/ip firewall raw
add action=add-src-to-address-list address-list=online_lan address-list-timeout=10s chain=prerouting in-interface=bridge_LAN

/ip firewall address-list
add address=8 list=A_online_LAN_count

/system script
add dont-require-permissions=no name=count_online

{
:local pc 0
:local lanonline [/ip firewall address-list get [/ip firewall address-list find list=A_online_LAN_count] address]
:foreach i in=[/ip firewall address-list find list=online_lan ] do= {:set pc ($pc+1)}
:if ($lanonline != $pc) do={
/ip firewall address-list set [/ip firewall address-list find list=A_online_LAN_count] address=$pc
}
}

/system scheduler
add interval=2m name=online on-event=”/system script run count_online” start-time=startup