1#!/usr/local/bin/python3
2# check wether path mtu to dst is 1300
3
4import os
5from addr import *
6from scapy.all import *
7
8dstaddr=sys.argv[1]
9eid=os.getpid() & 0xffff
10hdr=IP(flags="DF", src=SRC_OUT, dst=dstaddr)/ICMP(type='echo-request', id=eid)
11payload=b"a" * (1400 - len(bytes(hdr)))
12ip=hdr/payload
13eth=Ether(src=SRC_MAC, dst=PF_MAC)/ip
14a=srp1(eth, iface=SRC_IF, timeout=2)
15
16if a is None:
17	print("no packet sniffed")
18	exit(2)
19if a and a.payload.payload.type==3 and a.payload.payload.code==4:
20	mtu=a.payload.payload.nexthopmtu
21	print("mtu=%d" % (mtu))
22	if mtu == 1300:
23		exit(0)
24	print("MTU!=1300")
25	exit(1)
26print("MTU=UNKNOWN")
27exit(2)
28