Redirect Output with Iptables

Question

Is possible on Debian to change the port of packets that are going to a specific port, using iptables?

Example:

I want packets going in the outbound direction to a.b.c.d for port 1723 to be redirected to the address a.b.c.d on port 10000. Is this possible?

Solution

for proto in tcp udp; do
  sudo iptables -t nat -A OUTPUT -d a.b.c.d -p "$proto" --dport 1723 -j DNAT --to-destination a.b.c.d:10000
done

Comments

[jw013]

Please use standard terminology like source and destination. Am I correct in assuming you want iptables to change the destination port on outbound packets to a specific host from 1723 to 10000 for both TCP and UDP?

[Jhonathan]

@jw013 You're right

[Leahkim]

This only works if ip forwarding is activated: echo 1 > /proc/sys/net/ipv4/ip_forward