MAC Address Configuration

Ethernet drivers can delegate most MAC address handling during initialization to net_eth_mac_config and net_eth_mac_load(). The structure is typically stored in the driver configuration and initialized with NET_ETH_MAC_DT_CONFIG_INIT or NET_ETH_MAC_DT_INST_CONFIG_INIT, which translate the devicetree properties into one of the following behaviors:

NET_ETH_MAC_STATIC – use the full local-mac-address property.
NET_ETH_MAC_RANDOM – generate a random locally administered MAC address, optionally using the bytes provided in zephyr,mac-address-prefix as the first octets.
NET_ETH_MAC_NVMEM – read the remaining bytes from the "mac-address" NVMEM cell, again optionally prefixed by zephyr,mac-address-prefix.
NET_ETH_MAC_DEFAULT – fall back to the driver’s default logic (for example, a factory-programmed MAC address stored in peripheral registers).

Driver integration

Embed the net_eth_mac_config structure inside the driver’s configuration and a static buffer inside the driver’s data:

struct my_eth_config {
    struct net_eth_mac_config mac_cfg;
    /* more config fields */
};

struct my_eth_data {
    uint8_t mac_addr[NET_ETH_ADDR_LEN];
    /* more data fields */
};

static const struct my_eth_config my_eth_config_0 = {
    .mac_cfg = NET_ETH_MAC_DT_INST_CONFIG_INIT(0),
};
static struct my_eth_data my_eth_data_0;

During initialization, call net_eth_mac_load() before registering the address with the network interface. The helper copies any statically provided bytes, fills the remaining octets, and performs the necessary validation. Drivers can still fall back to SoC-specific storage when no configuration was provided:

static int my_eth_init(const struct device *dev)
{
    const struct my_eth_config *cfg = dev->config;
    struct my_eth_data *data = dev->data;
    int ret;

    ret = net_eth_mac_load(&cfg->mac_cfg, data->mac_addr);
    if (ret == -ENODATA) {
        ret = my_eth_hw_read_mac(dev, data->mac_addr);
    }

    return ret;
}

static void my_eth_iface_init(struct net_if *iface)
{
    const struct device *dev = net_if_get_device(iface);
    struct my_eth_data *data = dev->data;

    net_if_set_link_addr(iface, data->mac_addr, sizeof(data->mac_addr), NET_LINK_ETHERNET);
}

Devicetree examples

The examples below show how to pick a MAC address configuration for an ethernet controller node such as &eth0.

Static MAC address

&eth0 {
    local-mac-address = [00 11 22 33 44 55];
};

Random MAC address with prefix

&eth0 {
    zephyr,mac-address-prefix = [00 04 25];
    zephyr,random-mac-address;
};

NVMEM-provided MAC address with prefix

&eth0 {
    zephyr,mac-address-prefix = [00 12 34];
    nvmem-cells = <&macaddr_cell>;
    nvmem-cell-names = "mac-address";
};

&eeprom0 {
    nvmem-layout {
        compatible = "fixed-layout";
        #address-cells = <1>;
        #size-cells = <1>;

        macaddr_cell: cell@0 {
            reg = <0x0 0x6>;
            #nvmem-cell-cells = <0>;
        };
    };
};

When no MAC-related properties are present, net_eth_mac_load() returns -ENODATA and the driver is expected to use its existing mechanism (for example, reading the hardware registers or using a build-time constant).

Changing the MAC address at runtime

Applications that need to set MAC addresses dynamically (for example to adopt an address obtained from a management interface) need to enable the networking management API with CONFIG_NET_MGMT and use net_mgmt with NET_REQUEST_ETHERNET_SET_MAC_ADDRESS. The request internally calls the driver’s ethernet_api.set_config() implementation.

static int app_set_mac_address(const struct device *dev)
{
    struct net_if *iface = net_if_lookup_by_dev(dev);
    struct ethernet_req_params params = {
        .mac_address = { { 0x02, 0x00, 0x5E, 0x01, 0x02, 0x03 } },
    };

    /* Make sure the iface is down */

    return net_mgmt(NET_REQUEST_ETHERNET_SET_MAC_ADDRESS, iface,
                    &params, sizeof(params));
}