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Multiple ethernets on one cable modem



In a previous episode Niall Kavanagh said...

:: So if I throw in a new NIC, power cycle the modem so it picks up the new
:: MAC, will I still be able to get an IP address?

no.. you'll be able to get through the modem by doing this, but the
DHCP server does use the hardcoded MAC to decide whether or not to
serve you.. if the new NIC isn't registered it won't give you an
address..

you can test this out if you want.. if you've got a perfectly working
setup check how long your lease is good for. (I'm not sure how to do
that the standard way, mine logs all it's renewals for me).. writedown
your current config info and reboot the box with a new NIC. It
obviously won't work.. then statically configure thew new NIC with the
old information.. it still won't work ;(.. now power cycle the
modem.. it will now work ;) (as the modem passes your traffic and you
aren't using the DHCP server)..

I've done this for very short periods of time (5 minutes).

but this isn't a real solution because you can't run like this for
longer than the time you have left on your old lease.. and you can't
run DHCP because the DHCP server will ignore the new MAC
address.. that's why you have to give m1x the new info (or remap the
new NIC to the old MAC.. less desireable imho)


:: > From: Jerry Feldman {75562} [mailto:gzf at gbrmail.msd.ray.com]
[..]
:: > That is correct. M1X will not let any traffic through unless 
:: > it has the
:: > registered MAC address.

again, not strictly right.. the dhcp server won't talk to you without
a registered MAC address. The briding is auto-learned. (at least until
the very recent past)
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