On Mon, Feb 8, 2016 at 5:52 PM, John Levine <johnl@xxxxxxxxx> wrote:
>2. What kind of UDP applications use such big packets, over 1280 bytes ?
>Um, the DNS with EDNS0, and particularly with DNSSEC? Is this a trick question?
Yes.
The trick lies right there in IPv6 specification:
"A node must be able to accept a fragmented packet that, after
reassembly, is as large as 1500 octets."
... which is not much greater than 1280 bytes defined as minimum MTU for IPv6.
Basically, Fragmentation, as specified in RFC-2460 (IPv6), solves the problem ONLY for packet-sized between 1280 and 1500 bytes. Which is why I doubt if it is useful at all.
(I also understand, that IPv4 fragmentation is much more flexible, yes. It can go as small as 68 byte packets.)