Subject: [ipcdn] draft-ietf-ipcdn-igmp-mib-02.txt comments

From: Schmidt Karl <[email-masked]>
Date: Thu, 15 Nov 2001 18:31:39 -0600

Folks,

I just read through the IGMP MIB draft and have two comments.

1. In passive mode the value of igmpInterfaceRobustness for both the CMTS
and CM is specified as must be 0. This is not a legal value in RFC2933.
Additionally, a passive mode device still needs to manage timers for each
multicast group cache which have a duration of the group membership
interval. The group membership interval uses the robustness value when
computed. I would propose either always setting this value to 2 or making it
read-create like it is in the active mode case.

2. The value of igmpCacheSelf on the CMTS in active mode on the HFC-side is
specified as must be false. This is done so that a CMTS can not be a member
of a multicast group on the HFC side. Although there may be no immediate
need for this at this time, I think disallowing this would be a bad idea as
there might be good reasons to allow this in the future if the CMTS wants to
participate in a group application that is HFC wide.

Karl Schmidt
Cadant

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From: "Nakanishi, Greg (SD-EX)" <[email-masked]>
Date: Fri, 16 Nov 2001 13:11:23 -0500

Karl,

comments inline

greg

> -----Original Message-----
> From: Schmidt Karl [mailto:[email-masked]]
> Sent: Thursday, November 15, 2001 4:32 PM
> To: [email-masked]'
> Subject: [ipcdn] draft-ietf-ipcdn-igmp-mib-02.txt comments
> 
> 
> Folks,
> 

igmpInterfaceRobustness is not used in passive mode for computing the
membership interval timeout.  The DOCSIS OSSI spec has the formula to be
used to compute the membership interval and is based on the interarrival
time of the membership queries.

So, this object has no use for devices operating in passive-mode, hence
setting it to zero.

> participate in a group application that is HFC wide.

I tend to agree with your assessment.  Whether the CMTS can belong to a
multicast group should be a policy decision and should not be disallowed
through a spec.

How about rewording to:

   HFC-side:  SHOULD be set to FALSE. The CMTS is typically not a member of
any 
               group on the HFC.

---

From: Schmidt Karl <[email-masked]>
Date: Fri, 16 Nov 2001 14:07:37 -0600

Greg,

Thanks for your comments.

Regarding the igmpInterfaceRobustness value, I haven't seen a formula in the
DOCSIS OSSI spec which computes the membership interval. However section
3.3.1.3 and Appendix L of the DOCSIS RFI spec both give a formula which is
the standard formula used in RFC2236 with the robustness value of 2. The
robustness value is the 2 in the ((2 * MQI) + QRI) DOCSIS formula. This
implies that the robustness is really used as a constant of 2 in passive
mode. However, even if we assume that robustness being 0 means that the
robustness is not used, 0 is syntactically invalid as a
igmpInterfaceRobustness value which ranges from 1 to 255. Therefore I would
rather see 2 as the value since it's a valid value and it's being used as
such anyway.

The wording you suggested for the second point works well for me.

Karl

-----Original Message-----
From: Nakanishi, Greg (SD-EX)
[mailto:[email-masked]]
Sent: Friday, November 16, 2001 12:11 PM
To: 'Schmidt Karl'; [email-masked]'
Subject: RE: [ipcdn] draft-ietf-ipcdn-igmp-mib-02.txt comments

Karl,

comments inline

greg

How about rewording to:

---

From: "Nakanishi, Greg (SD-EX)" <[email-masked]>
Date: Fri, 16 Nov 2001 13:11:23 -0500

Karl,

comments inline

greg

How about rewording to:

---

From: Schmidt Karl <[email-masked]>
Date: Fri, 16 Nov 2001 14:07:37 -0600

Greg,

Karl

-----Original Message-----

Karl,

comments inline

greg

How about rewording to: