RE: IGMP router behavior during LMQT period,

Hi,
About question a, I agree to sandeep. It is not necessary for router to
distinguish the leaves if two hosts are connected to the same interface.

About question b, router should ignore the second leave during the LMQI.
This problem and section 8.14.1. in RFC 3376 are not same. The reason of 
increasing leave latency is that it take longer (LMQT=LMQC*LMQI, 
for LMQC(LV) increases) to stop traffic flowing.

Regards, 

Fergus Huang


>From: <[email protected]>
>Subject: RE: [magma] IGMP router behavior during LMQT period
>To: <[email protected]>,	<[email protected]>
>Message-ID:
>	<[email protected]>
>Content-Type: text/plain; charset="us-ascii"
>
>Hi,
> 
>If host tracking is not implemented on router it makes sense to reset
>the timers on reception of leave from H2. Since H2 showed its interest
>by sending a report to the Query, Router has to refresh the group timer
>and subsequent leave should be used to reset the timer to LMQT in
>Router. 
> 
>"But how can the router distinguish between leaves from 2 different
>hosts unless it is explicitly tracking hosts?"
>Why should Router distinguish between leaves from 2 different hosts
>(considering they are connected to same interface)? Router has to make a
>decision whether to forward the streams for the multicast group or not
>on that interface. Even if a host is leaving the group but some other
>host is interested then it needs to forward the streams.  
> 
>I too faced a similar if not exact problem. The issue was that the group
>timer was reset every time (until RV) the leave was received for a
>multicast group. This resulted in higher leave latency. Higher the RV
>value higher the leave latency. Resetting the timers only for first
>leave solves the problem, but should it be done that way, can anyone
>tell me? 
> 
>Does RFC 3376 section quoted below is referring to the same problem as I
>have faced or is it referring to something else? 
> 
>8.14.1. Robustness Variable
> 
>   The Robustness Variable tunes IGMP to expected losses on a link.
>   IGMPv3 is robust to (Robustness Variable - 1) packet losses, e.g., if
>   the Robustness Variable is set to the default value of 2, IGMPv3 is
>   robust to a single packet loss but may operate imperfectly if more
>   losses occur.  On lossy subnetworks, the Robustness Variable should
>   be increased to allow for the expected level of packet loss. However,
>   increasing the Robustness Variable increases the leave latency of the
>   subnetwork.  (The leave latency is the time between when the last
>   member stops listening to a source or group and when the traffic
>   stops flowing.)
> 
> 
>Regards,
>Sandeep.
>