Rebroadcast packetFw to another server

What would be easyest way to capture packets that packetforwarder sends to one serever and formward them to a one more server.
I do not want to touch gateway.
And it would be nice if I do not need to change gateway bridge.
Sniffing 1700 would be ok, but i did not manage to forward package for other server understand.

I am just interested in sending messaged in one direction - i am not interested in downlink…