Home / server / Questions / 380752
Accepted
fadedbee
Asked: 2012-04-19 08:21:35 +0800 CST

How do you redirect (one way only) udp packets to another host using netcat?

  • 772

How do you redirect (one way only) udp packets to another host using netcat?

nc -l -u 0.0.0.0 12345 | nc -u 192.168.1.128 12345

stops after successfully redirecting the first packet.

(Note: an iptables solution would also be useful.)

Thanks,

Chris.

netcat iptables

2 Answers

  1. For the iptables solution, you'll basically be doing an destination NAT on the packets. Something like:

    iptables -t nat -I PREROUTING -p udp --dport 12345 -j DNAT --to 192.168.1.128:12345

    With netcat, hmm. You can use the -k option to keep the listen side up after you process the packets, but you'll need to do something to keep sending. Named pipes, maybe?

    mknod /tmp/nc.pipe p
nc -l -k -u 0.0.0.0 12345 > /tmp/nc.pipe &

while [1]
do
  nc -u 192.168.1.128 12345 < /tmp/nc.pipe
done

    Untested, clearly.

    • 2
  2. Best Answer

    So long as you don't receive more than one message per second, this will forward 99%+ of them.

    (It's a really horrible fudge.)

    #!/bin/bash 
while :
do
  bash -c "nc -l -u 0.0.0.0 12345 | nc -u 192.168.1.128 12345" &
  sleep 1
  kill $!
done
    • 0