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I've gone through various combinations of cable modems, routers, computers, and apartments in my life, and one thing has always puzzled me. Why is it so difficult to get these things to connect to the internet? Once I'm connected, they work great, but establishing the initial connection is always painful.

I dread the days when I need to unplug my modem or router, because it usually results in something like this:

  1. Plug everything back in.
  2. Wait, fruitlessly trying to load google.com every few minutes.
  3. Check router's status, and see that it has IP 0.0.0.0.
  4. Unplug one device at random.
  5. Wait five minutes, while facing Jerusalem.
  6. Plug device back in.
  7. Check router again, now it has a private address like 192.168.x.x.
  8. Unplug something else.
  9. Call my cable company.
  10. While waiting on hold, google.com finally loads.

Why is this? Is this an inherently difficult problem? Is there a foolproof technique that I'm not aware of?

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8  
... What? I've always just plugged it in and it's worked. You must have terrible luck with ISPs or infrastructure. –  Ignacio Vazquez-Abrams Jul 14 '10 at 0:49
4  
@Ignacio: Ah, the famous "it works for me" fumble. That is the worst argument in history. This is a VERY common problem, and unless you have a particularly simple network (i.e. modem -> router -> 1 computer), it is an entirely legitimate question. –  jrista Jul 14 '10 at 0:57
1  
@jrista: "it just works" is on par with "it does not work", i can't see any difference in the quality of both arguments. –  akira Jul 14 '10 at 13:31
    
I've always faced the Bermuda Triangle and somehow lost track of time... –  A.Donahue Aug 2 '10 at 16:42

7 Answers 7

I have often found that if you plug in the cable modem and give it a minute or so to fully boot and get the necessary IP info, then power up the router, things go more smoothly. However, that experience has all been with Rogers in Canada

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1  
I can second that for the Austrian UPC-branch called Chello. It's most likely for every cable modem and provider a good advise. –  Bobby Jul 14 '10 at 13:27
    
Time Warner Cable in Wisconsin here. Same thing. Always plugin / boot cable modem first, then router, then PCs. –  steve.lippert Jul 14 '10 at 14:52
    
And make sure the one is fully booted before booting the 2nd one. –  Xavierjazz Jul 15 '10 at 19:46

Like DaveM, I have learned that you need to get your cable modem squared away first, before you hook anything else up. I follow this procedure whenever I have to reconfigure my networking for any reason:

  1. Power everything down, including cable modem and routers
  2. Let cable modem sit for about a minute, then power it up, and wait for it to initialize
  3. Power up router, and wait for it to initialize, and let it sit for a minute
    • I have a Linksys E3000, which, while powerful and feature filled, MUST fully initialize before any device, wired or wireless, is connected to it
  4. Power up one system at a time, and wait for it to completely connect before moving on to the next
    • You may need to rerun any router setup disc you have to properly reconfigure the router (depends)

While I can't say this is 100% foolproof, but it is very reliable. (I have a variety of devices I connect to my router, including a NAS, wireless laptop, iPhone, as well as hardwired computers, so I am not sure if the diversity of devices causes the infrequent glitch or not...but most of the time, this procedure is stable and effective.)

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For me, when ever my internet goes down (most likley due to my el-cheapo router) I simply unplug everything, wait a minute, plug in in my router, wait for it to initialize, plug in in my cable modem, walk to my computer, and go to google. This has worked on two networks, one with 3 computers over wireless and wired, and another with 7 devices over wireless and wired and a vonage middleman device.

If you have a 0.0.0.0 issue, have you even tried checking the drivers/settings on the computer? Are you waiting for the router to fully initialize? Are you waiting for even the connection phase to finish? Is this reproducible with other routers (borrow one if you have to)?

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^^^ This is the order that works for me, too. 1)Everything off 2) router on, 3)cable modem on, 4)everything else. And if I change the MAC address on the router, I need to power cycle the cable modem to get reconnected to the internet. It usually leases me a new IP, too. –  hyperslug Jul 14 '10 at 2:39

It might be due to DOCSIS specifications. DOCSIS cable (Videotron ISP) must be reseted everytime the cable modem sees another MAC address attached to it.

So, if your computer is connected to your PC, you will need to reset your cable modem if you connect it the router. Over and over..

I've been working for an ISP as a second level IT and we were using DOCSIS cable modem and it was hard for customers to have it done with a router but when it's done, it's fun! ;)

You can read a bit more about DOCSIS but it's not related to your issue. Just follow a simple procedure to reset it and it should work.

I hope that I helped you!

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The need to reset the cable modem to work with a new MAC address is unrelated to the DOCSIS standard, this is a provider specific configuration. For example, Excite@Home issued IP addresses based on the host name (CP########) using DOCSIS modems. While resetting the modem may help, tying it to the DOCSIS specification is incorrect. –  DHayes Jul 14 '10 at 20:47

I guess it's about the expectations ...

if you want a standard service with pre-configured router, my experience is that they work pretty well, with the drawback that they offer limited functionality ... just enough to google.

For some providers a reset to "factory defaults" will not reset a router to the vanilla-config provided with the service which can be a pain and some 20-hours debugging sessions with the helpdesks.

If a vanilla config is not what you want (you want DHCP, your home LAN is on 10.0.0.x addresses, you want the router to establish PPP automatically, integrate an access point, switch ports, VLANS, etc, etc), you are into network design already.

A systematic approach is needed here. Make a design drawing and consult the router's manaual to see what elements / services need to be configured. Search for default config files of service providers offering the same router model

  • get a console connection to the router and configure basic network params (IP/mask) to fit your LAN
  • use PC to complete / test configuration: interfaces, routing, VLAN, other functions, one at a time
  • save config file
  • test the power cycle (often you need to save current config to boot config)
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some comcast cable modems have a backup battery and they memorize the MAC of the last device that was plugged into their Ethernet port. If you unplug a PC and plug in a router you also have to push the reset button on the cable modem to get it to accept the router MAC instead of the PC MAC, or you have to clone the PC MAC to your router.

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Here is a good overall troubleshooting walk through to narrow down the problem:

  • Power down EVERYTHING, if the modem has a battery make sure its out
  • Power up cable modem, and a PC
  • Plug cable modem into PC
  • If your provider gave you special instructions like a static IP, be sure to set that up. Otherwise most cable providers use DHCP and it "should just work"(TM) when you plug it into your computer
  • Grab a cup of coffee and count to 10, at this point the DHCP IP should be assigned to the PC and your PC and the modem should know about each other.
  • Hit win+r and type cmd and enter
  • Type ipconfig and enter
  • You should see an IP address
  • Try surfing

  • If you can surf, massage it for awhile and see what happens. If the internet drops out, it does NOT mean there is something wrong at the ISP end, but that generally is the case.

  • If the internet drops out, contact your ISP for a new modem, in reality you will probably get a used one, but that is beside the point.
  • Repeat the above steps again, and see if there are issues.

  • If there were no issues the first time around, go through the shutdown steps again but this time plug the modem into the router

  • After everything is powered up, try surfing
  • If you can't surf, then it may mean that:

    1. The router is bad
    2. There is a setting in the router that is incompatible with the ISP, or the modem doesn't like
  • Try swapping the router for a new one if you experience problems

  • If the new one works, then the problem probably lies with the router
  • If the new one doesn't work, then the ethernet cable may be bad
  • If you swap out ethernet cables and the router still doesn't work, then there is some issue on the ISPs side. Or it could be the modem is bad.
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