[pim] Re: draft-ietf-pim-pfm-forwarding-enhancements-00.txt

[Stig Venaas <[e-mail]>]

Hi James

Responding as author here.

PIM PFM is a way of providing the ASM service model where only SPT is
used for forwarding, there are no shared trees or RPs. You can say
that the SPT state and forwarding is the SSM part of PIM-SM.
But the key is that applications can still join a group and receive
from any active source, so it is still ASM. There is no need for PIM
PFM if you only need the SSM model with applications doing source
discovery and joining specific sources.

The motivation behind PFM was that there was a need for ASM without
having any single point of failure such as RPs, forwarding should work
as long as there is a path. You can say it is also a bit like DM, but
without flooding of data packets. Also it simplifies configuration as
there is no RP config or MSDP.

Regards,
Stig

On Fri, Aug 2, 2024 at 4:44 PM Stevens, Jim A Collins
<[e-mail]> wrote:
>
> > Date: Mon, 22 Jul 2024 11:16:16 -0700
> > Subject: [pim] I-D Action:
> >       draft-ietf-pim-pfm-forwarding-enhancements-00.txt
> > Internet-Draft draft-ietf-pim-pfm-forwarding-enhancements-00.txt is now
> > available. It is a work item of the Protocols for IP Multicast (PIM) WG of the
> > IETF.
> >
> >    Title:   PIM Flooding Mechanism and Source Discovery Enhancements
> >
> > The IETF datatracker status page for this Internet-Draft is:
> > https://urldefense.com/v3/__https://datatracker.ietf.org/doc/draft-ietf-pim-
> > pfm-forwarding-enhancements/__;!!MvWE!HI_-
> > Lj9Ci4nSpetHlhVhcx892mBjEzRZ9DWWYmxk62IpTp6izur_9o2RT-
> > zlGuKimbrO70wuxV3JRqd9RRU0Z0Cy_c9QLhJY$
> >
> This draft references RFC 8364 which defined PIM Flooding Mechanism and Source Discovery and says that it is "a lightweight source discovery mechanism on top of the Source-Specific Multicast (SSM) [RFC4607] parts of PIM-SM"
>
> This implies to me that PIM Flooding Mechanism and Source Discovery is only valid for Sparse Mode and not for Any Source Mode (ASM).
>
> Is that correct?
>
> If yes, then the draft needs to explain that this RFC is only relevant to PIM-SM & the title should be changed to PIM-SSM Flooding Mechanism & Source Discovery.  For example, this would not apply to ASM and other versions of PIM such as BIDIR-PIM.
>
> If no, then the draft should provide examples of uses for PIM Flooding Mechanism and Source Discovery for ASM operations as well.  (and in hindsight if there are applications to ASM, then RFC 8364 should be updated or maybe have errata added?
>
> Jim
>