Table of Contents
There are many who approach MS Windows networking with incredible misconceptions. That's okay, because it gives the rest of us plenty of opportunity to be of assistance. Those who really want help would be well advised to become familiar with information that is already available.
The reader is advised not to tackle this section without having first understood and mastered some basics. MS Windows networking is not particularly forgiving of mis-configuration. Users of MS Windows networking are likely to complain of persistent niggles that may be caused by a broken network configuration. To a great many people, however, MS Windows networking starts with a Domain Controller that in some magical way is expected to solve all network operational ills.
The diagram shows a typical MS Windows Domain Security network environment. Workstations A, B and C are representative of many physical MS Windows network clients.
From the Samba mailing list one can readily identify many common networking issues. If you are not clear on the following subjects, then it will do much good to read the sections of this HOWTO that deal with it. These are the most common causes of MS Windows networking problems:
Basic TCP/IP configuration.
NetBIOS name resolution.
Authentication configuration.
User and group configuration.
Basic file and directory permission control in UNIX/Linux.
Understanding how MS Windows clients interoperate in a network environment.
Do not be put off; on the surface of it MS Windows networking seems so simple that anyone can do it. In fact, it is not a good idea to set up an MS Windows network with inadequate training and preparation. But let's get our first indelible principle out of the way: It is perfectly okay to make mistakes! In the right place and at the right time, mistakes are the essence of learning. It is very much not okay to make mistakes that cause loss of productivity and impose an avoidable financial burden on an organization.
Where is the right place to make mistakes? Only out of harms way. If you are going to make mistakes, then please do it on a test network, away from users and in such a way as to not inflict pain on others. Do your learning on a test network.
What is the key benefit of Microsoft Domain Security?
In a word, Single Sign On, or SSO for short. To many, this is the Holy Grail of MS Windows NT and beyond networking. SSO allows users in a well-designed network to log onto any workstation that is a member of the domain that their user account is in (or in a domain that has an appropriate trust relationship with the domain they are visiting) and they will be able to log onto the network and access resources (shares, files and printers) as if they are sitting at their home (personal) workstation. This is a feature of the Domain Security protocols.
The benefits of Domain Security are available to those sites that deploy a Samba PDC. A Domain provides a unique network security identifier (SID). Domain user and group security identifiers are comprised of the network SID plus a relative identifier (RID) that is unique to the account. User and Group SIDs (the network SID plus the RID) can be used to create Access Control Lists (ACLs) attached to network resources to provide organizational access control. UNIX systems recognize only local security identifiers.
Note
Network clients of an MS Windows Domain Security Environment must be Domain Members to be able to gain access to the advanced features provided. Domain Membership involves more than just setting the workgroup name to the Domain name. It requires the creation of a Domain trust account for the workstation (called a machine account). Refer to Domain Membership for more information.
The following functionalities are new to the Samba-3 release:
Windows NT4 domain trusts.
Adding users via the User Manager for Domains. This can be done on any MS Windows client using the Nexus.exe toolkit for Windows 9x/Me, or using the SRVTOOLS.EXE package for MS Windows NT4/200x/XP platforms. These packages are available from Microsoft's Web site.
Introduces replaceable and multiple user account (authentication) backends. In the case where the backend is placed in an LDAP database, Samba-3 confers the benefits of a backend that can be distributed, replicated and is highly scalable.
Implements full Unicode support. This simplifies cross locale internationalization support. It also opens up the use of protocols that Samba-2.2.x had but could not use due to the need to fully support Unicode.
The following functionalities are not provided by Samba-3:
SAM replication with Windows NT4 Domain Controllers (i.e., a Samba PDC and a Windows NT BDC or vice versa). This means Samba cannot operate as a BDC when the PDC is Microsoft-based or replicate account data to Windows BDCs.
Acting as a Windows 2000 Domain Controller (i.e., Kerberos and Active Directory). In point of fact, Samba-3 does have some Active Directory Domain Control ability that is at this time purely experimental that is certain to change as it becomes a fully supported feature some time during the Samba-3 (or later) life cycle. However, Active Directory is more then just SMB it's also LDAP, Kerberos, DHCP, and other protocols (with proprietary extensions, of course).
The Windows 200x/XP MMC (Computer Management) Console can not be used to manage a Samba-3 server. For this you can use only the MS Windows NT4 Domain Server manager and the MS Windows NT4 Domain User Manager. Both are part of the SVRTOOLS.EXE package mentioned later.
Windows 9x/Me/XP Home clients are not true members of a domain for reasons outlined in this chapter. The protocol for support of Windows 9x/Me style network (domain) logons is completely different from NT4/Windows 200x type domain logons and has been officially supported for some time. These clients use the old LanMan Network Logon facilities that are supported in Samba since approximately the Samba-1.9.15 series.
Samba-3 implements group mapping between Windows NT groups and UNIX groups (this is really quite complicated to explain in a short space). This is discussed more fully in Group Mapping MS Windows and UNIX.
Samba-3, like an MS Windows NT4 PDC or a Windows 200x Active Directory, needs to store user and Machine Trust Account information in a suitable backend data-store. Refer to MS Windows Workstation/Server Machine Trust Accounts. With Samba-3 there can be multiple backends for this. A complete discussion of account database backends can be found in Account Information Databases.
Over the years, public perceptions of what Domain Control really is has taken on an almost mystical nature. Before we branch into a brief overview of Domain Control, there are three basic types of Domain Controllers.
Primary Domain Controller
Backup Domain Controller
ADS Domain Controller
The Primary Domain Controller or PDC plays an important role in MS Windows NT4. In Windows 200x Domain Control architecture, this role is held by Domain Controllers. Folklore dictates that because of its role in the MS Windows network, the Domain Controller should be the most powerful and most capable machine in the network. As strange as it may seem to say this here, good overall network performance dictates that the entire infrastructure needs to be balanced. It is advisable to invest more in Stand-alone (Domain Member) servers than in the Domain Controllers.
In the case of MS Windows NT4-style domains, it is the PDC that initiates a new Domain Control database. This forms a part of the Windows registry called the Security Account Manager (SAM). It plays a key part in NT4-type domain user authentication and in synchronization of the domain authentication database with Backup Domain Controllers.
With MS Windows 200x Server-based Active Directory domains, one Domain Controller initiates a potential hierarchy of Domain Controllers, each with their own area of delegated control. The master domain controller has the ability to override any downstream controller, but a down-line controller has control only over its down-line. With Samba-3, this functionality can be implemented using an LDAP-based user and machine account backend.
New to Samba-3 is the ability to use a backend database that holds the same type of data as the NT4-style SAM database (one of the registry files)[1].
The Backup Domain Controller or BDC plays a key role in servicing network authentication requests. The BDC is biased to answer logon requests in preference to the PDC. On a network segment that has a BDC and a PDC, the BDC will most likely service network logon requests. The PDC will answer network logon requests when the BDC is too busy (high load). A BDC can be promoted to a PDC. If the PDC is online at the time that a BDC is promoted to PDC, the previous PDC is automatically demoted to a BDC. With Samba-3, this is not an automatic operation; the PDC and BDC must be manually configured and changes also need to be made.
With MS Windows NT4, a decision is made at installation to determine what type of machine the server will be. It is possible to promote a BDC to a PDC and vice versa. The only way to convert a Domain Controller to a Domain Member server or a Stand-alone Server is to reinstall it. The install time choices offered are:
Primary Domain Controller the one that seeds the domain SAM.
Backup Domain Controller one that obtains a copy of the domain SAM.
Domain Member Server one that has no copy of the domain SAM, rather it obtains authentication from a Domain Controller for all access controls.
Stand-alone Server one that plays no part is SAM synchronization, has its own authentication database and plays no role in Domain Security.
With MS Windows 2000, the configuration of Domain Control is done after the server has been installed. Samba-3 is capable of acting fully as a native member of a Windows 200x server Active Directory domain.
New to Samba-3 is the ability to function fully as an MS Windows NT4-style Domain Controller, excluding the SAM replication components. However, please be aware that Samba-3 also supports the MS Windows 200x Domain Control protocols.
At this time any appearance that Samba-3 is capable of acting as an Domain Controller in native ADS mode is limited and experimental in nature. This functionality should not be used until the Samba Team offers formal support for it. At such a time, the documentation will be revised to duly reflect all configuration and management requirements. Samba can act as a NT4-style DC in a Windows 2000/XP environment. However, there are certain compromises:
No machine policy files.
No Group Policy Objects.
No synchronously executed AD logon scripts.
Can't use Active Directory management tools to manage users and machines.
Registry changes tattoo the main registry, while with AD they do not leave permanent changes in effect.
Without AD you cannot perform the function of exporting specific applications to specific users or groups.
There are two ways that MS Windows machines may interact with each other, with other servers and with Domain Controllers: either as Stand-alone systems, more commonly called Workgroup members, or as full participants in a security system, more commonly called Domain members.
It should be noted that Workgroup membership involves no special configuration other than the machine being configured so the network configuration has a commonly used name for its workgroup entry. It is not uncommon for the name WORKGROUP to be used for this. With this mode of configuration, there are no Machine Trust Accounts and any concept of membership as such is limited to the fact that all machines appear in the network neighborhood to be logically grouped together. Again, just to be clear: workgroup mode does not involve security machine accounts.
Domain Member machines have a machine account in the Domain accounts database. A special procedure must be followed on each machine to effect Domain Membership. This procedure, which can be done only by the local machine Administrator account, will create the Domain machine account (if it does not exist), and then initializes that account. When the client first logs onto the Domain it triggers a machine password change.
Note
When Samba is configured as a Domain Controller, secure network operation demands that all MS Windows NT4/200x/XP Professional clients should be configured as Domain Members. If a machine is not made a member of the Domain, then it will operate like a workgroup (Stand-alone) machine. Please refer to Domain Membership chapter for information regarding Domain Membership.
The following are necessary for configuring Samba-3 as an MS Windows NT4-style PDC for MS Windows NT4/200x/XP clients:
Configuration of basic TCP/IP and MS Windows networking.
Consistent configuration of Name Resolution[2].
Domain logons for Windows NT4/200x/XP Professional clients.
Configuration of Roaming Profiles or explicit configuration to force local profile usage.
Configuration of network/system policies.
Adding and managing domain user accounts.
Configuring MS Windows client machines to become Domain Members.
The following provisions are required to serve MS Windows 9x/Me clients:
Configuration of basic TCP/IP and MS Windows networking.
Network Logon Configuration (since Windows 9x/Me/XP Home are not technically domain members, they do not really participate in the security aspects of Domain logons as such).
Roaming Profile Configuration.
Configuration of System Policy handling.
Installation of the network driver “Client for MS Windows Networks” and configuration to log onto the domain.
Placing Windows 9x/Me clients in User Level Security if it is desired to allow all client share access to be controlled according to domain user/group identities.
Adding and managing domain user accounts.
Note
Roaming Profiles and System/Network policies are advanced network administration topics that are covered in the Desktop Profile Management and System and Account Policies chapters of this document. However, these are not necessarily specific to a Samba PDC as much as they are related to Windows NT networking concepts.
A Domain Controller is an SMB/CIFS server that:
Registers and advertises itself as a Domain Controller (through NetBIOS broadcasts as well as by way of name registrations either by Mailslot Broadcasts over UDP broadcast, to a WINS server over UDP uni-cast, or via DNS and Active Directory).
Provides the NETLOGON service. (This is actually a collection of services that runs over multiple protocols. These include the LanMan Logon service, the Netlogon service, the Local Security Account service, and variations of them.)
Provides a share called NETLOGON.
It is rather easy to configure Samba to provide these. Each Samba Domain Controller must provide the NETLOGON service that Samba calls the domain logons functionality (after the name of the parameter in the smb.conf file). Additionally, one server in a Samba-3 Domain must advertise itself as the Domain Master Browser[3]. This causes the Primary Domain Controller to claim a domain-specific NetBIOS name that identifies it as a Domain Master Browser for its given domain or workgroup. Local master browsers in the same domain or workgroup on broadcast-isolated subnets then ask for a complete copy of the browse list for the whole wide area network. Browser clients will then contact their Local Master Browser, and will receive the domain-wide browse list, instead of just the list for their broadcast-isolated subnet.
The first step in creating a working Samba PDC is to understand the parameters necessary in smb.conf. An example smb.conf for acting as a PDC can be found in the next example.
Example 4.1. smb.conf for being a PDC
The basic options shown in this example are explained as follows:
- passdb backend
This contains all the user and group account information. Acceptable values for a PDC are: smbpasswd, tdbsam, and ldapsam. The “guest” entry provides default accounts and is included by default, there is no need to add it explicitly.
Where use of backup Domain Controllers (BDCs) is intended, the only logical choice is to use LDAP so the passdb backend can be distributed. The tdbsam and smbpasswd files cannot effectively be distributed and therefore should not be used.
- Domain Control Parameters
The parameters os level, preferred master, domain master, security, encrypt passwords, and domain logons play a central role in assuring domain control and network logon support.
The os level must be set at or above a value of 32. A Domain Controller must be the Domain Master Browser, must be set in user mode security, must support Microsoft-compatible encrypted passwords, and must provide the network logon service (domain logons). Encrypted passwords must be enabled. For more details on how to do this, refer to Account Information Databases.
- Environment Parameters
The parameters logon path, logon home, logon drive, and logon script are environment support settings that help to facilitate client logon operations and that help to provide automated control facilities to ease network management overheads. Please refer to the man page information for these parameters.
- NETLOGON Share
The NETLOGON share plays a central role in domain logon and Domain Membership support. This share is provided on all Microsoft Domain Controllers. It is used to provide logon scripts, to store Group Policy files (NTConfig.POL), as well as to locate other common tools that may be needed for logon processing. This is an essential share on a Domain Controller.
- PROFILE Share
This share is used to store user desktop profiles. Each user must have a directory at the root of this share. This directory must be write-enabled for the user and must be globally read-enabled. Samba-3 has a VFS module called “fake_permissions” that may be installed on this share. This will allow a Samba administrator to make the directory read-only to everyone. Of course this is useful only after the profile has been properly created.
Note
The above parameters make for a full set of parameters that may define the server's mode of operation. The following smb.conf parameters are the essentials alone:
| netbios name = BELERIAND |
| workgroup = MIDEARTH |
| domain logons = Yes |
| domain master = Yes |
| security = User |
The additional parameters shown in the longer listing above just makes for a more complete explanation.
Samba-3 is not, and cannot act as, an Active Directory Server. It cannot truly function as an Active Directory Primary Domain Controller. The protocols for some of the functionality of Active Directory Domain Controllers has been partially implemented on an experimental only basis. Please do not expect Samba-3 to support these protocols. Do not depend on any such functionality either now or in the future. The Samba Team may remove these experimental features or may change their behavior. This is mentioned for the benefit of those who have discovered secret capabilities in Samba-3 and who have asked when this functionality will be completed. The answer is maybe or maybe never!
To be sure, Samba-3 is designed to provide most of the functionality that Microsoft Windows NT4-style Domain Controllers have. Samba-3 does not have all the capabilities of Windows NT4, but it does have a number of features that Windows NT4 domain controllers do not have. In short, Samba-3 is not NT4 and it is not Windows Server 200x, it is not an Active Directory server. We hope this is plain and simple enough for all to understand.
The subject of Network or Domain Logons is discussed here because it forms an integral part of the essential functionality that is provided by a Domain Controller.
All Domain Controllers must run the netlogon service (domain logons in Samba). One Domain Controller must be configured with domain master = Yes (the Primary Domain Controller); on all Backup Domain Controllers domain master = No must be set.
To be completely clear: If you want MS Windows XP Home Edition to integrate with your MS Windows NT4 or Active Directory Domain Security, understand it cannot be done. The only option is to purchase the upgrade from MS Windows XP Home Edition to MS Windows XP Professional.
Note
MS Windows XP Home Edition does not have the ability to join any type of Domain Security facility. Unlike MS Windows 9x/Me, MS Windows XP Home Edition also completely lacks the ability to log onto a network.
Now that this has been said, please do not ask the mailing list or email any of the Samba Team members with your questions asking how to make this work. It can't be done. If it can be done, then to do so would violate your software license agreement with Microsoft, and we recommend that you do not do that.
A domain and a workgroup are exactly the same in terms of network browsing. The difference is that a distributable authentication database is associated with a domain, for secure login access to a network. Also, different access rights can be granted to users if they successfully authenticate against a domain logon server. Samba-3 does this now in the same way as MS Windows NT/200x.
The SMB client logging on to a domain has an expectation that every other server in the domain should accept the same authentication information. Network browsing functionality of domains and workgroups is identical and is explained in this documentation under the browsing discussions. It should be noted that browsing is totally orthogonal to logon support.
Issues related to the single-logon network model are discussed in this section. Samba supports domain logons, network logon scripts and user profiles for MS Windows for workgroups and MS Windows 9X/ME clients, which are the focus of this section.
When an SMB client in a domain wishes to logon, it broadcasts requests for a logon server. The first one to reply gets the job, and validates its password using whatever mechanism the Samba administrator has installed. It is possible (but ill advised ) to create a domain where the user database is not shared between servers, i.e., they are effectively workgroup servers advertising themselves as participating in a domain. This demonstrates how authentication is quite different from but closely involved with domains.
Using these features you can make your clients verify their logon via the Samba server; make clients run a batch file when they logon to the network and download their preferences, desktop and start menu.
MS Windows XP Home edition is not able to join a domain and does not permit the use of domain logons.
Before launching into the configuration instructions, it is worthwhile to look at how a Windows 9x/Me client performs a logon:
The client broadcasts (to the IP broadcast address of the subnet it is in) a NetLogon request. This is sent to the NetBIOS name DOMAIN<#1c> at the NetBIOS layer. The client chooses the first response it receives, which contains the NetBIOS name of the logon server to use in the format of \\SERVER.
The client connects to that server, logs on (does an SMBsessetupX) and then connects to the IPC$ share (using an SMBtconX).
The client does a NetWkstaUserLogon request, which retrieves the name of the user's logon script.
The client then connects to the NetLogon share and searches for said script. If it is found and can be read, it is retrieved and executed by the client. After this, the client disconnects from the NetLogon share.
The client sends a NetUserGetInfo request to the server to retrieve the user's home share, which is used to search for profiles. Since the response to the NetUserGetInfo request does not contain much more than the user's home share, profiles for Windows 9x clients must reside in the user home directory.
The client connects to the user's home share and searches for the user's profile. As it turns out, you can specify the user's home share as a share name and path. For example, \\server\fred\.winprofile. If the profiles are found, they are implemented.
The client then disconnects from the user's home share and reconnects to the NetLogon share and looks for CONFIG.POL, the policies file. If this is found, it is read and implemented.
The main difference between a PDC and a Windows 9x/Me logon server configuration is:
Password encryption is not required for a Windows 9x/Me logon server. But note that beginning with MS Windows 98 the default setting is that plain-text password support is disabled. It can be re-enabled with the registry changes that are documented in System and Account Policies.
Windows 9x/Me clients do not require and do not use Machine Trust Accounts.
A Samba PDC will act as a Windows 9x/Me logon server; after all, it does provide the network logon services that MS Windows 9x/Me expect to find.
Note
Use of plain-text passwords is strongly discouraged. Where used they are easily detected using a sniffer tool to examine network traffic.
There are a few comments to make in order to tie up some loose ends. There has been much debate over the issue of whether it is okay to configure Samba as a Domain Controller in security modes other than user. The only security mode that will not work due to technical reasons is share-mode security. Domain and server mode security are really just a variation on SMB User Level Security.
Actually, this issue is also closely tied to the debate on whether Samba must be the Domain Master Browser for its workgroup when operating as a DC. While it may technically be possible to configure a server as such (after all, browsing and domain logons are two distinctly different functions), it is not a good idea to do so. You should remember that the DC must register the DOMAIN<#1b> NetBIOS name. This is the name used by Windows clients to locate the DC. Windows clients do not distinguish between the DC and the DMB. A DMB is a Domain Master Browser see Configuring WORKGROUP Browsing section. For this reason, it is wise to configure the Samba DC as the DMB.
Now back to the issue of configuring a Samba DC to use a mode other than security = user. If a Samba host is configured to use another SMB server or DC in order to validate user connection requests, it is a fact that some other machine on the network (the password server) knows more about the user than the Samba host. About 99% of the time, this other host is a Domain Controller. Now to operate in domain mode security, the workgroup parameter must be set to the name of the Windows NT domain (which already has a Domain Controller). If the domain does not already have a Domain Controller, you do not yet have a Domain.
Configuring a Samba box as a DC for a domain that already by definition has a PDC is asking for trouble. Therefore, you should always configure the Samba DC to be the DMB for its domain and set security = user. This is the only officially supported mode of operation.
A machine account, typically stored in /etc/passwd, takes the form of the machine name with a “$” appended. FreeBSD (and other BSD systems) will not create a user with a “$” in the name.
The problem is only in the program used to make the entry. Once made, it works perfectly. Create a user without the “$”. Then use vipw to edit the entry, adding the “$”. Or create the whole entry with vipw if you like; make sure you use a unique user login ID.
Note
The machine account must have the exact name that the workstation has.
Note
The UNIX tool vipw is a common tool for directly editing the /etc/passwd file.
“I get told, `You already have a connection to the Domain....' or `Cannot join domain, the credentials supplied conflict with an existing set...' when creating a Machine Trust Account.”
This happens if you try to create a Machine Trust Account from the machine itself and already have a connection (e.g., mapped drive) to a share (or IPC$) on the Samba PDC. The following command will remove all network drive connections:
C:\> net use * /d
Further, if the machine is already a “member of a workgroup” that is the same name as the domain you are joining (bad idea) you will get this message. Change the workgroup name to something else, it does not matter what, reboot, and try again.
“I joined the domain successfully but after upgrading to a newer version of the Samba code I get the message, `The system cannot log you on (C000019B), Please try again or consult your system administrator when attempting to logon.'”
This occurs when the domain SID stored in the secrets.tdb database is changed. The most common cause of a change in domain SID is when the domain name and/or the server name (NetBIOS name) is changed. The only way to correct the problem is to restore the original domain SID or remove the domain client from the domain and rejoin. The domain SID may be reset using either the net or rpcclient utilities.
To reset or change the domain SID you can use the net command as follows:
root# net getlocalsid 'OLDNAME' root# net setlocalsid 'SID'
Workstation Machine Trust Accounts work only with the Domain (or network) SID. If this SID changes Domain Members (workstations) will not be able to log onto the domain. The original Domain SID can be recovered from the secrets.tdb file. The alternative is to visit each workstation to re-join it to the domain.
“When I try to join the domain I get the message, `The machine account for this computer either does not exist or is not accessible'. What's wrong?”
This problem is caused by the PDC not having a suitable Machine Trust Account. If you are using the add machine script method to create accounts then this would indicate that it has not worked. Ensure the domain admin user system is working.
Alternately, if you are creating account entries manually then they have not been created correctly. Make sure that you have the entry correct for the Machine Trust Account in smbpasswd file on the Samba PDC. If you added the account using an editor rather than using the smbpasswd utility, make sure that the account name is the machine NetBIOS name with a “$” appended to it (i.e., computer_name$). There must be an entry in both /etc/passwd and the smbpasswd file.
Some people have also reported that inconsistent subnet masks between the Samba server and the NT client can cause this problem. Make sure that these are consistent for both client and server.
“When I attempt to login to a Samba Domain from a NT4/W200x workstation, I get a message about my account being disabled.”
Enable the user accounts with smbpasswd -e username . This is normally done as an account is created.
“Until a few minutes after Samba has started, clients get the error `Domain Controller Unavailable'”
A Domain Controller has to announce its role on the network. This usually takes a while. Be patient for up to fifteen minutes, then try again.
After successfully joining the domain, user logons fail with one of two messages: one to the effect that the Domain Controller cannot be found; the other claims that the account does not exist in the domain or that the password is incorrect. This may be due to incompatible settings between the Windows client and the Samba-3 server for schannel (secure channel) settings or smb signing settings. Check your Samba settings for client schannel, server schannel, client signing, server signing by executing:
testparm -v | more and looking for the value of these parameters.
Also use the Microsoft Management Console Local Security Settings. This tool is available from the Control Panel. The Policy settings are found in the Local Policies/Security Options area and are prefixed by Secure Channel: ..., and Digitally sign .....
It is important that these be set consistently with the Samba-3 server settings.