Very interesting. Thanks for sharing this with the list. I'm going to make that change here and disable the policy routes that I was using to force traffic to certain websites out our t1. To see if the problem continues. -- David
On Mon, Sep 20, 2010 at 11:15 AM, Greg Rundlett (freephile) < g...@freephile.com> 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> 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>> 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> >> > 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 >> 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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