---
name: "mdio"
section: "4"
platform: "freebsd"
package: "base"
version: "16.0-CURRENT-20261027-61c70dc16a79"
release: "FreeBSD 16.0-CURRENT (2026-10-27)"
platforms: ["freebsd"]
url: "https://new.carta.tech/mdio"
---

# mdio(4)

IEEE 802.3 Management Data Input/Output interface

## NAME

**mdio** – IEEE 802.3 Management Data Input/Output interface

## SYNOPSIS

To compile this driver into the kernel, place the following line in your kernel configuration file:

**device mdio**

## DESCRIPTION

The **mdio** driver provides an interconnection between the Media Access Control (MAC) sublayer and Physical Layer (PHY) entities' control and status registers, as defined by the IEEE 802.3 Standard.

The **mdio** layer allows device drivers to share common support code for various external PHY devices.

MDIO is one of two signal interfaces that comprise the Media Independent Interface (MII) defined by the IEEE 802.3 Standard. The [miibus(4)](/miibus/4.md) driver provides support for devices that require full MII support.

## SEE ALSO

[miibus(4)](/miibus/4.md)

## STANDARDS

More information on MDIO can be found in the IEEE 802.3 Standard.

## HISTORY

The **mdio** driver first appeared in FreeBSD 10.0.

## AUTHORS

The driver was written by Stefan Bethke ⟨*stb@lassitu.de*⟩.