A simple traceroute(8) implementation in Python
traceroute(8) is one of these tools that sysadmins often use
when a networking issue arises and needs troubleshooting.
The traceroute(8) tool is used to trace the route packets take
in a network to a destination host. The tool is used to diagnose
possible problems in the network and also measure the latency
between systems.
The way that traceroute(8) works is by sending a sequence of UDP
ICMP Echo Request
packets to a destination host with a specified Time-To-Live (TTL)
value.
Each time a packet reaches a gateway, the gateway checks if the TTL of a packet is greater than one, reduces the TTL of the packet by one and transmits the packet to its next hop. If the TTL of a packet is one, then the gateway discards the packet and sends back a Time exceeded response to the source client informing it that the destination host could not be reached as the packet TTL has exceeded.
These Time exceeded responses are then being used by the source
client to determine the intermediate gateways sitting between the
source and destination system by manipulating the TTL of packets on
each iteration until we finally reach our destination host or the
max number of iterations (hops limit) has been reached.
You can read more about traceroute(8) at the
Traceroute page on Wikipedia.
Below you can find a Python module that creates a very basic
implementation of traceroute(8).
Please also note, that the receiver socket used in the class below is a
raw socket (socket.SOCK_RAW), so you will need root privileges when
binding it.
You can also find the code below in the pytraceroute repository on Github.
"""
A very simple Python traceroute(8) implementation
"""
import socket
import random
__all__ = ['Tracer']
class Tracer(object):
def __init__(self, dst, hops=30):
"""
Initializes a new tracer object
Args:
dst (str): Destination host to probe
hops (int): Max number of hops to probe
"""
self.dst = dst
self.hops = hops
self.ttl = 1
# Pick up a random port in the range 33434-33534
self.port = random.choice(range(33434, 33535))
def run(self):
"""
Run the tracer
Raises:
IOError
"""
try:
dst_ip = socket.gethostbyname(self.dst)
except socket.error as e:
raise IOError('Unable to resolve {}: {}', self.dst, e)
text = 'traceroute to {} ({}), {} hops max'.format(
self.dst,
dst_ip,
self.hops
)
print(text)
while True:
receiver = self.create_receiver()
sender = self.create_sender()
sender.sendto(b'', (self.dst, self.port))
addr = None
try:
data, addr = receiver.recvfrom(1024)
except socket.error:
raise IOError('Socket error: {}'.format(e))
finally:
receiver.close()
sender.close()
if addr:
print('{:<4} {}'.format(self.ttl, addr[0]))
else:
print('{:<4} *'.format(self.ttl))
self.ttl += 1
if addr[0] == dst_ip or self.ttl > self.hops:
break
def create_receiver(self):
"""
Creates a receiver socket
Returns:
A socket instance
Raises:
IOError
"""
s = socket.socket(
family=socket.AF_INET,
type=socket.SOCK_RAW,
proto=socket.IPPROTO_ICMP
)
try:
s.bind(('', self.port))
except socket.error as e:
raise IOError('Unable to bind receiver socket: {}'.format(e))
return s
def create_sender(self):
"""
Creates a sender socket
Returns:
A socket instance
"""
s = socket.socket(
family=socket.AF_INET,
type=socket.SOCK_DGRAM,
proto=socket.IPPROTO_UDP
)
s.setsockopt(socket.SOL_IP, socket.IP_TTL, self.ttl)
return s