Windows mistakes in case of routing

We have two networks with distinct IP class C address and a router.

I have about 10 Windows (2000|2003) servers on the DMZ and about 20 Workstations (XP|Vista) on the other part.

Sometimes connections are broken while copying large files from DMZ to the Office zone. Windows XP or Vista need to be manually (harware) rebooted.
The problem appear only when the Router are used.

I have placed into the Offcie zone a Debian with SMB service activated and using it as a gateway to access shared folders (the folder is shared from a Windows 2003 Server into the DMZ, mounted into the linux smb into the Offcie zone with a link). The files are always copied fine !

Does anyone have experienced troubles with Windows and routing solutions ?

 

Are the two networks physically separate or do they run over the same cabling and switches?

 

Physically separed by a FireWall

The networks are joinded throught a FireWall (the most recent CheckPoint FW1 solution).

Schema :
NETWORK 1 (Office with cascadind Switches) <==> FireWall Office Interface <==> FireWall Material <==> FireWall DMZ Interface <==> NETWORK 2 (DMZ with cascading Switches)

I have also tried to bypass the FireWall by using this second schema :
NETWORK 1 (Office with cascadind Switches) <==> W2003WinRoute Office Interface <==> WinRoute <==> W2003WinRoute DMZ Interface <==> NETWORK 2 (DMZ with cascading Switches)
where W2003WinRoute is a PC specialy mounted and dedicated to be a router (using WinRoute on Windows 2003).

Important information : i'm running now from 4 hours ping from Office network to a server based onto the DMZ. Some ping are long (>30ms) but very rarelly. In all case the ping has never failed !

I have also tried large ftp transfer (files larger than 1 Gb, folder with about 10,000 files and subfolders) from both side and all is ok.

 

The first thing I would look at is name resolution. Windows system use two types of name resolution: DNS and NetBIOS. DNS routes correctly, NetBIOS doesn't. So what could be happening is your systems are trying to resolve names by NetBIOS first and only going over to DNS after the NetBIOS attempt times out.

So first thing I'd do is make sure all the XP PC are set not to use NetBIOS over TCP/IP.