I've got a NetBSD-1.2-sparc system setup call my ISP
    over PPP.  Everything is working, however, I've added
    a second machine to my network and I can't get it to
    connect outside. It appears that the datagrams are
    getting routed out over the PPP line, but not making
    it back.

Many ISPs don't support this setup (multiple machines routed over
one phone line).  Some will if you talk to them and maybe pay them
extra.  There may well be nothing you can do on your end (after
all, the problem is that you need them to route your second machine
back to you).

If you have a cooperative machine on the outside Internet, you might
be able to get it to tunnel packets back to you via your ISP-supported
machine, but I don't know of an out-of-the-box way to do this.

Dave Eckhardt
davide@cs.cmu.edu