> On 20. May 2021, at 00:44, mleitner@xxxxxxxxxx wrote: > > On Wed, May 19, 2021 at 02:44:20PM -0400, Xin Long wrote: >> On Wed, May 19, 2021 at 2:15 PM Michael Tuexen <tuexen@xxxxxxxxxxx> wrote: >>> >>>> On 19. May 2021, at 18:18, Xin Long <lucien.xin@xxxxxxxxx> wrote: >>>> >>>> On Tue, May 18, 2021 at 2:33 PM 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? >>>> I just noticed that with multiple versions supported, and without extending >>>> this API, all applications will have to use the same version as it's >>>> controlled by >>>> sysctl. And when switching to another version by sysctl, all >>>> applications will be >>>> affected and have to do the switch. that seems not nice. >>> That is true, but an application can not expect any specific behaviour >>> right now when they are not disabling PMTUD. >>> >>> What about adding a sysctl variable, which defines the default >>> algorithm and a socket option, which allows to get and set >>> the algorithm being used. >> yes, that's also what I'm thinking. > > +1 > >> sysctl is always used for the default value for future sockets. >> and the socket option should be added for a socket/asoc's setting. > > Speaking of inheritance, it should also use the SCTP_FUTURE_ASSOC / > SCTP_CURRENT_ASSOC / SCTP_ALL_ASSOC mechanism. Like > SCTP_PEER_ADDR_PARAMS, for example. Yepp. > > The system can provide defaults but if the application requires > something, it should have a good way of requesting it. > > Speaking of SCTP_PEER_ADDR_PARAMS, maybe reuse spp_pathmtu field? > As in, if SPP_PMTUD_ENABLE is enabled, spp_pathmtu of "1" or "2" bytes > doesn't make sense, and it could mean the algorithm used. Thing is, > the field is currently ignored, and it could lead to some unexpected > behavior change. It's probably safer to just add another sockopt, but > wanted to share the idea anyway. I leave it completely up to you what you implement in Linux. But I would prefer to use a separate socket option instead of overloading an existing one. Best regards Michael > >> >> SCTP_PTMUD_METHOD? > > s/PTMUD/PMTUD/ :-) > >> 0: PTB one >> 1. PLPMTUD >> >>> >>> Best regards >>> Michael >>>> >>>>> 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? >>>>> As the HB for PLPMTUD probe might get lost, which we don't want to >>>>> affect the link's >>>>> connectivity. >>>>> >>>>>> >>>>>> Best regards >>>>>> Michael >>>>>>> >>>>>>> Thanks. >>>>>> >>> >> >
