[X4U] DHCP Renewal

[godfatherK]

I got a strange problem.
I just got installed with Adelphia cable.  Everything seemed dandy 
until the DHCP lease expired after 12 hours.  Apparently, there wasn't 
any DHCP lease renewal request made.

The set up is simple.
cable modem > Linksys router > Macs
As it is set up, using the Linksys router web interface, I have to 
manually request DHCP renewal.  In fact, it's the same without the 
router.
Linksys has no answers.  Adelphia has already swapped the modem for me, 
but the problem persists.

Am I missing something?
How do I tell the modem to automatically renew the DHCP lease?