Routing issue

[Web Walrus (Robert Wall)]

> > ifconfig_dc0 inet 1.2.3.4 netmask 255.255.255.248
> > ifconfig_dc0_alias0 inet 2.3.4.5 netmask 255.255.255.248
> > defaultrouter="1.2.3.1"
>
> You need to change your netmask for the alias to 255.255.255.255 if it's
> on the same network.

It's not on the same network; that's the problem.  Two complete separate
networks, same interface card.  The issue is that one of the networks
works, and the other doesn't, depending on what network the default router
happens to be on.