Technically the packets don't get fragmented. It is the tunnel that fragments. For example, in the bad old days, when there was still a lot of ATM, packets wou

Technically the packets don't get fragmented. It is the tunnel that fragments. For example, in the bad old days, when there was still a lot of ATM, packets would routinely get transmitted in 48 byte pieces (with a 5 byte header). Nobody wondered whether this kind of fragmentation should honor the DF bit. If I recall correctly, multi-link PPP could also split a packet in smaller pieces to transmit it over multiple links at the same time. So for IPv6, anything that is 1280 octets or smaller needs to forwarded without triggering a packet too big ICMP. Otherwise the link violates the IPv6 standard.