Integrating-with-Windows.xml [plain text]
<chapter id="integrate-ms-networks">
<chapterinfo>
&author.jht;
<pubdate> (Jan 01 2001) </pubdate>
</chapterinfo>
<title>Integrating MS Windows networks with Samba</title>
<indexterm><primary>NetBIOS</primary></indexterm>
<para>
This section 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 use of
NetBIOS over TCP/IP then this section may help you to resolve networking problems.
</para>
<note>
<para>
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 - the existence of such a protocol is a complete
and utter mis-apprehension.
</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
it's IP address for each operating system environment.
</para>
</sect1>
<sect1>
<title>Background Information</title>
<para>
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 TCP port 445 will be
used and UDP port 137 and TCP port 139 will 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>
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 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>
<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>
Contains a static list of IP addresses and names.
eg:
</para>
<para><programlisting>
127.0.0.1 localhost localhost.localdomain
192.168.1.1 bigbox.caldera.com bigbox alias4box
</programlisting></para>
<para>
The purpose of <filename>/etc/hosts</filename> is to provide a
name resolution mechanism so that uses do not need to remember
IP addresses.
</para>
<para>
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 (4) decimal
numbers that are separated by a dot (or period). eg: 168.192.1.1.
</para>
<indexterm><primary>MAC Addresses</primary></indexterm>
<para>
MAC Addresses use 48 bits (or 6 bytes) and are typically represented
as two digit hexadecimal numbers separated by colons. eg:
40:8e:0a:12:34:56
</para>
<para>
Every network interface must have an MAC address. Associated with
a MAC address there 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 takes place using MAC addressing. Since MAC
addresses must be globally unique, and generally remains 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,
this is the address that will be returned in the ARP reply.
</para>
<para>
When a user or a process wants to communicate with another machine
the protocol implementation ensures that the "machine name" or "host
name" 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>
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 stands for Address
Resolution Protocol, and is a broadcast oriented method that
uses UDP (User Datagram Protocol) to send a request to all
interfaces on the local network segment using the all 1's 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>
<indexterm><primary>/etc/hosts</primary></indexterm>
<para>
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 that 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>
<indexterm><primary>/etc/host.conf</primary></indexterm>
<para>
<filename>/etc/host.conf</filename> is the primary means by
which the setting in /etc/resolv.conf may be affected. It is a
critical configuration file. This file controls the order by
which name resolution may proceed. The typical structure is:
</para>
<para><programlisting>
order hosts,bind
multi on
</programlisting></para>
<para>
then both addresses should be returned. Please refer to the
man page for host.conf for further details.
</para>
</sect2>
<sect2>
<title><filename>/etc/nsswitch.conf</filename></title>
<indexterm><primary>/etc/nsswitch.conf</primary></indexterm>
<para>
This file controls the actual name resolution targets. The
file typically has resolver object specifications as follows:
</para>
<para><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 assumes a
principal of speaking only when necessary.
</para>
<indexterm><primary>libnss_wins.so</primary></indexterm>
<para>
Starting with version 2.2.0 samba has Linux support for extensions to
the name service switch infrastructure so that 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 "wins" parameter needs to be added to the "hosts:" 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, so 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>
MS Windows networking is predicated about the name each machine
is given. This name is known variously (and inconsistently) as
the "computer name", "machine name", "networking name", "netbios name",
or "SMB name". All terms mean the same thing with the exception of
"netbios name" which can apply also to the name of the workgroup or the
domain name. The terms "workgroup" and "domain" are really just a
simple name with which the machine is associated. All NetBIOS names
are exactly 16 characters in length. The 16th character is reserved.
It is used to store a one 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>
The following are typical NetBIOS name/service type registrations:
</para>
<table frame="all">
<title>Unique NetBIOS names</title>
<tgroup cols="2">
<colspec align="left"/>
<colspec align="justify"/>
<tbody>
<row><entry>MACHINENAME<00></entry><entry>Server Service is running on MACHINENAME</entry></row>
<row><entry>MACHINENAME<03></entry><entry>Generic Machine Name (NetBIOS name)</entry></row>
<row><entry>MACHINENAME<20></entry><entry>LanMan Server service is running on MACHINENAME</entry></row>
<row><entry>WORKGROUP<1b></entry><entry>Domain Master Browser</entry></row>
</tbody>
</tgroup>
</table>
<table frame="all">
<title>Group Names</title>
<tgroup cols="2">
<colspec align="left"/>
<colspec align="justify"/>
<tbody>
<row><entry>WORKGROUP<03></entry><entry>Generic Name registered by all members of WORKGROUP</entry></row>
<row><entry>WORKGROUP<1c></entry><entry>Domain Controllers / Netlogon Servers</entry></row>
<row><entry>WORKGROUP<1d></entry><entry>Local Master Browsers</entry></row>
<row><entry>WORKGROUP<1e></entry><entry>Internet Name Resolvers</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 the above. This is in vast contrast to TCP/IP
installations where traditionally the system administrator will
determine in the /etc/hosts or in the DNS database what names
are associated with each IP address.
</para>
<indexterm><primary>NetBIOS</primary></indexterm>
<para>
One further point of clarification should be noted, the <filename>/etc/hosts</filename>
file and the DNS records do not provide the NetBIOS name type 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 *<1c>. A logon request is then sent to each
IP address that is returned in the enumerated list of IP addresses.
Whichever machine first replies then ends up providing the logon services.
</para>
<para>
The name "workgroup" or "domain" really can be confusing since these
have the added significance of indicating what is the security
architecture of the MS Windows network. The term "workgroup" 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 use of
just a password (known as SHARE MODE 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 MODE security in a WORKGROUP environment, thus requiring use
of a user name and a matching password.
</para>
<para>
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 - 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 - 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>
All MS Windows machines employ an in memory buffer in which is
stored the NetBIOS names and IP addresses for all external
machines that that machine has communicated with over the
past 10-15 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>
If a machine whose name is in the local name cache has been shut
down before the name had been expired and flushed from the cache, then
an attempt to exchange a message with that machine will be subject
to time-out delays. i.e.: Its name is in the cache, so a name resolution
lookup will succeed, but the machine can not respond. This can be
frustrating for users - but it is a characteristic of the protocol.
</para>
<indexterm><primary>nbtstat</primary></indexterm>
<indexterm><primary>nmblookup</primary></indexterm>
<para>
The MS Windows utility that allows examination of the NetBIOS
name cache is called "nbtstat". The Samba equivalent of this
is called <command>nmblookup</command>.
</para>
</sect2>
<sect2>
<title>The LMHOSTS file</title>
<indexterm><primary>LMHOSTS</primary></indexterm>
<para>
This file is usually located in MS Windows NT 4.0 or
2000 in <filename>C:\WINNT\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:
</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 computernames
# (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 computername. The address and the computername
# 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:<domain>
# #INCLUDE <filename>
# #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:<domain>" tag will associate the
# entry with the domain specified by <domain>. This affects 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 <domain> is always preloaded although it will not
# be shown when the name cache is viewed.
#
# Specifying "#INCLUDE <filename>" will force the RFC NetBIOS (NBT)
# software to seek the specified <filename> and parse it as if it were
# local. <filename> 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
# LanManServer 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
# preloaded, 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 2000 in
<filename>C:\WINNT\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>
<indexterm><primary>DNS</primary></indexterm>
<para>
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 dependant 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>
<indexterm><primary>WINS</primary></indexterm>
<para>
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</name><value>Yes</value></smbconfoption>
</smbconfblock></para>
<para>
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</name><value>No</value></smbconfoption>
<smbconfoption><name>wins server</name><value>xxx.xxx.xxx.xxx</value></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">the chapter on 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, forgetfulness, simple mistakes, and
carelessness. Of course, no one is every deliberately careless!
</para>
<sect2>
<title>Pinging works only in one way</title>
<para>
<quote>I can ping my samba server from Windows, but I can
not 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 - logically a different network.
</para>
</sect2>
<sect2>
<title>Very Slow Network Connections</title>
<para>
A common causes of slow network response includes:
</para>
<itemizedlist>
<listitem><para>Client is configured to use DNS and DNS server is down</para></listitem>
<listitem><para>Client is configured to use remote DNS server, but 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 our 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, samba server can not be
pinged by new name from MS Windows NT4 Workstation, but it does still respond to ping using
the old name. Why?</quote>
</para>
<para>
From this description three (3) things are rather 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 10-15 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 cmd shell, then:
</para>
<para>
<screen>
&dosprompt;<userinput>nbtstat -n</userinput>
NetBIOS Local Name Table
Name Type Status
------------------------------------------------
&example.workstation.windows; <03> UNIQUE Registered
ADMINSTRATOR <03> UNIQUE Registered
&example.workstation.windows; <00> UNIQUE Registered
SARDON <00> GROUP Registered
&example.workstation.windows; <20> UNIQUE Registered
&example.workstation.windows; <1F> UNIQUE Registered
&dosprompt;nbtstat -c
NetBIOS Remote Cache Name Table
Name Type Host Address Life [sec]
--------------------------------------------------------------
&example.server.samba; <20> UNIQUE 192.168.1.1 240
&dosprompt;
</screen>
</para>
<para>
In the above 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), 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>