Re: [pim] Robert Wilton's No Objection on draft-ietf-pim-bfd-p2mp-use-case-09: (with COMMENT)

[Greg Mirsky <[e-mail]>]

Hi Rob,
thank you for the review and comments. Please find my notes in-lined below
under the GIM>> tag.

Regards,
Greg

On Mon, Nov 29, 2021 at 3:23 AM Robert Wilton via Datatracker <
[e-mail]> wrote:

> Robert Wilton has entered the following ballot position for
> draft-ietf-pim-bfd-p2mp-use-case-09: No Objection
>
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>
> ----------------------------------------------------------------------
> COMMENT:
> ----------------------------------------------------------------------
>
> Hi,
>
> I was surprised by both of the statements in section 2.3 (but that may
> just be
> due to my lack of BFD expertise):
>
> 1. Wouldn't the base BFD protocol specify the TTL or Hop Limit?  Or is
> there a
> special/different consideration when BFD is being used for this use case
> that
> justifies RFC 2119 language?
>
GIM>> BFD base specification (RFC 5880) requires using GTSM in a single-hop
case. In a multi-hop BFD (RFC 5883), setting TTL/Hop Limit to 255 as a
security/antispoofing measure doesn't work across multiple hops. BFD for
multipoint networks (p2mp) might also be applied in single-hop and
multi-hop environments but there's no discussion of TTL/Hop Limit use in
RFC 8562. Since this document specifies the use of p2mp BFD over a single
hop, we've found it necessary to use the normative language in regard to
the handling of TT:/Hop Limit values. I hope I didn't make it more
confusing.

>
> 2. This may just be my lack of BFD knowledge because I had assumed that BFD
> sessions could be shared between different protocols wanting fast failure
> detection, and hence I was surprised that the p2mp BFD session MUST be
> targeted
> to the ALL-PIM-ROUTERs multicast address?
>
GIM>> That is an interesting question. You're absolutely right pointing
that a p2p BFD session may be used to monitor continuity between BFD
systems for a number of applications, e.g., routing protocols. For the case
of BFD for multipoint networks, it seems that a p2mp BFD session needs to
be per the multicast distribution tree. Thus, we require the use of the
ALL-PIM-ROUTERS multicast address. What do you think?

>
> Thanks,
> Rob
>
>
>
>