HCNP学习笔记之ICMP协议与ping原理以及用Python实现ping

import subprocess
import shlexcmd = "ping -c 1 www.baidu.com"
args = shlex.split(cmd)try:
subprocess.check_call(args, stdout=subprocess.PIPE, stderr=subprocess.PIPE)
print "baidu server is up!"
except subprocess.CalledProcessError:
print "Failed to get ping."

# 定义Pinger类，初始化创建实例import os
import argparse
import socket
import struct
import select
import timeICMP_ECHO_REQUEST = 8 # Platform specific
DEFAULT_TIMEOUT = 2
DEFAULT_COUNT = 4 class Pinger(object):
""" Pings to a host -- the Pythonic way""" def __init__(self, target_host, count=DEFAULT_COUNT, timeout=DEFAULT_TIMEOUT):
self.target_host = target_host
self.count = count
self.timeout = timeout

def do_checksum(self, source_string):
""" Verify the packet integritity """
sum = 0
max_count = (len(source_string)/2)*2
count = 0
while count < max_count: # 分割数据每两比特(16bit)为一组
val = ord(source_string[count + 1])*256 + ord(source_string[count])
sum = sum + val
sum = sum & 0xffffffff
count = count + 2 if max_count<len(source_string): <span class="hljs-comment"># 如果数据长度为基数,则将最后一位单独相加</span>
sum = sum + ord(source_string[len(source_string) - 1])
sum = sum & 0xffffffff sum = (sum >> 16) + (sum & 0xffff) # 将高16位与低16位相加直到高16位为0
sum = sum + (sum >> 16)
answer = ~sum
answer = answer & 0xffff
answer = answer >> 8 | (answer << 8 & 0xff00)
return answer # 返回的是十进制整数

def receive_ping(self, sock, ID, timeout):
"""
Receive ping from the socket.
"""
time_remaining = timeout
while True:
start_time = time.time()
readable = select.select([sock], [], [], time_remaining)
time_spent = (time.time() - start_time)
if readable[0] == []: # Timeout
return time_received = time.time()
recv_packet, addr = sock.recvfrom(1024)
icmp_header = recv_packet[20:28]
type, code, checksum, packet_ID, sequence = struct.unpack(
"bbHHh", icmp_header
)
if packet_ID == ID:
bytes_In_double = struct.calcsize("d")
time_sent = struct.unpack("d", recv_packet[28:28 + bytes_In_double])[0]
return time_received - time_sent time_remaining = time_remaining - time_spent
if time_remaining <= 0:
return

def send_ping(self, sock, ID):
"""
Send ping to the target host
"""
target_addr = socket.gethostbyname(self.target_host) my_checksum = 0 # Create a dummy heder with a 0 checksum.
header = struct.pack("bbHHh", ICMP_ECHO_REQUEST, 0, my_checksum, ID, 1)
bytes_In_double = struct.calcsize("d")
data = (192 - bytes_In_double) * "Q"
data = struct.pack("d", time.time()) + data # Get the checksum on the data and the dummy header.
my_checksum = self.do_checksum(header + data)
header = struct.pack(
"bbHHh", ICMP_ECHO_REQUEST, 0, socket.htons(my_checksum), ID, 1
)
packet = header + data
sock.sendto(packet, (target_addr, 1))

def ping_once(self):
"""
Returns the delay (in seconds) or none on timeout.
"""
icmp = socket.getprotobyname("icmp")
try:
sock = socket.socket(socket.AF_INET, socket.SOCK_RAW, icmp)
except socket.error, (errno, msg):
if errno == 1:
# Not superuser, so operation not permitted
msg += "ICMP messages can only be sent from root user processes"
raise socket.error(msg)
except Exception, e:
print "Exception: %s" %(e) my_ID = os.getpid() & 0xFFFF self.send_ping(sock, my_ID)
delay = self.receive_ping(sock, my_ID, self.timeout)
sock.close()
return delay

def ping(self):
"""
Run the ping process
"""
for i in xrange(self.count):
print "Ping to %s..." % self.target_host,
try:
delay = self.ping_once()
except socket.gaierror, e:
print "Ping failed. (socket error: '%s')" % e[1]
break if delay == None:
print "Ping failed. (timeout within %ssec.)" % self.timeout
else:
delay = delay * 1000
print "Get ping in %0.4fms" % delayif __name__ == '__main__':
parser = argparse.ArgumentParser(description='Python ping')
parser.add_argument('--target-host', action="store", dest="target_host", required=True)
given_args = parser.parse_args()
target_host = given_args.target_host
pinger = Pinger(target_host=target_host)
pinger.ping()