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#!/usr/local/bin/python2.7
import os
from addr import *
from scapy.all import *
ip=IP(src=FAKE_NET_ADDR, dst=REMOTE_ADDR)
port=os.getpid() & 0xffff
print "Send SYN packet, receive SYN+ACK."
syn=TCP(sport=port, dport='chargen', seq=1, flags='S', window=(2**16)-1)
synack=sr1(ip/syn, iface=LOCAL_IF, timeout=5)
if synack is None:
print "ERROR: no SYN+ACK from chargen server received"
exit(1)
print "Send ACK packet, receive chargen data."
ack=TCP(sport=synack.dport, dport=synack.sport, seq=2, flags='A',
ack=synack.seq+1, window=(2**16)-1)
data=sr1(ip/ack, iface=LOCAL_IF, timeout=5)
if data is None:
print "ERROR: no data from chargen server received"
exit(1)
print "Fill our receive buffer."
time.sleep(1)
print "Send ICMP fragmentation needed packet with MTU 1300."
icmp=ICMP(type="dest-unreach", code="fragmentation-needed",
nexthopmtu=1300)/data
send(IP(src=LOCAL_ADDR, dst=REMOTE_ADDR)/icmp, iface=LOCAL_IF)
print "Path MTU discovery will resend first data with length 1300."
data=sr1(ip/ack, iface=LOCAL_IF, timeout=5)
if data is None:
print "ERROR: no data retransmit from chargen server received"
exit(1)
print "Cleanup the other's socket with a reset packet."
rst=TCP(sport=synack.dport, dport=synack.sport, seq=2, flags='AR',
ack=synack.seq+1)
send(ip/rst, iface=LOCAL_IF)
len = data.len
print "len=%d" % len
if len != 1300:
print "ERROR: TCP data packet len is %d, expected 1300." % len
exit(1)
exit(0)
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