How to FORWARD ports inside LAN via iptables?

Question

iptables

There are a lot of articles on port forwarding inside the local network from the outside, but I can't figure out port forwarding inside the network itself.

Here I have 3 computers connected to 1 router, when accessing from 1 computer to the second via tcp / udp, I should be transferred to the 3rd computer.

What entries are needed in iptables of the 2nd computer for such a move?

Answer 1

when accessing from the first computer to the second, you are referring directly to the second computer, and not to the router, so port forwarding to the third computer from the second computer must be configured directly on the second computer