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[Michael ODonnell]

I'm glad to see this thread as I've also puzzled
over this issue on and off since forever as a ComCast
customer with multiple Linux boxes behind a NAT box.
The more general question in my case is: Given
that ComCast only knows me by the single interface
associated with my cable modem and that interface is
in the comcast.net TLD, how should I configure all
the systems behind that interface?  I can't tell my
email software (let's say it's running on a host named
"waldo" that's behind my firewall) that it's running
on a host in the comcast.net domain because it ain't;
ComCast has no idea that waldo exists and can't
route to waldo.  But I also can't tell waldo that
it's in some other domain (either real or fictitious)
because that ain't true, either.  So, where's waldo?