I cannot draw a valid IP address.

[Frank12345]

What do you get for the default gateway with the      ipconfig /all   command?

Alan <>< 

On the non-connecting computer, when I run IPCOnfig/all, it shows a 169 IP address and nothing for the default gateway. 

[Frank12345]

Yes.  You basically summed up my frustration here.  As far as I can tell, I have 2 functioning computers, functioning cables, a functioning cable modem, functional NICs, and a router that is functional for my local home network.  I have been through the settings a dozen times, and they are fine.  Yet I have TWO different problems, neither of which I can resolve.

My secondary computer connects to the internet when directly connected, but then if I

1)  simply pull the ethernet cord from the back of that computer and put it into my main computer, the main computer will not connect to the internet.   

 OR

2)  If I leave the main computer completely off and hooked up to nothing, but I simply try to connect the router as an intermediate device between my secondary computer and the cable modem, the secondary computer suddenly will not connect to the internet!   

What you do know is
1) If networking between coputers attached to the router works fine (then Nic's shouldn't be your problem)
 forget the fact that your secondary PC doesn''t seem to be responding to Ping requests fro the main one (this is likely to be because of a firewall on the 2nd PC blocking/ignoring ping requests)
2) If your secondary machine connects to the internet fine direct in to the modem but your Main one doesn't due to not recieving an IP Address (Have you powered down the modem and retried?

Knowing that with your original setup i.e router, modem and both PC's all was fine except for the internet - are you able to log into the router to run diagnostics (what Make and Model is it??)
It may be that it's no longer set to pick up an IP address from your modem automatically using DHCP, making your internet not work.

It does worry me though that your Main PC won't connect directly via the modem - this should definately work if the modem has been rebooted as you state that it's fine on the internal network via your router

 

[Frank12345]

Bear with me here as I try to make some sense of this. 

When I have both computers hooked up to the router and the router to the cable modem, both computers are receiving 192.168 addresses and my home network is fully functional.  Neither computer connects to the internet. 

When I hook the main computer up to the cable modem directly, it receives a 169 IP. 

When I hook my secondary computer up to the cable modem, it works. 

What about this as a theory:  Something is wrong with the cable modem that prevents my main computer AND the router from communicating with it; however, for some unknown reason, my older secondary computer is unaffected by this problem. 

[MendMyComputer]

Getting back to seeing what the router can tell us about the link from it to the modem.

When you have your PC's hooked up to the router and you run ipconfig from a dos prompt what is your gateway address? (This will be the routers ip address for your home network)

You should be able to enter this into your web browser to get up the routers configuration page. Almost all brands of router will have a diagnostics section and detailed information for the WAN connection (i.e the link from it to the modem)

Can you try logging into your router for us and letting us know what you find?

[Frank12345]

It's a linksys Router 192.168.1.1

But, I am not sure what I am supposed to do next.  I typed this into my browser bar but all that di was perform a google search for that address, which returned a bunch of hits telling me this address is for LinkSys routers, which I already knew.  One of the links brought me to the LinkSys page, and I found a page that seems to giev steps to troubleshoot a problem, but whne trying to follow the steps, I ran into a problem trying to access the routers setup page:

<<<After connecting the router, open a Web Browser (Such as Internet Explorer or Netscape)
When the browser opens, go to the "Address" bar and input the Routers IP Address (The Routers default IP Address is 192.168.1.1) then click on the Go button or hit the [Enter] key.
A window will pop up prompting for a "User Name" and "Password", leave the "User Name" blank and input the Routers password (admin is the routers default Password) then click on the OK button.
After inputting the Password, the "Setup" page should appear. >>>


This did not happen.  All it does is bring up that same google search. 

[BC_Programmer]

you have to enter

Code: [Select]

http://192.168.1.1


[Frank12345]

Careless error on my part.  I was able to get into the setup page. 

On the "stauts" tab it is showing the IP address and subnet mask for the LAN. For the WAN, everything is showing zeroes. 

[Frank12345]

Can you try logging into your router for us and letting us know what you find?

What specifically am I looking for?

[midsail]

If u have a Firewall turn it off for testing purposes. See if u can connect to the internet without going thru the router. Connect to the modem directly. Do this on both computers. If u can connect to internet this way, we have narrowed the problem to 2 areas, Firewall or router.
1-If u have connected to the internet on each PC just turn on the Firewall one at a time on each PC.
2- go to the router manufacture and follow direction to reset router to factory defaults.
 I am inclined to start pionting a finger to the router. BTW can u barrow a router from a friend and connect to your network?

[Frank12345]

I have had firewalls turned off the entire time.  Also, I have been connecting the computers directly to the cable modem; that is the only way I can get online.  The secondary computer works when connected directly to the cable modem.

But the main computer will NOT connect (router not involved at all), AND, the secondary computer stops connecting if I try to use the router (main computer not involved at all). 

So I have two different failures there, each one involving isolation of equipment.  The only constant is the Cable modem.  I suspect that is the problem.  I cannot explain why the secondary computer (which I am on now) can connect.  But the issue is not the router.  My home network is working fine, and also, I swapped out the router for a new one, and all problems remained the same.

If u have a Firewall turn it off for testing purposes. See if u can connect to the internet without going thru the router. Connect to the modem directly. Do this on both computers. If u can connect to internet this way, we have narrowed the problem to 2 areas, Firewall or router.
1-If u have connected to the internet on each PC just turn on the Firewall one at a time on each PC.
2- go to the router manufacture and follow direction to reset router to factory defaults.
 I am inclined to start pionting a finger to the router. BTW can u barrow a router from a friend and connect to your network?

[Geek-9pm]

You need to be more specific.
You have a com cast cable internet service?
Which modem?
Why did you not rent the wireless router from them?
Which router do you have?
When you did get it to work. did you log all the information for reference?
You need to do a ipconfig /all and copy all the addresses.

I have Com cast cable modem here and have it  into a Net gear router.
It tool about 6 hours of research to find the answer. The answer  is in the documentai0on of the router and on many forums on the internet. YYou just google the name of your router and  comcast and find lots of people who had this problem.
The answer is the is almost always you have to ask the router do do a MAC clone.

Com cast blocks a port used for DHCP.  So you set the router to a MAC the modem knows. Then tghe router will do DHCP for the other PCs on the network.
It is late and I don't have time to edit this. 

Anyway, I now have about four PCs on the connection Using a older Net gear router. I set it to clone the MAC of the PC that works.

[Frank12345]

Comcast service, Motorolla SB5120.  I did not do wireless because I have no need for it.  The Router is a LinkSys Router.  I have written down all the working IP address info from when the computer is hooked up directly to the cable modem.  I went on the linksys website troubleshooting section and read the part where it says to do the MAC clone.  However, I could not find ANYTHING in the router's setup page that gave me an option to actually do this.  It certainly wasn't where the troubleshooting page said it would be. 

But the most imporetant thing is this: 

I do not care about the router right now.  I appreciate everyone's help with the networking issues, but right now my primary concern is that my MAIN computer will NOT connect to the internet even when connected directly to the cable modem. 

I fail to see how a router issue could be causing this, since the router is not involved in that equation.  All I need right now is to get my main computer hooked up to the internet.  I can deal with getting my home network reconfigured later. 

You need to be more specific.
You have a com cast cable internet service?
Which modem?
Why did you not rent the wireless router from them?
Which router do you have?
When you did get it to work. did you log all the information for reference?
You need to do a ipconfig /all and copy all the addresses.

I have Com cast cable modem here and have it  into a Net gear router.
It tool about 6 hours of research to find the answer. The answer  is in the documentai0on of the router and on many forums on the internet. YYou just google the name of your router and  comcast and find lots of people who had this problem.
The answer is the is almost always you have to ask the router do do a MAC clone.

Com cast blocks a port used for DHCP.  So you set the router to a MAC the modem knows. Then tghe router will do DHCP for the other PCs on the network.
It is late and I don't have time to edit this. 

Anyway, I now have about four PCs on the connection Using a older Net gear router. I set it to clone the MAC of the PC that works.

[Geek-9pm]

The modem wants the MAC of the PC that it made friends with. Otherwise you have to turn off the modem, turn off the computer. Turn both back on and let them get intimate. The modem wannest the MAC.
If that is the same modem I have. Which modem is it?

aaaaa... goodf nited. i am failiing asleeppp.

[Frank12345]

The modem wants the MAC of the PC that it made friends with. Otherwise you have to turn off the modem, turn off the computer. Turn both back on and let them get intimate. The modem wannest the MAC.
If that is the same modem I have. Which modem is it?

aaaaa... goodf nited. i am failiing asleeppp.

It's a motorolla SB5120.  And unfortunately, this problem is long past the point of restarting things and power cycling things.  I've been at this for  two weeks off and on; it's going to take more sophisticated measures.   I can try a MAC clone but I am having a hard time doing it?

[Geek-9pm]

Docs for Motorola SB5120.
http://support.cox.com/sdccommon/asp/contentredirect.asp?sprt_cid=be19f914-eb7a-4c96-a480-c4082dfb1791

Linksys Router Docs? We need the model number so we can search the docs and find out out how to change the MAC of the router so that it is the same as whatever PC gets into the modem.

As stated earlier, the modem does not care a bit about l your local IP address. It wants a MAC. It fell in love with your old computer and will not talk to anybody else. So you have to give the router that MAC
It has to have the MAC. Everything else is automatic once the modem sees the right MAC.

Once the router has the MAC, it knows what to do. It will hide the old PC from the modem and pretend to be the old PC. The modem will gush lots of TCP//IP and the router will do DHCP and you can have many PCs on the router.

Reset the old PC and the router will give it a local IP.

Sorry about my poor writing skills.