Convert raw atm pcap files (from GNS3) to sun atm (for Wireshark)

rawatm2sunatm.py

#!/usr/bin/env python

import sys
import struct
from scapy.all import *

inputfile = ''
outputfile = ''
if len(sys.argv) < 3:
    print 'Usage: ./rawatm2sunatm.py <inputfile> <outputfile>'
    sys.exit(2)

inputfile = sys.argv[1]
outputfile = sys.argv[2]

conf.l2types.register(100, Raw) # Wrong LLC in file, importing as raw
pcap = rdpcap(inputfile)

pcap2 = PacketList()
buff = ''

for p in pcap:
    data = p.fields['load']
    h1,h2,h3,h4 = struct.unpack('!BBBB', data[:4]) # 5th byte is error control

    vpi = (h1<<4) + (h2>>4)
    vci = ((h2&0xF)<<12) + (h3<<4) + (h4>>4)
    pt = (h4&0xF)>>1
    
    if pt&4: # AAL5 Management
        flag = 0
        data = data[5:]
    else: # AAL5 User
        flag = 2 # LLC
        buff += data[5:]
        if not pt&1:
            continue
        data = buff
        buff = ''
    
    head = struct.pack("!BBH", flag, vpi, vci) # flag(1b), vpi(1b), vci(2b)
    data = head + data
    pcap2.append(Raw(data))

wrpcap(outputfile, pcap2, linktype=123) # 123 = SUNATM