U-Boot has networking support for VLANs (802.1q), and CDP (Cisco Discovery Protocol). You control the sending/receiving of VLAN tagged packets with the "vlan" environmental variable. When not present no tagging is performed. CDP is used mainly to discover your device VLAN(s) when connected to a Cisco switch. Note: In order to enable CDP support a small change is needed in the networking driver. You have to enable reception of the 01:00:0c:cc:cc:cc MAC address which is a multicast address. Various defines control CDP; see the README section.