If the Solaris CIFS server is in domain mode, local users are required to prefix username with hostname of the server in order to access CIFS shares. However, this is not one should expect when logging in a Windows server.
Test results (against Windows 2000 system)
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Define a share on Windows 2000 system. Attempt to connect to the share from the following Windows clients succeeds by specifying only the username.
1) a client is is in workgroup mode
2) a client is in a member of domain A while the Solaris CIFS server is a member of domain B.