On Thu, May 20, 2021 at 3:06 AM <tuexen@xxxxxxxxxxx> wrote: > > > On 20. May 2021, at 04:05, Xin Long <lucien.xin@xxxxxxxxx> wrote: > > > > On Wed, May 19, 2021 at 6:24 PM <mleitner@xxxxxxxxxx> wrote: > >> > >> On Tue, May 18, 2021 at 09:19:21PM +0200, Michael Tuexen wrote: > >>> > >>> > >>>> On 18. May 2021, at 20:33, Xin Long <lucien.xin@xxxxxxxxx> wrote: > >>>> > >>>> On Tue, May 18, 2021 at 1:38 PM Michael Tuexen <tuexen@xxxxxxxxxxx> wrote: > >>>>> > >>>>>> On 18. May 2021, at 18:43, Xin Long <lucien.xin@xxxxxxxxx> wrote: > >>>>>> > >>>>>> Hi, Michael, > >>>>>> > >>>>>> We're implementing RFC8899 (PLPMTUD) on Linux SCTP recently, > >>>>>> and to make this be controlled by setsockopt with > >>>>>> SCTP_PEER_ADDR_PARAMS, as in > >>>>>> > >>>>>> https://datatracker.ietf.org/doc/html/rfc6458#section-8.1.12: > >>>>>> > >>>>>> we need another two flags to add for spp_flags: > >>>>>> > >>>>>> SPP_PLPMTUD_ENABLE > >>>>>> SPP_PLPMTUD_DISABLE > >>>>>> > >>>>>> Do you think it makes sense? if yes, does the RFC6458 need to update? > >>>>>> if not, do you have a better suggestion for it? > >>>>> It is great new that you want to implement RFC 8899. I plan to do the > >>>>> same for the FreeBSD stack. > >>>>> > >>>>> In my view, RFC 8899 is the right way to implement PMTU discovery. > >>>>> So I will just use the SPP_PMTUD_ENABLE and SPP_PMTUD_DISABLE. I don't > >>>>> think that the user needs to control which method is used. > >>>>> I you want to support multiple versions, I would make that > >>>>> controllable via a sysctl variable. But I think for FreeBSD, support > >>>>> for RFC 8899 will be the only way of doing PMTU discovery. There > >>>>> might be multiple choices for details like how to do the searching, > >>>>> how long to wait for some events. These will be controllable via > >>>>> sysctl. > >>>>> > >>>>> So in my view, there is no need to extend the socket API. What do you think? > >>>> OK, that makes sense to me. > >>>> > >>>> Another thing I want to know your opinion on is: do you think the HB > >>>> should be created > >>>> separately for PLPMTUD probe, instead of reusing the old HB that > >>>> checks the link connectivity? > >>> Yes. I think testing for connectivity is conceptually different > >>> from testing a particular PMTU. When testing for PMTU, I think > >>> about sending probe packets. Not that they consist of a HB chunk > >>> bundled with a PAD chunk. > >>>> As the HB for PLPMTUD probe might get lost, which we don't want to > >>>> affect the link's > >>>> connectivity. > >>> Yes, I agree completely. > >> > >> With this, Xin, seems we should have a separate timer for the > >> PROBE_TIMER, other than the heartbeat one. > >> > >> Otherwise, converging the two logics into one single timer is not > >> worth the hassle for saving a timer. For example, we would have to > >> have it fire on the active transport but to send only the probe. > >> Also, considering they can and (AFAIU the RFC) should have different > >> expire timeouts from time to time. > >> > >> With a separate timer, we won't have issues converging the > >> user-selectable heartbeat interval to the recommended 600s > >> PMTU_RAISE_TIMER, for example. > >> > >> Maybe I am missing something. But it seems the hassle for reusing the > >> timer here is just not worth it. Thoughts? > > You're right, when I was doing testing, I had to set the hb_interval to 5s. > > the common value of hb_interval really doesn't fit in the probe_interval. > > I will try adding a new timer, but at the same time a probe_interval > > by sysctl/sockopt may be needed, or we can use a value equal to > > (hb_interval / n) for it? > Yeah, this is why I did not write a socket API section for RFC 8899. I think > when implementing it, one will find some parameters which can or should > be controlled by the application. So I guess there will be more than this > one. > > Timo (CCed) is working on some algorithmic explorations, since RFC 8899, gives > you some freedom. Right now, his work is done in a simulation environment, but > once that is finished and he came to some conclusions, we will implement this. > > So what about: > > * Try to implement PLPMTUD and figure out what you need as user controllable > parameters. > * Bring this up for discussion and we can agree on them and also on how > to control them via socket options. > * Then you get the code into the Linux tree. > > That way we would know what parameters are really needed in an implementation > and we would have a common interface. Makes sense. > > Does that make sense to you and sounds like an acceptable plan? That sounds a good plan, :-) Thanks. > > Best regards > Michael > > > >> > >> Best, > >> Marcelo > >> > >>> > >>> Best regards > >>> Michael > >>>> > >>>>> > >>>>> Best regards > >>>>> Michael > >>>>>> > >>>>>> Thanks. > >>>>> > >>> > >> >
