$packet .= pack_ethaddr($flow{DL_DST});
$packet .= pack_ethaddr($flow{DL_SRC});
if ($flow{DL_VLAN} != 0xffff) {
$packet .= pack('nn', 0x8100, $flow{DL_VLAN});
$packet .= pack_ethaddr($flow{DL_DST});
$packet .= pack_ethaddr($flow{DL_SRC});
if ($flow{DL_VLAN} != 0xffff) {
$packet .= pack('nn', 0x8100, $flow{DL_VLAN});