I have high-speed internet with Comcast - an Arris modem, model TM502G with a single ethernet port. I've hooked it up to two different Cisco switches as well as a LinkSys workgroup switch. I've connected several computers to the switches. My problem is that no more than one computer at a time can acquire an internet connection. Right now, for example, I have two PCs and a laptop connected to my switch. Only my PC has an internet connection. On my other PC and laptop I get the following error message from the "ipconfig /renew" command:
"An error occurred while renewing interface Local Area Connection : unable to contact your DHCP server. Request has timed out."
The "ipconfig" command gives me an address of 169.254.112.220.
When I disconnect my PC, neither of the other computers pick up a connection automatically, but when I reset the modem, one, but not the other, computer becomes the computer that gets the IP address. The other computer continues to get the error.
Normally I get a public address from Comcast when I connect to the internet; something in the range of 71.x.x.x to 76.x.x.x. But when I disconnected all the PCs except for one and then reset the modem I got an IP addres of 192.X.x.x - a private address. Then when I connected a second PC I got a public address! 73.x.x.x. And what's more, even with this address I couldn't connect to the internet! Then I went back to the original computer - the one that had the 192 address - and the address had changed to 71.x.x.x and I still have connectivity. This is just nuts. Other info: The subnet mask is always 255.255.252.0. The DNS Suffix Search List is "hsd1.ma.comcast.net".
Comcast tech support assures me that they are not doing anything to prevent the use of switches, but they also offer a modem with four ethernet jacks for an extra $150.00. By the way, when I had DSL I couls attach the modem to a switch with no problems. Can anyone tell me what I can do to be able to add more computers to my switches?