odd lack of some internet connectivity

[dninja at gmail.com (Robin Wood)]

2008/11/4 Richer Dinelle <monkey at monkeycoder.org>:
> You could easily test it by pinging a pingable target (of course) with
> the "Don't Fragment" option set and a packet size of 1300 bytes. After
> that you just increment till the ping drops packets. It's gonna give
> you the best MTU for the link you're using ... (ping for windows and
> linux can be set that way)

I'll give that a try next time I get in.

Robin

> Rick
> On 08-11-03, at 16:56, Robin Wood wrote:
>
> > 2008/11/3 Richer Dinelle <monkey at monkeycoder.org>:
> > > As you may know, if the website you're trying to reach is blocking
> > > icmp at large then the pmtu won't work and won't be able to adjust
> > > its
> > > mtu. For example, an ADSL connection is using 1492 as its mtu but I
> > > had problems in the past with some websites (windows update or
> > > hotmail
> > > for example ...) and would timeout. By lowering the mtu at say 1456
> > > or
> > > 1484 it solved the problem. I hope it helps.
> >
> > Sounds reasonable as windows update and hotmail are two things that
> > are playing up, but why would this suddenly happen, and why would I
> > still see the problem from my linux laptop?
> >
> > To test it I would need to drop the MTU on one of the windows boxes.
> > To exagerate it I could drop it to 1300 which would then be the lowest
> > on the network so would show if it was the problem or not. Correct?
> >
> > Robin
> >
> >
> > > Rick
> > >
> > > On 08-11-03, at 10:29, Robin Wood wrote:
> > >
> > > > Thanks for the suggestions. I agree that it probably isn't DNS as I
> > > > tried dig'ing the sites that failed and they all got responses, I
> > > > could also ping some of them but not the hotmail one but I think
> > > > that
> > > > is because MS block pings for everyone.
> > > >
> > > > The MTU I could go with if it was a large network but it is about 10
> > > > PC's sat behind a switch then firewall then SOHO modem and nothing
> > > > (I've been told) has changed.
> > > >
> > > > I looked at taking smoothwall out of the picture but the modem was
> > > > plugged in though usb rather than ethernet and as I was doing it
> > > > as a
> > > > favour I didn't fancy pulling plugs and spending all day there on my
> > > > own time. I've suggested the guy who comes in to upgrade smoothwall
> > > > does this if it is still bust after he has done the upgrade.
> > > >
> > > > The peering info is interesting but as I can get at areas of a
> > > > site/ftp and not others I'm going to discount it. I would expect to
> > > > have complete blackholes rather than partial ones.
> > > >
> > > > All good suggestions and ones I'll keep in mind for the next weird
> > > > outage.
> > > >
> > > > Robin
> > > >
> > > > 2008/11/3 David Grubers <david.grubers at gmail.com>:
> > > > > I can't really offer any advise, but I have the same issue with
> > > > > gmail.com in my dorm room. google.com will load happily,  as well
> > > > > as
> > > > > several other sites, but gmail will take a good couple minutes. I
> > > > > know
> > > > > it isn't DNS, as my browser successfully looks up the IP and then
> > > > > the
> > > > > connection gets slow while it connects. I'm not sure if google
> > > > > analytics automatically is loaded by gmail, but if not, I notice
> > > > > that
> > > > > it often loads at this time too (perhaps my ISP is doing some
> > > > > monitoring with analytics?).
> > > > >
> > > > > 2008/11/3 Bugbear <gbugbear at gmail.com>:
> > > > > > I am not familar with Smoothwall but does that have any sort of
> > > > > > IPS,
> > > > > > application shaping, web filter, or app inspection in it? In my
> > > > > > experience
> > > > > > when I have had issues like this it almost always one of these
> > > > > > types of
> > > > > > products.
> > > > > >
> > > > > > I would put a system on the outside of Smoothwall and see if the
> > > > > > issue can
> > > > > > be reproduced - just to rule it out quickly. You can always throw
> > > > > > wireshark
> > > > > > inline too but taking the firewall appliance out of the equation
> > > > > > would be
> > > > > > where I star.
> > > > > >
> > > > > > Doesnt sound like a DNS issue since it saounds like some of the
> > > > > > pages are
> > > > > > loading partially and the FTP behavior you described.
> > > > > >
> > > > > > Could very well be the ISP and worth a call post taking the
> > > > > > Firewall
> > > > > > appliance out of the loop.
> > > > > >
> > > > > > Tim
> > > > > >
> > > > > >
> > > > > >
> > > > > >
> > > > > > On Mon, Nov 3, 2008 at 8:15 AM, Robin Wood <dninja at gmail.com>
> > > > > > wrote:
> > > > > > > Hi
> > > > > > > See if anyone can help me with this weird problem ...
> > > > > > >
> > > > > > > I've just been to see a friend at his company as he was
> > > > > > > complaining
> > > > > > > about not being able to access certain websites or certain
> > > > > > > parts of
> > > > > > > sites that used to work fine. My first thought was browser or
> > > > > > > local
> > > > > > > firewall problem so I took my laptop along to eliminate the
> > > > > > > possibility of that being the fault.
> > > > > > >
> > > > > > > After some playing we found a couple of sites (hotmail and part
> > > > > > > of the
> > > > > > > Ryan Air booking system) that just timed out when we tried to
> > > > > > > access
> > > > > > > them, this was through my laptop and through their machines. I've
> > > > > > > just
> > > > > > > tried the same sites 10 mins later at home and they are working
> > > > > > > fine
> > > > > > > so it isn't that the sites aren't down. I also tried hitting the
> > > > > > > site
> > > > > > > through netcat and again, it just timed out.
> > > > > > >
> > > > > > > It isn't a http vs https issue as I successfully visited a number
> > > > > > > of
> > > > > > > sites of both types.
> > > > > > >
> > > > > > > It isn't even just web traffic, the ftp connection they use to
> > > > > > > publish
> > > > > > > their website allowed us to login and get a directory listing of
> > > > > > > the
> > > > > > > root directory and change into a subdirectory but getting a
> > > > > > > directory
> > > > > > > listing of that directory timed out. The same connection works
> > > > > > > fine
> > > > > > > from my friends home network so it isn't a permissions issue.
> > > > > > >
> > > > > > > I'm at a loss of what to suggest, they are using smoothwall
> > > > > > > express v2
> > > > > > > between their switch and modem but that hasn't been updated for
> > > > > > > months
> > > > > > > so is unlikely to be the cause, just in case it was playing up we
> > > > > > > tried rebooting it and the problem still persisted.
> > > > > > >
> > > > > > > The problem has been happening for over a month now but nothing
> > > > > > > has
> > > > > > > been changed in a lot longer than that so it shouldn't be a
> > > > > > > config
> > > > > > > issue.
> > > > > > >
> > > > > > > I've suggested talking to their ISP (BT) to see if they can
> > > > > > > suggest
> > > > > > > anything. Has anyone here got any suggestions of what to try, I'm
> > > > > > > completely stumped!
> > > > > > >
> > > > > > > Robin
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