4 ms·

I think it's only that in v4 the node has the option of requesting MTU discovery, like everyone practically does, or having the on-path routers do fragmentation

I think it's only that in v4 the node has the option of requesting MTU discovery, like everyone practically does, or having the on-path routers do fragmentation transparently. In v6 it always works similarly as requesting path MTU discovery in v4 ("don't fragment", aka DF, header bit turned on). So the simplification is that in v6 the legacy mode was eliminated.

zamadatix 4y ago
The change with IPv6 was more than a simplification of removing fragmentation (though that was welcomed since most devices didn't do it anyways). In v4 you had the option to probe, you had to the option play it safe with the minimum 576 bytes, or you had the option to assume it was a larger value. In v6 spec compliant clients must either use the minimum 1280 or probe, the ability to assume anything is no more. The only reason things didn't fall apart in IPv4 despite the rampant blocking of ICMP for "security" reasons is everyone started using TCP which has MSS negotiation and MSS clamping.