Author Topic: Diagnostic info for checking internet connection, cable modem  (Read 2767 times)


  • Member
  • *****
  • Posts: 2381
Diagnostic info for checking internet connection, cable modem
« on: December 12, 2012, 04:11:15 AM »
This may help someone diagnosing connection problems with a cable modem, etc.

I connect from a router -> computer

If you go from cable modem -> computer for testing purposes, you will need to power off modem for 30 seconds.

I think I have eliminated hardware issues at this point.

Next is to see if the wireless network is setup right.

Well, if I was working on it, as a lowly home user (which I am),
I'd split the problem in two. The very last thing I'd want
to throw into the mix, is having the 802.11 wireless
as a variable ( -=-=- in the diagram ). You can work
on the wireless part, once you've proved Comcast isn't
ripping you off. The wired portion should be more reliable.

See if the computer in question, has an option to disable the
wireless portion. (My laptop, has an option to turn off the
radio on the Wifi, as an example of a control.) Once the wireless
is off, and the Ethernet cable is detected running from the
computer on the right, to the cable modem in the center,
the computer should switch over to Ethernet.

    Cable_Company ---------- CC or User ------------------ wired link
                             provided cable                    or
                             modem  -=-=-=-=-=-=-=-=-=-=-  wireless to the

If the Cable Modem includes a one port or multi-port router
(modern devices are all-in-one), it likely supports DHCP and
dishes out 192.168.x.x private addresses for the computers
in the house.

If you can ping the cable modem from a command prompt...


or use your web browser on it, that proves the wiring from the
right of the diagram, to the center of the diagram is working.
I got the IP address from the FAQ link below. The address to reach
the router setup page, is probably in your paper documentation
somewhere. Using a browser, you might try


The right-hand sidebar here, has a few FAQ entries for Comcast
Cable. There's one for signal strength, if you like to dabble
in such things (that's signal strength on the Comcast cable
TV wire). Or, talk to Comcast, and listen to the script
their tech has to offer (the ole "turn it off and turn it on"
crap).    <--- logging into modem from
                                            a web browser...

ISPs either allow users to own their own modems, or the
modem is a rental. If it's a rental, it might be covered
in the FAQ. If it was purchased separately, it might have
manuals in the box, or available online, for probing it.

The modem should collect statistics. And that's one way of
determining whether basic operation is present or not.
The status lights on the box, provide a simple go-nogo
status. But the signal level page delivered by the
router to your browser, can also give some info.


I'm on ADSL, and for us as users, there is "DMT". I think
I read somewhere, it uses telnet protocol on the local LAN
to talk to the ADSL box, and it downloads the stats and
makes that colorful graph. There are websites, such as
dslreports, that have more info on how to interpret the
numbers in DMT. I've never run this on mine (because my
ADSL is in bridged mode), but I understand some people
use the results of such testing, to ask for a profile
bump to a higher bandwidth setting.

I doubt the operation of the cable, is quite that crude.

We have to work a bit harder, if we want to debug
our broken ADSL setups. But the phone company can
also wring out the line from their end, and check
parameters. It's just more reassuring to have a
graph to offer as proof they're not delivering
the level of service they should.
This may help someone in the future.

If you get it working right, while using the
Ethernet cable, then that might point to the
Wifi as the busted part. But first, I'd want
to make sure the setup is rock solid over
Ethernet cable, before letting Comcast off
the hook in terms of delivering service. Getting
the Wifi working, is for "bonus points".

Take care,