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#!/usr/local/bin/python2.7
print "fragments of a large packet that has to be refragmented by reflector"
# |--------|
# |------------------|
# ...
# |------------------|
# |----|
import os
from addr import *
from scapy.all import *
pid=os.getpid()
eid=pid & 0xffff
payload=100 * "ABCDEFGHIJKLMNOP"
packet=IP(src=LOCAL_ADDR, dst=REMOTE_ADDR)/ \
ICMP(type='echo-request', id=eid)/payload
request_cksum=ICMP(str(packet.payload)).chksum
print "request cksum=%#x" % (request_cksum)
frag=[]
fid=pid & 0xffff
frag.append(IP(src=LOCAL_ADDR, dst=REMOTE_ADDR, proto=1, id=fid, flags='MF')/
str(packet)[20:36])
offset=2
chunk=4
while 40+8*(offset+chunk) < len(payload):
frag.append(IP(src=LOCAL_ADDR, dst=REMOTE_ADDR, proto=1, id=fid,
frag=offset, flags='MF')/
str(packet)[20+(8*offset):20+8*(offset+chunk)])
offset+=chunk
frag.append(IP(src=LOCAL_ADDR, dst=REMOTE_ADDR, proto=1, id=fid,
frag=offset)/str(packet)[20+(8*offset):])
eth=[]
for f in frag:
eth.append(Ether(src=LOCAL_MAC, dst=REMOTE_MAC)/f)
if os.fork() == 0:
time.sleep(1)
sendp(eth, iface=LOCAL_IF)
os._exit(0)
ans=sniff(iface=LOCAL_IF, timeout=3, filter=
"ip and src "+REMOTE_ADDR+" and dst "+LOCAL_ADDR+" and icmp")
for a in ans:
if a and a.type == ETH_P_IP and \
a.payload.proto == 1 and \
a.payload.frag == 0 and a.payload.flags == 1 and \
icmptypes[a.payload.payload.type] == 'echo-reply':
id=a.payload.payload.id
print "id=%#x" % (id)
if id != eid:
print "WRONG ECHO REPLY ID"
exit(2)
reply_cksum=a.payload.payload.chksum
print "reply cksum=%#x" % (reply_cksum)
# change request checksum incrementaly and check with reply
diff_cksum=~(~reply_cksum+~(~request_cksum+~0x0800+0x0000))
if diff_cksum & 0xffff != 0xffff and diff_cksum & 0xffff != 0:
print "CHECKSUM ERROR diff cksum=%#x" % (diff_cksum)
exit(1)
exit(0)
print "NO ECHO REPLY"
exit(2)
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