Estimate multicast DNS packet rate, bandwidth and wireless airtime cost for a device population.
mDNS floods the whole layer-2 segment, so packet rate is the total record count divided by the refresh interval. On Wi-Fi the cost is far worse than the bit count suggests, because multicast is transmitted at the lowest basic rate and cannot be aggregated. A few hundred Bonjour devices on one flat wireless VLAN can consume double-digit percentages of airtime with nothing but announcements, which is why large deployments proxy mDNS instead of bridging it.
mDNS
packet rate = devices × services per device ÷ announcement interval.
Wireless airtime cost
airtime = packets/s × packet bits ÷ multicast basic rate
packet rate = devices × services per device ÷ announcement interval. mDNS floods the whole layer-2 segment, so packet rate is the total record count divided by the refresh interval. On Wi-Fi the cost is far worse than the bit count suggests, because multicast is transmitted at the lowest basic rate and cannot be aggregated.
A few hundred Bonjour devices on one flat wireless VLAN can consume double-digit percentages of airtime with nothing but announcements, which is why large deployments proxy mDNS instead of bridging it.
This calculator takes 5 inputs: Devices advertising services, Services per device, Announcement interval, Bytes per mDNS packet, Multicast basic rate. The pre-filled defaults are a realistic starting point — replace them with figures from your own environment for a result you can act on.
Access points send multicast at the lowest configured basic rate so every associated client can decode it, and without a unicast acknowledgement there is no aggregation. A 200-byte frame at 1 Mbit/s occupies roughly 1.6 ms of channel time — hundreds of times what the same frame costs at modern data rates.