Subject: [magma] IGMP report suppression

From: "P K S" <[email-masked]>
Date: Mon, 24 Oct 2005 00:09:33 -0700

Why is the IGMP report suppression required in the first place? 

Regards 
 Parit

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From: Princy Elizabeth <[email-masked]>
Date: Thu, 2 Nov 2006 21:32:12 -0800 (PST)

IGMP V1 and V2 reports are sent per group. Consider a LAN with 10 hosts each interested in the same 10 groups. If reports suppression were not employed, every Query interval there would be 10 reports sent out by each of the 10 hosts ==> 100 reports which unnecessarily increase the traffic on the LAN. For the router, it is sufficient to know that there is one interested member for a group on the LAN. So 1 report per group would have sufficed. This precisely is what is done through report suppression. In IGMP V3, a single report can contain the report for all the groups a host is interested in. Thus there is no need for report suppression here since the number of reports would be generally, equal to the number of hosts only. 
   
  I hope that clarifies your query.
   
  - Princy

P K S <[email-masked]> wrote:
          Why is the IGMP report suppression required in the first place? 
   
  Regards 
   Parit

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From: Christy L Norman <[email-masked]>
Date: Fri, 3 Nov 2006 16:37:55 -0600

I agree with the answer to Parit's question. IGMPv1 and v2 reports can be 
suppressed to reduce unnecessary traffic. However, in regards to the 
reason for the absence of report suppression in v3 - I believe it is due 
to the presence of sources in an IGMPv3 report. One record could easily be 
omitted from a report (record suppression?). All listeners to a group may 
have different sources making up their per-interface states and to check 
the sources of  all hosts' reports would be a bit of work for the host. 

In addition to this reason, RFC 2236 states in 5.2,  "Instead of using a 
single interface timer, implementations are recommended to spread 
transmission of such Report messages over the interval (0, [Max Resp 
Time])."  In this case, the operation will be much like IGMPv1 & v2 - but 
report suppression isn't required if you happen to be implementing that 
method of reporting - because of the issue with the sources.

Do you agree?

- Christy

Princy Elizabeth <[email-masked]> 
11/02/2006 11:32 PM

To
P K S <[email-masked]>, [email-masked]
cc

Subject
Re: [magma] IGMP report suppression

IGMP V1 and V2 reports are sent per group. Consider a LAN with 10 hosts 
each interested in the same 10 groups. If reports suppression were not 
employed, every Query interval there would be 10 reports sent out by each 
of the 10 hosts ==> 100 reports which unnecessarily increase the traffic 
on the LAN. For the router, it is sufficient to know that there is one 
interested member for a group on the LAN. So 1 report per group would have 
sufficed. This precisely is what is done through report suppression. In 
IGMP V3, a single report can contain the report for all the groups a host 
is interested in. Thus there is no need for report suppression here since 
the number of reports would be generally, equal to the number of hosts 
only. 

- Princy

Regards 
 Parit

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