Re: WG LC: draft-ietf-l3vpn-2547bis-mcast-bgp

[Yakov Rekhter <[e-mail]>]

Maria,

> PIM-SM/RFC 4601 permits, quote, "a receiver to join a group and specify
> that it only wants to receive traffic for a group if that traffic comes
> from a particular source. If a receiver does this, and no other receiver
> on the LAN requires all the traffic for the group, then the DR may omit
> performing a (*,G) join to set up the shared tree, and instead issue a
> source-specific (S,G) join only."
> 
> Such behavior of end systems in PIM-SM means that a PE can receive Join
> (C-S, C-G) even for sources that are not active. 
> 
> Section 13.1 of draft-ietf-l3vpn-2547bis-mcast-bgp-05 requires that
> "whenever a PE creates an <C-S,C-G> state as a result of receiving a
> Source Tree Join C-multicast route for <C-S, C-G> from some other PE,
> the PE that creates the state MUST originate a Source Active A-D route."
> 
> The procedure as described in section 13.1 might lead to useless S-PMSI
> creation for C-sources operating in sparse groups which are not active.
> This procedure should be enhanced to prevent triggering of S-PMSIs in
> such cases.

Could you please provide an example of how "the procedures as described
in section 13.1 might lead to useless S-PMSI creation for C-sources
operating in sparse groups which are not active".

Yakov.