Looking for a little education or links concerning MTU values with respect to DSL connections and PPPoE.
It seems we can't connect from our home via our DSL line to our school's web application called - Blackboard - There are lots of postings on the web about this DSL problem.
The normal MTU setting for a DSL line using PPPoE is 1492. With that setting, we can't use some of the Blackboard features - they hang. HOWEVER, if we modify our laptop MTU setting to 1362 - IT WORKS
Also - we have not been able to "send" or "forward" email using our school's web based Exchange OWA from home.
I found a TCP utility called TCP Optimizer that makes it easy to change and test the MTU value, and therefore easy to replicate the web application problems.
I just tried the MTU modification to 1362 as a test, and now the Exchange OWA "sending" works. If I change the MTU back to 1492 - the OWA "sending" hangs... So - there's another web application mystery related to the MTU values.
At this point I have no idea how MTU works or what's actually involved. I'm technically curious about it, and will pursue an explanation.
The bottom line is that it appears when the local computer or router is working with an DSL + PPPoE imposed MTU setting of 1492 - things fail. When the local MTU is modified to 1362 - things work.
Any education on why a "smaller" MTU makes things work, and yet a "larger" MTU makes them fail or hang ?????