By default, any computer that you plug into wall ports in the department is dynamically assigned in IP address. If you want the machine plugged into a port to be accessible from the outside world, however, you have to register it with the department.
To do that, fill out this form: http://www-cse.ucsd.edu/node/1868#top
See this page for more information on wired access: http://www-cse.ucsd.edu/node/1992
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