sounds like a delightful session with some productive ideas.
On Wed, Jul 24, 2019 at 5:23 PM Paul Vixie <p...@redbarn.org> wrote: > one other matter emerged during this discussion. path mtu discovery is > dead at > the moment, for valid security reasons. however, a jumbogram sized campus > can > be described in static routes, using MTU 1500 only for "default". and > also, > any future path mtu discovery functions will, as in the past, simply > create > "host routes" (/32 or /128) to memorialize the MTU known for that host, > since > that is where the TCP MSS computation will expect to find it. so, the lack > of > path mtu discovery in today's networks does not invalidate the method of > calculating TCP MSS from the route MTU; thus, this should be safe for EDNS > buffer size as well. > > paul > > re: > > On Thursday, 25 July 2019 00:19:18 UTC Paul Vixie wrote: > > with four of us in attendance monday evening, i presented my appreciation > > for fujimora-san's draft and admitted that EDNS0 ought to have required > DF > > and ought to have used examples which would fit in a then-common MTU 1500 > > network. > > > > i then asked that numbers like 1220, 1280, 576, and 1500 not be > specified as > > fixed constants, but rather, should be computed in the same way and for > the > > same reasons as TCP MSS. those of us running jumbograms or still running > > FDDI or perhaps speaking POS should not be artificially limited in our > DNS > > payload sizes. > > > > in discussion, the following details appeared: > > > > TCP MSS is calculated from the routing table. on microsoft windows, > there's > > an easy way to find the route for a destination... > > > > > https://docs.microsoft.com/en-us/windows/win32/rras/search-for-the-best-rout > > e > > > > ....and while there's no portable way to do this from user mode in Linux > or > > BSD or other UNIX-style systems such as Android, there is always a way. > > > > it is the route's MTU and not any one interface's MTU, and not any > constant, > > that should be used to calculate EDNS0 buffer size. that will probably be > > 1280 or 1220 for most V6 routes (including "default", the route of last > > resort) and 1460 for most V4 routes (including default). > > > > (noting, i've made a similar plea to the QUIC team. the 1500 MTU will not > > last our lifetimes, and we must not hard code the 1500 MTU assumption... > > anywhere.) > > > > also, there were beer and snacks. > > > -- > Paul > > > _______________________________________________ > DNSOP mailing list > DNSOP@ietf.org > https://www.ietf.org/mailman/listinfo/dnsop >
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