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Chapter 3. Integrating MS Windows networks with Samba

3.1. Agenda

To identify the key functional mechanisms of MS Windows networking +to enable the deployment of Samba as a means of extending and/or +replacing MS Windows NT/2000 technology.

We will examine:

Name resolution in a pure Unix/Linux TCP/IP + environment +
Name resolution as used within MS Windows + networking +
How browsing functions and how to deploy stable + and dependable browsing using Samba +
MS Windows security options and how to + configure Samba for seemless integration +
Configuration of Samba as:

3.2. Name Resolution in a pure Unix/Linux world

The key configuration files covered in this section are:

/etc/hosts
/etc/resolv.conf
/etc/host.conf
/etc/nsswitch.conf

3.2.1. `/etc/hosts`

Contains a static list of IP Addresses and names. +eg:

	127.0.0.1	localhost localhost.localdomain
+	192.168.1.1	bigbox.caldera.com	bigbox	alias4box

The purpose of /etc/hosts is to provide a +name resolution mechanism so that uses do not need to remember +IP addresses.

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

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

Every network interfrace 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 arbitary 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.

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 +/etc/hosts is one such file.

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.

The /etc/hosts file is foundational to all +Unix/Linux TCP/IP installations and as a minumum 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.

3.2.2. `/etc/resolv.conf`

This file tells the name resolution libraries:

The name of the domain to which the machine + belongs +
The name(s) of any domains that should be + automatically searched when trying to resolve unqualified + host names to their IP address +
The name or IP address of available Domain + Name Servers that may be asked to perform name to address + translation lookups +

3.2.3. `/etc/host.conf`

/etc/host.conf 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 procede. The typical structure is:

	order hosts,bind
+	multi on

then both addresses should be returned. Please refer to the +man page for host.conf for further details.

3.2.4. `/etc/nsswitch.conf`

This file controls the actual name resolution targets. The +file typically has resolver object specifications as follows:

	# /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+ hesoid db compat ldap wins
+	networks:	nis files dns
+
+	ethers:		nis files
+	protocols:	nis files
+	rpc:		nis files
+	services:	nis files

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

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.

Samba version 2.2.0 will add 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 (ie: make +nsswitch/libnss_wins.so). The resulting library should +then be installed in the /lib directory and +the "wins" parameter needs to be added to the "hosts:" line in +the /etc/nsswitch.conf file. At this point it +will be possible to ping any MS Windows machine by it's NetBIOS +machine name, so long as that machine is within the workgroup to +which both the samba machine and the MS Windows machine belong.

3.3. Name resolution as used within MS Windows networking

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", +"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 +simply 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.

The following are typical NetBIOS name/service type registrations:

	Unique NetBIOS Names:
+		MACHINENAME<00>	= Server Service is running on MACHINENAME
+		MACHINENAME<03> = Generic Machine Name (NetBIOS name)
+		MACHINENAME<20> = LanMan Server service is running on MACHINENAME
+		WORKGROUP<1b> = Domain Master Browser
+
+	Group Names:
+		WORKGROUP<03> = Generic Name registered by all members of WORKGROUP
+		WORKGROUP<1c> = Domain Controllers / Netlogon Servers
+		WORKGROUP<1d> = Local Master Browsers
+		WORKGROUP<1e> = Internet Name Resolvers

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.

One further point of clarification should be noted, the /etc/hosts +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 find 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. Which +ever machine first replies then ends up providing the logon services.

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.

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.

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.

3.3.1. The NetBIOS Name Cache

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.

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.

The MS Windows utility that allows examination of the NetBIOS +name cache is called "nbtstat". The Samba equivalent of this +is called "nmblookup".

3.3.2. The LMHOSTS file

This file is usually located in MS Windows NT 4.0 or +2000 in C:\WINNT\SYSTEM32\DRIVERS\ETC and contains +the IP Address and the machine name in matched pairs. The +LMHOSTS file performs NetBIOS name +to IP address mapping oriented.

It typically looks like:

	# 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 comptername
+	# 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 addtion 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.

3.3.3. HOSTS file

This file is usually located in MS Windows NT 4.0 or 2000 in +C:\WINNT\SYSTEM32\DRIVERS\ETC 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 /etc/hosts file.

3.3.4. DNS Lookup

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 isdependant on what the NetBIOS +Node Type parameter is configured to. A Node Type of 0 means use +NetBIOS broadcast (over UDP broadcast) is first 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.

3.3.5. WINS Lookup

A WINS (Windows Internet Name Server) service is the equivaent 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.

To configure Samba to be a WINS server the following parameter needs +to be added to the smb.conf file:

	wins support = Yes

To configure Samba to use a WINS server the following parameters are +needed in the smb.conf file:

	wins support = No
+	wins server = xxx.xxx.xxx.xxx

where xxx.xxx.xxx.xxx is the IP address +of the WINS server.

3.4. How browsing functions and how to deploy stable and +dependable browsing using Samba

As stated above, MS Windows machines register their NetBIOS names +(i.e.: the machine name for each service type in operation) on start +up. Also, as stated above, the exact method by which this name registration +takes place is determined by whether or not the MS Windows client/server +has been given a WINS server address, whether or not LMHOSTS lookup +is enabled, or if DNS for NetBIOS name resolution is enabled, etc.

In the case where there is no WINS server all name registrations as +well as name lookups are done by UDP broadcast. This isolates name +resolution to the local subnet, unless LMHOSTS is used to list all +names and IP addresses. In such situations Samba provides a means by +which the samba server name may be forcibly injected into the browse +list of a remote MS Windows network (using the "remote announce" parameter).

Where a WINS server is used, the MS Windows client will use UDP +unicast to register with the WINS server. Such packets can be routed +and thus WINS allows name resolution to function across routed networks.

During the startup process an election will take place to create a +local master browser if one does not already exist. On each NetBIOS network +one machine will be elected to function as the domain master browser. This +domain browsing has nothing to do with MS security domain control. +Instead, the domain master browser serves the role of contacting each local +master browser (found by asking WINS or from LMHOSTS) and exchanging browse +list contents. This way every master browser will eventually obtain a complete +list of all machines that are on the network. Every 11-15 minutes an election +is held to determine which machine will be the master browser. By the nature of +the election criteria used, the machine with the highest uptime, or the +most senior protocol version, or other criteria, will win the election +as domain master browser.

Clients wishing to browse the network make use of this list, but also depend +on the availability of correct name resolution to the respective IP +address/addresses.

Any configuration that breaks name resolution and/or browsing intrinsics +will annoy users because they will have to put up with protracted +inability to use the network services.

Samba supports a feature that allows forced synchonisation +of browse lists across routed networks using the "remote +browse sync" parameter in the smb.conf file. This causes Samba +to contact the local master browser on a remote network and +to request browse list synchronisation. This effectively bridges +two networks that are separated by routers. The two remote +networks may use either broadcast based name resolution or WINS +based name resolution, but it should be noted that the "remote +browse sync" parameter provides browse list synchronisation - and +that is distinct from name to address resolution, in other +words, for cross subnet browsing to function correctly it is +essential that a name to address resolution mechanism be provided. +This mechanism could be via DNS, /etc/hosts, +and so on.

3.5. MS Windows security options and how to configure +Samba for seemless integration

MS Windows clients may use encrypted passwords as part of a +challenege/response authentication model (a.k.a. NTLMv1) or +alone, or clear text strings for simple password based +authentication. It should be realized that with the SMB +protocol the password is passed over the network either +in plain text or encrypted, but not both in the same +authentication requets.

When encrypted passwords are used a password that has been +entered by the user is encrypted in two ways:

An MD4 hash of the UNICODE of the password + string. This is known as the NT hash. +
The password is converted to upper case, + and then padded or trucated to 14 bytes. This string is + then appended with 5 bytes of NULL characters and split to + form two 56 bit DES keys to encrypt a "magic" 8 byte value. + The resulting 16 bytes for the LanMan hash. +

You should refer to the Password Encryption chapter in this HOWTO collection +for more details on the inner workings

MS Windows 95 pre-service pack 1, MS Windows NT versions 3.x +and version 4.0 pre-service pack 3 will use either mode of +password authentication. All versions of MS Windows that follow +these versions no longer support plain text passwords by default.

MS Windows clients have a habit of dropping network mappings that +have been idle for 10 minutes or longer. When the user attempts to +use the mapped drive connection that has been dropped, the client +re-establishes the connection using +a cached copy of the password.

When Microsoft changed the default password mode, they dropped support for +caching of the plain text password. This means that when the registry +parameter is changed to re-enable use of plain text passwords it appears to +work, but when a dropped mapping attempts to revalidate it will fail if +the remote authentication server does not support encrypted passwords. +This means that it is definitely not a good idea to re-enable plain text +password support in such clients.

The following parameters can be used to work around the +issue of Windows 9x client upper casing usernames and +password before transmitting them to the SMB server +when using clear text authentication.

	passsword level = integer
+	username level = integer

By default Samba will lower case the username before attempting +to lookup the user in the database of local system accounts. +Because UNIX usernames conventionally only contain lower case +character, the username level parameter +is rarely even needed.

However, password on UNIX systems often make use of mixed case +characters. This means that in order for a user on a Windows 9x +client to connect to a Samba server using clear text authentication, +the password level must be set to the maximum +number of upper case letter which could appear +is a password. Note that is the server OS uses the traditional +DES version of crypt(), then a password level +of 8 will result in case insensitive passwords as seen from Windows +users. This will also result in longer login times as Samba +hash to compute the permutations of the password string and +try them one by one until a match is located (or all combinations fail).

The best option to adopt is to enable support for encrypted passwords +where ever Samba is used. There are three configuration possibilities +for support of encrypted passwords:

3.5.1. Use MS Windows NT as an authentication server

This method involves the additions of the following parameters +in the smb.conf file:

	encrypt passwords = Yes
+	security = server
+	password server = "NetBIOS_name_of_PDC"

There are two ways of identifying whether or not a username and +password pair was valid or not. One uses the reply information provided +as part of the authentication messaging process, the other uses +just and error code.

The down-side of this mode of configuration is the fact that +for security reasons Samba will send the password server a bogus +username and a bogus password and if the remote server fails to +reject the username and password pair then an alternative mode +of identification of validation is used. Where a site uses password +lock out after a certain number of failed authentication attempts +this will result in user lockouts.

Use of this mode of authentication does require there to be +a standard Unix account for the user, this account can be blocked +to prevent logons by other than MS Windows clients.

3.5.2. Make Samba a member of an MS Windows NT security domain

This method involves additon of the following paramters in the smb.conf file:

	encrypt passwords = Yes
+	security = domain
+	workgroup = "name of NT domain"
+	password server = *

The use of the "*" argument to "password server" will cause samba +to locate the domain controller in a way analogous to the way +this is done within MS Windows NT.

In order for this method to work the Samba server needs to join the +MS Windows NT security domain. This is done as follows:

On the MS Windows NT domain controller using + the Server Manager add a machine account for the Samba server. +
Next, on the Linux system execute: + smbpasswd -r PDC_NAME -j DOMAIN_NAME +

Use of this mode of authentication does require there to be +a standard Unix account for the user in order to assign +a uid once the account has been authenticated by the remote +Windows DC. This account can be blocked to prevent logons by +other than MS Windows clients by things such as setting an invalid +shell in the /etc/passwd entry.

An alternative to assigning UIDs to Windows users on a +Samba member server is presented in the Winbind Overview chapter in +this HOWTO collection.

3.5.3. Configure Samba as an authentication server

This mode of authentication demands that there be on the +Unix/Linux system both a Unix style account as well as an +smbpasswd entry for the user. The Unix system account can be +locked if required as only the encrypted password will be +used for SMB client authentication.

This method involves addition of the following parameters to +the smb.conf file:

## please refer to the Samba PDC HOWTO chapter later in 
+## this collection for more details
+[global]
+	encrypt passwords = Yes
+	security = user
+	domain logons = Yes
+	; an OS level of 33 or more is recommended
+	os level = 33
+
+[NETLOGON]
+	path = /somewhare/in/file/system
+	read only = yes

in order for this method to work a Unix system account needs +to be created for each user, as well as for each MS Windows NT/2000 +machine. The following structure is required.

3.5.3.1. Users

A user account that may provide a home directory should be +created. The following Linux system commands are typical of +the procedure for creating an account.

	# useradd -s /bin/bash -d /home/"userid" -m "userid"
+	# passwd "userid"
+	  Enter Password: <pw>
+	  
+	# smbpasswd -a "userid"
+	  Enter Password: <pw>

3.5.3.2. MS Windows NT Machine Accounts

These are required only when Samba is used as a domain +controller. Refer to the Samba-PDC-HOWTO for more details.

	# useradd -s /bin/false -d /dev/null "machine_name"\$
+	# passwd -l "machine_name"\$
+	# smbpasswd -a -m "machine_name"

3.6. Conclusions

Samba provides a flexible means to operate as...

A Stand-alone server - No special action is needed + other than to create user accounts. Stand-alone servers do NOT + provide network logon services, meaning that machines that use this + server do NOT perform a domain logon but instead make use only of + the MS Windows logon which is local to the MS Windows + workstation/server. +
An MS Windows NT 3.x/4.0 security domain member. +
An alternative to an MS Windows NT 3.x/4.0 + Domain Controller. +

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