How to forward traffic to the server in the internal network?

Question

Debian

Given:
- server-A - vpn host
- server-B - internal host It is
required to forward clients that connect to server-A through VPN access to server-B.
This means that all calls to IP server-B from the external network (from clients) through the VPN must be correctly processed.
Server-A has eth0 as external and eth1 as internal. tun0 is the VPN interface.

Answer 1

1. On server A, enable packet redirection (depending on the distribution, a change directly in the config may be overwritten later).
2. On clients, add a route to server B
3. On server B, add a route to clients