Chapter 4. Server Types and Security Modes

This chapter provides information regarding the types of server that Samba may be configured to be. A Microsoft network administrator who wishes to migrate to or to use Samba will want to know what, within a Samba context, terms familiar to MS Windows @@ -8,10 +8,11 @@ modes function BEFORE we get into the details of how to configure the server its The chapter provides an overview of the security modes of which Samba is capable and how these relate to MS Windows servers and clients.

-Firstly we should recognise the question so often asked, "Why would I want to use Samba?" -So, in those chapters where the answer may be important you will see a section that highlights -features and benefits. These may be for or against Samba. -

Features and Benefits

+A question often asked is, "Why would I want to use Samba?" Most chapters contain a section +that highlights features and benefits. We hope that the information provided will help to +answer this question. Be warned though, we want to be fair and reasonable, so not all +features are positive towards Samba so the benefit may be on the side of our competition. +

Features and Benefits

Two men were walking down a dusty road, when one suddenly kicked up a small red stone. It hurt his toe and lodged in his sandal. He took the stone out and cursed it with a passion and fury fitting his anguish. The other looked at the stone and said, that is a garnet - I @@ -23,7 +24,7 @@ pleasure, but if you are forced upon it and have no time for its secrets then it a source of discomfort.

Samba started out as a project that sought to provide interoperability for MS Windows 3.x -clients with a Unix server. It has grown up a lot since its humble beginnings and now provides +clients with a UNIX server. It has grown up a lot since its humble beginnings and now provides features and functionality fit for large scale deployment. It also has some warts. In sections like this one we will tell of both.

@@ -47,14 +48,14 @@ So now, what are the benefits of features mentioned in this chapter? greater flexibility than MS Windows NT4 and in many cases a significantly higher utility than Active Directory domains with MS Windows 200x. -

Server Types

Administrators of Microsoft networks often refer to three -different type of servers:

Domain Controller
Primary Domain Controller
Backup Domain Controller
ADS Domain Controller
Domain Member Server
Active Directory Member Server
NT4 Style Domain Member Server
Stand Alone Server

Server Types

Administrators of Microsoft networks often refer to three +different type of servers:

Domain Controller
- Primary Domain Controller
- Backup Domain Controller
- ADS Domain Controller
Domain Member Server
- Active Directory Domain Server
- NT4 Style Domain Domain Server
Stand Alone Server

The chapters covering Domain Control, Backup Domain Control and Domain Membership provide -pertinent information regarding Samba-3 configuration for each of these server roles. +pertinent information regarding Samba configuration for each of these server roles. The reader is strongly encouraged to become intimately familiar with the information presented. -

Samba Security Modes

-In this section the function and purpose of Samba's security +

Samba Security Modes

+In this section the function and purpose of Samba's security modes are described. An accurate understanding of how Samba implements each security mode as well as how to configure MS Windows clients for each mode will significantly reduce user complaints and administrator heartache. @@ -69,7 +70,7 @@ ways that allow the security levels to be implemented. In actual fact, Samba imp ADS, and SERVER modes. They are documented in this chapter.

-A SMB server tells the client at startup what security level + A SMB server tells the client at startup what security level it is running. There are two options: share level and user level. Which of these two the client receives affects the way the client then tries to authenticate itself. It does not directly affect @@ -77,8 +78,8 @@ the way the client then tries to authenticate itself. It does not directly affec but it fits in with the client/server approach of SMB. In SMB everything is initiated and controlled by the client, and the server can only tell the client what is available and whether an action is allowed. -

User Level Security

-We will describe user level security first, as it's simpler. +

User Level Security

+We will describe user level security first, as it's simpler. In user level security, the client will send a session setup command directly after the protocol negotiation. This contains a username and password. The server can either accept or reject that @@ -95,13 +96,11 @@ It is also possible for a client to send multiple ses requests. When the server responds, it gives the client a uid to use as an authentication tag for that username/password. The client can maintain multiple authentication contexts in this way (WinDD is an example of an application that does this). -

Example Configuration

The smb.conf parameter that sets User Level Security is: -

-	security = user
-

security = user

This is the default setting since samba-2.2.x. -

Share Level Security

Ok, now for share level security. In share level security, the client authenticates itself separately for each share. It will send a password along with each tree connection (share mount). It does not explicitly send a @@ -121,104 +120,92 @@ level security. They normally send a valid username but no password. Samba recor this username in a list of possible usernames. When the client then does a tree connection it also adds to this list the name of the share they try to connect to (useful for home directories) and any users -listed in the user = smb.conf line. The password is then checked +listed in the user smb.conf line. The password is then checked in turn against these possible usernames. If a match is found then the client is authenticated as that user. -

Example Configuration

The smb.conf parameter that sets Share Level Security is: -

-	security = share
-

security = share

Please note that there are reports that recent MS Windows clients do not like to work with share mode security servers. You are strongly discouraged from using share level security. -

Domain Security Mode (User Level Security)

-When Samba is operating in security = domain mode, +

Domain Security Mode (User Level Security)

+When Samba is operating in security = domain mode, the Samba server has a domain security trust account (a machine account) and will cause all authentication requests to be passed through to the domain controllers. -

Example Configuration

Samba as a Domain Member Server

This method involves addition of the following parameters in the smb.conf file: -

-        security = domain
-        workgroup = "name_of_NT_domain"
-

security = domain

workgroup = MIDEARTH

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

On the MS Windows NT domain controller, using the Server Manager, add a machine account for the Samba server. -
Next, on the Unix/Linux system execute:
root# smbpasswd -j DOMAIN_NAME -r PDC_NAME (samba-2.x)
root# net join -U administrator%password (samba-3)

Note

-As of Samba-2.2.4 the Samba 2.2.x series can auto-join a Windows NT4 style Domain just -by executing: +

Next, on the UNIX/Linux system execute:

root# net rpc join -U administrator%password

Note

+Samba-2.2.4 and later can auto-join a Windows NT4 style Domain just by executing:

-root# smbpasswd -j DOMAIN_NAME -r PDC_NAME -U Administrator%password
+root# smbpasswd -j DOMAIN_NAME -r PDC_NAME \
+	 -U Administrator%password

-As of Samba-3 the same can be done by executing: +Samba-3 can do the same by executing:

-root# net join -U Administrator%password
+root# net rpc join -U Administrator%password

-It is not necessary with Samba-3 to specify the DOMAIN_NAME or the PDC_NAME as it -figures this out from the smb.conf file settings. +It is not necessary with Samba-3 to specify the DOMAIN_NAME or the +PDC_NAME as it figures this out from the smb.conf file settings.

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

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

-For more information of being a domain member, see the Domain -Member section of this Howto. -

ADS Security Mode (User Level Security)

+ For more information of being a domain member, see the chapter about domain membership. +

ADS Security Mode (User Level Security)

Both Samba 2.2 and 3.0 can join an Active Directory domain. This is -possible even if the domain is run in native mode. Active Directory in -native mode perfectly allows NT4-style domain members, contrary to +possible if the domain is run in native mode. Active Directory in +native mode perfectly allows NT4-style domain members. This is contrary to popular belief. The only thing that Active Directory in native mode prohibits is Backup Domain Controllers running NT4.

-If you are running Active Directory starting with Samba 3.0 you can -however join as a native AD member. Why would you want to do that? +If you are using Active Directory, starting with Samba-3 you can +join as a native AD member. Why would you want to do that? Your security policy might prohibit the use of NT-compatible authentication protocols. All your machines are running Windows 2000 -and above and all use full Kerberos. In this case Samba as a NT4-style +and above and all use Kerberos. In this case Samba as a NT4-style domain would still require NT-compatible authentication data. Samba in -AD-member mode can accept Kerberos. -

Example Configuration

-	realm = your.kerberos.REALM
-	security = ADS
-

- The following parameter may be required: -

-	ads server = your.kerberos.server
-

-Please refer to the Domain Membership and Active Directory -Membership sections for more information regarding this configuration option. -

Server Security (User Level Security)

+AD-member mode can accept Kerberos tickets. +

Example Configuration

realm = your.kerberos.REALM

security = ADS

+The following parameter may be required: +

ads server = your.kerberos.server

+Please refer to the chapter on domain membership +for more information regarding this configuration option. +

Server Security (User Level Security)

Server security mode is a left over from the time when Samba was not capable of acting as a domain member server. It is highly recommended NOT to use this feature. Server security mode has many draw backs. The draw backs include: -

Potential Account Lockout on MS Windows NT4/200x password servers

Lack of assurance that the password server is the one specified

Does not work with Winbind, particularly needed when storing profiles remotely

This mode may open connections to the password server, and keep them open for extended periods.

Security on the Samba server breaks badly when the remote password server suddenly shuts down

With this mode there is NO security account in the domain that the password server belongs to for the Samba server.

Potential Account Lockout on MS Windows NT4/200x password servers
Lack of assurance that the password server is the one specified
Does not work with Winbind, particularly needed when storing profiles remotely
This mode may open connections to the password server, and keep them open for extended periods.
Security on the Samba server breaks badly when the remote password server suddenly shuts down
With this mode there is NO security account in the domain that the password server belongs to for the Samba server.

In server security mode the Samba server reports to the client that it is in user level security. The client then does a session setup as described earlier. The Samba server takes the username/password that the client sends and attempts to login to the -password server by sending exactly the same username/password that +password server by sending exactly the same username/password that it got from the client. If that server is in user level security and accepts the password, then Samba accepts the clients connection. This allows the Samba server to use another SMB -server as the password server. +server as the password server.

You should also note that at the very start of all this, where the server tells the client what security level it is in, it also tells the client if it supports encryption. If it does then it supplies the client with a random cryptkey. The client will then send all passwords in encrypted form. Samba supports this type of encryption by default.

-The parameter security = server means that Samba reports to clients that +The parameter security = server means that Samba reports to clients that it is running in user mode but actually passes off all authentication requests to another user mode server. This requires an additional -parameter password server that points to the real authentication server. +parameter password server that points to the real authentication server. That real authentication server can be another Samba server or can be a Windows NT server, the later natively capable of encrypted password support.

Note

@@ -229,17 +216,13 @@ lookups because the choice of the target authentication server is arbitrary and be determined from a domain name. In essence, a Samba server that is in server security mode is operating in what used to be known as workgroup mode. -

Example Configuration

Using MS Windows NT as an authentication server

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

-        encrypt passwords = Yes
-        security = server
-        password server = "NetBIOS_name_of_a_DC"
-

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

encrypt passwords = Yes

security = server

password server = "NetBIOS_name_of_a_DC"

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

The down-side of this mode of configuration is the fact that for security reasons Samba @@ -248,9 +231,9 @@ server fails to reject the username and password pair then an alternative mode o identification of validation is used. Where a site uses password lock out after a certain number of failed authentication attempts this will result in user lockouts.

-Use of this mode of authentication does require there to be a standard Unix account +Use of this mode of authentication does require there to be a standard UNIX account for the user, though this account can be blocked to prevent logons by non-SMB/CIFS clients. -