Chapter 10. Samba / MS Windows Network Browsing Guide

Chapter 10. Samba / MS Windows Network Browsing Guide
Prev	Part III. Advanced Configuration	Next

John H. Terpstra

Samba Team

<jht@samba.org>

July 5, 1998

Updated: April 21, 2003

-This document contains detailed information as well as a fast track guide to -implementing browsing across subnets and / or across workgroups (or domains). -WINS is the best tool for resolution of NetBIOS names to IP addresses. WINS is -NOT involved in browse list handling except by way of name to address resolution. -

Note

-MS Windows 2000 and later can be configured to operate with NO NetBIOS -over TCP/IP. Samba-3 and later also supports this mode of operation. -When the use of NetBIOS over TCP/IP has been disabled then the primary -means for resolution of MS Windows machine names is via DNS and Active Directory. -The following information assumes that your site is running NetBIOS over TCP/IP. -

Features and Benefits

-Someone once referred to the past in terms of: They were the worst of times, -they were the best of times. The more we look back, them more we long for what was and -hope it never returns!. -

-For many MS Windows network administrators, that statement sums up their feelings about -NetBIOS networking precisely. For those who mastered NetBIOS networking, its fickle -nature was just par for the course. For those who never quite managed to tame its -lusty features, NetBIOS is like Paterson's Curse. -

-For those not familiar with botanical problems in Australia: Paterson's curse, -Echium plantagineum, was introduced to Australia from Europe during the mid-nineteenth -century. Since then it has spread rapidly. The high seed production, with densities of -thousands of seeds per square metre, a seed longevity of more than seven years, and an -ability to germinate at any time of year, given the right conditions, are some of the -features which make it such a persistent weed. -

-In this chapter we explore vital aspects of SMB (Server Message Block) networking with -a particular focus on SMB as implemented through running NetBIOS (Network Basic -Input / Output System) over TCP/IP. Since Samba does NOT implement SMB or NetBIOS over -any other protocols we need to know how to configure our network environment and simply -remember to use nothing but TCP/IP on all our MS Windows network clients. -

-Samba provides the ability to implement a WINS (Windows Internetworking Name Server) -and implements extensions to Microsoft's implementation of WINS. These extensions -help Samba to affect stable WINS operations beyond the normal scope of MS WINS. -

-Please note that WINS is exclusively a service that applies only to those systems -that run NetBIOS over TCP/IP. MS Windows 200x / XP have the capacity to turn off -support for NetBIOS, in which case WINS is of no relevance. Samba-3 supports this also. -

-For those networks on which NetBIOS has been disabled (ie: WINS is NOT required) -the use of DNS is necessary for host name resolution. -

What is Browsing?

-To most people browsing means that they can see the MS Windows and Samba servers -in the Network Neighborhood, and when the computer icon for a particular server is -clicked, it opens up and shows the shares and printers available on the target server. -

-What seems so simple is in fact a very complex interaction of different technologies. -The technologies (or methods) employed in making all of this work includes: -

MS Windows machines register their presence to the network

Machines announce themselves to other machines on the network

One or more machine on the network collates the local announcements

The client machine finds the machine that has the collated list of machines

The client machine is able to resolve the machine names to IP addresses

The client machine is able to connect to a target machine

-The Samba application that controls browse list management and name resolution is -called nmbd. The configuration parameters involved in nmbd's operation are: -

-		
-	Browsing options:
-	-----------------
-		* os level
-		  lm announce
-		  lm interval
-		* preferred master
-		* local master
-		* domain master
-		  browse list
-		  enhanced browsing
-
-	Name Resolution Method:
-	-----------------------
-		* name resolve order
-
-	WINS options:
-	-------------
-		  dns proxy
-		  wins proxy
-		* wins server
-		* wins support
-		  wins hook
-

-For Samba, the WINS Server and WINS Support are mutually exclusive options. Those marked with -an '*' are the only options that commonly MAY need to be modified. Even if not one of these -parameters is set nmbd will still do it's job. -

Discussion

-Firstly, all MS Windows networking uses SMB (Server Message Block) based messaging. -SMB messaging may be implemented with or without NetBIOS. MS Windows 200x supports -NetBIOS over TCP/IP for backwards compatibility. Microsoft is intent on phasing out NetBIOS -support. -

NetBIOS over TCP/IP

-Samba implements NetBIOS, as does MS Windows NT / 200x / XP, by encapsulating it over TCP/IP. -MS Windows products can do likewise. NetBIOS based networking uses broadcast messaging to -affect browse list management. When running NetBIOS over TCP/IP, this uses UDP based messaging. -UDP messages can be broadcast or unicast. -

-Normally, only unicast UDP messaging can be forwarded by routers. The -remote announce parameter to smb.conf helps to project browse announcements -to remote network segments via unicast UDP. Similarly, the -remote browse sync parameter of smb.conf -implements browse list collation using unicast UDP. -

-Secondly, in those networks where Samba is the only SMB server technology, -wherever possible nmbd should be configured on one (1) machine as the WINS -server. This makes it easy to manage the browsing environment. If each network -segment is configured with it's own Samba WINS server, then the only way to -get cross segment browsing to work is by using the -remote announce and the remote browse sync -parameters to your smb.conf file. -

-If only one WINS server is used for an entire multi-segment network then -the use of the remote announce and the -remote browse sync parameters should NOT be necessary. -

-As of Samba 3 WINS replication is being worked on. The bulk of the code has -been committed, but it still needs maturation. This is NOT a supported feature -of the Samba-3.0.0 release. Hopefully, this will become a supported feature -of one of the Samba-3 release series. -

-Right now Samba WINS does not support MS-WINS replication. This means that -when setting up Samba as a WINS server there must only be one nmbd -configured as a WINS server on the network. Some sites have used multiple Samba WINS -servers for redundancy (one server per subnet) and then used -remote browse sync and remote announce -to affect browse list collation across all segments. Note that this means clients -will only resolve local names, and must be configured to use DNS to resolve names -on other subnets in order to resolve the IP addresses of the servers they can see -on other subnets. This setup is not recommended, but is mentioned as a practical -consideration (ie: an 'if all else fails' scenario). -

-Lastly, take note that browse lists are a collection of unreliable broadcast -messages that are repeated at intervals of not more than 15 minutes. This means -that it will take time to establish a browse list and it can take up to 45 -minutes to stabilise, particularly across network segments. -

TCP/IP - without NetBIOS

-All TCP/IP using systems use various forms of host name resolution. The primary -methods for TCP/IP hostname resolutions involves either a static file (/etc/hosts -) or DNS (the Domain Name System). DNS is the technology that makes -the Internet usable. DNS based host name resolution is supported by nearly all TCP/IP -enabled systems. Only a few embedded TCP/IP systems do not support DNS. -

-When an MS Windows 200x / XP system attempts to resolve a host name to an IP address -it follows a defined path: -

- Checks the hosts file. It is located in - C:\WinNT\System32\Drivers\etc. -
- Does a DNS lookup -
- Checks the NetBIOS name cache -
- Queries the WINS server -
- Does a broadcast name lookup over UDP -
- Looks up entries in LMHOSTS. It is located in - C:\WinNT\System32\Drivers\etc. -

-Windows 200x / XP can register it's host name with a Dynamic DNS server. You can -force register with a Dynamic DNS server in Windows 200x / XP using: -ipconfig /registerdns -

-With Active Directory (ADS), a correctly functioning DNS server is absolutely -essential. In the absence of a working DNS server that has been correctly configured, -MS Windows clients and servers will be totally unable to locate each other, -consequently network services will be severely impaired. -

-The use of Dynamic DNS is highly recommended with Active Directory, in which case -the use of BIND9 is preferred for it's ability to adequately support the SRV (service) -records that are needed for Active Directory. -

DNS and Active Directory

-Occasionally we hear from Unix network administrators who want to use a Unix based Dynamic -DNS server in place of the Microsoft DNS server. While this might be desirable to some, the -MS Windows 200x DNS server is auto-configured to work with Active Directory. It is possible -to use BIND version 8 or 9, but it will almost certainly be necessary to create service records -so that MS Active Directory clients can resolve host names to locate essential network services. -The following are some of the default service records that Active Directory requires: -

_ldap._tcp.pdc.ms-dcs.Domain
- This provides the address of the Windows NT PDC for the Domain. -
_ldap._tcp.pdc.ms-dcs.DomainTree
- Resolves the addresses of Global Catalog servers in the domain. -
_ldap._tcp.site.sites.writable.ms-dcs.Domain
- Provides list of domain controllers based on sites. -
_ldap._tcp.writable.ms-dcs.Domain
- Enumerates list of domain controllers that have the writable - copies of the Active Directory data store. -
_ldap._tcp.GUID.domains.ms-dcs.DomainTree
- Entry used by MS Windows clients to locate machines using the - Global Unique Identifier. -
_ldap._tcp.Site.gc.ms-dcs.DomainTree
- Used by MS Windows clients to locate site configuration dependent - Global Catalog server. -

How Browsing Functions

-MS Windows machines register their NetBIOS names -(ie: the machine name for each service type in operation) on start -up. 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 synchronisation -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. -

Setting up WORKGROUP Browsing

-To set up cross subnet browsing on a network containing machines -in up to be in a WORKGROUP, not an NT Domain you need to set up one -Samba server to be the Domain Master Browser (note that this is *NOT* -the same as a Primary Domain Controller, although in an NT Domain the -same machine plays both roles). The role of a Domain master browser is -to collate the browse lists from local master browsers on all the -subnets that have a machine participating in the workgroup. Without -one machine configured as a domain master browser each subnet would -be an isolated workgroup, unable to see any machines on any other -subnet. It is the presence of a domain master browser that makes -cross subnet browsing possible for a workgroup. -

-In an WORKGROUP environment the domain master browser must be a -Samba server, and there must only be one domain master browser per -workgroup name. To set up a Samba server as a domain master browser, -set the following option in the [global] section -of the smb.conf file : -

-	domain master = yes
-

-The domain master browser should also preferrably be the local master -browser for its own subnet. In order to achieve this set the following -options in the [global] section of the smb.conf file : -

-	domain master = yes
-	local master = yes
-	preferred master = yes
-	os level = 65
-

-The domain master browser may be the same machine as the WINS -server, if you require. -

-Next, you should ensure that each of the subnets contains a -machine that can act as a local master browser for the -workgroup. Any MS Windows NT/2K/XP/2003 machine should be -able to do this, as will Windows 9x machines (although these -tend to get rebooted more often, so it's not such a good idea -to use these). To make a Samba server a local master browser -set the following options in the [global] section of the -smb.conf file : -

-	domain master = no
-	local master = yes
-	preferred master = yes
-	os level = 65
-

-Do not do this for more than one Samba server on each subnet, -or they will war with each other over which is to be the local -master browser. -

-The local master parameter allows Samba to act as a -local master browser. The preferred master causes nmbd -to force a browser election on startup and the os level -parameter sets Samba high enough so that it should win any browser elections. -

-If you have an NT machine on the subnet that you wish to -be the local master browser then you can disable Samba from -becoming a local master browser by setting the following -options in the [global] section of the -smb.conf file : -

-	domain master = no
-	local master = no
-	preferred master = no
-	os level = 0
-

Setting up DOMAIN Browsing

-If you are adding Samba servers to a Windows NT Domain then -you must not set up a Samba server as a domain master browser. -By default, a Windows NT Primary Domain Controller for a domain -is also the Domain master browser for that domain, and many -things will break if a Samba server registers the Domain master -browser NetBIOS name (DOMAIN<1B>) -with WINS instead of the PDC. -

-For subnets other than the one containing the Windows NT PDC -you may set up Samba servers as local master browsers as -described. To make a Samba server a local master browser set -the following options in the [global] section -of the smb.conf file : -

-	domain master = no
-	local master = yes
-	preferred master = yes
-	os level = 65
-

-If you wish to have a Samba server fight the election with machines -on the same subnet you may set the os level parameter -to lower levels. By doing this you can tune the order of machines that -will become local master browsers if they are running. For -more details on this see the section -Forcing Samba to be the master browser -below. -

-If you have Windows NT machines that are members of the domain -on all subnets, and you are sure they will always be running then -you can disable Samba from taking part in browser elections and -ever becoming a local master browser by setting following options -in the [global] section of the smb.conf -file : -

-        domain master = no
-        local master = no
-        preferred master = no
-        os level = 0
-

Forcing Samba to be the master

-Who becomes the master browser is determined by an election -process using broadcasts. Each election packet contains a number of parameters -which determine what precedence (bias) a host should have in the -election. By default Samba uses a very low precedence and thus loses -elections to just about anyone else. -

-If you want Samba to win elections then just set the os level global -option in smb.conf to a higher number. It defaults to 0. Using 34 -would make it win all elections over every other system (except other -samba systems!) -

-A os level of 2 would make it beat WfWg and Win95, but not MS Windows -NT/2K Server. A MS Windows NT/2K Server domain controller uses level 32. -

The maximum os level is 255

-If you want Samba to force an election on startup, then set the -preferred master global option in smb.conf to yes. Samba will -then have a slight advantage over other potential master browsers -that are not preferred master browsers. Use this parameter with -care, as if you have two hosts (whether they are Windows 95 or NT or -Samba) on the same local subnet both set with preferred master to -yes, then periodically and continually they will force an election -in order to become the local master browser. -

-If you want Samba to be a domain master browser, then it is -recommended that you also set preferred master to yes, because -Samba will not become a domain master browser for the whole of your -LAN or WAN if it is not also a local master browser on its own -broadcast isolated subnet. -

-It is possible to configure two Samba servers to attempt to become -the domain master browser for a domain. The first server that comes -up will be the domain master browser. All other Samba servers will -attempt to become the domain master browser every 5 minutes. They -will find that another Samba server is already the domain master -browser and will fail. This provides automatic redundancy, should -the current domain master browser fail. -

Making Samba the domain master

-The domain master is responsible for collating the browse lists of -multiple subnets so that browsing can occur between subnets. You can -make Samba act as the domain master by setting domain master = yes -in smb.conf. By default it will not be a domain master. -

-Note that you should not set Samba to be the domain master for a -workgroup that has the same name as an NT Domain. -

-When Samba is the domain master and the master browser, it will listen -for master announcements (made roughly every twelve minutes) from local -master browsers on other subnets and then contact them to synchronise -browse lists. -

-If you want Samba to be the domain master then I suggest you also set -the os level high enough to make sure it wins elections, and set -preferred master to yes, to get Samba to force an election on -startup. -

-Note that all your servers (including Samba) and clients should be -using a WINS server to resolve NetBIOS names. If your clients are only -using broadcasting to resolve NetBIOS names, then two things will occur: -

- your local master browsers will be unable to find a domain master - browser, as it will only be looking on the local subnet. -
- if a client happens to get hold of a domain-wide browse list, and - a user attempts to access a host in that list, it will be unable to - resolve the NetBIOS name of that host. -

-If, however, both Samba and your clients are using a WINS server, then: -

- your local master browsers will contact the WINS server and, as long as - Samba has registered that it is a domain master browser with the WINS - server, your local master browser will receive Samba's IP address - as its domain master browser. -
- when a client receives a domain-wide browse list, and a user attempts - to access a host in that list, it will contact the WINS server to - resolve the NetBIOS name of that host. as long as that host has - registered its NetBIOS name with the same WINS server, the user will - be able to see that host. -

Note about broadcast addresses

-If your network uses a "0" based broadcast address (for example if it -ends in a 0) then you will strike problems. Windows for Workgroups -does not seem to support a 0's broadcast and you will probably find -that browsing and name lookups won't work. -

Multiple interfaces

-Samba now supports machines with multiple network interfaces. If you -have multiple interfaces then you will need to use the interfaces -option in smb.conf to configure them. -

Use of the Remote Announce parameter

-The remote announce parameter of -smb.conf can be used to forcibly ensure -that all the NetBIOS names on a network get announced to a remote network. -The syntax of the remote announce parameter is: -

-	remote announce = a.b.c.d [e.f.g.h] ...
-

-or -

-	remote announce = a.b.c.d/WORKGROUP [e.f.g.h/WORKGROUP] ...
-

- -where: -

a.b.c.d and -e.f.g.h: is either the LMB (Local Master Browser) IP address -or the broadcast address of the remote network. -ie: the LMB is at 192.168.1.10, or the address -could be given as 192.168.1.255 where the netmask -is assumed to be 24 bits (255.255.255.0). -When the remote announcement is made to the broadcast -address of the remote network, every host will receive -our announcements. This is noisy and therefore -undesirable but may be necessary if we do NOT know -the IP address of the remote LMB.
WORKGROUP: is optional and can be either our own workgroup -or that of the remote network. If you use the -workgroup name of the remote network then our -NetBIOS machine names will end up looking like -they belong to that workgroup, this may cause -name resolution problems and should be avoided. -

Use of the Remote Browse Sync parameter

-The remote browse sync parameter of -smb.conf is used to announce to -another LMB that it must synchronise its NetBIOS name list with our -Samba LMB. It works ONLY if the Samba server that has this option is -simultaneously the LMB on its network segment. -

-The syntax of the remote browse sync parameter is: - -

-remote browse sync = a.b.c.d
-

- -where a.b.c.d is either the IP address of the -remote LMB or else is the network broadcast address of the remote segment. -

WINS - The Windows Internetworking Name Server

-Use of WINS (either Samba WINS or MS Windows NT Server WINS) is highly -recommended. Every NetBIOS machine registers its name together with a -name_type value for each of several types of service it has available. -eg: It registers its name directly as a unique (the type 0x03) name. -It also registers its name if it is running the LanManager compatible -server service (used to make shares and printers available to other users) -by registering the server (the type 0x20) name. -

-All NetBIOS names are up to 15 characters in length. The name_type variable -is added to the end of the name - thus creating a 16 character name. Any -name that is shorter than 15 characters is padded with spaces to the 15th -character. ie: All NetBIOS names are 16 characters long (including the -name_type information). -

-WINS can store these 16 character names as they get registered. A client -that wants to log onto the network can ask the WINS server for a list -of all names that have registered the NetLogon service name_type. This saves -broadcast traffic and greatly expedites logon processing. Since broadcast -name resolution can not be used across network segments this type of -information can only be provided via WINS or via statically configured -lmhosts files that must reside on all clients in the -absence of WINS. -

-WINS also serves the purpose of forcing browse list synchronisation by all -LMB's. LMB's must synchronise their browse list with the DMB (domain master -browser) and WINS helps the LMB to identify it's DMB. By definition this -will work only within a single workgroup. Note that the domain master browser -has NOTHING to do with what is referred to as an MS Windows NT Domain. The -later is a reference to a security environment while the DMB refers to the -master controller for browse list information only. -

-Use of WINS will work correctly only if EVERY client TCP/IP protocol stack -has been configured to use the WINS server/s. Any client that has not been -configured to use the WINS server will continue to use only broadcast based -name registration so that WINS may NEVER get to know about it. In any case, -machines that have not registered with a WINS server will fail name to address -lookup attempts by other clients and will therefore cause workstation access -errors. -

-To configure Samba as a WINS server just add -wins support = yes to the smb.conf -file [globals] section. -

-To configure Samba to register with a WINS server just add -wins server = a.b.c.d to your smb.conf file [globals] section. -

Important

-Never use both wins support = yes together -with wins server = a.b.c.d -particularly not using it's own IP address. -Specifying both will cause nmbd to refuse to start! -

Setting up a WINS server

-Either a Samba machine or a Windows NT Server machine may be set up -as a WINS server. To set a Samba machine to be a WINS server you must -add the following option to the smb.conf file on the selected machine : -in the [globals] section add the line -

-	wins support = yes
-

-Versions of Samba prior to 1.9.17 had this parameter default to -yes. If you have any older versions of Samba on your network it is -strongly suggested you upgrade to a recent version, or at the very -least set the parameter to 'no' on all these machines. -

-Machines with wins support = yes will keep a list of -all NetBIOS names registered with them, acting as a DNS for NetBIOS names. -

-You should set up only ONE WINS server. Do NOT set the -wins support = yes option on more than one Samba -server. -

-To set up a Windows NT Server as a WINS server you need to set up -the WINS service - see your NT documentation for details. Note that -Windows NT WINS Servers can replicate to each other, allowing more -than one to be set up in a complex subnet environment. As Microsoft -refuses to document these replication protocols, Samba cannot currently -participate in these replications. It is possible in the future that -a Samba->Samba WINS replication protocol may be defined, in which -case more than one Samba machine could be set up as a WINS server -but currently only one Samba server should have the -wins support = yes parameter set. -

-After the WINS server has been configured you must ensure that all -machines participating on the network are configured with the address -of this WINS server. If your WINS server is a Samba machine, fill in -the Samba machine IP address in the Primary WINS Server field of -the Control Panel->Network->Protocols->TCP->WINS Server dialogs -in Windows 95 or Windows NT. To tell a Samba server the IP address -of the WINS server add the following line to the [global] section of -all smb.conf files : -

-	wins server = <name or IP address>
-

-where <name or IP address> is either the DNS name of the WINS server -machine or its IP address. -

-Note that this line MUST NOT BE SET in the smb.conf file of the Samba -server acting as the WINS server itself. If you set both the -wins support = yes option and the -wins server = <name> option then -nmbd will fail to start. -

-There are two possible scenarios for setting up cross subnet browsing. -The first details setting up cross subnet browsing on a network containing -Windows 95, Samba and Windows NT machines that are not configured as -part of a Windows NT Domain. The second details setting up cross subnet -browsing on networks that contain NT Domains. -

WINS Replication

-Samba-3 permits WINS replication through the use of the wrepld utility. -This tool is not currently capable of being used as it is still in active development. -As soon as this tool becomes moderately functional we will prepare man pages and enhance this -section of the documentation to provide usage and technical details. -

Static WINS Entries

-Adding static entries to your Samba-3 WINS server is actually fairly easy. -All you have to do is add a line to wins.dat, typically -located in /usr/local/samba/var/locks. -

-Entries in wins.dat take the form of - -

-"NAME#TYPE" TTL ADDRESS+ FLAGS
-

- -where NAME is the NetBIOS name, TYPE is the NetBIOS type, TTL is the -time-to-live as an absolute time in seconds, ADDRESS+ is one or more -addresses corresponding to the registration and FLAGS are the NetBIOS -flags for the registration. - -A typical dynamic entry looks like: -

-"MADMAN#03" 1055298378 192.168.1.2 66R
-

- -To make it static, all that has to be done is set the TTL to 0: - -

-"MADMAN#03" 0 192.168.1.2 66R
-

-Though this method works with early Samba-3 versions, there's a -possibility that it may change in future versions if WINS replication -is added. -

Helpful Hints

-The following hints should be carefully considered as they are stumbling points -for many new network administrators. -

Windows Networking Protocols

Warning

-Do NOT use more than one (1) protocol on MS Windows machines -

-A very common cause of browsing problems results from installing more than -one protocol on an MS Windows machine. -

-Every NetBIOS machine takes part in a process of electing the LMB (and DMB) -every 15 minutes. A set of election criteria is used to determine the order -of precedence for winning this election process. A machine running Samba or -Windows NT will be biased so that the most suitable machine will predictably -win and thus retain it's role. -

-The election process is "fought out" so to speak over every NetBIOS network -interface. In the case of a Windows 9x machine that has both TCP/IP and IPX -installed and has NetBIOS enabled over both protocols the election will be -decided over both protocols. As often happens, if the Windows 9x machine is -the only one with both protocols then the LMB may be won on the NetBIOS -interface over the IPX protocol. Samba will then lose the LMB role as Windows -9x will insist it knows who the LMB is. Samba will then cease to function -as an LMB and thus browse list operation on all TCP/IP only machines will -fail. -

-Windows 95, 98, 98se, Me are referred to generically as Windows 9x. -The Windows NT4, 2000, XP and 2003 use common protocols. These are roughly -referred to as the WinNT family, but it should be recognised that 2000 and -XP/2003 introduce new protocol extensions that cause them to behave -differently from MS Windows NT4. Generally, where a server does NOT support -the newer or extended protocol, these will fall back to the NT4 protocols. -

-The safest rule of all to follow it this - USE ONLY ONE PROTOCOL! -

Name Resolution Order

-Resolution of NetBIOS names to IP addresses can take place using a number -of methods. The only ones that can provide NetBIOS name_type information -are: -

WINS: the best tool!

LMHOSTS: is static and hard to maintain.

Broadcast: uses UDP and can not resolve names across remote segments.

-Alternative means of name resolution includes: -

/etc/hosts: is static, hard to maintain, and lacks name_type info

DNS: is a good choice but lacks essential name_type info.

-Many sites want to restrict DNS lookups and want to avoid broadcast name -resolution traffic. The name resolve order parameter is -of great help here. The syntax of the name resolve order -parameter is: -

-name resolve order = wins lmhosts bcast host
-

-or -

-name resolve order = wins lmhosts  	(eliminates bcast and host)
-

-The default is: -

-name resolve order = host lmhost wins bcast
-

-where "host" refers the the native methods used by the Unix system -to implement the gethostbyname() function call. This is normally -controlled by /etc/host.conf, /etc/nsswitch.conf and /etc/resolv.conf. -

Technical Overview of browsing

-SMB networking provides a mechanism by which clients can access a list -of machines in a network, a so-called browse list. This list -contains machines that are ready to offer file and/or print services -to other machines within the network. Thus it does not include -machines which aren't currently able to do server tasks. The browse -list is heavily used by all SMB clients. Configuration of SMB -browsing has been problematic for some Samba users, hence this -document. -

-MS Windows 2000 and later, as with Samba 3 and later, can be -configured to not use NetBIOS over TCP/IP. When configured this way, -it is imperative that name resolution (using DNS/LDAP/ADS) be correctly -configured and operative. Browsing will NOT work if name resolution -from SMB machine names to IP addresses does not function correctly. -

-Where NetBIOS over TCP/IP is enabled use of a WINS server is highly -recommended to aid the resolution of NetBIOS (SMB) names to IP addresses. -WINS allows remote segment clients to obtain NetBIOS name_type information -that can NOT be provided by any other means of name resolution. -

Browsing support in Samba

-Samba facilitates browsing. The browsing is supported by nmbd -and is also controlled by options in the smb.conf file. -Samba can act as a local browse master for a workgroup and the ability -to support domain logons and scripts is now available. -

-Samba can also act as a domain master browser for a workgroup. This -means that it will collate lists from local browse masters into a -wide area network server list. In order for browse clients to -resolve the names they may find in this list, it is recommended that -both Samba and your clients use a WINS server. -

-Note that you should NOT set Samba to be the domain master for a -workgroup that has the same name as an NT Domain: on each wide area -network, you must only ever have one domain master browser per workgroup, -regardless of whether it is NT, Samba or any other type of domain master -that is providing this service. -

Note

-Nmbd can be configured as a WINS server, but it is not -necessary to specifically use Samba as your WINS server. MS Windows -NT4, Server or Advanced Server 2000 or 2003 can be configured as -your WINS server. In a mixed NT/2000/2003 server and Samba environment on -a Wide Area Network, it is recommended that you use the Microsoft -WINS server capabilities. In a Samba-only environment, it is -recommended that you use one and only one Samba server as your WINS server. -

-To get browsing to work you need to run nmbd as usual, but will need -to use the workgroup option in smb.conf -to control what workgroup Samba becomes a part of. -

-Samba also has a useful option for a Samba server to offer itself for -browsing on another subnet. It is recommended that this option is only -used for 'unusual' purposes: announcements over the internet, for -example. See remote announce in the -smb.conf man page. -

Problem resolution

-If something doesn't work then hopefully the log.nmbd file will help -you track down the problem. Try a debug level of 2 or 3 for finding -problems. Also note that the current browse list usually gets stored -in text form in a file called browse.dat. -

-Note that if it doesn't work for you, then you should still be able to -type the server name as \\SERVER in filemanager then -hit enter and filemanager should display the list of available shares. -

-Some people find browsing fails because they don't have the global -guest account set to a valid account. Remember that the -IPC$ connection that lists the shares is done as guest, and thus you must -have a valid guest account. -

-MS Windows 2000 and upwards (as with Samba) can be configured to disallow -anonymous (ie: Guest account) access to the IPC$ share. In that case, the -MS Windows 2000/XP/2003 machine acting as an SMB/CIFS client will use the -name of the currently logged in user to query the IPC$ share. MS Windows -9X clients are not able to do this and thus will NOT be able to browse -server resources. -

-The other big problem people have is that their broadcast address, -netmask or IP address is wrong (specified with the "interfaces" option -in smb.conf) -

Browsing across subnets

-Since the release of Samba 1.9.17(alpha1), Samba has supported the -replication of browse lists across subnet boundaries. This section -describes how to set this feature up in different settings. -

-To see browse lists that span TCP/IP subnets (ie. networks separated -by routers that don't pass broadcast traffic), you must set up at least -one WINS server. The WINS server acts as a DNS for NetBIOS names, allowing -NetBIOS name to IP address translation to be done by doing a direct -query of the WINS server. This is done via a directed UDP packet on -port 137 to the WINS server machine. The reason for a WINS server is -that by default, all NetBIOS name to IP address translation is done -by broadcasts from the querying machine. This means that machines -on one subnet will not be able to resolve the names of machines on -another subnet without using a WINS server. -

-Remember, for browsing across subnets to work correctly, all machines, -be they Windows 95, Windows NT, or Samba servers must have the IP address -of a WINS server given to them by a DHCP server, or by manual configuration -(for Win95 and WinNT, this is in the TCP/IP Properties, under Network -settings) for Samba this is in the smb.conf file. -

How does cross subnet browsing work ?

-Cross subnet browsing is a complicated dance, containing multiple -moving parts. It has taken Microsoft several years to get the code -that achieves this correct, and Samba lags behind in some areas. -Samba is capable of cross subnet browsing when configured correctly. -

-Consider a network set up as follows : -

- -

-                                   (DMB)
-             N1_A      N1_B        N1_C       N1_D        N1_E
-              |          |           |          |           |
-          -------------------------------------------------------
-            |          subnet 1                       |
-          +---+                                      +---+
-          |R1 | Router 1                  Router 2   |R2 |
-          +---+                                      +---+
-            |                                          |
-            |  subnet 2              subnet 3          |
-  --------------------------       ------------------------------------
-  |     |     |      |               |        |         |           |
- N2_A  N2_B  N2_C   N2_D           N3_A     N3_B      N3_C        N3_D 
-                    (WINS)
-

-Consisting of 3 subnets (1, 2, 3) connected by two routers -(R1, R2) - these do not pass broadcasts. Subnet 1 has 5 machines -on it, subnet 2 has 4 machines, subnet 3 has 4 machines. Assume -for the moment that all these machines are configured to be in the -same workgroup (for simplicity's sake). Machine N1_C on subnet 1 -is configured as Domain Master Browser (ie. it will collate the -browse lists for the workgroup). Machine N2_D is configured as -WINS server and all the other machines are configured to register -their NetBIOS names with it. -

-As all these machines are booted up, elections for master browsers -will take place on each of the three subnets. Assume that machine -N1_C wins on subnet 1, N2_B wins on subnet 2, and N3_D wins on -subnet 3 - these machines are known as local master browsers for -their particular subnet. N1_C has an advantage in winning as the -local master browser on subnet 1 as it is set up as Domain Master -Browser. -

-On each of the three networks, machines that are configured to -offer sharing services will broadcast that they are offering -these services. The local master browser on each subnet will -receive these broadcasts and keep a record of the fact that -the machine is offering a service. This list of records is -the basis of the browse list. For this case, assume that -all the machines are configured to offer services so all machines -will be on the browse list. -

-For each network, the local master browser on that network is -considered 'authoritative' for all the names it receives via -local broadcast. This is because a machine seen by the local -master browser via a local broadcast must be on the same -network as the local master browser and thus is a 'trusted' -and 'verifiable' resource. Machines on other networks that -the local master browsers learn about when collating their -browse lists have not been directly seen - these records are -called 'non-authoritative'. -

-At this point the browse lists look as follows (these are -the machines you would see in your network neighborhood if -you looked in it on a particular network right now). -

Table 10.1. Browse subnet example 1

Subnet	Browse Master	List
Subnet1	N1_C	N1_A, N1_B, N1_C, N1_D, N1_E
Subnet2	N2_B	N2_A, N2_B, N2_C, N2_D
Subnet3	N3_D	N3_A, N3_B, N3_C, N3_D

-Note that at this point all the subnets are separate, no -machine is seen across any of the subnets. -

-Now examine subnet 2. As soon as N2_B has become the local -master browser it looks for a Domain master browser to synchronize -its browse list with. It does this by querying the WINS server -(N2_D) for the IP address associated with the NetBIOS name -WORKGROUP<1B>. This name was registered by the Domain master -browser (N1_C) with the WINS server as soon as it was booted. -

-Once N2_B knows the address of the Domain master browser it -tells it that is the local master browser for subnet 2 by -sending a MasterAnnouncement packet as a UDP port 138 packet. -It then synchronizes with it by doing a NetServerEnum2 call. This -tells the Domain Master Browser to send it all the server -names it knows about. Once the domain master browser receives -the MasterAnnouncement packet it schedules a synchronization -request to the sender of that packet. After both synchronizations -are done the browse lists look like : -

Table 10.2. Browse subnet example 2

Subnet	Browse Master	List
Subnet1	N1_C	N1_A, N1_B, N1_C, N1_D, N1_E, N2_A(), N2_B(), N2_C(), N2_D()
Subnet2	N2_B	N2_A, N2_B, N2_C, N2_D, N1_A(), N1_B(), N1_C(), N1_D(), N1_E(*)
Subnet3	N3_D	N3_A, N3_B, N3_C, N3_D

- -Servers with a (*) after them are non-authoritative names. -

-At this point users looking in their network neighborhood on -subnets 1 or 2 will see all the servers on both, users on -subnet 3 will still only see the servers on their own subnet. -

-The same sequence of events that occured for N2_B now occurs -for the local master browser on subnet 3 (N3_D). When it -synchronizes browse lists with the domain master browser (N1_A) -it gets both the server entries on subnet 1, and those on -subnet 2. After N3_D has synchronized with N1_C and vica-versa -the browse lists look like. -

Table 10.3. Browse subnet example 3

Subnet	Browse Master	List
Subnet1	N1_C	N1_A, N1_B, N1_C, N1_D, N1_E, N2_A(), N2_B(), N2_C(), N2_D(), N3_A(), N3_B(), N3_C(), N3_D()
Subnet2	N2_B	N2_A, N2_B, N2_C, N2_D, N1_A(), N1_B(), N1_C(), N1_D(), N1_E(*)
Subnet3	N3_D	N3_A, N3_B, N3_C, N3_D, N1_A(), N1_B(), N1_C(), N1_D(), N1_E(), N2_A(), N2_B(), N2_C(), N2_D(*)

- -Servers with a (*) after them are non-authoritative names. -

-At this point users looking in their network neighborhood on -subnets 1 or 3 will see all the servers on all subnets, users on -subnet 2 will still only see the servers on subnets 1 and 2, but not 3. -

-Finally, the local master browser for subnet 2 (N2_B) will sync again -with the domain master browser (N1_C) and will receive the missing -server entries. Finally - and as a steady state (if no machines -are removed or shut off) the browse lists will look like : -

Table 10.4. Browse subnet example 4

Subnet	Browse Master	List
Subnet1	N1_C	N1_A, N1_B, N1_C, N1_D, N1_E, N2_A(), N2_B(), N2_C(), N2_D(), N3_A(), N3_B(), N3_C(), N3_D()
Subnet2	N2_B	N2_A, N2_B, N2_C, N2_D, N1_A(), N1_B(), N1_C(), N1_D(), N1_E(), N3_A(), N3_B(), N3_C(), N3_D(*)
Subnet3	N3_D	N3_A, N3_B, N3_C, N3_D, N1_A(), N1_B(), N1_C(), N1_D(), N1_E(), N2_A(), N2_B(), N2_C(), N2_D(*)

- -Servers with a (*) after them are non-authoritative names. -

-Synchronizations between the domain master browser and local -master browsers will continue to occur, but this should be a -steady state situation. -

-If either router R1 or R2 fails the following will occur: -

- Names of computers on each side of the inaccessible network fragments - will be maintained for as long as 36 minutes, in the network neighbourhood - lists. -
- Attempts to connect to these inaccessible computers will fail, but the - names will not be removed from the network neighbourhood lists. -
- If one of the fragments is cut off from the WINS server, it will only - be able to access servers on its local subnet, by using subnet-isolated - broadcast NetBIOS name resolution. The effects are similar to that of - losing access to a DNS server. -

Common Errors

-Many questions are asked on the mailing lists regarding browsing. The majority of browsing -problems originate out of incorrect configuration of NetBIOS name resolution. Some are of -particular note. -

How can one flush the Samba NetBIOS name cache without restarting Samba?

-Samba's nmbd process controls all browse list handling. Under normal circumstances it is -safe to restart nmbd. This will effectively flush the Samba NetBIOS name cache and cause it -to be rebuilt. Note that this does NOT make certain that a rogue machine name will not re-appear -in the browse list. When nmbd is taken out of service another machine on the network will -become the browse master. This new list may still have the rogue entry in it. If you really -want to clear a rogue machine from the list then every machine on the network will need to be -shut down and restarted at after all machines are down. Failing a complete restart, the only -other thing you can do is wait until the entry times out and is then flushed from the list. -This may take a long time on some networks (months). -

My client reports "This server is not configured to list shared resources"

-Your guest account is probably invalid for some reason. Samba uses the -guest account for browsing in smbd. Check that your guest account is -valid. -

See also guest account in the smb.conf man page.