On my debian6 server is a process that only listen on IPv6 but I also need to listen on IPv4. It seems the program is IPv6 only. Is there a way to route the traffic fom IPv6 to IPv4 on the same host ?
This happens automatically when IPv4-mapped IPv6 is in use.
Check the sysctl
net.ipv6.bindv6only; if it is set to 0, then IPv4-mapped IPv6 is in use, and incoming IPv4 connections will be mapped and sent to the IPv6 listener.
However, individual processes can override this behavior so it's not a cure-all. If you want a specific answer for your circumstance, you'll have to name the program.