Subject: [magma] IGMP-MLD Proxying Draft Comments No. 2

From: Karen Kimball <[email-masked]>
Date: Sun, 9 Mar 2003 09:57:53 -0800 (PST)

Comments on    IGMP/MLD-based Multicast Forwarding ("IGMP/MLD Proxying")

This next set of comments will deal with smaller issues in the forwarding 
behaviors described by the protocol.

In Section 3. Abstract protocol definition  paragraph 7, there is the 
phrase, "... A can be configured to forward packets even though B is the 
Querier."  

How is this to occur? An explanation is needed. Is this supposed to mean 
that an explicit "IGMP forward" configuration should be allowed for 
interfaces of Proxy devices? "IGMP forward" configuration is something that 
some IGMP switch and/or router vendors support, but it is not a required 
part of any IGMP standard. Thus, I believe it needs to be spelled out here 
if this is what is desired.

Also in Section 3, the figures for LAN 1 and LAN 2 with Proxy Devices A 
and B could be improved in both cases to explicitly label B as the Querier.

In section 4.3. SSM Considerations, I regret that I am not familiar enough
with SSM to know the impact of the following phrase in paragraph 2:

     "... a proxy device that supports this document should ignore those
     IGMPv1 or IGMPv2 subscriptions sent to SSM addresses. And more
     importantly, the packets with source-specific addresses SHOULD not
     be forwarded to interfaces with IGMPv2 or IGMPv1 subscriptions for
     these addresses."

What will happen at a higher level if these IGMPv1 and/or IGMPv2 
subscriptions are ignored? Will the server and client renegotiate for a 
new multicast group number? Will the service simply fail to be provided?

For those more familiar with SSM, this may clearly be a non-issue. But as
I cannot be sure, I wish to bring this to the group's attention.

My remaining comments are all editorial, and will be sent in a final email.

Best regards,
        Karen Kimball
        [email-masked]
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From: Haixiang He <[email-masked]>
Date: Sun, 09 Mar 2003 16:18:17 -0500

> phrase, "... A can be configured to forward packets even though B is the

Paragraph 7 is an example to illustrate the rule described in Paragraph 6.

>
> How is this to occur? An explanation is needed.

This can occur if B has a lower IP address. This is the normal IGMP rule. The
sentence you omitted is that "..if A is the only proxy device...". So the
condition here is that B is a not Proxy device.

> Is this supposed to mean

Not really. It is more like Proxy forwarder configuration.

> and B could be improved in both cases to explicitly label B as the Querier.

I am not sure what you really want. Querier label is more confusing than
downstream or upstream labels IMHO.

In case 1, paragraph 7, B may or may not be a Querier for LAN2. B cannot be the
Querier for LAN1.

In case 2, paragraph 8, B is the Querier for LAN1. B cannot be a Querier for
LAN2.

> I cannot be sure, I wish to bring this to the group's attention.

Please refer to the SSM reference.

Regards,

Haixiang

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From: Haixiang He <[email-masked]>
Date: Sun, 09 Mar 2003 16:18:17 -0500

Regards,

Haixiang