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: <sandeep.kulambiwipro.com>
>Subject: RE: [magma] IGMP router behavior during LMQT
period
>To: <princyteyahoo.com>,	<magmaietf.org>
>Message-ID:
>	<3618F6648762DD40B3D44D484E115FCF02E5E0B8BLR-EC-MBX04.wipro.com>
>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.
> 




_______________________________________________
magma mailing list
magmaietf.org
https://
www1.ietf.org/mailman/listinfo/magma

Thanks for the responses. I too agree that, 

a) On receiving the leave from the second host, H2 the grp
timer should ideally be reset to LMQI again. 
As Sandeep said "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." 
Which means that in case (a) we want to reset the timer.

But what if it is a repeat leave from the first host itself
- 

b) Do we still reset the grp timer to LMQI? Won't this
result in increase in leave latency by "(number of
repeat leaves - 1) * LMQI"? Is that acceptable?
Fergus states in his mail "... router should ignore the
second leave during the LMQI." 
Which means in case (b) we do not want to reset the timer.

The reason I was talking about the need to differentiate
between the hosts was for distinguishing between (a) &
(b) i.e leave from a new host and repeat leave from the
previous host itself. Without doing so how do we ensure that
for case (a) we reset the timer and for case (b) we do not?

Also, does the decision to reset the grp timer for cases (a)
& (b) differ for the following two conditions:

i) No overriding join has been received from H2 before the
repeat leave is received from H1 or first leave is received
from H2
ii) An overriding join has been received from H2 before the
repeat leave is received from H1 or first leave is received
from H2

Thanks,
Princy

-----Original Message-----
From: 黄晓锋(Fergus Huang) [mailto:hxiaofenghuawei.com] 
Sent: Tuesday, September 18, 2007 4:07 PM
To: magmaietf.org
Subject: RE: [magma] 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: <sandeep.kulambiwipro.com>
>Subject: RE: [magma] IGMP router behavior during LMQT
period
>To: <princyteyahoo.com>,	<magmaietf.org>
>Message-ID:
>	<3618F6648762DD40B3D44D484E115FCF02E5E0B8BLR-EC-MBX04.wipro.com>
>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.
> 




_______________________________________________
magma mailing list
magmaietf.org
https://
www1.ietf.org/mailman/listinfo/magma
_______________________________________________
magma mailing list
magmaietf.org
https://
www1.ietf.org/mailman/listinfo/magma

Hi,

i) No overriding join has been received from H2 before the
repeat leave is received from H1 or first leave is received
from H2
	You don¡¯t have to distinguish the leave here, the first
leave can be used for setting the timers the other leave can
be ignored as Fergus said.

ii) An overriding join has been received from H2 before the
repeat leave is received from H1 or first leave is received
from H2
	When H1 sends a leave message, Router would send a Group
Specific Query for which H2 would reply with a report
message. This report message from H2 tells that there is
some other host other than H1 which will be the
distinguishing factor. On reception of report message from
H2 your timers will be set to ((robust * query interval) +
Query resp time). If H2 sends a leave message the timers
will be set to LMQT by Router. 

I still don¡¯t see any reason why you should distinguish
between hosts. If both the hosts are sending leave message
at the same time you still can use the first leave received
for setting timers and ignoring rest.

Regards,
Sandeep.


-----Original Message-----
From: Princy Elizabeth [mailto:princyjuniper.net] 
Sent: Wednesday, September 19, 2007 9:34 AM
To: magmaietf.org
Subject: RE: [magma] IGMP router behavior during LMQT
period,


Thanks for the responses. I too agree that, 

a) On receiving the leave from the second host, H2 the grp
timer should ideally be reset to LMQI again. 
As Sandeep said "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." 
Which means that in case (a) we want to reset the timer.

But what if it is a repeat leave from the first host itself
- 

b) Do we still reset the grp timer to LMQI? Won't this
result in increase in leave latency by "(number of
repeat leaves - 1) * LMQI"? Is that acceptable?
Fergus states in his mail "... router should ignore the
second leave during the LMQI." 
Which means in case (b) we do not want to reset the timer.

The reason I was talking about the need to differentiate
between the hosts was for distinguishing between (a) &
(b) i.e leave from a new host and repeat leave from the
previous host itself. Without doing so how do we ensure that
for case (a) we reset the timer and for case (b) we do not?

Also, does the decision to reset the grp timer for cases (a)
& (b) differ for the following two conditions:

i) No overriding join has been received from H2 before the
repeat leave is received from H1 or first leave is received
from H2
ii) An overriding join has been received from H2 before the
repeat leave is received from H1 or first leave is received
from H2

Thanks,
Princy

-----Original Message-----
From: »ÆÏþ·æ(Fergus Huang) [mailto:hxiaofenghuawei.com] 
Sent: Tuesday, September 18, 2007 4:07 PM
To: magmaietf.org
Subject: RE: [magma] 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: <sandeep.kulambiwipro.com>
>Subject: RE: [magma] IGMP router behavior during LMQT
period
>To: <princyteyahoo.com>,	<magmaietf.org>
>Message-ID:
>	<3618F6648762DD40B3D44D484E115FCF02E5E0B8BLR-EC-MBX04.wipro.com>
>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.
> 




_______________________________________________
magma mailing list
magmaietf.org
https://
www1.ietf.org/mailman/listinfo/magma

_______________________________________________
magma mailing list
magmaietf.org
https://
www1.ietf.org/mailman/listinfo/magma

My understanding of 3376 is that the lowering of timers to
LMQT is part of "Send Q(G)" / "Send
Q(G,X)" Router Actions. The instructions provided in
6.6.3.1 / 6.6.3.2 are to (A) immediately send a query, (B)
schedule [Last Member Query Count - 1] query retransmissions
to be sent every [Last Member Query Interval] over [Last
Member Query Time], and (C) lower the the group / source
timer to LMQT. However, it is my belief that actions (A),
(B), and (C) should only be performed for group / source
timers larger than LMQT -- this is explicitly indicated in
6.6.3.2 ("source timers larger than LMQT"), but is
not indicated in 6.6.3.1, which instead suggests that (A),
(B), and (C) should always be performed, even if group
timers are smaller than LMQT. I think the instructions in
6.6.3.2 to only perform actions (A), (B), and (C) if the
group / source timers are larger than LMQT are a more
accurate intention of the protocol's design WRT building and
sending specific queries. Otherwise, as Sandeep indicates,
you introduce leave latency and unnecessary specific query
transmissions if you always perform actions (A), (B), and
(C), even if the group timer is smaller than LMQT.

>From the examples below, if H1's leave arrives BEFORE
H2's report, operations (A), (B), and (C) would not be
performed since the group timer will be less than LMQT; if
H1's leave arrives AFTER H2's report, operations (A), (B),
and (B) would be performed since the group timer will be
greater than LMQT (H2's report would have set the group to
GMI).

-----Original Message-----
From: sandeep.kulambiwipro.com [mailto:sandeep.kulambiwipro.com] 
Sent: Wednesday, September 19, 2007 8:51 PM
To: princyjuniper.net; magmaietf.org
Subject: RE: [magma] IGMP router behavior during LMQT
period,

Hi,

i) No overriding join has been received from H2 before the
repeat leave is received from H1 or first leave is received
from H2
	You don¡¯t have to distinguish the leave here, the first
leave can be used for setting the timers the other leave can
be ignored as Fergus said.

ii) An overriding join has been received from H2 before the
repeat leave is received from H1 or first leave is received
from H2
	When H1 sends a leave message, Router would send a Group
Specific Query for which H2 would reply with a report
message. This report message from H2 tells that there is
some other host other than H1 which will be the
distinguishing factor. On reception of report message from
H2 your timers will be set to ((robust * query interval) +
Query resp time). If H2 sends a leave message the timers
will be set to LMQT by Router. 

I still don¡¯t see any reason why you should distinguish
between hosts. If both the hosts are sending leave message
at the same time you still can use the first leave received
for setting timers and ignoring rest.

Regards,
Sandeep.


-----Original Message-----
From: Princy Elizabeth [mailto:princyjuniper.net]
Sent: Wednesday, September 19, 2007 9:34 AM
To: magmaietf.org
Subject: RE: [magma] IGMP router behavior during LMQT
period,


Thanks for the responses. I too agree that, 

a) On receiving the leave from the second host, H2 the grp
timer should ideally be reset to LMQI again. 
As Sandeep said "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." 
Which means that in case (a) we want to reset the timer.

But what if it is a repeat leave from the first host itself
- 

b) Do we still reset the grp timer to LMQI? Won't this
result in increase in leave latency by "(number of
repeat leaves - 1) * LMQI"? Is that acceptable?
Fergus states in his mail "... router should ignore the
second leave during the LMQI." 
Which means in case (b) we do not want to reset the timer.

The reason I was talking about the need to differentiate
between the hosts was for distinguishing between (a) &
(b) i.e leave from a new host and repeat leave from the
previous host itself. Without doing so how do we ensure that
for case (a) we reset the timer and for case (b) we do not?

Also, does the decision to reset the grp timer for cases (a)
& (b) differ for the following two conditions:

i) No overriding join has been received from H2 before the
repeat leave is received from H1 or first leave is received
from H2
ii) An overriding join has been received from H2 before the
repeat leave is received from H1 or first leave is received
from H2

Thanks,
Princy

-----Original Message-----
From: »ÆÏþ·æ(Fergus Huang) [mailto:hxiaofenghuawei.com] 
Sent: Tuesday, September 18, 2007 4:07 PM
To: magmaietf.org
Subject: RE: [magma] 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: <sandeep.kulambiwipro.com>
>Subject: RE: [magma] IGMP router behavior during LMQT
period
>To: <princyteyahoo.com>,	<magmaietf.org>
>Message-ID:
>	<3618F6648762DD40B3D44D484E115FCF02E5E0B8BLR-EC-MBX04.wipro.com>
>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.
> 




_______________________________________________
magma mailing list
magmaietf.org
https://
www1.ietf.org/mailman/listinfo/magma

_______________________________________________
magma mailing list
magmaietf.org
https://
www1.ietf.org/mailman/listinfo/magma

_______________________________________________
magma mailing list
magmaietf.org
https://
www1.ietf.org/mailman/listinfo/magma