# $Id: arp.py 23 2006-11-08 15:45:33Z dugsong $

"""Address Resolution Protocol."""

import dpkt

# Hardware address format
ARP_HRD_ETH	= 0x0001	# ethernet hardware
ARP_HRD_IEEE802	= 0x0006	# IEEE 802 hardware

# Protocol address format
ARP_PRO_IP	= 0x0800	# IP protocol

# ARP operation
ARP_OP_REQUEST		= 1	# request to resolve ha given pa
ARP_OP_REPLY		= 2	# response giving hardware address
ARP_OP_REVREQUEST	= 3	# request to resolve pa given ha
ARP_OP_REVREPLY		= 4	# response giving protocol address

class ARP(dpkt.Packet):
    __hdr__ = (
        ('hrd', 'H', ARP_HRD_ETH),
        ('pro', 'H', ARP_PRO_IP),
        ('hln', 'B', 6),	# hardware address length
        ('pln', 'B', 4),	# protocol address length
        ('op', 'H', ARP_OP_REQUEST),
        ('sha', '6s', ''),
        ('spa', '4s', ''),
        ('tha', '6s', ''),
        ('tpa', '4s', '')
        )