Hello, every one!

I have a problem using Iptables and Forward.

First some data to explain the problem:
OS: RedHat Enterprice 3 WS

Use of service: transmit small text files using sockets, the sofware contact
the remote server, transmit the file and disconnect it.

Connection: From a Linux Server to a Remote Unix Server using Frame Relay
Technology.

This schemes was working perfectly for two year:

Server --Router ---FrameRelay---Router---Other equipment--Server
<----- Transmitting and receiving connections ------->


But for some requirements we have to add en LinuxServer before the remote
other equipment:

Server --Router --FrameRelay--Router--New Linux Server--Other equiment--Server
<------ Transmitting and receiving connections -------------->


The new Linux server, must to make NAT, forward and redirect connections, using IPtables.

The problems is, since we add the new server, we start to have tree problems: 1) loose some connections; 2) The connection some time is slowly; and 3) some files are transmit it empty.

I reduce the function of the New Linux Server to just make forward (the connection get in from one network card and get out from other) with out any security rule to test, but the problem still happen.

Any idea?

Thank you so much, regards.