Linux causing probs where SCO doesn't

Hello All

We have an MRP system, the server side of which resides on a RedHat 7.3 box.
One of the (Windows 98) clients is at a remote site and is connected to the
main network by a freeswan VPN (a linux gateway on each network). When this
remote client attempts to connect to the MRP system tcpdump shows that the
machines send a few packets backwards and forwards on random ports and then
give up.

A slightly older version of the system is still running on a SCO Openserver
box and the client CAN connect to it over the VPN. (tcpdump shows the
machines exchanging lots of packets on random ports to establish a
connection).

This leads me to believe that there might be some sort of filtering going on
on the linux MRP box which doesn't like the VPN traffic, or that linux is
somehow more fussy than SCO. There is no firewall running on the MRP box, so
anything causing the problem must go deeper than that.

Does anyone have any ideas on this one? The MRP system runs on 'build
professional' just in case anyone has heard of it.

Thanks
Tim