odd lack of some internet connectivity

[monkey at monkeycoder.org (Richer Dinelle)]

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)

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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