9.2.10 Troubleshooting NetBIOS Names

Historically, SMB protocols have depended on the NetBIOS name system, also called the LAN Manager name system. This was a simple scheme where each machine had a unique 20-character name and broadcast it on the LAN for everyone to know. With TCP/IP, we tend to use names like client.example.com stored in /etc/hosts files, through DNS or WINS.

The usual mapping to domain names such as server.example.com simply uses the server part as the NetBIOS name and converts it to uppercase. Alas, this doesn't always work, especially if you have a machine with a 21-character name; not everyone uses the same NetBIOS and DNS names. For example, corpvm1 along with vm1.corp.com is not unusual.

A machine with a different NetBIOS name and domain name is confusing when you're troubleshooting; we recommend that you try to avoid this wherever possible. NetBIOS names are discoverable with smbclient :

• If you can list shares on your Samba server with smbclient and a -L option (list shares) of short_name_of_server, the short name is the NetBIOS name.

• If you get "Get_Hostbyname: Unknown host name," there is probably a mismatch. Check in the smb.conf file to see if the NetBIOS name is explicitly set.

• Try again, specifying -I and the IP address of the Samba server (e.g., smbclient -L server -I 192.168.236.86). This overrides the name lookup and forces the packets to go to the IP address. If this works, there was a mismatch.

• Try with -I and the full domain name of the server (e.g., smbclient -L server -I server.example.com). This tests the lookup of the domain name, using whatever scheme the Samba server uses (e.g., DNS). If it fails, you have a name service problem. You should reread the section Section 9.2.8" after you finish troubleshooting the NetBIOS names.

• Try with -n (NetBIOS name) and the name you expect to work (e.g., smbclient -n server -L server-12) but without overriding the IP address through -I. If this works, the name you specified with -n is the actual NetBIOS name of the server. If you receive "Get-Hostbyname: Unknown host MARY," it's not the right server yet.

• If nothing is working so far, repeat the tests specifying -U username and -W workgroup, with the username and workgroup in uppercase, to make sure you're not being derailed by a user or workgroup mismatch.

• If nothing works still and you had evidence of a name service problem, troubleshoot name service in the section Section 9.2.8," and then return to NetBIOS name service.