Not if you know what you're doing. A good practice is to shutdown any switch interfaces that aren't in use. Once you've done that, you can implement a rudimenta

Not if you know what you're doing. A good practice is to shutdown any switch interfaces that aren't in use. Once you've done that, you can implement a rudimentary access policy using MAC based ACLs. While a MAC based ACL won't prevent an attacker from gaining access to your network like a real authentication system (802.1X), it will help you notice the disruption. If you shut all ports that aren't in use, and you implement MAC ACLs, someone will notice the disruption. You'd have to unplug a network device in order to get an active port, and if you plugged in a hub, you'd have to spoof a MAC address, which would disrupt traffic to/from the device belonging to the MAC you just stole. Even rudimentary measures can help secure a network to some degree.