This per-port setting determines whether a given switch port is trusted to relay legitimate DHCP server responses, or untrusted and therefore has its DHCP server-side traffic filtered and monitored by the snooping feature; ports default to untrusted. Administrators set uplink ports connecting to the legitimate DHCP server as trusted, while leaving user-facing access ports untrusted so any rogue DHCP server plugged into them gets blocked. For example, an admin would set the port connecting to the switch's uplink toward the real DHCP server to trust(1), while leaving all end-user access ports at the default untrust(2).