Comcast Modem - random Self-Assigned IP problem
 

Hello, lately I've been randomly cut from the internet due to the Comcast modem's self-assigned IP. It happens at the most obscure times, and I've found no conclusive evidence to point to a singular source of trouble (such as Flash, time of day, certain website/program). However, I am able to get back online just by restarting my Mac.

I've tried renewing the DHCP, re-powering the modem (for more than 2 minutes)...and everything in this thread: http://forums.macrumors.com/showthread.php?t=502512...except for operator207's advice. Would that be the possible reason for it cutting out randomly? I'm still not sure if it's the Mac's fault or the modem's fault...or perhaps Comcast's fault.

Thank you,

Crandall R.

It's not clear exactly what device has a self-assigned IP. Devices that are only modems don't have an IP address, they simply modulate and demodulate the analog carrier frequencies into digital form. If you have a modem that includes a router (a not uncommon type of modem), then the router might have a self-assigned IP address. If that is the case, then the fault is your internet provider's.

Or is it your computer that gets a self-assigned IP address?

Trevor

I believe it's the computer that gets the self-assigned IP, because it only takes a restart of the computer to get a new IP address. I'm not really sure what exactly my modem is...

This is the modem I have

Sorry about the link to ebay, but it was the only link I could find that shows it.

I deduced that the self-assigned IP problem occurs at nighttime, despite my previous belief that it occurred randomly throughout the day/night. Has anyone had a similar problems?

Also, I'm not sure if it's ok to bump this...if it's not let me know. :)

Check the terms of service. Some plans require you to log out once per day.

I did, no mention of having to log in/out once a day. :(

Some people have said that creating a static IP works, but I'm not sure how to do it properly.

Not if it's just a modem (I believe the one you linked is). You need to have Comcast assign you your ip.

The fact that it's fixed by restarting seems to indicate that it's a problem on the mac side, though I can't think of what.

OK, so the modem you pointed to is only a modem, not containing a router, and does not have an IP address as far as I'm aware. So if your computer is getting a self-assigned IP address, then there's something wrong with Comcast's DHCP server, or the connection, or your configuration.

It's possible that the cable is bad between modem and computer, or even the cable going into the modem could be bad. Those are easy enough to replace.

Once you've replaced the cables, or otherwise confirmed that they are good, if the problem continues then the best probable solution, both for your security and safety, and for fixing whatever is happening, is for you to buy a router. You can get them quite inexpensively if you're not picky about brand--go to your nearest computer superstore and get the one that is on sale this week. Then install it between your modem and your computer.

It will provide NAT--network address translation--giving you a secure local network, making it much much harder for crackers to get into your computer. It will also allow you to add more computers to your network as needed, each with internet connectivity.

Then the router will be receiving the (routable) IP address from Comcast, then distributing (non-routable local area network) IP addresses to your computer(s). Assuming that the modem isn't bad, this should fix the problem.

Trevor

How old is the house? If it's had cable tv for 30 years, it may need a new drop from the street. There could also be a filter recently installed on the street. Cable techs go around looking for signal feedback caused by exposed cable (unplugged on one end and connected to the wall on the other end, for example) and when they find it, they install a filter to protect the system. That filter can interfere with internet access for the house.

Sorry for bumping this/not responding...I was on vacation :)

Anyway, it's been happening more and more. I tried using a different cable, didn't work. I also tried using a Linksys router, that didn't work (still got self-assigned IP)

I am leaning toward the possibility that it may be the Mac's fault. But I'm not sure what to do now.

If this* is true, how could it be the Mac? It tells me that the problem is somewhere between your modem and Comcast. Did you read post (#9)?

*Or did the Mac get a self assigned address, not the router?

You need to use the router's config utility (usually a web-based page that you access by going to a certain IP address on your Mac - read the router's manual) and check what IP address the router itself is getting. Only after you are sure that the router itself is getting a good IP address (and otherwise is working properly) should you worry about the Mac.

Well I talked to Comcast, and they said that the modem has been working for a few weeks now. I just tried it on my PC, and it works.

@cwtnospam - I think it's the Mac getting the self-assigned IP since the modem seems to be operational

@hayne - Are you saying I should hook my modem into the router and check the options there? Because I can't check anything on the Comcast modem alone.

All I was saying is that if you are using the router (I understand that you don't usually use it - you connect your Mac directly to the modem) then you need to go into its configuration page and set it up - at least look at what IP address it is getting assigned.

But if you've got a PC as well as a Mac, then you probably need to use a router in order to have both of them connected to the Internet at the same time.

Ok, I have both computers connected into the Linksys router, and I get connection on the PC but still the self-assigned IP address on the Mac.

I can't configure anything on the Linksys or the Comcast modem...I tried putting 192.168.1.1 into my browser but no luck.

Do I need to put in any specific DNS servers or search domains into my Mac?

Try switching ethernet cables, and show us a screenshot of your network settings.

You need to be able to configure the Linksys router. Although many Linksys routers use 192.168.1.1 as their configuration page, not all do. What does the documentation that came with your Linksys router say to do when you need to configure it? What model of Linksys router is it exactly?

If you follow the directions for configuring the router, and you still cannot access the configuration page for it, then do a hard reset of the router. This is usually done by holding in the recessed reset button on the back of the router for 30 seconds. This will reset all of the settings in the router to their factory defaults.

Trevor

I have switched cables, but not luck.

This is what I have here

Is that even a router? :confused:

If not, I'll go buy one. If I get the right one, will the 192.168.1.1 (or whatever the address is) work while being plugged into the Comcast modem?

Here's my network settings when it's working...I don't know if it's ok to share all the information in the screenshot:

Network Settings

No, that's a switch. If you have a lot of computers on your local area network, you can plug the switch into the router to get more ethernet ports. But you do need to get a router to share the Comcast cable connection to the internet between more than one computer.

Yes. So you'll have a connection like this:

[ Internet ] <---> Comcast modem <---> router <---> all of your computers and other networked devices

You will be able to configure the router using the directions that came with it. Not all routers use 192.168.1.1 for their configuration page, but some do, yes.

If you want to include wireless devices on your local area network, you can buy a wireless router, as they also include ports for wired devices too.

Common router manufacturers are Netgear, Buffalo, Linksys, Belkin, D-Link, and Apple. (The Apple Airport Base Stations are routers.)

Trevor

Ok, I think I've figured out the problem. I believe it was a heat issue from the Macbook. I put a fan close to the Macbook for several days and haven't had a problem since. Is this common? Or more importantly, should I talk to the "Genius" Bar people?

Don't just talk to them. Make an appointment to have them take a look at it.