Here are two tunnel proposals that do fragmentation as part of the
encapsulation layer instead of at the IP layer:
https://datatracker.ietf.org/doc/draft-herbert-gue-fragmentation/
https://datatracker.ietf.org/doc/draft-templin-intarea-grefrag/
Thanks - Fred
fred(_dot_)l(_dot_)templin(_at_)boeing(_dot_)com