> What ppp implementation?
> 
> I'd (as usual) suggest ppp (the userland package), www.awfulhak.org/brian.
> 
> - alex

  It's yet another user process ppp, called iij-ppp,
iij-ppp0.94+ondemand+nat patches.
A bit old implementation, though it works quite well, and it's quite
easy to configure NAT capability as well, just add a line "set taddr
YOUR-LOCAL-ADDRESS", my case,
"set taddr 192.168.10.0/24" in /etc/ppp.config file.

  -- kaz-k