How can I change live packet length and then forward them in scapy?

Question

I want to use scapy to manipulate network live packet (change the packet length of a special program) then forward them to dst. How can I do this and Is there better tool than scapy or not?

Answer 1

This is really easy to do using scapy, with the below sample for instance:

from scapy.all import *
def _handle(pkt):
    pkt[Ether].dst = None  # ask scapy to regenerate it
    pkt[IP].dst = “192.168.x.y”. # or any IP
    # packet edits
    # ...
    sendp(pkt)
sniff(prn=_handle). # on each packet received, execute _handle(pkt)

You may also specify an interface in sendp or sniff using the iface=... arg