Cool - I've been watching tcpdump on the Linux box, so I'm seeing the activity. I'll spare everybody and ask that people send me email (directly) only if they see a problem. I'm going to comb through the logs from the DOS box and the tcpdump when all is done to see if I missed any corner cases in the protocol. Straight TCP/IP is pretty fun to do. Getting the error handling down is not as easy. I'm also missing a few functions: - I'm not honoring the receive window from the other side. - I'm not detecting or cleaning up half-open connections. - I don't have a really robust algorithm for measuring round trip packet time and determining a timeout period. (I'm just defaulting to 10 secs ..) All of this will get fixed, but I was so desperate after a year of work to see this code do something. :-) Mike