Using SambaRobert Eckstein, David Collier-Brown, Peter Kelly
1st Edition November 1999
1-56592-449-5, Order Number: 4495
416 pages, $34.95
Before NetBIOS Name Servers (NBNS) came about, name resolution worked entirely by broadcast. If you needed a machine's address, you simply broadcast its name across the network and, in theory, the machine itself would reply. This approach is still possible: anyone looking for a machine named
fredcan still broadcast a query and find out if it exists and what its IP address is. (We use this capability to troubleshoot Samba name services with the
nmblookupcommand in Chapter 9, Troubleshooting Samba.)
As you saw in the first chapter, however, broadcasting - whether it be browsing or name registration and resolution - does not pass easily across multiple subnets. In addition, many broadcasts tend to bog down networks. To solve this problem, Microsoft now provides the Windows Internet Naming Service (WINS), a cross-subnet NBNS, which Samba supports. With it, an administrator can designate a single machine to act as a WINS server, and can then provide each client that requires name resolution the address of the WINS server. Consequently, name registration and resolution requests can be directed to a single machine from any point on the network, instead of broadcast.
WINS and broadcasting are not the only means of name resolution, however. There are actually four mechanisms that can be used with Samba:
Samba can use any or all of these name resolution methods in the order that you specify in the Samba configuration file using the
orderparameter. However, before delving into configuration options, let's discuss the one that you've probably not encountered before: the LMHOSTS file.
LMHOSTS is the standard LAN Manager hosts file used to resolve names into IP addresses on the system. It is the NBT equivalent of the /etc/hosts file that is standard on all Unix systems. By default, the file is usually stored as /usr/local/samba/lib/LMHOSTS and shares a format similar to /etc/hosts. For example:192.168.220.100 hydra 192.168.220.101 phoenix
The only difference is that the names on the right side of the entries are NetBIOS names instead of DNS names. Because they are NetBIOS names, you can assign resource types to them as well:192.168.220.100 hydra#20 192.168.220.100 simple#1b 192.168.220.101 phoenix#20
Here, we've assigned the
hydramachine to be the primary domain controller of the
SIMPLEdomain, as indicated by the resource type <1B> assigned to the name after
hydra's IP address in the second line. The other two are standard workstations.
If you wish to place an LMHOSTS file somewhere other than the default location, you will need to notify the nmbd process upon start up, as follows:nmbd -H /etc/samba/lmhosts -D
You can set up Samba to use a WINS server somewhere else on the network by simply pointing it to the IP address of the WINS server. This is done with the global
serverconfiguration option, as shown here:[global] wins server = 192.168.200.122
With this option enabled, Samba will direct all WINS requests to the server at 192.168.200.122. Note that because the request is directed at a single machine, we don't have to worry about any of the problems inherent to broadcasting. However, though you have specified an IP address for a WINS server in the configuration file, Samba will not necessarily use the WINS server before other forms of name resolution. The order in which Samba attempts various name-resolution techniques is given with the
orderconfiguration option, which we will discuss shortly.
If you have a Samba server on a subnet that still uses broadcasting and the Samba server knows the correct location of a WINS server on another subnet, you can configure the Samba server to forward any name resolution requests with the
proxyoption:[global] wins server = 192.168.200.12 wins proxy = yes
Use this only in situations where the WINS server resides on another subnet. Otherwise, the broadcast will reach the WINS server regardless of any proxying.
You can set up Samba as a WINS server by setting two global options in the configuration file, as shown below:[global] wins support = yes name resolve order = wins lmhosts hosts bcast
supportoption turns Samba into a WINS server. Believe it or not, that's all you need to do! Samba handles the rest of the details behind the scenes, leaving you a relaxed administrator. The
serveroption are mutually exclusive; you cannot simultaneously offer Samba as the WINS server and point to another system as the server.
If Samba is acting as a WINS server, you should probably get familiar with the
orderoption mentioned earlier. This option tells Samba the order of methods in which it tries to resolve a NetBIOS name. It can take up to four values:
Uses a LAN Manager LMHOSTS file
Uses the standard name resolution methods of the Unix system, /etc/hosts, DNS, NIS, or a combination (as configured for the system)
Uses the WINS server
Uses a broadcast method
The order in which you specify them in the value is the order in which Samba will attempt name resolution when acting as a WINS server. For example, let's look at the value specified previously:name resolve order = wins lmhosts hosts bcast
This means that Samba will attempt to use its WINS entries first for name resolution, followed by the LAN Manager LMHOSTS file on its system. Next, the hosts value causes it to use Unix name resolution methods. The word
hostsmay be misleading; it covers not only the /etc/hosts file, but also the use of DNS or NIS (as configured on the Unix host). Finally, if those three do not work, it will use a broadcast to try to locate the correct machine.
Finally, you can instruct a Samba server that is acting as a WINS server to check with the system's DNS server if a requested host cannot be found in its WINS database. With a typical Linux system, for example, you can find the IP address of the DNS server by searching the /etc/resolv.conf file. In it, you might see an entry such as the following:nameserver 127.0.0.1 nameserver 192.168.200.192
This tells us that a DNS server is located at 192.168.220.192. (The 127.0.0.1 is the localhost address and is never a valid DNS server address.)
Use the global
proxyoption to alert Samba to use the configured DNS server:[global] wins support = yes name resolve order = wins lmhosts hosts bcast dns proxy = yes
Samba's WINS options are shown in Table 7.5.
Table 7.5: WINS Options
If set to
yes, Samba will act as a WINS server.
string (IP address or DNS name)
Identifies a WINS server for Samba to use for name registration and resolution.
Allows Samba to act as a proxy to a WINS server on another subnet.
If set to
yes, a Samba WINS server will search DNS if it cannot find a name in WINS.
name resolve order
Specifies an order of the methods used to resolve NetBIOS names.
lmhosts hosts wins bcast
Specifies the maximum time-to-live in seconds for a requested NetBIOS names.
max wins ttl
Specifies the maximum time-to-live in seconds for NetBIOS names given out by Samba as a WINS server.
min wins ttl
Specifies the minimum time-to-live in seconds for NetBIOS names given out by Samba as a WINS server.
Samba will provide WINS name service to all machines in the network if you set the following in the
[global]section of the smb.conf file:[global] wins support = yes
The default value is
no, which is typically used to allow another Windows NT server to become a WINS server. If you do enable this option, remember that a Samba WINS server currently cannot exchange data with any backup WINS servers. If activated, this option is mutually exclusive with the
serverparameter; you cannot set both to
yesat the same time or Samba will flag an error.
Samba will use an existing WINS server on the network if you specify the
serverglobal option in your configuration file. The value of this option is either the IP address or DNS name (not NetBIOS name) of the WINS server. For example:[global] wins server = 192.168.220.110
or:[global] wins server = wins.example.com
In order for this option to work, the
supportoption must be set to
no(the default). Otherwise, Samba will report an error. You can specify only one WINS server using this option.
This option allows Samba to act as a proxy to another WINS server, and thus relay name registration and resolution requests from itself to the real WINS server, often outside the current subnet. The WINS server can be indicated through the
serveroption. The proxy will then return the WINS response back to the client. You can enable this option by specifying the following in the
[global]section:[global] wins proxy = yes
If you want the domain name service (DNS) to be used if a name isn't found in WINS, you can set the following option:[global] dns proxy = yes
This will cause nmbd to query for machine names using the server's standard domain name service. You may wish to deactivate this option if you do not have a permanent connection to your DNS server. Despite this option, we recommend using a WINS server. If you don't already have any WINS servers on your network, make one Samba machine a WINS server. Do not, however, make two Samba machines WINS servers (one primary and one backup) as they currently cannot exchange WINS databases.
orderoption specifies the order of services that Samba will use in attempting name resolution. The default order is to use the LMHOSTS file, followed by standard Unix name resolution methods (some combination of /etc/hosts, DNS, and NIS), then query a WINS server, and finally use broadcasting to determine the address of a NetBIOS name. You can override this option by specifying something like the following:[global] name resolve order = lmhosts wins hosts bcast
This causes resolution to use the LMHOSTS file first, followed by a query to a WINS server, the system password file, and finally broadcasting. You need not use all four options if you don't want to. This option is covered in more detail in the section Section 7.3.3, Setting Up Samba as a WINS Server, earlier in this chapter.
This option gives the maximum time to live (TTL) during which a NetBIOS name registered with the Samba server will remain active. You should never need to alter this value.
This option give the maximum time to live (TTL) during which a NetBIOS name resolved from a WINS server will remain active. You should never need to change this value from its default.
This option give the minimum time to live (TTL) during which a NetBIOS name resolved from a WINS server will remain active. You should never need to alter this value from its default.
© 1999, O'Reilly & Associates, Inc.