#!/usr/local/bin/python3
# check wether path mtu to dst is 1300

import os
from addr import *
from scapy.all import *

dstaddr=sys.argv[1]
eid=os.getpid() & 0xffff
hdr=IP(flags="DF", src=SRC_OUT, dst=dstaddr)/ICMP(type='echo-request', id=eid)
payload=b"a" * (1400 - len(bytes(hdr)))
ip=hdr/payload
eth=Ether(src=SRC_MAC, dst=PF_MAC)/ip
a=srp1(eth, iface=SRC_IF, timeout=2)

if a is None:
	print("no packet sniffed")
	exit(2)
if a and a.payload.payload.type==3 and a.payload.payload.code==4:
	mtu=a.payload.payload.nexthopmtu
	print("mtu=%d" % (mtu))
	if mtu == 1300:
		exit(0)
	print("MTU!=1300")
	exit(1)
print("MTU=UNKNOWN")
exit(2)