Subject: [magma] Re: [Fwd: I-D ACTION:draft-ietf-magma-igmp-proxy-03.txt]

From: Haixiang He <[email-masked]>
Date: Wed, 02 Jul 2003 18:25:40 -0400

Erik Nordmark wrote:

>1. Add a new section in Section 1: Introduction to address applicability 
>of IGMP/MLD Proxy.
>
> "In certain topologies, it is not necessary to run a multicast routing
>  protocol. It is sufficient to learn and proxy group membership
>  information and simply forward based upon that information.  One
>  typical example is on an edge aggregation box such as Digital
>  Subscriber Line Access Multiplexer (DSLAM). In most deployment
>  scenarios, an edge box has only one connection to the core network
>  side and has many connections to the customer side. Using IGMP/MLD-
>  based forwarding to replicate multicast traffic on such edge boxes
>  can not only make them independent of the multicast routing protocol
>  used by the core network routers but also greatly simplify the design
>  and implementation of such boxes.  For example, such boxes don't need
>  more complicated multicast routing protocols such as PIM to
>  communicate with the routers on the core network side."
>  
>
>
>I still don't understand the implications from this i.e. where would it and
>would it not make sense to use proxying. Detailed questions:
>
I am just using DSLAM as an example. There are many other examples such 
as home gateway box as Dave pointed out.

>
>Is such a DSLAM an entity in the IP path? (i.e. would it appear in a unicast
>traceroute).
>
As far as I know, it does not appear in a unicast traceroute. It looks 
like L2 (ATM) switch. However the IGMP packets are terminated at the 
DSLAM and are separated from other packets (unicast) using different L2 
encapsulation. The advantage of replicating multicast traffic on DSLAM 
is that the uplink between DSLAM and the core is efficiently used (i.e., 
one copy of the packets to the DSLAM).

>Is the intent to make it an entity in the IP path in the future?
>
I heard people talking about it. But  I have not seen one. It all comes 
down to whether it is cost effective or not to make it an entity in the 
IP path.

>
>Isn't there effectively an assumption that the link between the proxy 
>and the subscriber is a point-to-point link? 
>
In most DSLAM deployments, the link is a point-to-point link. But it is 
not an assumption.

>If not how can you ensure,
>since a different admin domain might operate the subscriber and the proxy,
>that the proxy has the lowest IP address from a queries selection perspective?
>
I think this is really an IGMP deployment issue. For another example, 
two IGMP queries that belong to two different admin domains may use 
different version of IGMP (v2 or v3). The IGMP spec requires admin work 
to solve two different version of IGMP queries on the same link. Two 
admin domains complicate the work.

>
>What would happen if the subscriber decides to run a multicast routing protocol
>and peer with some router in the operator's network? Will the proxy be 
>  
>
>transparent to the multicast routers?
>
In this case, there are two routers connected to the Proxy. The 
assumption of the Proxy does not stand. The Proxy should not be used in 
such environments.

regards,
haixiang

>  Erik

---

From: Haixiang He <[email-masked]>
Date: Wed, 02 Jul 2003 18:25:40 -0400

regards,
haixiang