# Modem fails to assign IP address



## DaneBrooke (Jan 21, 2008)

Yesterday: Comcast cable modem service to Motorola DOCSIS 3.0 modem allows her pc or my pc (both ThinkPad centrinos running XP Pro SP 3) to connect to internet at Home (Seattle).

We moved to Seatac (a nearby town) and Comcast switched service to the new address, so TODAY: she connects fine, I do not.

ipconfig for her includes autoconfig enabled, DHCP 68.87.69.19, DNS 68.87.69.150, subnet mask 255.255.248.0, default gateway 76.22.24.1 and no autoconfig ip, IP 76.22.24.61.

ipconfig for me has autoconfig ip 169.254.75.81, subnet mask 255.255.0.0 and nothing else; system event log contains message that modem failed to assign me an IP address. I ping 169.254.75.81 successfully, so I believe that is the physical modem. I can't ping anything else. SHE pings just about everything successfully, but gets a timeout on 169.254.75.81. 

Any ideas? Because the router isn't working right either, but I can't move on to that until I can connect to the internet via the modem using my own pc (hers is inconveniently gone or in use 95% of the time) TY!


----------



## johnwill (Sep 26, 2002)

You can only connect a single device to a standard plain cable modem ISP connection.

You need that router to get both machines connected.


The following procedure should get you a connection with any broadband modem that is configured to use DHCP for the router connection, such as cable modems, and many DSL modems. If you require PPPoE configuration for the DSL modem, that will have to be configured to match the ISP requirements.

Note that the wireless encryption and channel selection will have to be done after the basic wired connection is established, the first step is to get wired connections working.



Reset the router to factory defaults by holding the reset button down for 15 seconds with power on. 
Turn off everything, the modem, router, computer.
Connect the modem to the router's WAN/Internet port.
Disconnect any USB connection to the modem, it will not be used.
Connect the computer to one of the router's LAN/Network ports.
Turn on the modem, wait for a steady connect light.
Turn on the router, wait for two minutes.
Boot the computer.

When the computer is completely booted, let's see this.

Hold the *Windows* key and press *R*, then type *CMD* (_COMMAND for W98/WME)_ to open a command prompt:

*NOTE:* For the items below in *red* surrounded with *< >*, see comments below for the actual information content, they are value substitutions from the previous command output! 

In the command prompt window that opens, type type the following commands one at a time, followed by the _*Enter*_ key:

IPCONFIG /ALL

PING <computer_IP_address>

PING <default_gateway_address>

PING <dns_servers>

PING 206.190.60.37

PING yahoo.com

Right click in the command window and choose *Select All*, then hit *Enter* to copy the contents to the clipboard.
Paste the results in a message here.

*<computer_IP_address>* - The *IP Address* of your computer, obtained from the IPCONFIG command above.

*<default_gateway_address>* - The IP address of the *Default Gateway*, obtained from the IPCONFIG command above.

*<dns_servers>* - The IP address of the first (or only) address for *DNS Servers*, obtained from the IPCONFIG command above.

If you are on a machine with no network connection, use a floppy, USB disk, or a CD-RW disk to transfer a text file with the information to allow pasting it here.


----------



## DaneBrooke (Jan 21, 2008)

TY, John. I know I need the router to get both computers connected *at the same time*. But I don't want to involve the router until I resolve the problem that I have - if the modem is connected to her machine (and my pc is nowhere) she connects fine, but if the modem is connected to my machine (and her pc is nowhere) the modem fails to assign an IP address to my pc.

Most of what you suggest I do with the router can't be done from my pc because the ipconfig returns no values for my machine; and I can only do those steps with her machine when it becomes available (rarely). Like right now she has her pc at her office and I am using mine from a library net/hotspot (because I can't connect from home.) And Comcast is no help; having established that she can connect just like she did before the move, they say the cable feed and modem are good, end of story. And I don't believe the problem is my pc, because I plugged in just fine here at the library. (And everything was fine before I moved.)


----------



## johnwill (Sep 26, 2002)

You must power cycle the modem whenever you change the attached device, be it a computer or the router.


----------



## DaneBrooke (Jan 21, 2008)

TY, John. Did that. No change. Finally called Comcast (again), got a new guy (the one we spoke with yesterday sounded dicey) who said "Let me try something". Whatever he did seems to have solved the problem = Every computer connected to the modem established an internet connection, so we attached the router and have both wired and wireless connections up and running. Problem solved.

But here is a new question -

When we were in Seattle, our 'office' spaces were adjacent, so we could reach the router for hardline connections easily. In our new place, our offices are two floors apart. Am I likely to experience any issues connecting two modems to the same cable feed?


----------



## johnwill (Sep 26, 2002)

You will most certainly experience issues unless you get two cable accounts! :smile: The modems are provisioned by MAC address, so they have to be enabled by Comcast and you'll be paying for two accounts.

If you can get a CAT5 cable between the offices, you can extend the network that way.


----------

