Two PCs, same settings, different results

[briandwest]

My co-worker and I have set up an instance of SC for customers to contact us. We have two separate hosts listed in helpdesk.txt. Same external IP address, two different port numbers. We have the external firewall set up to forward the two different ports to our two separate machines. Those systems have static DHCP IP addresses.

When someone on the outside runs the SC exe and double-clicks the line for my co-worker's system (tech support 1), everything goes through just fine. When the customer closes that connection and starts from scratch with the SC again, just clicking my line (tech support 2) instead of my co-worker's, nothing happens.

I've sniffed both ends, and individual packets are making it through from the customer's system to my system. I have the same version of UltraVNC on my machine as my co-worker, using a link with the same settings (except for the port it listens on). Still no luck with my system.

We even switched IP addresses between the two machines. Then when the customer clicked on tech support 2 (now pointing to my co-worker's system), it worked, while again, mine didn't. That proved to me that there's something wrong inside my machine.

But here's the kicker: my co-worker created a new exe file, this time pointing to my system directly at my in-house LAN IP address--and it worked. My listener was able to receive his request.

So we can use SC in-house, and from the outside to my co-worker's system, but for some unknown reason it won't let people connect to my machine (which has ICS and ICF turned completely off now)

Does anybody have any ideas of what is happening to my system?
Why will it accept only local (LAN) connections, but not those that are initiated from outside the firewall? Thanks in advance.

Another bit: I edited the vncviewer shortcut to have it keep a log, level 10. It says at first:

Started and Winsock (v 2) initialised
In listening mode - staring daemons
Adding tray icon

Then it goes on for dozens of lines with the same thing: "Checking tray icon." Is this normal?

[briandwest]

In sniffing the packets, I found that my system receives one single packet at a time from the external single-clicker, but nothing more. My system apparently doesn't know to ACK back. It seems like there's something in my system that will allow and respond to connections from within the internal network, but not from outside. Outside-sourced packets get ignored. Thoughts? Guesses? Anyone?

[bevtech]

Complex firewall at work blocking the ACK request from your pc..but just a guess..

[briandwest]

We've gone through the various policies, etc. set on the firewall box, and can't find any differences between the way the firewall treats my co-worker's machine (the one that works) and mine. Today I assigned my machine a new IP number, created a VMWare virtual machine and gave it my old one (the one that SC and the firewall point towards). The virtual machine was able to receive the SC calls from outside the firewall, using the same network adapter and other hardware. So I think we've conclusively proven that there's something, somewhere in the software or settings of my machine that is not happy, not replying to the SYN packets.

I've done an in-place upgrade (XP Media Center 2005) on my machine, done a system file checker on it, and reinstalled the WMI (which some earlier error messages pointed to as a problem).

The only option that we can think of that's left is to reinstall Windows from scratch. Of course, I've been hoping it wouldn't come to that.

Can anyone think of anything else we can try? Thanks...

[briandwest]

Still digging on this one. I don't think it's a firewall issue outside this machine, because the Wireshark capture didn't show this machine sending a reply to the packet it received from over the Internet. It's like the listening vncviewer doesn't know what to do with the packet.

Does anyone here know why a listening viewer would ignore a packet addressed to the port it's supposed to be listening on?