Understanding VPN tunnels

Help me understand…

I have two sites, each site has a 10Mb Internet connection that is connected to a SonicWall. I then set up a VPN tunnel between the SonicWalls to connect the two sites. First site is, internally, 192.168.1.x; second site is 192.168.2.x.

It all works fine. However… if I use remote desktop software from the .1 to .2 subnets, it is much slower than if I use the same software from .1 to the external IP of site 2 and forward the ports to the server I want to connect to.

Does the VPN tunnel really add that much overhead to the traffic that it would be approximately half as slow? Are there any settings I need to know about that could be causing slowness in the VPN tunnel?

Every packet needs to be encrypted and possibly compressed - that will definitely add some processing overhead and will thus result in slower speeds. How much slower will depend on the capability of the firewalls.

Nah, rdesktop consumes a negligible amount of bandwidth. Something is clearly wrong, but exactly what would be impossible to diagnose on an internet messageboard. Sonicwall is a commercial solution, so contact the vendor for support.

Also, you missed the opportunity to title this thread “F**king VPN tunnels, how do they work?!?”.

That’s what I get for skimming the topic. I mean, technically I’m right but stusser is right - on something like rdesktop the overhead should be small. Also, rdesktop has its own encrytion features.

Compare the throughput and latency of your VPN tunnel to non-VPN transfer between the two sites. Is there a difference?