Even though I have an IPv4 MTU of 1500 bytes achieved through PPPoE 1508 byte baby jumbo frames, we have to remember that as far as IP is concerned these numbers are just arbitrary. Some IPv6 applications, iirc, just stick to 1280 bytes because that is guaranteed to work in the IPv6 standard, and don’t bother with trying to get up to the path MTU. The number 1500 only comes from ethernet, and has nothing to do with IPv4 or IPv6. Having said all that, I wanted a 1500 byte IPv4 MTU for largely illogical reasons, wanted best byte overhead efficiency, and best compatibility with IPv4 applications. For IPv6, for reasons that have been discussed in earlier threads, I use an MTU of 1408 though.