[brainwave89]

When I hook up an ethernet connection from my Comcast modem to my Mac Pro (10.5.0) and PowerBook G4 (10.5.3) I end up getting an self-assigned ip address (169.254.x.x). When I hook up an ethernet connection to my Dell Dimension desktop from the cable modem I have no problem getting online.
I have shut off the modem at various times from 30 seconds to 4 minutes before I plugged it back in with the same result on the Macs.
I would love to hook up my Airport Extreme to the cable modem but I would be happy just to get this resolved first.
My Firewall allows all incoming connections.

Once or twice I was able to get an 192.168.x.x ip address on the mac's before it switched to 169.254.x.x.
Any suggestions to get this resolved would be appreciated.
Thanks for looking.

[SoltoN]

sounds like the modem is only set to give out 1 ip at a time I'm assuming this is a motorola modem). the 192 IP is a diagnostic mode that you will get if the modem has not locked in and you plug something into it. you will get a 192.168.100.11 ip.

to get online, unplug the ethernet from the modem, powercycle the modem (doesnt matter how long, as long as it powers down), wait until the top 4 are solid green, then plug in the ethernet cable.

it is important to make sure you leave the ethernet unplugged until it is fully locked in, or you will end up with a 192 ip.

[brainwave89]

Thank you for your help SoltoN.

The original modem was a Linksys cable modem. I replaced it with a Motorola modem and now I am able to hook it up to an Aiport Extreme base station successfully.