On Thu, Feb 7, 2013 at 10:39 AM, Brandon Allbery <email@example.com> wrote: > Subset of, yes. All? So many sites on the Internet can't be accessed reliably from the many OSes that do PMTUD? Somehow, I doubt. If you want to be sure, use the RFC mandated minimum MTU of 576 for IPv4 (1280 for IPv6). You want larger packets? Then get used to disappointment (at least some of the time).