通过UDP探测端到端MTU

P_MTU_D（Path MTU Discovery）

socket的UDP功能，去发现端到端MTU

#!/usr/bin/env python3
#-*- encoding:utf8 -*-
#Used UDP to learn the MTU of the end_to_end PATH_MTU

import IN,argparse,socket

if not hasattr(IN,'IP_MTU'):
    raise RuntimeError('cannot perform MTU discovery on this combination')

def send_big_datagram(host,port):
    sock = socket.socket(socket.AF_INET,socket.SOCK_DGRAM)
    sock.setsockopt(socket.IPPROTO_IP,IN.IP_MTU_DISCOVER,IN.IP_PMTUDISC_DO)
    sock.connect((host,port))
    try:
        sock.send(b'#'*65535)
    except socket.error:
        print("also,the datagram did not make it")
        max_mtu = sock.getsockopt(socket.IPPROTO_IP,IN.IP_MTU)
        print('Actual MTU:{}'.format(max_mtu))

if __name__ == '__main__':
    parser = argparse.ArgumentParser(description='Send UDP Packet to Get PATH_MTU')
    parser.add_argument('host',help='the target host')
    parser.add_argument('-p',metavar='port',type=int,default=1060,help='UDP port((default 1060)')
    args = parser.parse_args()
    send_big_datagram(args.host,args.p)