> On 20. May 2021, at 02:45, Marcelo Ricardo Leitner <mleitner@xxxxxxxxxx> wrote: > > On Thu, May 20, 2021 at 01:16:38AM +0200, Michael Tuexen wrote: >>> 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. > > Wait. Somehow I thought we were talking about extending the RFC with > these new definitions here, no? Or at least agreeing on a common > interface. It would be beneficial for the application to be able to > use the same API on FreeBSD or Linux. Hi Marcelo, sorry for not being clear. What I wanted to say: 1. I really appreciate the discussion and I agree that it would be great if we can agree on a common interface allowing to write portable applications. 2. I don't like the idea of overloading the spp_pathmtu. 3. I'm not in a position to put in a veto to what anyone is implementing in any implementation (except maybe the FreeBSD implementation). Regarding the extension of the RFC. An RFC can't be changed. One can file erratas, but I think we are discussing here an extension of the socket API to cope with RFC 8899. So I don't think it is an errata. It would have been appropriate to add a socket API section to RFC 8899, but it is too late for that, too. So I guess we can discuss it here and come to an agreement how to extend the socket API for RFC 8899. I'm more that happy to do this. I hope I expressed my view now clearer. Best regards Michael > > Thanks, > Marcelo > >> >> 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. >>>>>>>> >>>>> >>>> >>> >> >
