change mtu

[kvonb]

The MTU thing can be a right royal pain in the arse, my ISP uses PPPoE
and goes through a Motorola Canopy system, then up to a 2-way satellite
to the other side of the country, then back to my ISP who quite frankly
knows more about chicken soup than he does about MTUs!



After a recent "scheduled maintenance" on some of their equipment, all
of my computers except 1 were unable to access certain pages on the
net, such as hotmail, IPSs webmail, and even posting replies to
ubuntuforums!



NOTHING had changed on my server.



I could browse other sights, and downloads weren't effected, but bugger
me I could not log into hotmail, and was constantly being pestered by my
wife and kids!



I wasted 4 days fiddling with firewall settings, re-installed Ununtu,
built a new server, tried to connect with a clean copy of Windows on
another machine, punched several holes in my workbench, lost lots of
hair and sleep, still the same problem.



But - one Windows SP1 machine on my network was connecting, and I could
not figure out why.



Had I angered the computer gods THAT much?  I haven't even loaded
Windows once this month on my computer, hadn't even thought about
committing that most hideous, most blasphemous sin!



Of course my ISP knew nothing!



Then one bleary-eyed morning, I remembered - I'd used a prog called
DrTCP on that machine a few months ago, and I changed the MTU to
1412!!!!!!



That was the killer, some moron somewhere down the line had changed the
MTU!



So don't talk to me about MTU not being a problem, one tiny change can
and WILL ruin your whole Internet.



I finally settled on an MTU on my server of 1452, although even now it
seems to stop every now and then, so I change it to 1412 for a day or
so, then back to 1452.



If you are running a server (shared internet connection), then you
should change your MTU to a max of 1492, if hotmail doesn't work (full
login and can actually see your e-mails), drop it to 1452, then 1412
until it works.  Check the speed at the same time to find an optimal
setting.  The default for Ubuntu seems to be 1500 if you haven't change
anything.



DON'T rely on "should work", and "shouldn't need to do that with modern
equipment", all it takes is one wrong number by a careless or unknowing
ISP employee, and the games will begin!!!



Try downloading DrTCP and playing with the MTU on the Windows box, it
will tell you the current MTU setting, then try it with a smaller ona
and see what happens.



Regards,



Kev


-- 
kvonb