This service at
http://www.letmecheck.it/mtu-test.phptests your
MRU / MTU. A simple-to-use tool, this website just does what it says on the tin. This service is really useful in tracking down potential nagging MRU-related problems if you have changed service type, changed to
a two-box system of separate modem and router, or to a different model of separate modem. (See
http://aa.net.uk/kb-broadband-mtu.html for explanation.) It
speaks IPv6 too, which I need. Shows a real commitment to quality in design there.
I needed to test whether I could now dare to use full 1500 byte MRU / MTU with my DLink DSL-320B-Z1 modems instead of the annoying restriction to MTU 1492 that you often get with separate modems and PPPoE. When I changed from BTW 20CN to 21CN, I was finally able to use 1500 byte MRU despite having a separate router and PPPoE modem.
