This is just a guess, but it could some sort of spoofing/caching mechanism - that's clearly broken in some way they can't determine.
--Bruce On 09/20/2010 11:15 AM, Greg Rundlett (freephile) wrote: > This problem happened again today. We were unable to access a website > that we access repeatedly for business. This time we couldn't access > our intranet. I called Comcast and they said right away that they > would disable the "Smart Packet Detection" setting in the modem. The > support person couldn't tell me what "Smart Packet Detection" was, but > did say that nearly 100% of the time it resolved problems like this. > Now that I know what the problem was, I can find similar stories all > over the Internet going back several years. > > Quote from one story: > > "Our Comcast business class cable modem (SMC make, model escapes me at > the moment) has a packet dropping feature called "Gateway Smart Packet > Detection". > > I've yet to see any documentation on this "feature" but when left > unchecked, as is by default, you may black hole certain IP addresses > simply by visiting them too much. Or uploading to them too often. Our > web team was editing a site and this feature would constantly black > hole the IP they were sending to when this feature was left enabled." > > http://nwlinux.com/blog/comcast-business-class-router-and-smart-packet-detection/ > http://lmgtfy.com/?q=smart+packet+detection > > Greg Rundlett > > > > > On Fri, Sep 3, 2010 at 4:32 PM, Dan Jenkins <d...@rastech.com > <mailto:d...@rastech.com>> wrote: > > On 9/3/2010 11:19 AM, David Miller wrote: > > > > On Fri, Sep 3, 2010 at 10:37 AM, Greg Rundlett (freephile) > > <g...@freephile.com <mailto:g...@freephile.com> > <mailto:g...@freephile.com <mailto:g...@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 > <http://nnerenmls.com> <http://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. > > > > We've had this strange routing problem several times over the last > year. > It makes no sense to me either, but power cycling the Comcast-provided > SMSC cable modem/router has solved the problem in all four cases at > three different clients. In one instance, the traceroute made it > to the > very last hop before their web server, and then died. I wondered if it > could be some odd TTL issue. Comcast's tech support has been pleasant, > but not very informative about the cause. Since power cycling > works, and > is quick, I haven't tried to diagnose it further though I'd like > to know > why it happens. In one of the other cases the route to a specific IP > number immediately went along a completely different path than another > IP that was in the same destination network. The other case > appeared to > start playing leap frog half way to the destination (hop E to hop F to > hop E, etc.). The fourth occurrence I just had them power cycle. There > may have been more cases, but I documented how to power cycle the > cable > modem for them (they are all small enough that it hasn't been a major > issue) and haven't heard about recurrences. > > > > > _______________________________________________ > gnhlug-discuss mailing list > gnhlug-discuss@mail.gnhlug.org <mailto:gnhlug-discuss@mail.gnhlug.org> > http://mail.gnhlug.org/mailman/listinfo/gnhlug-discuss/ > > > > _______________________________________________ > gnhlug-discuss mailing list > gnhlug-discuss@mail.gnhlug.org > http://mail.gnhlug.org/mailman/listinfo/gnhlug-discuss/
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