Re: [IPFIX] IPFIX export: SNMP versus physical Interface

Andrew Feren <andrewf@plixer.com> Tue, 26 July 2011 23:02 UTC

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Date: Tue, 26 Jul 2011 19:02:36 -0400
From: Andrew Feren <andrewf@plixer.com>
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To: Benoit Claise <bclaise@cisco.com>
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Subject: Re: [IPFIX] IPFIX export: SNMP versus physical Interface
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On 07/26/2011 04:29 PM, Benoit Claise wrote:
> Juergen,
>
>> On Tue, Jul 26, 2011 at 10:54:52AM -0400, Andrew Feren wrote:
>>
>>>  From a collection and reporting perspective the important
>>> difference for
>>> me in these two sets of definitions isn't physical vs maybe not
>>> physical, but that "The value matches the value of managed object
>>> 'ifIndex' as defined in RFC 2863 ..." and everything that implies for
>>> elements 10/14.
>>>
>>> So I agree with Paul's approach.  There are situations where either
>>> 10/14 or 252/253 could be used, but if RFC 2863 applies to your
>>> interface use 10/14.
>>>
>>> Maybe rather than replacing "IP interface" with "logical or virtual
>>> interface" it could just be "interface" or "network interface".
>>>
>>> On a related not I'm not sure the references for 252/253 need to refer
>>> readers to "[RFC2863] for the definition of the ifIndex object."
>> RFC2863 always applies to an ifIndex object. I fail to see the
>> problem. I find the definitions of these elements rather clear as they
>> are written.
> I agree.
> Both sets (10/14 and 252/253( are ifIndex.
> The second set applies to the physical ifIndex, while the first one
> might be non-physical.
> A Flow Record can contain both, and the Collector can draw the
> conclusions if the sets are different.
>
> So I would not change the definitions.
> A clarification might be welcome (even though I'm not convinced).
> However, where?
> - not in IANA, which specifies individual IE, and not the relation
> between them
> - maybe in the RFC5102 Proposed Draft RFC
>
> Regards, Benoit.

Thanks.  This makes sense to me now.

Two things could have made this clearer to me when I read the docs.

1) if the IANA description of 252/253 contained similar language to what
is in the descriptions for 10/14.  Something like "The value matches the
value of a physical 'ifIndex' as defined in RFC 2863."
I know when I see one description (10/14) specify RFC 2862 and the
description for a different, but similar, element (252/253) makes no
mention of RFC 2862 it is not clear to me if the second element must be
"as defined in RFC 2862".  I start to wonder if the description is
incomplete or the reference section is a cut and paste error or something.

2) I like Benoit's suggestion of putting a description of the 
relationship between these two sets of elements somewhere.
I don't have an opinion on the right location for #2.

-Andrew