http://www.rfc-editor.org/rfc/rfc7588.txt
RFC 7588: A Widely Deployed Solution to the Generic Routing Encapsulation (GRE) Fragmentation Problem, R. Bonica, C. Pignataro, J. Touch2015-07-01T23:00:00-00:00This memo describes how many vendors have solved the Generic Routing Encapsulation (GRE) fragmentation problem. The solution described herein is configurable. It is widely deployed on the Internet in its default configuration.