In the last few months I've run across a number of IP fragmentation issues, as you've probably noticed through my blog posts. I've also encountered a lot of misconceptions about IP fragmentation, its impact on GRE and IPSec as well as the fragmentation-related mechanisms, for example MTU Path Discovery. I hope that you'll find my January IP Corner article The Never-Ending Story of IP Fragmentation a good summary of the subject.
Ivan Pepelnjak, CCIE#1354, is the chief technology advisor for NIL Data Communications. He has been designing and implementing large-scale data communications networks as well as teaching and writing books about advanced technologies since 1990. See his full profile, contact him or follow @ioshints on Twitter.