Two Networks on one System

[Lars Kellogg-Stedman]

>        When I set up the secondary interface, I have not been
> able to come up with a statement or statements that tell fxp1
> that it's default router is y.y.y.y so you can't ever reach it
> from outside the new subnet.

What you want to do is called "policy routing" or "source routing",
since you want to select a route based on your local address.  While
I've done this frequently under Linux, I've never had to set this up
on a FreeBSD system.  It looks like you would do this through the "pf"
subsystem...unfortunately, openbsd.org appears to be down right now,
and that appears to be the repository for the pf documentation.  Look
at the "ROUTING" section of the pf.conf(5) man page.