dpkt GRE stripping

unwrap-gre.py

#!/usr/bin/env python
# -*- coding: utf-8 -*-
# Extracts IP content from GRE and writes to arg[1].out 
# Drops non GRE
# requires dpkt gre patch
import dpkt
import sys 
fin = open(sys.argv[1])
fout = open(sys.argv[1] + ".out", "w")
pcap = dpkt.pcap.Reader(fin)
pcapout = dpkt.pcap.Writer(fout)
frame_counter = 0
for ts, buf in pcap:
    eth = dpkt.ethernet.Ethernet(buf)
    ip = eth.data
    if ip.p == 47:
        payload = ip.data.data
        inner_ip = payload.data
        eth.data = inner_ip
        pcapout.writepkt(eth)
fin.close()
fout.close()