An Odd Server Migration Issue

Over the weekend my boss replaced the server which holds all of our student’s user data.  Though the operating system version, server name, domain membership, share names, and permissions all stayed identical from the old server to the new server none of our students could access their data when they came to school this morning. After a few hours of troubleshooting I realized that an nslookup of  the server wasn’t getting beyond our Extreme Network switches. Five minutes after rebooting our switches everyone was back up and running, and the users were able to access their data.  Has anyone else experienced this? And if so, can someone explain to me why this has happened so I know when to expect it in the future?