Re: add SPP_PLPMTUD_ENABLE/DISABLE flag for spp_flags

From: Xin Long <lucien.xin@gmail.com>
To: Michael Tuexen <tuexen@freebsd.org>
Cc: "linux-sctp @ vger . kernel . org" <linux-sctp@vger.kernel.org>,
	Marcelo Ricardo Leitner <marcelo.leitner@gmail.com>
Subject: Re: add SPP_PLPMTUD_ENABLE/DISABLE flag for spp_flags
Date: Wed, 19 May 2021 14:44:20 -0400	[thread overview]
Message-ID: <CADvbK_eujoHWiM88VDRHmtfXLWrBaBtUBjD2wYqQcQ=VssdaoQ@mail.gmail.com> (raw)
In-Reply-To: <8C3219EB-1BEF-4F96-B881-8BDCA2EC98EE@freebsd.org>

On Wed, May 19, 2021 at 2:15 PM Michael Tuexen <tuexen@freebsd.org> wrote:
>
> > On 19. May 2021, at 18:18, Xin Long <lucien.xin@gmail.com> wrote:
> >
> > On Tue, May 18, 2021 at 2:33 PM Xin Long <lucien.xin@gmail.com> wrote:
> >>
> >> 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?
> > 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.
sysctl is always used for the default value for future sockets.
and the socket option should be added for a socket/asoc's setting.

SCTP_PTMUD_METHOD?
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.
> >>>
>