UDP Options with Scapy
I am working on an implementation of the
UDP Options draft
at work, this
morning I got the
udp_input
side of processing building. This needs to be
test and gotten working before moving on, before setting up some VMs to test
this I need a way to generate packets with UDP Option data appended.
This seemed like a great occasion to use
go
a little more. There is the
gopacket
library from google that provides raw packet stuff.
I tried for ages to put together a send example that didn't depend on linux.
Eventually I got to the point where I could form crazy malformed arp packets. I
got to the point of generating the above traces in
wireshark
, for some reason
go was sticking 16 bytes into the address fields and creating madness. You will
note in the above arp packet that the length is much longer, that is because go
is appending some extra data for shits and giggles.
Giving up on go I had a look at the python libraries for generating packets,
they are all about the same level of insanity. The
pathspider
project has
some
test probes
for UDP Options using
scapy
.
pathspider
is a lot of stuff to pull in to generate UDP datagrams, I
extracted out the relevant stuff to use with
scapy
directly:
from scapy.all import IP
from scapy.all import UDP
from scapy.all import *
if __name__ == "__main__":
ip = IP(src="139.133.204.4", dst="139.133.204.64")
udp = UDP(sport=2600, dport=2600)
pkt = ip/udp/"Hello world"
pkt.getlayer(1).len = len(pkt.getlayer(1)) #force UDP len
send((pkt/"\x01\x01\x01\x00"))
You can add the numbers together to find that the extra option space is
include, you can also see the
01 01 01 00
bytes at the end of the packet
which are the options I add.
Reading: Gun Machine, The Difference Engine