Skip to content
Calcrivo

mDNS Calculator

Estimate multicast DNS packet rate, bandwidth and wireless airtime cost for a device population.

Inputs

devices
services
s
bytes
Mbit/s

Multicast Packet Rate

6.25pps

Multicast Bandwidth

10.00kbit/s

Airtime Consumed

10.00ms/s

Airtime Utilisation

1.00%

Packets Per Minute

375

Step by step

  1. Values used

    Devices advertising services = 250 devices; Services per device = 3 services; Announcement interval = 120 s; Bytes per mDNS packet = 200 bytes; Multicast basic rate = 1 Mbit/s

  2. mDNS

    packet rate = devices × services per device ÷ announcement interval.

  3. Wireless airtime cost

    airtime = packets/s × packet bits ÷ multicast basic rate

  4. Multicast Packet Rate

    = 6.25 pps

  5. Multicast Bandwidth

    = 10.00 kbit/s

  6. Airtime Consumed

    = 10.00 ms/s

  7. Airtime Utilisation

    = 1.00

  8. Packets Per Minute

    = 375

How it works

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.

Formulas

mDNS

packet rate = devices × services per device ÷ announcement interval.

devices × services
Total advertised service records on the segment
announcement interval
Seconds between unsolicited announcements or record refreshes

Wireless airtime cost

airtime = packets/s × packet bits ÷ multicast basic rate

multicast basic rate
Multicast frames are sent at the lowest basic rate, often 1–6 Mbit/s
airtime
Milliseconds of channel time consumed per second

Frequently Asked Questions

How is mDNS calculated?

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.

Why does mDNS matter?

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.

What values do I need to enter?

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.

Why does multicast cost so much airtime?

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.

You might also need

Related Calculators

Service Discovery CalculatorDNS Cache CalculatorDNS Query Rate Calculator