From: Bruno Carnazzi (bcarnazzigmail.com)
Date: Sun Oct 01 2006 - 07:25:42 CDT

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  Hi misc,

For my own education, I'm writing in C a PPTP proxy for pf-driven
NAT-boxes, based on libevent. A PPTP session is made of a TCP control
connection and a GRE tunnel. I've got no trouble handling the control
connection, but I don't know how to handle GRE packets. Actually, I
bind a first raw socket on 127.0.0.1, with protocol=IPPROTO_GRE,
rdr'ing with pf all outgoing GRE packet from lan here. I can read GRE
packets from this socket, great. The idea is to copy these packets on
a second gre raw socket, binded on the wan interface ip address. I
encounter these problems :
  * How can I find my wan interface ip address ?
  * How can I handle his dynamic nature ? (this is a pppoe(4) interface)
  * How can I handle multiple wan ip address ?

I though it should be possible to have only 1 "big" socket for the
whole proxy, listening on 0.0.0.0 (is that equivalent to INADDR_ANY
?). Reading GRE packets from clients should be the same way as before,
but what about writing GRE packets to servers ? Which source IP will
be choosen for these packet ? I feel that this design is bad but I
lack some raw socket background. I'd like the advice of sockets guru
:)

I've read this and didn't find something usefull :
UNIX Socket FAQ : http://www.developerweb.net/forum/index.php

Best regards,

Bruno.

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