I used to run Microsoft Exchange. I was a sysadmin back in the day. I ran the servers, checked their health, tuned the systems, etc.
Now I'm running NAC. I'm running the servers, checking health, tuning systems, etc. It's like I'm a sysadmin all over again. Not a bad thing, either. I'm actually using those sysadmin skillz alongside my network skillz.
That underlines an aspect of security: there's a lot of sysadmin-type stuff in this field, especially in maintaining the separate system as well as analyzing what it's doing. If you're a former sysadmin wanting to get into networking, consider getting familiar with a security product and using that as your entry point.
:matrix: