Launch System Preferences, then choose Network
Select the "Built-in Ethernet" icon on the "Show" drop-down list
Under the TCP/IP button: Set "Configure IPv4" drop down to "Using DHCP"
Also make sure the DNS Servers and Search Domains are filled in with the following information:
- alias.cs.cmu.edu
- cs.cmu.edu
- ri.cmu.edu
- edrc.cmu.edu
- cmu.edu
Click the Apply Now button when finished:
*Note: This does not require a reboot.