@ShadiusFirst create the new VLAN interface on the MX and make sure it has a DHCP server assigned to it. To do this go to Security & SD-WAN and pick the Addressing and VLANs menu, then click on the button to change from single VLAN to VLANs, next click on add VLAN and create a second VLAN, give it a name (AC) a subnet and interface IP similar to what is shown below:
Next go to the DHCP config menu and make sure both VLANs are set to Run a DHCP server like the second one shown below:
On the Wireless / SSIDs configuration page, create a second SSID and set the security (probably WPA2-PSK for an AC unit) and in the Addressing and traffic section make sure you change it to Use VLAN tagging as below
It is a good idea to change the existing SSID to also use VLAN tagging but just pick the original VLAN (usually 1 unless you have changed this. SSIDs must be in bridge mode or layer 3 roaming mode (you don't want that) to use VLAN tagging.
If you connect the AC units to the new SSID they will now be in a separate VLAN and separate associated subnet and you can create access rules to only allow certain traffic between the VLANs (subnets).
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