Hoping this is a simple fix:

- I have cable modem service with Ethernet running to different rooms in the house via wall jacks.

- In one room, I have Airport plugged into the jack and it works fine serving a G4 powerbook (computer A).

- If I plug a different powerbook (B) into the Airport's Ethernet port, it gets on the Internet no problem via Ethernet.

- However, if I unplug Airport from the wall jack, and plug B into that jack, I get an IP of 169.x.x.x and cannot get on the Internet. The same happens with yet a different powerbook (C).

I've tried resetting the cable modem, renewing DHCP lease, entering manual IP address, reconfiguring ports, etc., but nothing works. Any suggestions?

If I understand you...a cable goes from the cable modem to the Airport jack, right? And that works, but if you disconnect the cable from the AirPort and plug a computer into it, so that the cable goes from the cable modem to the computer, it does not, right?

If so, that is normal and expected.

Some cable companies use "MAC address tracking." A MAC address, which stands for Media Access Control address, is like a serial number. Every single Ethernet device--computers, AirPort hubs, routers, switches, you name it--has a different and unique MAC address.

With some cable companies, the first time you plug a gadget into the cable modem, the cable modem makes a record fo the gadget's MAC address. From that instant onward, that cable modem will never again work with any other computer or device, unless the cable company resets it.

If your cable company does MAC address tracking, that means your cable modem has locked on to the MAC address of your AirPort hub, and from now on it will never work with any other hub or computer or router or switch or anything unless the cable company resets it.

Tacit's reply may be onto something with MAC tracking. Have you tried changing the connection from Airport to your computer and then rebooting that cable "modem"?

At my parents' house, there is a Comcast cable modem, and that's what makes it work when changing computers.

Neal

Right, if I plugged the computer into the ethernet wall jack, I could not get on.

However, I discovered the solution. Comcast sent customers a notice a while ago about switching network settings to Automatic via DHCP. I had all the computers set that way, but not the Linksys router that serves the ethernet jacks in the house. By going into the router via my browser (location 192.168.1.1), I enabled DHCP which was disabled by default. Now all computers connected via the ethernet jacks or Airport can get online.

Thanks to all for your assistance.