title: How to read whole ip layer and tcp layer from a packet when using scapy?
body: <p>I am doing a TCP retransmission behavior test when receiving ICMP Destination unreachable (Fragmentation needed ICMP TYPE=3 CODE=4) message with scapy.  </p>
  
  <p>The test flow like this:<br>
  1. Establish a TCP connection to the server<br>
  2. Send a HTTP GET request to the server when TCP is established<br>
  3. When HTTP Response back<br>
  4. Send an ICMP type 3 code 4 message to the server with s small MTU set  </p>
  
  <p>The question is that ICMP TYPE=3 CODE=4 message include the IP Header and partial TCP header (srt, dst and seq number) of that HTTP Response packets. Currently, I just read each paramemter (like IP identification, frag tag, ttl etc.) from that HTTP Response packets. The question is: is there any way that I can read the whole IP and TCP header from that packet:</p>
  
  <p><code>ICMP(TYPE=3 CODE=4)/IP Header/TCP Header</code></p>