cable modem requires reboot because one site falls off DNS?

[Greg Rundlett (freephile)]

On Fri, Sep 3, 2010 at 11:36 AM, David Miller <david3d at gmail.com> wrote:

>
>
> On Fri, Sep 3, 2010 at 11:19 AM, David Miller <david3d at gmail.com> wrote:
>
>>
>> On Fri, Sep 3, 2010 at 10:37 AM, Greg Rundlett (freephile) <
>> greg at freephile.com> wrote:
>>
>>> I have a strange problem where one (and only one as far as we know)
>>> particular website becomes inaccessible to our office.
>>>
>>> The "fix" for this problem is to reboot the Comcast cable modem, however
>>> I don't understand how the modem could be the culprit.
>>>
>>> The website in question is nnerenmls.com  and the modem is configured to
>>> use Comcast's DNS servers....
>>> 68.87.71.226
>>> 68.87.73.242
>>>
>>> One red herring:  It would seem that Comcast changed their DNS servers,
>>> because the ones currenty in the modem configuration do not appear in the
>>> list http://dns.comcast.net/dns-ip-addresses.php  I thought to myself,
>>> "I just switch to Google's Public DNS servers" (8.8.8.8 and 8.8.4.4)  I'm
>>> pretty sure they are not going to change.  However, it doesn't make sense to
>>> me that one website would fail, while general DNS would still be working.
>>>  And, at the time of the failures, other people using Comcast can resolve
>>> that domain meaning it doesn't even appear to be an issue where the target
>>> domain is occasionally falling off the web.
>>>
>>> Any ideas on what could cause this and how to troubleshoot?
>>>
>>>
>> We have that problem here time to time.  It doesn't appear to be a DNS
>> issue in our case it's always been a very strange routing problem that
>> happens after a bunch of correct hops.
>>
>> We are lucky enough to have a 2nd internet connection and when we have
>> this problem here I can traceroute from each connection and the comcast one
>> normally will get to the correct datacenter and then take a different hop
>> from our T1.  I've never been able to make any sense out of it.  But for
>> this reason I have a few sites setup to route out our T1 so that it doesn't
>> cause any interruptions in our business.
>>
>> Rebooting the comcast router in our case has always resolved this routing
>> problem.  I'd be interested in any theories as to what causes the routing to
>> go awry after many hops and outside of comcast's network.
>>
>
> I guess I should have prefixed that with make sure it's a DNS issue and not
> a routing issue.  Because my prior experience with Comcast Business with the
> symptom being one site being inaccessible makes me believe that it's a weird
> routing issue.
>
> This routing issue is apparently a pretty common issue with Comcast
> Business.  The person who made the suggestion to reboot the router was tech
> support at SaaS provider that we were having a problem accessing.
>  Apparently they have had a few customers with strange routing issues with
> Comcast Business where rebooting the Comcast router resolved it.
>
> You can test for this issue by doing a traceroute before and after
> rebooting the router and comparing the output.  I think you'll find out that
> the DNS resolution is the same before and after you reboot.  At least if
> it's the same issue that I've run across with Comcast Business.
> --
> David
>

Thanks,

I think we're experiencing the same problem you describe.  I'm not actually
at the office that's affected, so I haven't done a traceroute or a dig at
the time when it's out.  I just know that the user's browser returns a "Site
not found" error as if DNS didn't work.  Granted, you'd get the same result
if routing didn't work, so I think it's actually a routing glitch.

I'll try getting some answer from Comcast, although I'm just plain fatigued
with dealing with them for any purpose. [1]

Greg Rundlett

[1] Did you know that as a business class customer, you get three mutually
exclusive logins to access and manage your account.  One uses credentials
that are given to you at the time of account creation (was likely setup
years ago, so of course you've forgotten those).  That login gives the
ability to subscribe to and setup additional services that you don't give a
crap about - like a sharepoint service.  You'll need a separate login to
manage the VOIP aka "digital voice" service (but the 'portal' doesn't
include access to important aspects like managing your billing address).
 Any you'll need another login to manage your customer profile etc. -- your
real account.  And if you call technical support to change something like
your billing address, they will need to reset your account username and
password in order to make the change.  Their procedure is to set your
username AND password  to the phone number of your service.  I suspect that
it's trivial to gain illegitimate access to a large number of comcast
digital voice subscriber accounts.
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