I used to manage shifts at the NOC of a very large ISP. It was great fun when everything worked fine (and really scary when things didn't). I learned loads and was responsible for monitoring the backbone, the ISP's servers such as mail, DNS and RADIUS servers, and also the hosting/co-location server farm.

I learned so much, specifically about networking and UNIX. I'm sure you'll learn loads too.

Good luck for your CEH.