<p><b>@bergzand</b> commented on this pull request.</p>

<hr>

<p>In <a href="https://github.com/RIOT-OS/RIOT/pull/11077#discussion_r290786940">sys/usb/usbus/cdc/ecm/cdc_ecm_netdev.c</a>:</p>
<pre style='color:#555'>> +    if (max_len && buf == NULL) {
+        _signal_rx_flush(cdcecm);
+        return cdcecm->len;
+    }
+    memcpy(buf, cdcecm->in_buf, max_len);
+    _signal_rx_flush(cdcecm);
+    return max_len;
+}
+
+static int _init(netdev_t *netdev)
+{
+    usbus_cdcecm_device_t *cdcecm = _netdev_to_cdcecm(netdev);
+
+    luid_get(cdcecm->mac_netdev, ETHERNET_ADDR_LEN);
+    cdcecm->mac_netdev[0] |= 0x02;      /* locally administered address */
+    cdcecm->mac_netdev[0] &= ~0x01;     /* unicast address */
</pre>
<p>Same as above, but now for the ethernet address on the host side</p>
<p>To explain, with ECM, we simulate a point to point link, on one side the host computer, on the other side the RIOT network interface. Both sides of the virtual network cable require a link layer address and with ECM the device specifies the host side link layer address via a descriptor.</p>
<p>This bit generates and clamps the generated link layer address for the host side to indicate a locally administrated unicast link layer address.</p>

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