[ale] Explain cable modem routing?

[Eric Webb]

So, Charter Pipeline came by yesterday and set up their cable modem service at
my residence.  Still one-way, but that'll have to do for now.  And now on to
the task of setting it up under Linux...

I can do all the configuring, and I guess it will work, but can anyone tell me
how the routing works??

The NIC attached to the cable modem is 10.0.0.1, and the dialup uplink PPP 
address turns out to be 208.168.59.217, which is the same as the cable modem's 
address ( I think ).

So, how does this work?  If I ping yahoo.com (ignoring the lookup process),
packets go OUT via ppp0 (default route), get to yahoo, and then come back down.
I assume Charter's end of the deal is smart enough to send return packets via
the cable (and not PPP).  But then what of Linux?  The packets addressed to
207.168.59.217 end up appearing on the box's 10.0.0.1 interface!  How does the
kernel know what's addressed to who?

Also, would this pseudo route table work?
	default -> ppp0
	net 208.168.59.0 -> ppp0
	net 10.0.0.0 -> eth0

(This is going to REALLY get confusing when I turn on both my analog dialup,
my cable dialup, my LAN NIC and my cable modem NIC all on the same box.....
woohoo!  So, help me understand this now :)

Eric