How to deal with server ip interception in LAN?

Question

Network administration

Hello. A friend had a problem to solve which my knowledge is clearly not enough, so I hope for your help.

So, a friend has his own small local area (<1000 computers) and everything worked well and great until a large provider came to the city and began to fight competitors in every way (cut cables, send checks, etc.). So, one of the ways to westernize turned out to be the inclusion of several computers with the vpn server IP set on them, at first this does not create problems and is not visible at all, but once the server is rebooted, it can no longer get its IP, and network clients cannot get into to the Internet - as it connects to the attacker's computer.

How can you fight this?

Answer 1

Static ARP table on the switch. Well, a static ip for the vpn server, of course.