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

[Yakov Rekhter <[e-mail]>]

Maria,

> Yakov,
> 
> > To avoid useless S-PMSI tunnels one could require that S-PMSIs be
> > created only when there is traffic to be carried over these S-PMSIs.
> 
> This is at the cost of requiring additional signaling to bind the
> C-flows to P-tunnels instead of advertising a S-PMSI together with the
> source active message. 

It is perfectly valid to advertise both a Source Active A-D route
and an S-PMSI A-D in the same BGP message.
  
> > > According to BGP spec, each (C-S,C-G) PIM route might have tree
> > > different BGP versions:, Source Active A-D
> > route,
> > > and possibly S-PMSI A-D route ...
> > 
> > That is incorrect - each (C-S, C-G) PIM route have just *one* version,
> > namely Source Tree Join C-multicast route.
> 
> I used the word "version" as a figure of speech... I meant that every
> (C-S,C-G) PIM-SM Join triggers additional BGP routes.
> Specifically, as described in section 13 of BGP spec, every PIM-SM
> Source Tree Join C-multicast route triggers a Source Active A-D route
> that has to be maintained on every MVPN PE. In addition, if S-PMSIs are
> used for carrying C-S traffic then for every PIM-SM Source Tree Join
> C-multicast route there is a S-PMSI A-D route also maintained on every
> MVPN PE. And those updates could be quite dynamic.
> For example, if there 1000 (C-S,C-G) mroutes in a MVPN, the procedures
> in section 13 will generate, besides 1000 Source Tree Join C-multicast
> routes, 1000 Source Active A-D routes, and 1000 S-PMSI A-D routes. And
> latter two type of updates have to be stored on every PE with the given
> MVPN. This is a lot of overhead. Even if those "C-S" flows are not
> active (and this could be due misconfiguration or it could be malicious)
> the procedures in section 13 will still generate Source Active A-D
> routes. As I pointed out before, those updates (and there can be 1000's
> of them, especially if it is the malicious) are useless yet they will
> use common BGP RR resources. I am surprised that it wouldn't be a
> concern to service provider with any meaningful MVPN deployment.  

To respond to your point about originating Source Active A-D route
for C-S flows that are not active please consider the following.

According to the procedures in section 13 Source Active A-D routes
are originated *only* in response to Source Tree Join C-multicast
routes, and withdrawn in response to withdraw of Source Tree Join
C-multicast routes.

A PE originates Source Tree Join C-multicast route for a given <C-S,
C-G> only after it receives PIM Join (C-S, C-G) from a CE, and
withdraws Source Tree Join C-multicast route when it receives PIM
Prune (C-S, C-G) from a CE.

With PIM-SM in ASM mode originating PIM Join (C-S, C-G) requires
(C-S,C-G) to be active.

Therefore, the procedures in section 13 result in origination of
Source Active A-D routes *only* for the sources that are active.

Yakov.