't need DMB capabilities. Those that do need them will have more
complex network topologies and they really need to choose themselves
which box will act as the "hub" for netbios name resolution. Doing it
via name queries will just lead to lag and propogation delays, because
if two parts of the net choose different DMBs then the data will be
very slow to propoogate.

If a DMB is configured then just send the master announcemnt to that
box! Thats all that needs to be done. Just send a udp 138 packet and
forget it. If the recipient is indeed a DMB (as it should be if the
config file is correct) then it should initiate a browse list sync
with us at some later time, but that is take care of by smbd and nmbd
doesn't even need to know it happened.

Additionally, if a DMB is configured we need to sync our workgroup
list and server list with them occasionally. Note that this is only
time a non-DMB should do a browse sync, and it should only do it with
a DMB. Essentially WAN based netbios is just a simple star. There is a
DMB in the centre, and the individual master browsers for each subnet
talk to it, but never talk to each other. If they start talking to
each other then the network load will go as the square of the number
of machines, which will result in meltdown :-)
-------------


/*************************************************************************
  announce_host()
  *************************************************************************/

this complex-looking function is responsible for announcing samba's
existence to other servers by broadcast. the actual announcement
is carried out by announce_server().

the time period between samba's announcement will stretch from one
minute to twelve minutes by one minute. if samba has received an
announce request from a master browser, then it should answer at
any random interval between zero and thirty seconds after the
request is received. this is to ensure that the master browser
does not get overloaded with responses!


/*************************************************************************
  announce_server()
  *************************************************************************/

this function is responsible for sending announcement packets.
these packets are received by other servers, which will then
update their records accordingly: what services we have, our
name, our comment field and our time to live (to name a few).

if samba is a non-master then we need to see if there is a
domain master (on a remote subnet) that we need to announce to
it.

if samba is not the WINS server (and it is using another
WINS server) then we need to do a name query to the WINS
server to ask it what the domain controller is. this is done
using a samba 'state' NAME_QUERY_ANNOUNCE_HOST, which passes
sufficient information on to be able to carry out the
host announcement using a unicasted do_announce_host() if and
when a reply comes back. if there is no reply to the name query,
this is not necessarily an error - there may genuinely be no
domain master currently up and running for samba's workgroup.

if samba is a WINS server, then samba will need to look up the
domain controller for its workgroup in its WINS records. an
over-cautious samba could carry out a name query on that
domain controller to make sure that it is alive and that samba's
WINS records are up-to-date. in any event, it will send a unicast
do_announce_host() to inform the domain master browser, if one
exists, of samba's server status.

if we are a master browser, then using do_announce_host() we
must send a broadcast announcement on the local interface
notifying members of that workgroup that we are their master
browser, and another announcement indicating to all backup
browsers and master browsers that we are a master browser.

(note: if another master browser receives this broadcasted
announcement and thinks that it is also the master browser
for this workgroup, it stops being a master browser and forces
an election).

if we are not a master browser, then we send a broacast 
announcement notifying the master browser that we are a member
of its workgroup, on the local interface.


/*************************************************************************
  remove_my_servers()
  *************************************************************************/

this function is responsible for informing other servers that
samba is about to go down. it announces, on all subnets, that
samba's time to live is zero and that it has no services.


/*************************************************************************
  do_announce_host()
  *************************************************************************/

this function is responsible for sending out an announcement
MAILSLOT browse packet. it contains information such as the
time to live, name of the server, services that the server
offers etc.

the format of this MAILSLOT browse packet is described in
draft-heizer-cifs-v1-spec-00.txt 3.9.50.4.1 page 165-6.


/*************************************************************************
  announce_backup()
  *************************************************************************/

this function is responsible for getting master browsers and domain
controllers to send us lists of backup servers. this is done by
sending an ANN_GetBackupListReq browse mailslot.

the local master browser, or domain master browser, should respond 
with an ANN_GetBackupListResp browse mailslot containing the list
of backup servers.

--------------
NOTE FROM TRIDGE: I don't see why nmbd should ever send one of
these. The only reason I can see for any part of Samba sending one of
these is if we implement it in smbclient. 

This packet is used to request a list of backup master browsers from
the master browser. It is used by clients (not servers!) to spread the
browse load over more than one server. The only server that needs to
know what the list of backups is is the master browser, and as it is
also responsible for generating this list it will never ask anyone
else for it.
--------------


/*************************************************************************
  sync_server()
  *************************************************************************/

this function is responsible for initiating a sync browse list
sequence and, if necessary, carrying out an ANN_MasterAnnouncement
to the domain master browser (that we are also sync'ing browse lists
with).

see nameservresp.c:response_name_status_check().


/*************************************************************************
  announce_request()
  *************************************************************************/

this function is responsible for sending an announcement request to
another server. this server should respond with an announcement.

if the announce request is sent to WORKGROUP(0x1e) then members of
the workgroup will respond (with ANN_HostAnnounce packets)

if the announce request is sent to WORKGROUP(0x1d) then the master
browser of the workgroup should respond (ANN_LocalMasterAnnounce).
this is untested.

if the announce request is sent to ^1^2__MSBROWSE__^2(0x1) then
(and this is pure speculation), all backup browsers and master
browsers should respond with ANN_DomainAnnounce packets.
this is untested.

-----------
NOTE FROM TRIDGE:

I had great trouble getting machines to actually respond to this
packet. Either we have the format wrong or MS chose not to implement
it.

Not implementing it doesn't break anything, it just means a new master
browser won't get a complete server list as quickly.

Also note that this packet should be used as little as possible as it
could easily cause meltdown if too many servers used it. Imagine a
dozen samba servers on a net all sending this packet! You will get 244
responses all within 30 seconds. now imagine 50 samba servers ....

So I think we should restrict ourselves to sending this packet only if
we are already the master browser for a workgroup. We could send a
single "announce request" when we become the master, just to prime our
server lists. From then on the normal announce cycles should take care
of keeping it uptodate.
-----------