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The third number 53 is significant because this number is appropriate subnet for valid static IP Addresses. So if you had an IS&T issued static in Building 4 it would be in the 18.53.*.* subnet pool.
DHCP for Wireless connected machines
Wireless devices at MIT are issued a temporary DHCP IP Address that may stop working if the user doesn't register their machine to the MIT network.
Registered wireless devices at MIT are issued IP Addreses in the 18.111.*.* subnet.