firewall setup xdsl: eth0/eth1/ppp0?

[Andreas Bohnert <abo@online.de>]

Hi,
   I don't know how to setup my firewall for my new xdsl connection. I 
saw some posting         concerning adsl, so maybe there are some 
people, who know how to handle this.

   here is my situation:

   eth0 is connect to my private network (192.168.0.1).
   my eth1 gets an lokal ip from my xdsl router (subnet 10.x.x.x).
   than I have to build up a tunnel connection with my router with pptp.
   now I have ppp0, which is my xdsl interface.
  
   this works fine, but now I have to setup my firewall!
  
   I know ppp0 is my external interface now, but what about eth1 (which 
is connect to my router)?
   I looked around and some people say, they setup the firewall like this:
   eth0 (private)           = FW_DEV_INT
   eth1 (connect to router) = FW_DEV_INT !!
   ppp0 (xdsl)              = FW_DEV_EXT
  
   but somehow I think, eth1 should be FW_DEV_EXT as well, because it's 
phyiscally connected to the internet.
   also, what about the firewall between ppp0 and eth1 - it shouldn't 
block communication.
  
   so, what do you think, if I configure eth1 as external?

   thanks for any advice!

andreas