[pptp-server] After pptp established, I cannot capture GRE packet.

[DaeSooChoi]

Hi.
I don't understand my PPTP connection.

My ISP filters pptp packets (protocol# 47 GRE) pass from remote user(MS clients) to PoPToP Server like below.

W98se client <--- dial-up ---> (through)ISP <------------internet------------> Linux PoPToP server
                                    filterd protocol #47(pptp packet)

so I make up small test-bed like below without filtering any packet.

W98se VPN client <---- dial-up ----------> W2K RAS server <--------local network -----> Linux PoPToP server
first connect          <----dial-up-connection -->
second connect     <------------------pptp connection through RAS server------------------------------>A
(pptp connection established successfully)

But I cannot understand encrypted turnelling process because of un-encrypted packet captured.
I captered some packet pass through W98se client to Linux PoPToP server.

I think that first some packet is tcp packet because this is PPTP control connection packet.
also after connection,  any other packets are GRE(protopol # 47) packet perfectly because turneling is established.
but my captured packet is not.
Almost packets are non-GRE packet as soon as turnelling is established.

I cannot understand this situation. 
I would like to understand how GRE packets can pass through turnelling.

and another question here
in PoPToP server log file (/var/log/pptpd.log)
when pptp connection is created, log file display below
"Feb 20 10:54:20 kikio pppd[2502]: MPPE 40 bit, stateless compression enabled"
I would like to know how to upgrade MPPE 56bit or 128bit. and related problem.

Any help appreciated.