Traceroute implementation in Python 2.

traceroute.py

#!/usr/bin/env python2.7

import argparse
import socket
import struct
import random
import time

MAX_HOP=64
MAX_ICMP_PACKET_SIZE=1508

class Protocol:

    def __init__(self, packet):
        self.packet = packet

    def shift(self, size):
        data = self.packet[:size]
        self.packet = self.packet[size:]
        return data

def probe(addr, ttl, port=60021):
    s = socket.socket(socket.AF_INET, socket.SOCK_DGRAM)
    s.setsockopt(socket.IPPROTO_IP, socket.IP_TTL, ttl)
    s.sendto("\x00"*16, (addr, port))

def traceroute(host):
    s_icmp = socket.socket(socket.AF_INET, socket.SOCK_RAW, socket.IPPROTO_ICMP)
    s_icmp.setsockopt(socket.SOL_IP, socket.IP_HDRINCL, 1)
    s_icmp.settimeout(5.0)
    for ttl in xrange(1, MAX_HOP + 1):
        dport = random.randint(60000, 61000)
        for i in xrange(3):
            probe(host, ttl, dport)
        t0 = time.time()
        while time.time() - t0 < 5.0:
            try:
                ip_packet, addr = s_icmp.recvfrom(MAX_ICMP_PACKET_SIZE)
            except socket.timeout:
                continue
            packet = Protocol(ip_packet)
            packet.shift(20) # skip IP header
            t, code, checksum = struct.unpack('!bbH', packet.shift(4))
            if t == 11 and code == 0:
                packet.shift(4)  # skip TEM reserved
                packet.shift(20) # skip IP  header
                udp_sport, udp_dport = struct.unpack('!HH', packet.shift(4))
                if udp_dport == dport:
                    yield (ttl, addr[0], time.time() - t0)
                    break
        else:
            yield (ttl, None, time.time() - t0)

if __name__ == '__main__':
    parser = argparse.ArgumentParser(description="print the route packets take to network host")
    parser.add_argument('host', help='destination host')
    args = parser.parse_args()
    print "traceroute to %s, %d hops max" % (args.host, MAX_HOP)
    for hop, addr, rtt in traceroute(args.host):
        print " %-2s %-15s  %9s" % (hop, addr if addr else '*', "%.3fms" % (rtt * 1000) if addr else '')