Which doesn’t work with IPv6 as UDP doesn’t have the field to clamp. -- Mark Andrews
> On 20 Jan 2018, at 03:35, Radu-Adrian Feurdean > <na...@radu-adrian.feurdean.net> wrote: > >> On Fri, Jan 19, 2018, at 01:14, Jared Mauch wrote: >> If you’re then doing DSL + PPPoE and your customers really see a MTU >> of 1492 or less, then another device has to fragment 5x again. > > In this part of the world we have even worse stuff around: PPP over L2TP over > over IP with 1500 MTU interconnection. Remove another 40 bytes. Add some more > headers for various tunneling scenarios and you may get into a situation > where even 1400 is too much. But it usually works with MSS clamping to the > correct value. Some small ISPs don't even make the effort to check if the > transport supports "more than 1500" in order to give the 1500 bytes to the > customer - they just clamp down MSS.
