[pptp-server] Firewalling Poptop

[Ed Padin]

Hello,

My firm is looking at employing the poptop server. It now seems to have
enough encryption with the availability of MSCHAP2 in the pppd. The one
question that came up is how to firewall the poptop server. 

Our current firewall is a Linux 2.0.36  box using ipfwadm and masquerading.
I'm pretty well versed in allowing incoming TCP ports to inside web and mail
servers. Would setting up the poptop VPN work in the same way. I reemeber
reading that it uses the GRE protocol which, I guess, is different than UDP,
TCP or ICMP. 

If that's the case then how would I implement a poptop that is inside the
Linux masq firewall? Is it all possible with any firewall?


Thanks in advance for any input.

Regards