samba-mirror/docs-xml/Samba3-HOWTO/TOSHARG-Integrating-with-Windows.xml

<?xml version="1.0" encoding="iso-8859-1"?>
<!DOCTYPE chapter PUBLIC "-//Samba-Team//DTD DocBook V4.2-Based Variant V1.0//EN" "http://www.samba.org/samba/DTD/samba-doc">
<chapter id="integrate-ms-networks">
 
<chapterinfo>
	&author.jht;
        <pubdate> (Jan 01 2001) </pubdate>
</chapterinfo>
 
<title>Integrating MS Windows Networks with Samba</title>
 
<para>
<indexterm><primary>NetBIOS</primary></indexterm>
This chapter deals with NetBIOS over TCP/IP name to IP address resolution. If
your MS Windows clients are not configured to use NetBIOS over TCP/IP, then this
section does not apply to your installation. If your installation involves the use of
NetBIOS over TCP/IP, then this chapter may help you to resolve networking problems.
</para>

<note>
<para>
<indexterm><primary>NetBEUI</primary></indexterm>
<indexterm><primary>LLC</primary></indexterm>
NetBIOS over TCP/IP has nothing to do with NetBEUI. NetBEUI is NetBIOS
over Logical Link Control (LLC). On modern networks it is highly advised
to not run NetBEUI at all. Note also that there is no such thing as
NetBEUI over TCP/IP &smbmdash; the existence of such a protocol is a complete
and utter misapprehension.
</para>
</note>

<sect1>
<title>Features and Benefits</title>

<para>
Many MS Windows network administrators have never been exposed to basic TCP/IP
networking as it is implemented in a UNIX/Linux operating system. Likewise, many UNIX and
Linux administrators have not been exposed to the intricacies of MS Windows TCP/IP-based
networking (and may have no desire to be, either).
</para>

<para>
This chapter gives a short introduction to the basics of how a name can be resolved to 
its IP address for each operating system environment.
</para>

</sect1>

<sect1>
<title>Background Information</title>

<para>
<indexterm><primary>NetBIOS over TCP/IP</primary></indexterm>
<indexterm><primary>UDP port 137</primary></indexterm>
<indexterm><primary>TCP port 139</primary></indexterm>
<indexterm><primary>TCP port 445</primary></indexterm>
<indexterm><primary>UDP port 137</primary></indexterm>
Since the introduction of MS Windows 2000, it is possible to run MS Windows networking
without the use of NetBIOS over TCP/IP. NetBIOS over TCP/IP uses UDP port 137 for NetBIOS
name resolution and uses TCP port 139 for NetBIOS session services. When NetBIOS over
TCP/IP is disabled on MS Windows 2000 and later clients, then only the TCP port 445 is
used, and the UDP port 137 and TCP port 139 are not.
</para>

<note>
<para>
When using Windows 2000 or later clients, if NetBIOS over TCP/IP is not disabled, then
the client will use UDP port 137 (NetBIOS Name Service, also known as the Windows Internet
Name Service, or WINS), TCP port 139, and TCP port 445 (for actual file and print traffic).
</para>
</note>

<para>
<indexterm><primary>DNS</primary></indexterm>
<indexterm><primary>ADS</primary></indexterm>
<indexterm><primary>DDNS</primary></indexterm>
<indexterm><primary>SRV RR</primary></indexterm>
<indexterm><primary>IXFR</primary></indexterm>
<indexterm><primary>DHCP</primary></indexterm>
When NetBIOS over TCP/IP is disabled, the use of DNS is essential. Most installations that disable NetBIOS
over TCP/IP today use MS Active Directory Service (ADS). ADS requires
<indexterm><primary>DNS</primary><secondary>Dynamic</secondary></indexterm> dynamic DNS with Service Resource
Records (SRV RR) and with Incremental Zone Transfers (IXFR).  <indexterm><primary>DHCP</primary></indexterm>
Use of DHCP with ADS is recommended as a further means of maintaining central control over the client
workstation network configuration.
</para>

</sect1>

<sect1>
<title>Name Resolution in a Pure UNIX/Linux World</title>

<para>
The key configuration files covered in this section are:
</para>

<indexterm><primary>/etc/hosts</primary></indexterm>
<indexterm><primary>/etc/resolv.conf</primary></indexterm>
<indexterm><primary>/etc/host.conf</primary></indexterm>
<indexterm><primary>/etc/nsswitch.conf</primary></indexterm>

<itemizedlist>
	<listitem><para><filename>/etc/hosts</filename></para></listitem>
	<listitem><para><filename>/etc/resolv.conf</filename></para></listitem>
	<listitem><para><filename>/etc/host.conf</filename></para></listitem>
	<listitem><para><filename>/etc/nsswitch.conf</filename></para></listitem>
</itemizedlist>

<sect2>
<title><filename>/etc/hosts</filename></title>

<para>
This file contains a static list of IP addresses and names.
<programlisting>
127.0.0.1	localhost localhost.localdomain
192.168.1.1	bigbox.quenya.org	bigbox	alias4box
</programlisting>
</para>

<para>
<indexterm><primary>/etc/hosts></primary></indexterm>
<indexterm><primary>name resolution</primary></indexterm>
The purpose of <filename>/etc/hosts</filename> is to provide a 
name resolution mechanism so users do not need to remember 
IP addresses.
</para>

<para>
<indexterm><primary>IP addresses</primary></indexterm>
<indexterm><primary>MAC address</primary></indexterm>
<indexterm><primary>physical network transport layer</primary></indexterm>
Network packets that are sent over the physical network transport 
layer communicate not via IP addresses but rather using the Media 
Access Control address, or MAC address. IP addresses are currently 
32 bits in length and are typically presented as four decimal 
numbers that are separated by a dot (or period) &smbmdash; for example, 168.192.1.1.
</para>

<para>
<indexterm><primary>MAC Addresses</primary></indexterm>
MAC addresses use 48 bits (or 6 bytes) and are typically represented 
as two-digit hexadecimal numbers separated by colons: 40:8e:0a:12:34:56.
</para>

<para>
Every network interface must have a MAC address. Associated with a MAC address may be one or more IP
addresses. There is no relationship between an IP address and a MAC address; all such assignments are
arbitrary or discretionary in nature. At the most basic level, all network communications take place using MAC
addressing. Since MAC addresses must be globally unique and generally remain fixed for any particular
interface, the assignment of an IP address makes sense from a network management perspective. More than one IP
address can be assigned per MAC address. One address must be the primary IP address &smbmdash; this is the
address that will be returned in the Address Resolution Protocol (ARP) reply.
</para>

<para>
<indexterm><primary>machine name</primary></indexterm>
When a user or a process wants to communicate with another machine, 
the protocol implementation ensures that the <quote>machine name</quote> or <quote>host 
name</quote> is resolved to an IP address in a manner that is controlled 
by the TCP/IP configuration control files. The file 
<filename>/etc/hosts</filename> is one such file.
</para>

<para>
<indexterm><primary>ARP/RARP</primary></indexterm>
When the IP address of the destination interface has been determined, a protocol called ARP/RARP is used to
identify the MAC address of the target interface. ARP is a broadcast-oriented method that uses User Datagram
Protocol (UDP) to send a request to all interfaces on the local network segment using the all 1s MAC address.
Network interfaces are programmed to respond to two MAC addresses only; their own unique address and the
address ff:ff:ff:ff:ff:ff. The reply packet from an ARP request will contain the MAC address and the primary
IP address for each interface.
</para>

<para>
<indexterm><primary>/etc/hosts</primary></indexterm>
The <filename>/etc/hosts</filename> file is foundational to all 
UNIX/Linux TCP/IP installations and as a minimum will contain 
the localhost and local network interface IP addresses and the 
primary names by which they are known within the local machine. 
This file helps to prime the pump so a basic level of name 
resolution can exist before any other method of name resolution 
becomes available.
</para>

</sect2>


<sect2>
<title><filename>/etc/resolv.conf</filename></title>

<para>
This file tells the name resolution libraries:
</para>

<itemizedlist>
	<listitem><para>The name of the domain to which the machine 
	belongs.
	</para></listitem>
	
	<listitem><para>The name(s) of any domains that should be 
	automatically searched when trying to resolve unqualified 
	host names to their IP address.
	</para></listitem>
	
	<listitem><para>The name or IP address of available domain 
	name servers that may be asked to perform name-to-address 
	translation lookups.
	</para></listitem>
</itemizedlist>

</sect2>


<sect2>
<title><filename>/etc/host.conf</filename></title>


<para>
<indexterm><primary>/etc/host.conf</primary></indexterm>
<filename>/etc/host.conf</filename> is the primary means by which the setting in
<filename>/etc/resolv.conf</filename> may be effected. It is a critical configuration file. This file controls
the order by which name resolution may proceed. The typical structure is:
<programlisting>
order hosts,bind
multi on
</programlisting></para>

<para>Both addresses should be returned. Please refer to the 
man page for <filename>host.conf</filename> for further details.
</para>

</sect2>


<sect2>
<title><filename>/etc/nsswitch.conf</filename></title>

<para>
<indexterm><primary>/etc/nsswitch.conf</primary></indexterm>
This file controls the actual name resolution targets. The 
file typically has resolver object specifications as follows:
<programlisting>
# /etc/nsswitch.conf
#
# Name Service Switch configuration file.
#

passwd:		compat
# Alternative entries for password authentication are:
# passwd:	compat files nis ldap winbind
shadow:		compat
group:		compat

hosts:		files nis dns
# Alternative entries for host name resolution are:
# hosts:	files dns nis nis+ hesiod db compat ldap wins
networks:	nis files dns

ethers:		nis files
protocols:	nis files
rpc:		nis files
services:	nis files
</programlisting></para>

<para>
Of course, each of these mechanisms requires that the appropriate 
facilities and/or services are correctly configured.
</para>

<para>
It should be noted that unless a network request/message must be 
sent, TCP/IP networks are silent. All TCP/IP communications assume a 
principal of speaking only when necessary.
</para>


<para>
<indexterm><primary>libnss_wins.so</primary></indexterm>
<indexterm><primary>NetBIOS names</primary></indexterm>
<indexterm><primary>make</primary></indexterm>
<indexterm><primary>/etc/nsswitch.conf</primary></indexterm>
<indexterm><primary>wins</primary></indexterm>
Starting with version 2.2.0, Samba has Linux support for extensions to 
the name service switch infrastructure so Linux clients will 
be able to obtain resolution of MS Windows NetBIOS names to IP 
addresses. To gain this functionality, Samba needs to be compiled 
with appropriate arguments to the make command (i.e., <userinput>make 
nsswitch/libnss_wins.so</userinput>). The resulting library should 
then be installed in the <filename>/lib</filename> directory, and 
the <parameter>wins</parameter> parameter needs to be added to the <quote>hosts:</quote> line in 
the <filename>/etc/nsswitch.conf</filename> file. At this point, it 
will be possible to ping any MS Windows machine by its NetBIOS 
machine name, as long as that machine is within the workgroup to 
which both the Samba machine and the MS Windows machine belong.
</para>

</sect2>
</sect1>


<sect1>
<title>Name Resolution as Used within MS Windows Networking</title>

<para>
<indexterm><primary>computer name</primary></indexterm>
<indexterm><primary>machine name</primary></indexterm>
<indexterm><primary>NetBIOS name</primary></indexterm>
<indexterm><primary>SMB name</primary></indexterm>
MS Windows networking is predicated on the name each machine is given. This name is known variously (and
inconsistently) as the <quote>computer name,</quote> <quote>machine name,</quote> <quote>networking
name,</quote> <quote>NetBIOS name,</quote> or <quote>SMB name.</quote> All terms mean the same thing with the
exception of <quote>NetBIOS name,</quote> which can also apply to the name of the workgroup or the domain
name. The terms <quote>workgroup</quote> and <quote>domain</quote> are really just a simple name with which
the machine is associated. All NetBIOS names are exactly 16 characters in length. The
16<superscript>th</superscript> character is reserved.  It is used to store a 1-byte value that indicates
service level information for the NetBIOS name that is registered. A NetBIOS machine name is therefore
registered for each service type that is provided by the client/server.
</para>

<para>
<link linkend="uniqnetbiosnames">Unique NetBIOS names</link> and <link linkend="netbiosnamesgrp">group names</link> tables 
list typical NetBIOS name/service type registrations.
</para>

<table frame="all" id="uniqnetbiosnames">
<title>Unique NetBIOS Names</title>
<tgroup cols="2">
<colspec align="left"/>
<colspec align="justify"/>
<tbody>
<row><entry>MACHINENAME&lt;00&gt;</entry><entry>Server Service is running on MACHINENAME</entry></row>
<row><entry>MACHINENAME&lt;03&gt;</entry><entry>Generic machine name (NetBIOS name)</entry></row>
<row><entry>MACHINENAME&lt;20&gt;</entry><entry>LanMan server service is running on MACHINENAME</entry></row>
<row><entry>WORKGROUP&lt;1b&gt;</entry><entry>Domain master browser</entry></row>
</tbody>
</tgroup>
</table>

<table frame="all" id="netbiosnamesgrp">
<title>Group Names</title>
<tgroup cols="2">
<colspec align="left"/>
<colspec align="justify"/>
<tbody>
<row><entry>WORKGROUP&lt;03&gt;</entry><entry>Generic name registered by all members of WORKGROUP</entry></row>
<row><entry>WORKGROUP&lt;1c&gt;</entry><entry>Domain cntrollers/netlogon servers</entry></row>
<row><entry>WORKGROUP&lt;1d&gt;</entry><entry>Local master browsers</entry></row>
<row><entry>WORKGROUP&lt;1e&gt;</entry><entry>Browser election service</entry></row>
</tbody>
</tgroup>
</table>

<para>
<indexterm><primary>NetBIOS</primary></indexterm>
It should be noted that all NetBIOS machines register their own 
names as per <link linkend="uniqnetbiosnames">Unique NetBIOS names</link> and <link
linkend="netbiosnamesgrp">group names</link>. This is in vast contrast to TCP/IP 
installations where the system administrator traditionally 
determines in the <filename>/etc/hosts</filename> or in the DNS database what names 
are associated with each IP address.
</para>

<para>
<indexterm><primary>NetBIOS</primary></indexterm>
<indexterm><primary>/etc/hosts</primary></indexterm>
<indexterm><primary>NetBIOS name</primary></indexterm>
One further point of clarification should be noted. The <filename>/etc/hosts</filename> 
file and the DNS records do not provide the NetBIOS name information 
that MS Windows clients depend on to locate the type of service that may 
be needed. An example of this is what happens when an MS Windows client 
wants to locate a domain logon server. It finds this service and the IP 
address of a server that provides it by performing a lookup (via a 
NetBIOS broadcast) for enumeration of all machines that have 
registered the name type *&lt;1C&gt;. A logon request is then sent to each 
IP address that is returned in the enumerated list of IP addresses.
Whichever machine first replies, it then ends up providing the logon services.
</para>

<para>
<indexterm><primary>domain</primary></indexterm>
<indexterm><primary>workgroup</primary></indexterm>
The name <quote>workgroup</quote> or <quote>domain</quote> really can be confusing, since these 
have the added significance of indicating what is the security 
architecture of the MS Windows network. The term <quote>workgroup</quote> indicates 
that the primary nature of the network environment is that of a 
peer-to-peer design. In a workgroup, all machines are responsible for 
their own security, and generally such security is limited to the use of 
just a password (known as share-level security). In most situations 
with peer-to-peer networking, the users who control their own machines 
will simply opt to have no security at all. It is possible to have 
user-level security in a workgroup environment, thus requiring the use 
of a username and a matching password.
</para>

<para>
<indexterm><primary>SMB</primary></indexterm>
<indexterm><primary>Network Basic Input/Output System</primary><see>NetBIOS</see></indexterm>
<indexterm><primary>Logical Link Control</primary><see>LLC</see></indexterm>
<indexterm><primary>Network Basic Extended User Interface</primary><see>NetBEUI</see></indexterm>
<indexterm><primary>Internetworking Packet Exchange</primary><see>IPX</see></indexterm>
<indexterm><primary>NetWare</primary></indexterm>
<indexterm><primary>NetBT</primary></indexterm>
<indexterm><primary>NBT</primary></indexterm>
MS Windows networking is thus predetermined to use machine names 
for all local and remote machine message passing. The protocol used is 
called Server Message Block (SMB), and this is implemented using 
the NetBIOS protocol (Network Basic Input/Output System). NetBIOS can 
be encapsulated using LLC (Logical Link Control) protocol &smbmdash; in which case 
the resulting protocol is called NetBEUI (Network Basic Extended User 
Interface). NetBIOS can also be run over IPX (Internetworking Packet 
Exchange) protocol as used by Novell NetWare, and it can be run 
over TCP/IP protocols &smbmdash; in which case the resulting protocol is called 
NBT or NetBT, the NetBIOS over TCP/IP.
</para>

<para>
MS Windows machines use a complex array of name resolution mechanisms. 
Since we are primarily concerned with TCP/IP, this demonstration is 
limited to this area.
</para>

<sect2>
<title>The NetBIOS Name Cache</title>

<para>
<indexterm><primary>n-memory buffer</primary></indexterm>
<indexterm><primary>local cache</primary></indexterm>
<indexterm><primary></primary></indexterm>
All MS Windows machines employ an in-memory buffer in which is 
stored the NetBIOS names and IP addresses for all external 
machines that machine has communicated with over the 
past 10 to 15 minutes. It is more efficient to obtain an IP address 
for a machine from the local cache than it is to go through all the 
configured name resolution mechanisms.
</para>

<para>
<indexterm><primary>name lookup</primary></indexterm>
If a machine whose name is in the local name cache is shut 
down before the name is expired and flushed from the cache, then 
an attempt to exchange a message with that machine will be subject 
to timeout delays. Its name is in the cache, so a name resolution 
lookup will succeed, but the machine cannot respond. This can be 
frustrating for users but is a characteristic of the protocol.
</para>

<para>
<indexterm><primary>nbtstat</primary></indexterm>
<indexterm><primary>nmblookup</primary></indexterm>
<indexterm><primary>NetBIOS</primary></indexterm>
The MS Windows utility that allows examination of the NetBIOS 
name cache is called <quote>nbtstat.</quote> The Samba equivalent
is called <command>nmblookup</command>.
</para>

</sect2>

<sect2>
<title>The LMHOSTS File</title>

<para>
<indexterm><primary>LMHOSTS</primary></indexterm>
This file is usually located in MS Windows NT 4.0 or Windows 200x/XP in the directory
<filename>%SystemRoot%\SYSTEM32\DRIVERS\ETC</filename> and contains the IP address
and the machine name in matched pairs. The <filename>LMHOSTS</filename> file
performs NetBIOS name to IP address mapping.
</para>

<para>
It typically looks like this:
</para>

<para><programlisting>
# Copyright (c) 1998 Microsoft Corp.
#
# This is a sample LMHOSTS file used by the Microsoft Wins Client (NetBIOS
# over TCP/IP) stack for Windows98
#
# This file contains the mappings of IP addresses to NT computer names
# (NetBIOS) names. Each entry should be kept on an individual line.
# The IP address should be placed in the first column followed by the
# corresponding computer name. The address and the computer name
# should be separated by at least one space or tab. The "#" character
# is generally used to denote the start of a comment (see the exceptions
# below).
#
# This file is compatible with Microsoft LAN Manager 2.x TCP/IP lmhosts
# files and offers the following extensions:
#
#      #PRE
#      #DOM:&lt;domain&gt;
#      #INCLUDE &lt;filename&gt;
#      #BEGIN_ALTERNATE
#      #END_ALTERNATE
#      \0xnn (non-printing character support)
#
# Following any entry in the file with the characters "#PRE" will cause
# the entry to be preloaded into the name cache. By default, entries are
# not preloaded, but are parsed only after dynamic name resolution fails.
#
# Following an entry with the "#DOM:&lt;domain&gt;" tag will associate the
# entry with the domain specified by &lt;domain&gt;. This effects how the
# browser and logon services behave in TCP/IP environments. To preload
# the host name associated with #DOM entry, it is necessary to also add a
# #PRE to the line. The &lt;domain&gt; is always pre-loaded although it will not
# be shown when the name cache is viewed.
#
# Specifying "#INCLUDE &lt;filename&gt;" will force the RFC NetBIOS (NBT)
# software to seek the specified &lt;filename&gt; and parse it as if it were
# local. &lt;filename&gt; is generally a UNC-based name, allowing a
# centralized lmhosts file to be maintained on a server.
# It is ALWAYS necessary to provide a mapping for the IP address of the
# server prior to the #INCLUDE. This mapping must use the #PRE directive.
# In addition the share "public" in the example below must be in the
# LanMan Server list of "NullSessionShares" in order for client machines to
# be able to read the lmhosts file successfully. This key is under
# \machine\system\currentcontrolset\services\lanmanserver\
# parameters\nullsessionshares
# in the registry. Simply add "public" to the list found there.
#
# The #BEGIN_ and #END_ALTERNATE keywords allow multiple #INCLUDE
# statements to be grouped together. Any single successful include
# will cause the group to succeed.
#
# Finally, non-printing characters can be embedded in mappings by
# first surrounding the NetBIOS name in quotations, then using the
# \0xnn notation to specify a hex value for a non-printing character.
#
# The following example illustrates all of these extensions:
#
# 102.54.94.97     rhino     #PRE #DOM:networking  #net group's DC
# 102.54.94.102    "appname  \0x14"       #special app server
# 102.54.94.123    popular   #PRE         #source server
# 102.54.94.117    localsrv  #PRE         #needed for the include
#
# #BEGIN_ALTERNATE
# #INCLUDE \\localsrv\public\lmhosts
# #INCLUDE \\rhino\public\lmhosts
# #END_ALTERNATE
#
# In the above example, the "appname" server contains a special
# character in its name, the "popular" and "localsrv" server names are
# pre-loaded, and the "rhino" server name is specified so it can be used
# to later #INCLUDE a centrally maintained lmhosts file if the "localsrv"
# system is unavailable.
#
# Note that the whole file is parsed including comments on each lookup,
# so keeping the number of comments to a minimum will improve performance.
# Therefore it is not advisable to simply add lmhosts file entries onto the
# end of this file.
</programlisting></para>

</sect2>

<sect2>
<title>HOSTS File</title>

<para>
This file is usually located in MS Windows NT 4.0 or Windows 200x/XP in 
the directory <filename>%SystemRoot%\SYSTEM32\DRIVERS\ETC</filename> and contains 
the IP address and the IP hostname in matched pairs. It can be 
used by the name resolution infrastructure in MS Windows, depending 
on how the TCP/IP environment is configured. This file is in 
every way the equivalent of the UNIX/Linux <filename>/etc/hosts</filename> file.
</para>
</sect2>


<sect2>
<title>DNS Lookup</title>


<para>
<indexterm><primary>DNS</primary></indexterm>
This capability is configured in the TCP/IP setup area in the network 
configuration facility. If enabled, an elaborate name resolution sequence 
is followed, the precise nature of which is dependent on how the NetBIOS 
Node Type parameter is configured. A Node Type of 0 means that
NetBIOS broadcast (over UDP broadcast) is used if the name 
that is the subject of a name lookup is not found in the NetBIOS name 
cache. If that fails, then DNS, HOSTS, and LMHOSTS are checked. If set to 
Node Type 8, then a NetBIOS Unicast (over UDP Unicast) is sent to the 
WINS server to obtain a lookup before DNS, HOSTS, LMHOSTS, or broadcast 
lookup is used.
</para>

</sect2>

<sect2>
<title>WINS Lookup</title>


<para>
<indexterm><primary>WINS</primary></indexterm>
<indexterm><primary>Windows Internet Name Server</primary><see>WINS</see></indexterm>
<indexterm><primary>NetBIOS Name Server</primary><see>NBNS</see></indexterm>
A WINS (Windows Internet Name Server) service is the equivalent of the 
rfc1001/1002 specified NBNS (NetBIOS Name Server). A WINS server stores 
the names and IP addresses that are registered by a Windows client 
if the TCP/IP setup has been given at least one WINS server IP address.
</para>

<para>
To configure Samba to be a WINS server, the following parameter needs 
to be added to the &smb.conf; file:
</para>

<para><smbconfblock>
<smbconfoption name="wins support">Yes</smbconfoption>
</smbconfblock></para>

<para>
<indexterm><primary>WINS</primary></indexterm>
To configure Samba to use a WINS server, the following parameters are 
needed in the &smb.conf; file:
</para>

<para><smbconfblock>
<smbconfoption name="wins support">No</smbconfoption>
<smbconfoption name="wins server">xxx.xxx.xxx.xxx</smbconfoption>
</smbconfblock></para>

<para>
where <replaceable>xxx.xxx.xxx.xxx</replaceable> is the IP address 
of the WINS server.
</para>

<para>For information about setting up Samba as a WINS server, read 
<link linkend="NetworkBrowsing">Network Browsing</link>.</para>

</sect2>
</sect1>

<sect1>
<title>Common Errors</title>

<para>
TCP/IP network configuration problems find every network administrator sooner or later.
The cause can be anything from keyboard mishaps to forgetfulness to simple mistakes to
carelessness. Of course, no one is ever deliberately careless!
</para>

	<sect2>
		<title>Pinging Works Only One Way</title>

	<para>
	<quote>I can ping my Samba server from Windows, but I cannot ping my Windows
	machine from the Samba server.</quote>
	</para>

	<para>
	The Windows machine was at IP address 192.168.1.2 with netmask 255.255.255.0, the
	Samba server (Linux) was at IP address 192.168.1.130 with netmask 255.255.255.128.
	The machines were on a local network with no external connections.
	</para>

	<para>
	Due to inconsistent netmasks, the Windows machine was on network 192.168.1.0/24, while
	the Samba server was on network 192.168.1.128/25 &smbmdash; logically a different network.
	</para>

	</sect2>

	<sect2>
	<title>Very Slow Network Connections</title>

	<para>
	A common cause of slow network response includes:
	</para>

	<itemizedlist>
		<listitem><para>Client is configured to use DNS and the DNS server is down.</para></listitem>
		<listitem><para>Client is configured to use remote DNS server, but the
		remote connection is down.</para></listitem>
		<listitem><para>Client is configured to use a WINS server, but there is no WINS server.</para></listitem>
		<listitem><para>Client is not configured to use a WINS server, but there is a WINS server.</para></listitem>
		<listitem><para>Firewall is filtering out DNS or WINS traffic.</para></listitem>
	</itemizedlist>

	</sect2>

	<sect2>
	<title>Samba Server Name-Change Problem</title>

	<para>
	<quote>The name of the Samba server was changed, Samba was restarted, and now the Samba server cannot be
	pinged by its new name from an MS Windows NT4 workstation, but it does still respond to pinging using
	the old name. Why?</quote>
	</para>

	<para>
	From this description, three things are obvious:
	</para>

	<itemizedlist>
		<listitem><para>WINS is not in use; only broadcast-based name resolution is used.</para></listitem>
		<listitem><para>The Samba server was renamed and restarted within the last 10 or 15 minutes.</para></listitem>
		<listitem><para>The old Samba server name is still in the NetBIOS name cache on the MS Windows NT4 workstation.</para></listitem>
	</itemizedlist>

	<para>
	To find what names are present in the NetBIOS name cache on the MS Windows NT4 machine,
	open a <command>cmd</command> shell and then:
	</para>

	<para>
<screen>
&dosprompt;<userinput>nbtstat -n</userinput>

              NetBIOS Local Name Table

   Name                 Type          Status
------------------------------------------------
&example.workstation.windows;            &lt;03&gt;  UNIQUE      Registered
ADMINISTRATOR     &lt;03&gt;  UNIQUE      Registered
&example.workstation.windows;            &lt;00&gt;  UNIQUE      Registered
SARDON           &lt;00&gt;  GROUP       Registered
&example.workstation.windows;            &lt;20&gt;  UNIQUE      Registered
&example.workstation.windows;            &lt;1F&gt;  UNIQUE      Registered


&dosprompt;nbtstat -c

             NetBIOS Remote Cache Name Table

   Name                 Type       Host Address     Life [sec]
--------------------------------------------------------------
&example.server.samba;	&lt;20&gt;  UNIQUE      192.168.1.1          240

&dosprompt;
</screen>
	</para>

	<para>
	In this example, &example.server.samba; is the Samba server and &example.workstation.windows; is the MS Windows NT4 workstation.
	The first listing shows the contents of the Local Name Table (i.e., identity information on
	the MS Windows workstation), and the second shows the NetBIOS name in the NetBIOS name cache.
	The name cache contains the remote machines known to this workstation.
	</para>

	</sect2>

</sect1>

</chapter>