I just upgraded my RB532A from RouterOS version 3.30 to 5.8 and since then I've been having trouble accessing Google and IMAP over my PPTP tunnel. I have a prerouting mangle rule in place to mark routing for IP addresses in an address list and have their tcp packets routed through the tunnel. It can make the connection to google.com on port 80 but the data that Google returns doesn't ever seem to reach the requesting machine. I've attached a pcap dump (had to rename to dump.txt because of file extension restrictions) of the connection but I don't really know where the problem is since it was working before. :/ I've had some strange issues with PPTP compression in the past but I don't think that's the issue now?

Any help would be greatly appreciated!

Actually it seems that after making a telnet connection to google.com on port 80 then just sending a GET request a few times it will eventually start to return the data but only partially and then it times out. I'm going to say it's probably my PPTP configuration then so I guess I'll be playing with that later.

After changing the MSS (by subtracting 40 from the MTU making it 1410) of packets using a mangle rule it appears to have resolved the issue. Is this a bug? I think I remember seeing this done automatically/dynamically in RouterOS v3.30 after a PPTP connection was established. Does anyone know?

Did you set "Change TCP MSS=yes" in your pptp profile?

Ah no. It was set to "default" and I see that the default is actually no considering my configuration. Ugh.

http://wiki.mikrotik.com/wiki/Manual:PPP_AAA

Thanks.