Mikrotik RouterOS is the main router of our cable network (EuroDOCSIS). It also serves as DHCP server for network CPEs. Activating the lease query would primarly aleviate some problems when for some RF problem the modem gets disconnected. In such cases, all computers/devices behind the modem have to renew the lease (manually), which with DHCPLEASEQUERY mechanism would not be necessary (CMTS queries the DHCP server instead for lost/unknown IP/MACs it encounters in the network, or when searching for a MAC address - does not throw broadcast ARP).
I'd test it myself, but its a live platform with thousands of clients, so I thought better to ask first
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cheers,
Shpend