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#!/usr/local/bin/python3
# check wether path mtu to dst is as expected
import os
import threading
from addr import *
from scapy.all import *
# usage: ping6_mtu src dst size icmp6-size
# work around the broken sniffing of packages with bad checksum
#a=srp1(eth, iface=SRC_IF, timeout=2)
class Sniff1(threading.Thread):
filter = None
captured = None
packet = None
def run(self):
self.captured = sniff(iface=SRC_IF, filter=self.filter,
count=1, timeout=3)
if self.captured:
self.packet = self.captured[0]
srcaddr=sys.argv[1]
dstaddr=sys.argv[2]
size=int(sys.argv[3])
expect=int(sys.argv[4])
eid=os.getpid() & 0xffff
hdr=IPv6(src=srcaddr, dst=dstaddr)/ICMPv6EchoRequest(id=eid)
payload="a" * (size - len(bytes(hdr)))
ip=hdr/payload
iplen=IPv6(bytes(ip)).plen
eth=Ether(src=SRC_MAC, dst=PF_MAC)/ip
sniffer = Sniff1();
# pcap cannot access icmp6, check for packet too big, avoid neighbor discovery
sniffer.filter = "ip6 and dst %s and icmp6 and ip6[40] = 2 and ip6[41] = 0" \
% srcaddr
sniffer.start()
time.sleep(1)
sendp(eth, iface=SRC_IF)
sniffer.join(timeout=5)
a = sniffer.packet
if a is None:
print("no packet sniffed")
exit(2)
if a and a.type == ETH_P_IPV6 and \
ipv6nh[a.payload.nh] == 'ICMPv6' and \
icmp6types[a.payload.payload.type] == 'Packet too big':
mtu=a.payload.payload.mtu
print("mtu=%d" % (mtu))
if mtu != expect:
print("MTU!=%d" % (expect))
exit(1)
iip=a.payload.payload.payload
iiplen=iip.plen
if iiplen != iplen:
print("inner IPv6 plen %d!=%d" % (iiplen, iplen))
exit(1)
isrc=iip.src
if isrc != srcaddr:
print("inner IPv6 src %d!=%d" % (isrc, srcaddr))
exit(1)
idst=iip.dst
if idst != dstaddr:
print("inner IPv6 dst %d!=%d" % (idst, dstaddr))
exit(1)
exit(0)
print("MTU=UNKNOWN")
exit(2)
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