text: #!/usr/bin/env python
  
  # Copyright (c) 2016 Cisco and/or its affiliates.
  # Licensed under the Apache License, Version 2.0 (the "License");
  # you may not use this file except in compliance with the License.
  # You may obtain a copy of the License at:
  #
  #     http://www.apache.org/licenses/LICENSE-2.0
  #
  # Unless required by applicable law or agreed to in writing, software
  # distributed under the License is distributed on an "AS IS" BASIS,
  # WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
  # See the License for the specific language governing permissions and
  # limitations under the License.
  
  from scapy.all import Ether, IP, ICMP
  from resources.libraries.python.PacketVerifier \
      import Interface, create_gratuitous_arp_request, auto_pad, checksum_equal
  from resources.libraries.python.TrafficScriptArg import TrafficScriptArg
  
  
  def check_ttl(ttl_begin, ttl_end, ttl_diff):
      if ttl_begin != ttl_end + ttl_diff:
          raise RuntimeError(
              "TTL changed from {} to {} but decrease by {} expected"
              .format(ttl_begin, ttl_end, ttl_diff))
  
  
  def ckeck_packets_equal(pkt_send, pkt_recv):
      pkt_send_raw = auto_pad(pkt_send)
      pkt_recv_raw = auto_pad(pkt_recv)
      if pkt_send_raw != pkt_recv_raw:
          print "Sent:     {}".format(pkt_send_raw.encode('hex'))
          print "Received: {}".format(pkt_recv_raw.encode('hex'))
          print "Sent:"
          pkt_send.show2()
          print "Received:"
          pkt_recv.show2()
          raise RuntimeError("Sent packet doesn't match received packet")
  
  
  def main():
      args = TrafficScriptArg(['src_mac', 'dst_mac', 'src_ip', 'dst_ip',
                               'hops', 'first_hop_mac', 'is_dst_tg'])
  
      src_if_name = args.get_arg('tx_if')
      dst_if_name = args.get_arg('rx_if')
      is_dst_tg = True if args.get_arg('is_dst_tg') == 'True' else False
  
      src_mac = args.get_arg('src_mac')
      first_hop_mac = args.get_arg('first_hop_mac')
      dst_mac = args.get_arg('dst_mac')
      src_ip = args.get_arg('src_ip')
      dst_ip = args.get_arg('dst_ip')
      hops = int(args.get_arg('hops'))
  
      if is_dst_tg and (src_if_name == dst_if_name):
          raise RuntimeError(
              "Source interface name equals destination interface name")
  
      src_if = Interface(src_if_name)
      src_if.send_pkt(str(create_gratuitous_arp_request(src_mac, src_ip)))
      if is_dst_tg:
          dst_if = Interface(dst_if_name)
          dst_if.send_pkt(str(create_gratuitous_arp_request(dst_mac, dst_ip)))
  
      pkt_req_send = (Ether(src=src_mac, dst=first_hop_mac) /
                      IP(src=src_ip, dst=dst_ip) /
                      ICMP())
      src_if.send_pkt(pkt_req_send)
  
      if is_dst_tg:
          pkt_req_recv = dst_if.recv_pkt()
          if pkt_req_recv is None:
              raise RuntimeError('Timeout waiting for packet')
  
          check_ttl(pkt_req_send[IP].ttl, pkt_req_recv[IP].ttl, hops)
          pkt_req_send_mod = pkt_req_send.copy()
          pkt_req_send_mod[IP].ttl = pkt_req_recv[IP].ttl
          del pkt_req_send_mod[IP].chksum  # update checksum
          ckeck_packets_equal(pkt_req_send_mod[IP], pkt_req_recv[IP])
  
          pkt_resp_send = (Ether(src=dst_mac, dst=pkt_req_recv.src) /
                           IP(src=dst_ip, dst=src_ip) /
                           ICMP(type=0))  # echo-reply
          dst_if.send_pkt(pkt_resp_send)
  
      pkt_resp_recv = src_if.recv_pkt()
      if pkt_resp_recv is None:
          raise RuntimeError('Timeout waiting for packet')
  
      if is_dst_tg:
          check_ttl(pkt_resp_send[IP].ttl, pkt_resp_recv[IP].ttl, hops)
          pkt_resp_send_mod = pkt_resp_send.copy()
          pkt_resp_send_mod[IP].ttl = pkt_resp_recv[IP].ttl
          del pkt_resp_send_mod[IP].chksum  # update checksum
          ckeck_packets_equal(pkt_resp_send_mod[IP], pkt_resp_recv[IP])
  
      if not pkt_resp_recv.haslayer(IP):
          raise RuntimeError('Received packet does not contain IPv4 header: {}'.
                             format(pkt_resp_recv.__repr__()))
  
      if pkt_resp_recv[IP].src != pkt_req_send[IP].dst:
          raise RuntimeError(
              'Received IPv4 packet contains wrong src IP address, '
              '{} instead of {}'.format(pkt_resp_recv[IP].src,
                                        pkt_req_send[IP].dst))
  
      if pkt_resp_recv[IP].dst != pkt_req_send[IP].src:
          raise RuntimeError(
              'Received IPv4 packet contains wrong dst IP address, '
              '{} instead of {}'.format(pkt_resp_recv[IP].dst,
                                        pkt_req_send[IP].src))
  
      # verify IPv4 checksum
      copy = pkt_resp_recv.copy()
      chksum = copy[IP].chksum
      del copy[IP].chksum
      tmp = IP(str(copy[IP]))
      if not checksum_equal(tmp.chksum, chksum):
          raise RuntimeError('Received IPv4 packet contains invalid checksum, '
                             '{} instead of {}'.format(chksum, tmp.chksum))
  
      if not pkt_resp_recv[IP].haslayer(ICMP):
          raise RuntimeError(
              'Received IPv4 packet does not contain ICMP header: {}'.
              format(pkt_resp_recv[IP].__repr__()))
  
      # verify ICMP checksum
      copy = pkt_resp_recv.copy()
      chksum = copy[IP][ICMP].chksum
      del copy[IP][ICMP].chksum
      tmp = ICMP(str(copy[IP][ICMP]))
      if not checksum_equal(tmp.chksum, chksum):
          raise RuntimeError('Received ICMP packet contains invalid checksum, '
                             '{} instead of {}'.format(chksum, tmp.chksum))
  
      pkt_req_send_mod = pkt_req_send.copy()
      pkt_req_send_mod[IP][ICMP].type = pkt_resp_recv[IP][ICMP].type
      del pkt_req_send_mod[IP][ICMP].chksum  # update checksum
      ckeck_packets_equal(pkt_req_send_mod[IP][ICMP], pkt_resp_recv[IP][ICMP])
  
  
  if __name__ == "__main__":
      main()
  