Mandatory, Basic and Supported Rates
What mandatory, basic and supported rates and the MBR really mean: build a rate set, see which clients can join and which rate beacons, broadcasts and ACKs use, and the risks of an MBR that isn't a mandatory rate.
How to use this tool controls and what to look for
Click the rates to build a rate set, or pick one of the ready-made sets under Try, and watch which clients can join and which rate every frame goes out at.
Controls to change
- Band: switch between 2.4 GHz (with the 802.11b rates) and 5 GHz.
- Try: load a ready-made rate set, such as the Default, MBR 24, or MBR 18 (optional rate) to see what goes wrong.
- Click a rate: each click cycles it through Basic, Supported and Disabled. The lowest Basic rate becomes the MBR.
What to look for
- Rates marked M are mandatory in the IEEE standard. A Basic rate without the M is the risky case: a compliant client may not support it and is refused with status code 18.
- Which clients can join: the minimum clients support only the mandatory rates, so an optional MBR such as 18 or 36 Mbps shuts them out.
- The ACK chart: when no Basic rate fits, the ACK falls back to a mandatory rate, even one you Disabled. The MBR is not a floor for ACKs.
- Basic 6 only sends every ACK at 6 Mbps. Adding 12 and 24 as Basic rates speeds them up.
About this tool
Access points let you mark each legacy data rate as Basic, Supported or Disabled, and the lowest Basic rate is known as the minimum basic rate (MBR). The IEEE standard also makes a few rates mandatory for every device, and vendors mix the words up: Cisco calls Basic rates "Mandatory". This tool lets you build a rate set for 2.4 or 5 GHz and shows which clients can join, the Supported Rates element the AP advertises, and the rate every beacon, broadcast and ACK really goes out at, including what goes wrong when the MBR is a rate the standard doesn't make mandatory.
What you'll learn
- The difference between mandatory rates (fixed by the IEEE standard), Basic rates (your configuration), Supported rates and the MBR
- Why a client that doesn't support every Basic rate can't see the network or is refused with status code 18
- How ACKs pick their rate, and why they can go out at a rate you disabled
- The risks of an MBR such as 18 or 36 Mbps that isn't a mandatory rate, and the safer choices next to it
Common questions
Is a basic rate the same as a mandatory rate?
No. Mandatory rates are fixed by the IEEE standard for each PHY: 6, 12 and 24 Mbps for OFDM, plus 1, 2, 5.5 and 11 Mbps on 2.4 GHz. Basic rates are the ones you configure as required to join. Cisco's interface calls Basic rates "Mandatory", which causes much of the confusion.
Can I set 18 Mbps or 36 Mbps as the minimum basic rate?
You can, and most modern clients will cope, but the standard doesn't require clients to support those rates. A compliant client without them can't decode the beacons or is refused. 12 or 24 Mbps give almost the same cell size without that risk.
Does disabling low data rates stop them being used?
Not completely. The AP stops using them for data, but ACKs to low-MCS frames still fall back to mandatory rates such as 6 or 12 Mbps, even when those rates are disabled.
Free for private and educational use. This interactive model is a simplified teaching aid and may contain mistakes. It is provided as is, without warranty. Use it to understand the concepts, not as a substitute for a site survey, vendor documentation or professional design advice.