> On Feb 14, 2017, at 10:33 AM, otroan@xxxxxxxxxxxxx wrote: > >> *If* you care about packet loss, then your only option is to probe the path with with >> synthetic data that exactly mimics the live data, or not to probe at all and live >> with the 1280. As I said 1280 is pretty close to 1496 which is all most networks >> will give you in practice. > > Yes, but sending at 1280 does not work for IP tunnels. The whole purpose of the minimum MTU was to give space for tunnel headers (1500-1280). I'm confused by that statement. https://tools.ietf.org/html/rfc7676#section-3.2 indicates that a GRE tunnel on IPv6 and carrying an IPv6 payload works with a PMTU of 1280, and AFAIK it is among the larger tunnel headers. What tunnels does a PMTU of 1280 not work for?