Subject: Re: Reporting of 224.0.0.[2,255] groups

From: Bill Fenner <[email-masked]>
Date: Wed, 19 Jul 2000 13:14:58 -0700

>> - Are groups in 224.0.0.[2,255] reported?
>> 
>>   Yes.
>
>This is against the common practice of most router implementations.
>This will break them right away.

Since there was never any spec that said not to report these groups,
there are presumably currently some implementations that report them
and some that don't.  Therefore, switches already have to deal with
this issue, right?

  Bill

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From: Yiqun Cai <[email-masked]>
Date: Wed, 19 Jul 2000 14:47:02 -0700 (PDT)

> and some that don't.  Therefore, switches already have to deal with

Well, there is one. RIPv2 RFC (rfc2453) says not to report 224.0.0.9. 
Here is the related text.

4.5 Multicasting

   In order to reduce unnecessary load on those hosts which are not
   listening to RIP-2 messages, an IP multicast address will be used for
   periodic broadcasts.  The IP multicast address is 224.0.0.9.  Note
   that IGMP is not needed since these are inter-router messages which
   are not forwarded.

This topic has been on and off the list for quite a while. I think 
it really helps if implementations of RIP, OSPF or PIM that _do_ 
send reports for the respectve groups can be made known, so that we 
know we are trying to solve a real interoperability problem.

One way or the other, I am sure the majority of the routers deployed
don't send reports for the routing protocols, let alone for 224.0.0.2.
The snooping switches pretty much have to flood packets addressed to 
these groups. Therefore, I would suggest that we keep the current
behavior, i.e. not to report 224.0.0.x.

-- 
Yiqun

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From: Beau Williamson <[email-masked]>
Date: Thu, 20 Jul 2000 09:33:59 -0700

>behavior, i.e. not to report 224.0.0.x.

That's the problem that Paras is talking about.  The current behavior is not what is documented in the IGMP spec.  

I too would like to see the spec changed to at least say that hosts MAY report these groups but also include a note that says that switches SHOULD always flood these groups since there is no way to know if that all implementations of OSPF, EIGRP, or protocol-foo, does or does not report.

Beau