We lose Internet connectivity everyday - not issue with ISP

Hello Experts,

For two months, a client of mine loses Internet connectivity 3-5 times a week for a few minutes to around an hour.  During an outage, we cannot ping known-good external IP addresses like 4.2.2.1, 4.2.2.2, 4.2.2.3 and 8.8.8.8 let alone external host names.

I've pestered Comcast as I was postive it was their issue. However, we found last week that if during an outage we jump on the Comcast modem's web interface and ping, say, 4.2.2.2 from it, we get responses yet other devices on the LAN cannont successfully ping the same IP address. If we wait long enough, connectivity returns.

Here's what we've tried:

1. Replacing the modem
2. Taking the ASA 5505 out of service
3. Replacing the only switch.

Other notes:

- when one computer fails to reach the Internet, all computers fail.
- Intra-LAN communication never falters.

Ideas?
LVL 1
nathanwcAsked:
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Sapphire_Commented:
You have a COMCAST "modem" (which is really a router) do you also have another ROUTER in place?

Are you using a Windows SERVER , if so, which version.

thanks

-sapphire
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nathanwcAuthor Commented:
Yes, I used "modem" to make clear which device it is. I understand that its is a modem (mod, demod) and a router. Currently, this device bridged to the firewall behind it. We've tried it both bridged and NATted. No difference in reliability.

Yes, we have a Windows Server 2003 box as a DC/file server for 8 computers.

Nathan
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Sapphire_Commented:
are u using, dual network cards in the Server 2003 one for internet in, one for network? connected to a Switch for all users?

Do you use the windows server 2003, for Exchange, email and stuff, or just a File Server?

-sapphire
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nathanwcAuthor Commented:
Nope, single NIC in the server. No Exchange on this server, just AD, DHCP, DNS and file/print.
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IT-Monkey-DaveCommented:
When the line is "down" can you ping the Comcast modem's internal-facing IP?  How about the modem's external first-hop gateway IP at Comcast?  Any sign of reboots or anything in the modem's logs?

Has Comcast performed a comprehensive onsite signal quality analysis for you?  We've had intermittent issues where the behavior didn't make any sense: We could ping 8.8.8.8 but not the Comcast gateway, which is one hop away.  Comcast was very responsive about digging into it.  First they said the signal was too high, which they corrected.  Then they found there was excessive "spectral shotgunning" at our demarc point.  They changed something at their side and the problem went away.
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nathanwcAuthor Commented:
During an outage, we're on the web server that runs on their modem so we're definitely communicating with it. It stands to reason that we could ping it, too. Right?

I don't understand how you could ping 8.8.8.8 but not a device in between. Can you explain that bit?

Yes, we've had Comcast reps on-site several times including a supervisor who've said that they've run all kinds of tests on their end and, of course, everything checks out.
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IT-Monkey-DaveCommented:
Nope, I can't explain it, but that's what I've seen.  Like I said, it doesn't make sense.  I run a 24/7 ping test from our internal firewall out through the Comcast line, pinging both the Comcast gateway and 8.8.8.8 every 10 seconds.  There are times when one target responds and the other doesn't.  Can be either one not responding.

Running tests "on their end" is not going to confirm the signal quality at the customer site.  Comcast should connect test equipment at the end of the cable they hand your client and validate that everything is within spec (if they haven't already).
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lewisgCommented:
There was another thread like this where the ASA5505 didn't have enough user licenses and it would reboot and throw everybody off the Internet connection. They had a 5 user license on the ASA and when user 6 connected everybody dropped. I figured it for a power supply problem, didn't think Cisco would be so rude, but I was wrong...
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nathanwcAuthor Commented:
lewisg: thanks for the suggestion - licensing can often bite one in the ass, but we've had the same issue with the ASA out of service.

IT-Monkey-Dave: I've asked my on-site contact to ping their gateway: 70.88.138.166 in case anyone else wants to do the same which I will also be monitoring.

Nathan
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lewisgCommented:
This sure sounds like a Comcast problem. An issue I have had with the cable companies is their test equipment does not always show a problem when one exists. In one case their spiffy $$$$ tester said the line was fine, my $$$$ spectrum analyzer showed a severe reverse tilt to the signal. Downstream was very low and upstream was very high. It turned out a splitter was connected incorrectly in their locked box on the side of the building. So much for their many assurances of "the signal is fine".

So just because they say there isn't a problem, that does not mean that a problem does not exist. If you can find a good RF/datacom guy in your area he might be able to help.

Have you tried the simplest configuration of fixed IP addresses on all your LAN machines and using the provided modem/router in default configuration? Of course you have to set your LAN machines to match the default IP range of the cable modem/router.
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IT-Monkey-DaveCommented:
Can you  maybe plug a PC into a LAN port on the Comcast modem/router and set it to ping some target every 10 seconds and monitor it.  Thus bypassing everything on your side that affects connectivity.  If that stops working at the same time everyone else loses connectivity, it pretty much seals the deal that it's a Comcast issue.
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Dr. KlahnPrincipal Software EngineerCommented:
I now relate the following war story which may have some bearing on the issue:

Once upon a time there was a network that went down between 5 and 9 PM at night.  The hardware vendor and the software vendor came to the site and scratched their heads; no problem could be found.  Then one night while two engineers were speculating on the problem, a vwoom-thwoosh-thwoosh-thwoosh was heard down the hall just as the network went down.  As they followed the power cord from the janitor's floor buffer back down the hall to where it was plugged into the bright red protected power outlet in the equipment closet ...

And the moral of the story is, sometimes it is the power, but it's not what you thought it might be.

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IanThCommented:
have you ruled out virus's this is a classic virus activety although a virus usually disable it permanently
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nathanwcAuthor Commented:
Thanks for everyone's input. Client hasn't reported any downtime recently. Will report when we have an outage.
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nathanwcAuthor Commented:
Connection went down again two weeks ago. A few days later I again removed the ASA. Since Comcast has replaced the modem, that leaves the possiblity that there were two things at fault - the Comcast router/modem and the ASA. Though I doubt that, I do have to disprove it. Work in progress.

Nathan
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nathanwcAuthor Commented:
After about a month of running without the ASA, I can only conclude that we had two faulty devices: the ASA and the Comcast modem. I've selected multiple people based on those who exhibited the greatest insight.
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