Chapter 26. Integrating MS Windows networks with Samba

Chapter 26. Integrating MS Windows networks with Samba
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John H. Terpstra

Samba Team

<jht@samba.org>

(Jan 01 2001)

Table of Contents

Features and Benefits

Background Information

Name Resolution in a pure UNIX/Linux world

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

Name resolution as used within MS Windows networking

The NetBIOS Name Cache
The LMHOSTS file
HOSTS file
DNS Lookup
WINS Lookup

Common Errors

Pinging works only in one way
Very Slow Network Connections
Samba server name change problem

+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. +

Note

+ 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. +

Features and Benefits

+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). +

+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. +

Background Information

+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. +

Note

+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). +

+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 + +Dynamic DNS with Service Resource Records (SRV RR) and with Incremental Zone Transfers (IXFR). + +Use of DHCP with ADS is recommended as a further means of maintaining central control +over client workstation network configuration. +

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

`/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 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. +

+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 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. +

`/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 +

`/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 proceed. 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. +

`/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+ hesiod 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. +

+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.: 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 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. +

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", +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. +

+The following are typical NetBIOS name/service type registrations: +

Table 26.1. 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

Table 26.2. 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 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. +

+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. +

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. +

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. +

+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 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.
+

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. +

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 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. +

WINS Lookup

+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. +

+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. +

For information about setting up Samba as a WINS server, read + the chapter on network browsing.

Common Errors

+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! +

Pinging works only in one way

+ “I can ping my samba server from Windows, but I can + not ping my Windows machine from the samba server.” +

+ 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. +

+ 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. +

Very Slow Network Connections

+ A common causes of slow network response includes: +

Client is configured to use DNS and DNS server is down
Client is configured to use remote DNS server, but remote connection is down
Client is configured to use a WINS server, but there is no WINS server
Client is NOT configured to use a WINS server, but there is a WINS server
Firewall is filtering our DNS or WINS traffic

Samba server name change problem

+ “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?” +

+ From this description three (3) things are rather obvious: +

WINS is NOT in use, only broadcast based name resolution is used
The samba server was renamed and restarted within the last 10-15 minutes
The old samba server name is still in the NetBIOS name cache on the MS Windows NT4 Workstation

+ To find what names are present in the NetBIOS name cache on the MS Windows NT4 machine, + open a cmd shell, then: +

+C:\> nbtstat -n
+
+              NetBIOS Local Name Table
+
+   Name                 Type          Status
+------------------------------------------------
+FRODO            <03>  UNIQUE      Registered
+ADMINSTRATOR     <03>  UNIQUE      Registered
+FRODO            <00>  UNIQUE      Registered
+SARDON           <00>  GROUP       Registered
+FRODO            <20>  UNIQUE      Registered
+FRODO            <1F>  UNIQUE      Registered
+
+
+C:\> nbtstat -c
+
+             NetBIOS Remote Cache Name Table
+
+   Name                 Type       Host Address     Life [sec]
+--------------------------------------------------------------
+GANDALF	<20>  UNIQUE      192.168.1.1          240
+
+C:\> 
+

+ In the above example, GANDALF is the Samba server and FRODO 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. +

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