def buildArpResponse(packet, mac):
if not isinstance(packet, Arp):
packet = base.extract(packet, Arp)
if packet is None:
return None
resp = Arp()
resp.hwdst = packet.hwsrc
resp.protodst = packet.protosrc
resp.hwsrc = mac
resp.protosrc = packet.protodst
resp.hwtype = Arp.HW_TYPE_ETHERNET
resp.hwlen = 6
resp.prototype = Arp.PROTO_TYPE_IP
resp.protolen = 4
resp.opcode = Arp.REPLY
return resp
