Here's the setup:

Main Office

Server:
Windows Server 2003 domain controller
IP address: 192.168.1.10
Subnet mask: 255.255.255.0
Gateway: 192.168.1.1
Services: Active Directory, DNS, DHCP

Clients:
Mixture of PCs running Windows 2000 Profressional with SP3 and Windows XP Professional with SP2

Network:
Dell 16-port switch
SBC 768K SDSL

Firewall:
Sonicwall TZ170 Internet Security Appliance
LAN IP = 192.168.1.1
LAN Subnet Mask = 255.255.255.0
Firmware version: SonicOS Standard 2.2.0.1
Revision: 2.2.0_pp_8s $
ROM version 2.0.0.3
Previous firmware version: 2.0.0.2
Fragment outbound packets larger than WAN MTU: 1
WAN MTU: 1404
CP Wan MTU: 1404
WAN Ignore DF Bit for non-VPN traffic: 1

Site-to-site VPN:
Encrypt/Auth - ESP DES HMAC MD5
Key Exchange: Manual Keys
VPN Terminated at: LAN
netbios off, ApplyNatAndRules off, ForwardPacketsToRemoteVPNs off
TunnelForAllOutboundTraffic off
Authentication of local users off, Authentication of remote users off
remote subnet for netbios 255.255.255.0
destIP begin 192.168.2.1, end 192.168.2.254



Remote Office

Clients:
4 Dell PCs running Windows XP Professional with SP2

Network:
Belkin 8-port 10/100 hub
Choice One 768K SDSL

Firewall:
Sonicwall TZ170 Internet Security Appliance
LAN IP = 192.168.2.1
LAN Subnet Mask = 255.255.255.0
Firmware version: SonicOS Standard 2.2.0.1
Revision: 2.2.0_pp_8s $
ROM version 2.0.0.3
Previous firmware version: 2.0.0.2
Fragment outbound packets larger than WAN MTU: 1
WAN MTU: 1404
CP Wan MTU: 1404
WAN Ignore DF Bit for non-VPN traffic: 1
DHCP Server:
Enable DHCP = 1
Lease Period = 1440 minutes
Range Start = 192.168.2.100
Range End = 192.168.2.110
Interface = LAN
Default Gateway = 192.168.2.1
Subnet Mask = 255.255.255.0
Domain Name = <NULL>
DNS Servers = 192.168.1.10

Site-to-site VPN:
Encrypt/Auth - ESP DES HMAC MD5
Key Exchange: Manual Keys
VPN Terminated at: LAN
netbios off, ApplyNatAndRules off, ForwardPacketsToRemoteVPNs off
TunnelForAllOutboundTraffic off
Authentication of local users off, Authentication of remote users off
remote subnet for netbios 255.255.255.0
destIP begin 192.168.2.1, end 192.168.2.254

A site-to-site VPN between both Sonicwall TZ170 connects the Remote Office to the Main Office. All four PCs at the Remote Office authenticate across the VPN to the Windows Server 2003 domain controller. At the Remote Office, DNS is resolving to the domain controller across the VPN.

Issue:

All users use a Windows-based application that connects to a database on the Windows Server 2003 domain controller.

There are not any performance issues in the Main Office. There are performance issues with clients accessing the database and copying/opening files from the server to the client PC over the VPN from the Remote Office.
We ran a packet trace (netcap.exe on a Windows XP SP2 PC at the Remote Office and netmon.exe on the Windows Server 2003 domain controller) while copying a 12.7MB file from the server to the client PC. What we found is that the client PC at the Remote Office is repeatedly sending ACKs across the VPN tunnel to the domain controller and the domain controller is yet the domain controller is repeatedly sending ACKs across the VPN tunnel to the client PC.

We do not know what's causing this issue. Sonicwall states that there's nothing wrong with their hardware or the VPN tunnel itself.

Does anyone have any ideas?

Thanks in advance!!

Rob

PS - I can send the packet trace capture files if needed. Just let me know.