RE: some questions about RFC4605 -- IGMP/MLD multicast proxy

Hi Yu-Jung,
 
Consider the following scenarios:
 
1. Querier election is implemented: If the proxy device receives an MLD
Query on a downstream, it should process it for finding out who the querier
should be.
 
---------       ---------
| Proxy |       | Proxy |
---------       ---------
    |               |
    |               |
    -----------------
            |
            |
     Downstream Tree
 
2. Querier election is not implemented: If the proxy device receives an MLD
Query on a downsream, it should not process it, as it should be the only
querier on the network, and no other device should send queries on the
downstream tree.
 
         ---------
         | Proxy |
         ---------
             |
             |
      Downstream Tree
 
In both these cases, MLD Reports received on the downstream should not be
forwared to any other downstream port, as this is not required for any
purpose. Consider the case of an MLD Report from one dowstream interface
(Interface 1) being forwarded on another downstream interface (Interface 2).
Any host on Interface 2 interested in that particular multicast group will
suppress its own MLD Report. So, when the group table is downloaded to the
hardware in the proxy device, it will not have Interface 2 in the forwarding
entry corresponding to that group. This will result in multicast data not
being forwarded to hosts connected to Interface 2.
 
MLD Reports are sent by the proxy device only on the upstream.
 
Regards,
 
Jayanth
 
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  _____  

From: Yu-Jung Lee [mailto:[email protected]] 
Sent: Friday, February 09, 2007 11:02 AM
To: Jayanth Chennamangalam; [email protected]
Subject: Re: [magma] some questions about RFC4605 -- IGMP/MLD multicast
proxy


Hi, Jayanth:
 
Thanks for your response.
Regarding the answer about (3), MLD Reports should not be sent in response
to MLD Queries received on the downstream. I suppose it means that the proxy
device does not forward received MLD reports on downstream interfaces.
However, the proxy does send out unsolicited reports on its downstream
interfaces whenever the interface itself has multicast address of interest,
and also send out solicited reports with group of interest in response to
MLD Queries received on the downstream interface. Is it right?
 
 
BR,
Yu-Jung
 
  _____  

----- Original Message ----- 
From:  <mailto:[email protected]> Jayanth Chennamangalam 
To:  <mailto:[email protected]> [email protected] 
Sent: Thursday, February 08, 2007 9:32 PM
Subject: RE: [magma] some questions about RFC4605 -- IGMP/MLD multicast
proxy
 
Hi Yu-Jung,
 
I have given my answers to your questions inline in your mail attached
below. Hope you will find it useful.
 
Regards,
 
Jayanth Chennamangalam
 
 
  _____  

From: Yu-Jung Lee [mailto:[email protected]] 
Sent: Thursday, February 08, 2007 5:57 PM
To: [email protected]
Subject: [magma] some questions about RFC4605 -- IGMP/MLD multicast proxy


Hi,
 
I have a few questions regarding RFC 4605.
 
(1) In RFC 4605, it defines that a proxy device has a single upstream
interface and one or more downstream interfaces. What's the reason for the
restriction of only one upstream interface? 
>> If there are more than one upstream port, it would result in upstream
looping. For the proxy device to work, the network should be a tree, with
the upstream interface pointing towards the root of the tree.
 
(2) It is said in the RFC that the proxy device MUST NOT perform the router
portion of IGMP/MLD on its upstream interface. There's no restriction on
performing the host portion of IGMP/MLD on the downstream interfaces. Does
that mean it's okay to send out reports which are received from one
downstream interface to other downstream interfaces? Wouldn't it cause
problems if the hosts attached to downstream interfaces support report
suppression? 
>> The reason behind the lack of restriction on performing the host portion
of IGMP/MLD proxying on the dowstream is to support querier election. The
host functionality does not involve forwarding received MLD Reports.
Besides, if the proxy device sends Reports on the downstream, it might lead
to Report suppression.
 
(3) What should the proxy device do except for querier election if it
receives MLD query on downstream interfaces? Shuold it send out MLD report
on downstream interfaces? (This question is related to (2) though.)
>> If querier election is not implemented, the proxy device should discard
the MLD Query received on the downstream interface. Even if querier election
is implemented, MLD Reports should not be sent in response to MLD Queries
received on the downstream.
 
It's not clear about the protocol behaviors in RFC 4605 and I'm quite
confused. Thanks in advance if anybody have explanations.
 
 
 
BR,
Yu-Jung

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