I believe this issue (or a related one) has been brought up before. But, I don't think I've seen a
solid solution or even a solid explanation.
I am connecting to our m0n0 1.21 PPTP server at work. My home machine is also behind a m0n0wall
1.21. I switched my home machine to m0n0 about 4 months ago. Originally, I was running GTA's
GNATBox Light Floppy Firewall (This is also built on FreeBSD).
When I first switched, I could connect to the VPN just fine. But, Remote Desktop would act like it
was starting and then just hang at a blank screen (Never getting the logon prompt) Eventually, it
times out and gives an error. From past experiences with Microsoft's ISA Firewall, I recognized
this symptom as a MTU/Fragmentation issue. (In ISA's case, a hotfix corrected the problem)
At that time, I played around with creating LAN rules specific for PPTP and checking the "Allow
Fragmented Packets" checkbox. I am unclear now if that actually did the trick or not. I remember
that it just "started working", so I left the rules alone.
Now out of the blue, this problem has re-emerged. I have rebooted several times both m0n0walls,
attempted unchecking/rechecking the Allow Fragmented Packets. All to no avail. Finally, I booted
my home firewall back up to GNATBox Light. After that, Remote Desktop works fine.
It appears that my home m0n0wall is having trouble with PPTP pass-through. Although, I have no idea
why it worked fine for 4 months. Unless the MTU of a router in the path from my home (cable
internet) through the Internet to my company has changed (Which is obviously out of my control).
I did try lowering the MTU on the WAN interface to 1000. That did not do anything. But, I'm not
sure if I needed to reboot everything for that to really take effect. Or do I need to try something
like 500. I also did not try playing with the MTU on my computer either.
Any insight would be appreciated!