From 99bde6889d3d8b7a9e950c86c30e82662e1dacdd Mon Sep 17 00:00:00 2001
From: Gerald Carter Table of Contents
+ Table of Contents
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
@@ -9,15 +9,15 @@ NetBIOS over TCP/IP then this section may help you to resolve networking problem
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.
-
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
+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.
-
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
@@ -30,17 +30,19 @@ Name Service or WINS), TCP port 139 AND TCP port 445 (for actual file and print
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.
-
The key configuration files covered in this section are:
- /etc/hosts /etc/resolv.conf /etc/host.conf /etc/nsswitch.conf
-Contains a static list of IP Addresses and names.
+ /etc/hosts /etc/resolv.conf /etc/host.conf /etc/nsswitch.conf
+Contains a static list of IP addresses and names.
eg:
-
The purpose of /etc/hosts is to provide a
name resolution mechanism so that uses do not need to remember
@@ -48,10 +50,10 @@ 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
+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
@@ -84,15 +86,15 @@ 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
+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.
-
This file tells the name resolution libraries:
The name of the domain to which the machine
belongs
@@ -102,41 +104,41 @@ This file tells the name resolution libraries:
The name or IP address of available Domain
Name Servers that may be asked to perform name to address
translation lookups
-
/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:
-
then both addresses should be returned. Please refer to the
man page for host.conf for further details.
-
This file controls the actual name resolution targets. The
file typically has resolver object specifications as follows:
-
Of course, each of these mechanisms requires that the appropriate
facilities and/or services are correctly configured.
@@ -144,27 +146,27 @@ 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 (ie: make
+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 it's NetBIOS
+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.
-
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
+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
-simply name with which the machine is associated. All NetBIOS names
+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
@@ -172,25 +174,14 @@ 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 Table 26.2. Group Names
+
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
@@ -199,8 +190,8 @@ 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. Which
-ever machine first replies then ends up providing the logon services.
+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
@@ -228,7 +219,7 @@ 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.
-
+
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
@@ -242,11 +233,11 @@ 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.
-
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
@@ -254,102 +245,103 @@ the IP Address and the machine name in matched pairs. The
to IP address mapping.
It typically looks like:
-
+
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.
-
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 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
+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.
-
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
@@ -357,24 +349,20 @@ 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:
-
+
To configure Samba to use a WINS server the following parameters are
needed in the smb.conf file:
-
+
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.
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!
-
- Well, the real complaint said, "I can ping my samba server from Windows, but I can
- not ping my Windows machine from the samba server."
+
+ “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.
@@ -382,46 +370,46 @@ carelessness. Of course, no one is every deliberately careless!
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.
-
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
- The name of the samba server was changed, samba was restarted, samba server can not be
+ 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
+ “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?
+ 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:\>
+
- In the above example, FRODO is the Samba server and SLACK is the MS Windows NT4 Workstation.
- The first listing shows the contents of the Local Name Table (ie: Identity information on
+ 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.
-
- 127.0.0.1 localhost localhost.localdomain
- 192.168.1.1 bigbox.caldera.com bigbox alias4box
+
+127.0.0.1 localhost localhost.localdomain
+192.168.1.1 bigbox.caldera.com bigbox alias4box
- order hosts,bind
- multi on
+
+order hosts,bind
+multi on
- # /etc/nsswitch.conf
- #
- # Name Service Switch configuration file.
- #
+
+# /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
+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
+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
+ethers: nis files
+protocols: nis files
+rpc: nis files
+services: nis files
- 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
-
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 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
- # 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.
-
+# 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.
+
- wins support = Yes
-
wins support = Yes
- wins support = No
- wins server = xxx.xxx.xxx.xxx
-
wins support = No wins server = xxx.xxx.xxx.xxx
- C:\temp\>nbtstat -n
+
+C:\> nbtstat -n
- NetBIOS Local Name Table
+ NetBIOS Local Name Table
- Name Type Status
- ------------------------------------------------
- SLACK <03> UNIQUE Registered
- ADMINISTRATOR <03> UNIQUE Registered
- SLACK <00> UNIQUE Registered
- SARDON <00> GROUP Registered
- SLACK <20> UNIQUE Registered
- SLACK <1F> UNIQUE Registered
+ 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:\Temp\>nbtstat -c
+C:\> nbtstat -c
- NetBIOS Remote Cache Name Table
+ NetBIOS Remote Cache Name Table
- Name Type Host Address Life [sec]
- --------------------------------------------------------------
- FRODO <20> UNIQUE 192.168.1.1 240
+ Name Type Host Address Life [sec]
+--------------------------------------------------------------
+GANDALF <20> UNIQUE 192.168.1.1 240
- C:\Temp\>
-