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Registered wireless devices on central campus at MIT are typically issued IP Addreses in the 18.111.*.* subnet.
Devices that rely on an Ethernet/wired interface but have no web browser
That would be all you console gamers on the Nintendo Wii, Playstation, and XBox, and users in the research areas with all the scientific wiz-bang doohickeys and apparatuses. You will need to contact IS&T either at computing-help@mit.edu or call the help desk at 3-1101 to have your device's MAC (Media Access Control) address registered.
Devices that DON'T require registration
iPads, smartphones, and most tablets do NOT require registration. The only thing you need is to have valid Kerberos credentials on the device to access MIT Secure and MIT Secure N as well as other online administrative apps and library resources. There are some devices that skim the line between smartphone/tablet and computer like the Windows Surface. If the device doesn't seem to behave correctly initially internet-wise unregistered, go ahead and register it and see if that fixes the problem.
Troubleshooting
Firewalls
Until MIT decides to implement up an Institute-wide firewall, machines on campus are fully accessible and potentially vulnerable from anyone out on the Internet. This has security implications for every section within the school. Hacking attacks should be expected and unnecessary guest accounts and services that use ports should be disabled on individual machines by turning on the machine's built in firewall. Unprotected machines can experience slow performance or slow internet access if they're being attacked. Or at worse, the machine could be compromised if it hasn't had its updates in a while. Though Macs are rarely compromised directly in this way, Windows machines can be, especially unpatched versions of Windows XP and lower. Machines access the internet and each other through numbered ports and firewalls should always be enabled to close down any ports users don't really use.
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Sometimes there are things that you DO want a computer to do through the protection of a computer firewall, for example file sharing, screen sharing or remote management. On Unix machines like Mac OS X, these services are controlled within System Preferences. But if all your other services are running, like web access and email, but for some reason the file sharing, screen sharing, or remote management doesn't work, the best thing to do is to uncheck these network services to turn them off. Then shut down the machine. After you count to ten, turn the machine back on and turn those services on again. This should hopefully restore those services back into a working state.
Acknowledgements
My thanks to my fellow co-worker Dan Irvine and IS&T collaborator Sparrow French for helping me make sure all the details of this document are as accurate as possible.