Re: add SPP_PLPMTUD_ENABLE/DISABLE flag for spp_flags

[Xin Long <lucien.xin@gmail.com>]

On Tue, May 18, 2021 at 1:38 PM Michael Tuexen <tuexen@freebsd.org> wrote:
>
> > On 18. May 2021, at 18:43, Xin Long <lucien.xin@gmail.com> 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?
As the HB for PLPMTUD probe might get lost, which we don't want to
affect the link's
connectivity.

>
> Best regards
> Michael
> >
> > Thanks.
>