Prevent Network-Discovery on Infrastructure side The Finder displays nearby Computers and Devices in the left column whenever a network connection is present. 

Sometimes we let clients use our network when we discuss projects in meetings (aka they bring their Notebooks along). In some cases we would prefer if they couldn't see all the machines and devices in our network. 

Is there a way to prevent the discovery of other network clients on the infrastructure side? I tried blocking Bonjour traffic, however, the Macs are still able to see who's around?
It's possible to block Bonjour traffic by configuring pf to disallow:


MAC addresses:
01:00:5E:00:00:FB – IPv4
33:33:00:00:00:FB – IPv6
IP addresses:
224.0.0.251 – multicast IPv4 address
FF02::FB – multicast IPv6 address
UDP port 5353


However, this will also impact your own regular and "desirable" hosts.

One possibility is to configure a VLAN and set it up as default network for your clients. A VLAN - properly set up - spans its own broadcast domain which can't be bypassed or bridged by Bonjour traffic. 

You need appropriate devices in your network environment to be able to create VLANs.