Section 6.1. Using NetBIOS Name Resolution

6.1. Using NetBIOS Name Resolution

As described in Chapter 3 and Chapter 5, NetBIOS provides a computer-naming system that's independent of DNS, which is used by most TCP/IP protocols. In fact, Windows enables its clients to use these NetBIOS names in place of DNS names for most protocols, at least for local computers. For this reason, some LANs rely heavily on these names, and if you want to refer to computers by name rather than by IP address from Linux, you may need to know how to configure Linux utilities to use these addresses. For the most part, this task can be handled with a setting or two in smb.conf. If your LAN doesn't use DNS hostnames for its local computers, though, you may want to expand this configuration to enable Linux to use NetBIOS names in non-SMB/CIFS tools, such as web browsers and email clients.

6.1.1. Setting Name Resolution Options in smb.conf

Most SMB/CIFS client tools in Linux support the use of NetBIOS names. These tools rely on libraries that ship with Samba and that are configured in the [global] section of your smb.conf file. In particular, you should review the name resolve order, wins server, and hostname lookups parameters, all of which are described in Chapter 3. For the most part, the default settings work well on small LANs that are configured to use broadcast name resolution. You might want to set hostname lookups = Yes if you want to specify computers by their DNS hostnames in smb.conf, though. If your network hosts an NBNS system, you may also want to point Linux systems to it with wins server.

If a computer functions as an NBNS system, do not set wins server. Even pointing the server to itself with this parameter can result in odd behavior.

The parameter that requires the most attention is name resolve order. This parameter takes one to four of several values: lmhosts, hosts, wins, and bcast. The default lookup order is lmhosts host wins bcast, which minimizes the use of network resources. You can change this order if you like, though, or even omit options entirely. For instance, suppose you know your lmhosts file is empty, and suppose you don't want to use DNS except as a last resort because of possible name conflicts. You might then include these lines in smb.conf:

name resolve order = wins bcast hosts wins server = 192.168.24.1

6.1.2. Using NetBIOS Name Resolution in Non-Samba Programs

In most cases, the NetBIOS name-resolution methods you set with name resolve order and other options in smb.conf apply only to Samba and related tools. These name-resolution methods have been split off into a library, though, and it's possible to splice this library into Linux's normal name-resolution system. When you configure Linux this way, you can use NetBIOS names in any Linux program that employs the normal name-resolution system, such as web browsers, mail clients, FTP clients, and so on. This can be a handy way to get name resolution working on a small network that doesn't have its own DNS server. (You'd presumably use your ISP's DNS server for handling names on the Internet, but it might not have entries for your local computers.)

Using NetBIOS names for non-SMB/CIFS tools can be convenient, but it can also cause problems. NetBIOS names lack Internet domain names, and so a few programs that rely on Internet domain names can choke if they're fed NetBIOS names. If DNS and NetBIOS names don't match, you can also cause problems when reverse lookups don't match forward lookups or when one name masks another one. These problems aren't always serious, but if you see strange error messages about failed lookups, you might want to consider using local /etc/hosts files or running your own DNS server for local use, as described in Chapter 15.

The first step to using NetBIOS name resolution in non-Samba programs is to check for the presence of the necessary support libraries. These appear under the name libnss_wins.so (typically with a symbolic link called libnss_wins.so.2), usually in /lib. If you can't find these files, you may need to install additional or newer Samba packages for your distribution. If you compiled Samba from source code, try typing make nsswitch from the Samba source directory, copying the resulting nsswitch/libnss_wins.so file to /lib, and creating a symbolic link called libnss_wins.so.2. Usually, you will need to type ldconfig to have the system recognize the new library.

Once the library is installed, you must configure Linux to use it. This task can be accomplished by editing /etc/nsswitch.conf. Look for the hosts line in this file. It probably contains entries for files, dns, and perhaps other name-resolution methods. Add wins to this list:

hosts: files dns wins

Linux tries name lookups in the order specified, so this example uses NetBIOS name lookups as the last resort. You might want to move wins earlier in the list, but doing so increases the odds for problems should a name be resolved in multiple ways and a program needs an Internet domain name.

Although the option in /etc/nsswitch.conf is called wins, the name-resolution system it enables works with both NBNS systems and broadcast name lookups. The libnss_wins.so library uses the NBNS computer specified by the wins server parameter in smb.conf, but it ignores the name resolve order parameter.