Troubleshooting internet connection

[CommonCents]

So my MIL stayed at our house yesterday while the cable guy came in to give us internet.  Apparently they have to do a housecall for this, even though they don't actually set up your modem or anything, so you can't really see if it's properly working.  So we got home to set it up, and it's not working.  We can see the wifi network on our devices, but can't actually get on the internet through it.  Any tips for troubleshooting on where the issue is?  (Note the modem, while older, was working just fine two weeks ago at the old home.)

[willn]

Make sure your pc's firewall is running, then connect your pc directly to the modem with an ethernet cable.  Then see if you can get to the internet.   If so, its a setting or issue on the wifi router.  Typically the router's "outside" interface should get a dynamic IP address from the modem.  If the internet side of the router is set to a static IP address, that could be the issue.  But there are about 100 other issues it could be also.

If your pc gets to the internet when connected directly to the modem, you could probably just do a factory reset of the router. Default settings will get it connected in most cases, then you need to set up your wifi name, security, etc.

[CommonCents]

Thanks.  I'll check on that when I get home.

[Daley]

There are two major issues that it could likely be, and there's a few extra bits that are worth knowing. We'll start with the knowledge.

1) Most cable modems require power cycling when switching between devices plugged in, as they tie communications to the MAC address of the ethernet adapter of the device plugged in.

2) Most cable ISPs will not let the cable modem communicate with devices that have MAC addresses associated with routers.

3) All cable modems will have some sort of diagnostics portal page that you can access, and this page can be useful in determining whether there's noise on the lines or not (basically cabling issue, either yours or the cable company's end). Here's a guide for the ranges you should expect. For Motorola/Arris modems, that portal address is http://192.168.100.1/ and should be reachable even behind most routers.

The two most common failure points after a fresh install is either the MAC address issue or line noise inside the house on a cheap coupler/splitter/wall jack or from older RJ59 (or lower spec) cabling. RJ59 should work but really old cable could have problems, and newer RJ6 is the preferred used coax cable. Typically, when the cable tech is sent out for a new service hookup, they're checking signal strength to the DMARC point (the box on the house that they hook up to to get to the wiring inside) to ensure service is usable. This is why if it is a signal/noise issue, it's likely on your cabling end. Given you didn't mention error lights blinking, I doubt it's that however, though it doesn't hurt to check the signal diagnostic page anyway.

That said, it's most likely the MAC address issue, and it's really easy to fix. On all routers, somewhere in the settings, there should be a WAN MAC address clone option and some sort of "Get Current PC MAC Address button" or something along those lines. (WAN is Wide Area Network, by the way... it's the end of the router that plugs into the modem.) Use this to change the MAC address of the router to that of your computer. While you're there, make sure your router is set to DHCP on the WAN end and not Static IP, PPPoE, PPTP or L2TP or whatnot. Once those settings are saved, power down the modem and the router and bring up the modem only. Once the lights go stable, power up the router and let those lights go stable as well. Then check your connection. Knock wood, it should all work. If not, let us know.

[willn]

IPDaley, interesting, can you explain further what's the issue with the MAC address?

Most home networks have many connected devices (thus many MAC addresses)---and routers don't pass MACs from pc through to the modem, at least by default, when a packet is passed from one subnet to another, the destination and source MAC's are swapped to the MAC's of the new source and destination on the recieving subnet interfaces)

Are you saying that the modem may have learned one MAC (say, a pc directly connected, or an old router's WAN interface MAC) and then won't connect if it sees a different one?

FWIW I haven't ever had this issue with Comcast in Northern VA area.  What I have seen is ISP's not transmit over a newly installed modem--the modem's MAC address needed to be registered with the ISP. But not the router's MAC.

[Nothlit]

First step, call your ISP and have them run diagnostics from their end to see if they can see your modem. If so, then the issue is internal to your home network. Then you should try some of the troubleshooting steps listed here (e.g., try connecting your computer directly to the modem with no router in between).

[Daley]

Are you saying that the modem may have learned one MAC (say, a pc directly connected, or an old router's WAN interface MAC) and then won't connect if it sees a different one?

Let me clear up a few things.

1) The cable modem associates and sets an IP address with the ISP based on the MAC address (not all cable ISPs do this, but most). This introduces the ability to blacklist certain MAC address ranges from being assigned IP addresses by the ISP as well, thus the issue with some routers not working with modems with some cable companies using the default MAC address. Switching devices without power cycling the modem or spoofing the MAC address of the last device will usually cease communications. A simple power cycle of the modem fixes that, however. I'm unsure on Comcast, but I know this is how Charter and Cox operate, and is typically done to make less technical people buy/lease their networking equipment over set up their own.

2) You are correct. When you use a router, only the WAN MAC address is visible to the modem no matter how many devices you have connected to the router.

3) MAC addresses can be spoofed. The easiest way to bypass the MAC blacklist with the modem on a router is to spoof the MAC address of one of the computers to be used as the WAN MAC address on the router itself.

Make sense?

[CommonCents]

We bought the house from a guy we've since labeled the "mad scientist" for the profusion of wires he has coming out of a wall in the office.  In there at least there is cable that a friend identified as something 6, so perhaps it's the RJ6 you mention above.  Whatever it was, the tech friend was pleased and felt it was good.  (That said, I don't know that there is the same cable where the modem is, but I would think yes.)

Thanks for the education here.  I've been vowing to learn more and be a bit less reliant on others to set up my devices for me.  (My BIL set it up initally for me in 2007, and DH or dad set it up for us in 2010.)  This is a good start and hopefully one of the suggested fixes will work tonight.

[willn]

Make sense?

Yep. Thanks.

[Daley]

Thanks for the education here.

Do what I can. :)

Silly, off the wall question worth asking though: Have you registered the cable modem's MAC address with your ISP yet? That's a pretty critical step in service provisioning as you can't just plug a modem into the wall and expect it to work. It needs to be set with your cable ISP so they know what device to provide the service to on their network. I kind of assumed you already had what with the tech out, and I suspect you have, but it never hurts to ask anyway.

[CommonCents]

Thanks for the education here.

Do what I can. :)

Silly, off the wall question worth asking though: Have you registered the cable modem's MAC address with your ISP yet? That's a pretty critical step in service provisioning as you can't just plug a modem into the wall and expect it to work. It needs to be set with your cable ISP so they know what device to provide the service to on their network. I kind of assumed you already had what with the tech out, and I suspect you have, but it never hurts to ask anyway.

*ehrm embarrassed cough*
My husband was fiddling around with it last night, so I don't know what he did, and he talked to his mom about the cable visit, not me.  Part of why I decided to post/educate myself, so I learn and I'm not so reliant on others!  (In fairness though, I was wiped after spending 4 hours after work cleaning the old condo so we don't need to hire a cleaning person.)  For the stupid question, how do you register it?

[Nothlit]

For the stupid question, how do you register it?

Sometimes you can do it by launching a web browser and attempting to browse to any web site. If the modem is not registered, you may get redirected to a service activation page. Kind of like how when you join a public Wi-Fi hotspot you might get redirected to a "capture" page to accept the terms of service before it will grant you unfettered access to the internet. If the technician left behind any setup instructions, you might check for that there.

Otherwise, just call your ISP, as I said above. They can verify whether your modem is registered and active on their network or not. You will most likely need to read the MAC address to them over the phone. A MAC address (stands for media access control; has nothing to do with Apple computers) is an alphanumeric serial number unique to your modem, made up of numbers 0-9 and letters A-F in a format like this: 01:23:45:67:89:ab. The MAC address can typically be found on a sticker somewhere on the modem itself, or perhaps on the box it came in.

[Daley]

For the stupid question, how do you register it?

Typically it's done during setup, and either the tech on site or the customer with a self-install kit has to call into the ISP and go through the provisioning portion of setup. This involves reading off the MAC address from the modem to the tech at the other end. On Motorola/Arris devices, it's listed as the HFC MAC ID on the bottom of the modem. If this number is recorded on the install paperwork left by the tech, it's likely already been done. If they told you you need to call in to finish setup, you still need to provide it. Just tell them the make and model of the modem and they'll tell you what number to read off. Alternately, some providers like Comcast just require a direct internet connection between a computer and the modem to try and browse, then you just enter your account information on the mandatory sign-up page that presents before you can start surfing.

I do suspect however, that the modem has already been provisioned. It doesn't hurt to call into support and ask, however. "Say, we had a cable internet install yesterday. Has our modem been provisioned with you yet?"

[CommonCents]

Update: It was indeed the MAC address.  The tech had apparently given Comcast the USB number instead.  Thanks for all of your help!  We were able to watch the superbowl via free Fox streaming, and we are now on day 16 of no cable!