cable modem requires reboot because one site falls off DNS?

[David Miller]

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.
--
David
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