CAL’s in general and NAS

Hi,

I’m going to setup an AD domain with 2 Win2K3 servers with about 75 machines. I plan on getting a NAS for file storage. I have a couple
of questions about CAL’s.

Does authentication to a domain consitute a use of a CAL? If I have a NAS box, which will have domain permissions set on folders for security,
will authenticating to the domain require a CAL even though the files/directories
are not located on the servers themselves?

Assuming that a CAL is used, once a person gets into a domain permission protected share is the connection concurrent over the whole time that
the user is viewing that share? Or is the authentication done once per share then the CAL is released?

Any insight will be helpful.

Thanks,