Subject: [magma] Questions about IGMP snooping

From: Koen Vermeulen <[email-masked]>
Date: Mon, 24 Nov 2003 18:03:55 +0100

Hello all,

I have been reading 'draft-ietf-magma-snoop-10.txt' and have some questions
concerning this document:

1. Somewhere in this document is mentioned that the snooping switch 
shouldn't
rely exclusively on the appearance of  'leave' messages. It is mentioned 
that a
membership timeout mechanism such as the router-side functionality of 
the IGMP
protocol should be implemented. This timeout value should be configurable.

This is not completely clear for me. Is this implying that the switch 
should also
send 'queries', like a router is doing? Or do we rely on the 'queries' 
sent by the
router? This would mean that the timeout value must be configured the same
as on the router.

2. When do we consider a router as being dead? In the document, I can't find
any reference to a value like this.

Thanks,
Koen

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---

From: "KIMBALL,KAREN (HP-Roseville,ex1)" <[email-masked]>
Date: Wed, 26 Nov 2003 12:19:38 -0800

Hello, Koen,

> Hello all,
> 
> I have been reading 'draft-ietf-magma-snoop-10.txt' and have 
> some questions concerning this document:
> 
> shouldn't rely exclusively on the appearance of  'leave' messages. It 
> is mentioned that a membership timeout mechanism such as the 
> router-side functionality of the IGMP protocol should be implemented. 
> This timeout value should be configurable.
> 
> should also send 'queries', like a router is doing? Or do we rely on 
> the 'queries' sent by the router? This would mean that the timeout 
> value must be configured the same as on the router.

The switch may snoop the queries sent by the router, and snoop the
timeout values in those queries. It is up to the switch vendor to decide
how to apply those timeout values for determining when to leave a group--
but the best way would probably be to mimic what the router will do.

> 2. When do we consider a router as being dead? In the 
> document, I can't find any reference to a value like this.

I'm not sure whether you are concerned about a dead Router, or a dead
Querier. IGMP in general does not concern itself with dead routers, other 
than a Version 1 Router Timeout value of 400 seconds. It would be up to 
the switch vendor to create a formula for deciding that a router is dead

The issue of a dead Querier is covered in the pecifications for IGMP 
itself, not in the snooping switch document. 

See RFC2236 for a description of
	8.5 Other Querier Present Interval

When that interval has expired, the other Querier is assumed to be dead
and a Querier Election begins. The default for that value is 255 seconds
if all other default values mentioned in the formula are used.

I hope this information is helpful to you.

Thanks,
	Karen Kimball

---

From: "KIMBALL,KAREN (HP-Roseville,ex1)" <[email-masked]>
Date: Wed, 26 Nov 2003 12:19:38 -0800

Hello, Koen,

Thanks,
	Karen Kimball