samba-mirror/docs/Samba-Developers-Guide/NetBIOS.xml

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<chapter id="netbios">
<chapterinfo>
	<author>
		<firstname>Luke</firstname><surname>Leighton</surname>
	</author>
	<pubdate>12 June 1997</pubdate>
</chapterinfo>

<title>Definition of NetBIOS Protocol and Name Resolution Modes</title>

<sect1>
<title>NETBIOS</title>

<para>
NetBIOS runs over the following tranports: TCP/IP; NetBEUI and IPX/SPX.
Samba only uses NetBIOS over TCP/IP.  For details on the TCP/IP NetBIOS 
Session Service NetBIOS Datagram Service, and NetBIOS Names, see
rfc1001.txt and rfc1002.txt.
</para>

<para> 
NetBEUI is a raw NetBIOS frame protocol implementation that allows NetBIOS
datagrams to be sent out over the 'wire' embedded within LLC frames.
NetBEUI is not required when using NetBIOS over TCP/IP protocols and it
is preferable NOT to install NetBEUI if it can be avoided.
</para>

<para> 
IPX/SPX is also not required when using NetBIOS over TCP/IP, and it is
preferable NOT to install the IPX/SPX transport unless you are using Novell
servers.  At the very least, it is recommended that you do not install
'NetBIOS over IPX/SPX'.
</para>

<para>
[When installing Windows 95, you will find that NetBEUI and IPX/SPX are
installed as the default protocols.  This is because they are the simplest
to manage: no Windows 95 user-configuration is required].
</para>

<para> 
NetBIOS applications (such as samba) offer their services (for example,
SMB file and print sharing) on a NetBIOS name.  They must claim this name
on the network before doing so.  The NetBIOS session service will then
accept connections on the application's behalf (on the NetBIOS name
claimed by the application).  A NetBIOS session between the application
and the client can then commence.
</para>

<para> 
NetBIOS names consist of 15 characters plus a 'type' character.  This is
similar, in concept, to an IP address and a TCP port number, respectively.
A NetBIOS-aware application on a host will offer different services under
different NetBIOS name types, just as a host will offer different TCP/IP
services on different port numbers.
</para>

<para> 
NetBIOS names must be claimed on a network, and must be defended.  The use
of NetBIOS names is most suitable on a single subnet; a Local Area Network
or a Wide Area Network.
</para>

<para> 
NetBIOS names are either UNIQUE or GROUP.  Only one application can claim a
UNIQUE NetBIOS name on a network.
</para>

<para>
There are two kinds of NetBIOS Name resolution: Broadcast and Point-to-Point.
</para>

</sect1>

<sect1>
<title>BROADCAST NetBIOS</title>

<para> 
Clients can claim names, and therefore offer services on successfully claimed
names, on their broadcast-isolated subnet.  One way to get NetBIOS services
(such as browsing: see ftp.microsoft.com/drg/developr/CIFS/browdiff.txt; and
SMB file/print sharing: see cifs4.txt) working on a LAN or WAN is to make
your routers forward all broadcast packets from TCP/IP ports 137, 138 and 139.
</para>

<para> 
This, however, is not recommended.  If you have a large LAN or WAN, you will
find that some of your hosts spend 95 percent of their time dealing with
broadcast traffic.  [If you have IPX/SPX on your LAN or WAN, you will find
that this is already happening: a packet analyzer will show, roughly
every twelve minutes, great swathes of broadcast traffic!].
</para>

</sect1>

<sect1>
<title>NBNS NetBIOS</title>

<para>
rfc1001.txt describes, amongst other things, the implementation and use
of, a 'NetBIOS Name Service'.  NT/AS offers 'Windows Internet Name Service'
which is fully rfc1001/2 compliant, but has had to take specific action
with certain NetBIOS names in order to make it useful.  (for example, it
deals with the registration of &lt;1c&gt; &lt;1d&gt; &lt;1e&gt; names all in different ways.
I recommend the reading of the Microsoft WINS Server Help files for full
details).
</para>

<para> 
The use of a WINS server cuts down on broadcast network traffic for
NetBIOS name resolution.  It has the effect of pulling all the broadcast
isolated subnets together into a single NetBIOS scope, across your LAN
or WAN, while avoiding the use of TCP/IP broadcast packets.
</para>

<para>
When you have a WINS server on your LAN, WINS clients will be able to
contact the WINS server to resolve NetBIOS names.  Note that only those
WINS clients that have registered with the same WINS server will be
visible.  The WINS server _can_ have static NetBIOS entries added to its
database (usually for security reasons you might want to consider putting
your domain controllers or other important servers as static entries,
but you should not rely on this as your sole means of security), but for
the most part, NetBIOS names are registered dynamically.
</para>

<para>
This provides some confusion for lots of people, and is worth mentioning
here:  a Browse Server is NOT a WINS Server, even if these services are
implemented in the same application.  A Browse Server _needs_ a WINS server
because a Browse Server is a WINS client, which is _not_ the same thing].
</para>

<para>
Clients can claim names, and therefore offer services on successfully claimed
names, on their broadcast-isolated subnet.  One way to get NetBIOS services
(such as browsing: see ftp.microsoft.com/drg/developr/CIFS/browdiff.txt; and
SMB file/print sharing: see cifs6.txt) working on a LAN or WAN is to make
your routers forward all broadcast packets from TCP/IP ports 137, 138 and 139.
You will find, however, if you do this on a large LAN or a WAN, that your
network is completely swamped by NetBIOS and browsing packets, which is why
WINS was developed to minimise the necessity of broadcast traffic.
</para>

<para> 
WINS Clients therefore claim names from the WINS server.  If the WINS
server allows them to register a name, the client's NetBIOS session service
can then offer services on this name.  Other WINS clients will then
contact the WINS server to resolve a NetBIOS name.
</para>

</sect1>

</chapter>