169.254.xxx.xxx, 192.168.100.xxx and 0.0.0.0, whats the difference?
This section applies if your PC or Mac is connected directly to the cable modem, without any intervening device such as a NAT router or hub.If your PC or Mac does not work at all when connected to the cable modem, first check that your basic network settings (above) are correctly configured, then check the IP address which has been allocated, by following the procedurein What's my IP address? above:
The possibilities at this stage are an IP address looking like: absent or 0.0.0.0 (ethernet interface not operational or DHCP failure); in the range 169.254.xxx.xxx (DHCP failure, with APIPA fall-back); in the range 192.168.100.xxx (cable modem internal DHCP fall-back);
If your IP address is absent or 0.0.0.0, then the network interface is not operational.
Possible causes for this are: The ethernet card (or USB driver) is not working. Required drivers are not installed. Check documentation for the card. You do not have a working ethernet/USB connection between your PC/Mac and the cable modem.
Check cable and plugs, check ethernet LINK lights are lit at both ends. You are running Windows 95, or later versions of Windows with APIPA disabled, and the DHCP client failed to obtain an IP address: continue reading the next section.
If your IP address is in the range 169.254.xxx.xxx, then this indicates that the DHCP client in your computer failed to contact a DHCP server on the network, and APIPA (Automatic Private IP Addressing) is enabled, and it has automatically assigned you a private IP address in the 169.254.xxx.xxx range.
With such an address, you will not be able to work with the public Internet, nor even read the cable modem diagnostic pages.
Possible causes for this are: Your PC/Mac booted up faster than the cable modem did, and the cable modem was not ready for service by the time the PC/Mac sent out its DHCP request. You should not boot up your PC/Mac until after the cable modem has finished its start-up sequence (see Flashing Lights above), or you should leave your cable modem powered on continuously.
You have recently swapped the computer or network interface card connected to the cable modem, and the cable operator's DHCP server has not yet recognised the MAC address of the new interface: see Swapping computers on the cable modem.
You do not have a working ethernet/USB connection between your PC/Mac and the cable modem. Check cable and plugs, check ethernet LINK lights are lit at both ends, check ethernet speed and duplex settings.
Your PC has multiple network interfaces and it is sending DHCP requests on an interface other than the one to the cable modem.
If your IP address is in the range 192.168.100.xxx, then this indicates that you have a working connection to your cable modem, and the cable modem is working, but is not in contact with the cable network. The cable modem has an internal DHCP server which has temporarily issued you with a 192.168.100.xxx number so that you can at least look at the cable modem diagnostic pages with a web browser. With this address, you will not be able to work with the Internet.
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