Question

I’m writing python program to build mac-address cache using pcap. But pcap module for python has no good documentation. I have found this page http://pylibpcap.sourceforge.net/ with code example and it works fine.

Can anybody modify this example to make it able to show the source mac-address for each packet? Or point me to the documentation where I can read about it …

updated

Here is a code part where information about mac addresses were cut.

def print_packet(pktlen, data, timestamp):
  if not data:
    return

  if data[12:14]=='\x08\x00':
    decoded=decode_ip_packet(data[14:])
    print '\n%s.%f %s > %s' % (time.strftime('%H:%M',
                                           time.localtime(timestamp)),
                             timestamp % 60,
                             decoded['source_address'],
                             decoded['destination_address'])
    for key in ['version', 'header_len', 'tos', 'total_len', 'id',
                'flags', 'fragment_offset', 'ttl']:
      print '  %s: %d' % (key, decoded[key])
    print '  protocol: %s' % protocols[decoded['protocol']]
    print '  header checksum: %d' % decoded['checksum']
    print '  data:'
    dumphex(decoded['data'])

First 14 octets in data are destination, source mac-addr and ether type.

    decoded=decode_ip_packet(data[14:])

I need to parse them to get this info. Task is done.

Answer 1

Google “Ethernet frame formats”. The first 6 octets of a packet is the destination MAC address, which is immediately followed by the 6 octets of source MAC address.

This Wikipedia page may help.