Re: [bess] WG adoption and IPR poll for draft-zzhang-bess-bgp-multicast-03

["Jeffrey (Zhaohui) Zhang" <[e-mail]>]

Gyan,

What embedded RP gives you is that you don't need to configure RP addresses. Once the RP is known for a group (however it is done - static config in case of IPv4/IPv6, dynamic learning via BSR/Auto-RP in case of v4, or embedded RP in case of IPv6), the rest is all the same: source sends register towards the RP and LHRs sends (*,g) join towards the RP. In case a set of RPs are used for a single group, the RPs learn the sources from each other either via MSDP (IPv4 only) or via PIM registers sent among themselves.

Once the traffic arrives at the LHR routers they learn the sources and can send (s,g) joins. When we say network-based source discovery we refer to the learning of sources by the LHRs (so that they can send (s,g) joins).

> via BGP multicast NLRI AFI 1 and 2 for v4 v6 with SAFI 2 to propagate the source information

That is not for source learning. It is for learning of the non-congruent routes to the sources. In many cases you only need to originate a few routes (in extreme cases a default route is enough), and it has no group information.

Jeffrey

-----Original Message-----
From: Lenny Giuliano <[e-mail]> 
Sent: Thursday, January 9, 2020 12:06 PM
To: Gyan Mishra <[e-mail]>
Cc: Jeffrey (Zhaohui) Zhang <[e-mail]>; [e-mail]; [e-mail]; [e-mail]; [e-mail]
Subject: Re: [bess] WG adoption and IPR poll for draft-zzhang-bess-bgp-multicast-03


On Thu, 9 Jan 2020, Gyan Mishra wrote:

<trimmed>

| 
|       Actually, Embedded RP provides interdomain ASM for IPv6 and is the reason
|       there is no need for MSDP in IPv6.
| 
| 
|   Gyan> With embedded RP how is the “source” SA propagated as is done 
| by MSDP with IPv4 accomplished with IPv6.  The only alternative and is a way that SSM for both IPv4 and IPv6 can provide network discovery that I know of and not have to rely on app based discovery ; is via BGP multicast NLRI AFI 1 and 2 for v4 v6 with SAFI 2 to propagate the source information.
| This is also used when migration from ASM to SSM and want to maintain inter domain boundaries you can use SAFI 2 for multicast NLRI source propagation.

With Embedded RP, the address of the RP is "embedded" in the group address, so just by looking at the group address, routers can derive the RP address and know where to send their (*,g) joins.  Hence there is no need for RPs to "talk" to one another as they do in IPv4 with MSDP.  See RFC 3956 for more details.

| 
| 
|       No one would disagree that SSM is simpler and the ideal way to go, hence
|       draft-ietf-mboned-deprecate-interdomain-asm recommends SSM-only for
|       interdomain deployments.  Unfortunately, for various (and sometimes
|       somewhat valid) reasons, ASM lives on, at least in intradomain
|       deployments.  Hence, BGP would still need to cover ASM scenarios, at
|       least for these intradomain deployments that still rely on ASM to work.
| 
|    
|   Gyan> Agreed ASM must be supported for intra domain

Then I suspect we are all in violent agreement.