[Gen-art] Gen-art Last Call/Telechat Review of draft-ietf-ipfix-mib-variable-export-09

Elwyn Davies <elwynd@dial.pipex.com> Sat, 14 November 2015 15:07 UTC

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Subject: [Gen-art] Gen-art Last Call/Telechat Review of draft-ietf-ipfix-mib-variable-export-09
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Document: draft-ietf-ipfix-mib-variable-export-09.txt
Reviewer: Elwyn Davies
Review Date: 2015/11/14
IETF LC End Date: 2015/10/26
IESG Telechat date: 2015/11/19

Summary: Ready except for some minor nits, chiefly associated with the 
unexplained use of 'magic numbers' that are defined elsewhere in the 
IPFIX specifications (see comments on ss5.3, 5.4.2 and 6.3).  I was 
(however) impressed by the quality of the document, which is consistent 
in its presentation and deals clearly with a complex (and, frankly, 
pretty dry as dust) specification.  Most of the points below are 
primarily to make the document more easily accessible to people (like 
me) with limited exposure to IPFIX. Caveat:  I have read through the 
examples (Section 6) but I cannot say that I have analysed them in gory 

Apologies for the late delivery of this review.  I missed the assignment 
during the last call period.  In the light of the quality of the 
document, I don't think this should have any effect on the progress of 
the document!

Major issues:

Minor issues:

Nits/editorial comments:
General: s/i.e./i.e.,/g (4 instances)
s/e.g./e.g.,/ (1 instance in s10)

s2, para 1:  Probably good to provide a pointer to the doc/section where 
Template Record and Data Record are defined as this section precedes s3 
where the terminology is specified.

s4, para 2: s/non columnar/non-columnar/ (?)

s4, third para from end: s/One common type/Two common types/

s5, para 5:
>     However, future versions of IPFIX may export the required MIB
>     metadata as part of newer set versions.
Is the phrase 'newer set versions' a term of art here?  Maybe change to 
'newly defined version(s)' or maybe 'newly defined Set versions [or just 

s5.1, para after Table 1: s/encoding references/encoding reference/

s5.3, bullet points: To clarify Set ID entries in the figures describing 
the various templates/data sets it would be worth noting the SetID(s) 
that can be used with the various template and data records and a 
reference to RFC 7011 Section 3.3.2.
I think that bullet 1 has Set ID 2, bullet 2 has Set ID 3 and bullets 3 
and 4 have Set IDs from 256 upwards (implementation choice).

s5.4.2, last para and Figure 5:  It would be helpful to remind people 
that the value 0xffff/65535 indicates variable length encoding  per RFC 
7011 Section 3.2 and that the RECOMMENDED use of variable length 
encoding for mibObjectIdentifier fields is indicated in subsequent 
figures by placing 65535 in the relevant length fields.  Presumably 
Collector implementations  MUST accept a specific length encoding in the 
usual IETF spirit!  It might be worth being explicit about this (this 
might usefully be said in Section 8).

s5.7.2, para 1:  The MUST ought to be qualified by 'except as allowed by 
the caveat of Section 5.7.1'.

s5.7.2: is there any need to explain how withdrawal is achieved?  I am 
not an IPFIX expert so I am not aware how the withdrawal might be achieved.

s5.8, para 5: s/may be used purely use as a data type./may be used 
purely as a data type./ ( I think)

s5.8, last para: is missing its terminal period/full stop. :-(

s5.8.1, last para: s/be exported/to be exported/

s6.2, bullet 2 after Table 3: is missing its terminal period/full stop. :-(

s6.2, 3rd from last para (top of page 40): s/encoded/encode/;  It would 
also be useful to point the reader back to the template for 
mibObjectValueGauge in Table 23 where the encoding size is specified.

s6.3:  This section is somewhat politically incorrect in that it deals 
(only) with IPv4 addresses ;-)

s6.3, Table 4 (also Table 9):  The aesthetics of this table could be 
improved by reducing the width of the Object column by 7 characters and 
reallocating them to the ID (+4) and mibObjectValue (+3) columns.  
Similarly in Table 5, moving a character from the Entity column to the 
Full OID column.

s6.3, Figure 28:  For the benefit of less clued up readers, it would be 
worth pointing out that this is a structured data type specification 
using the 'undefined' (= 0xFF) semantic (RFC 6313, Section 11.4/11.4.1) 
.  It would also be clearer to s/=FF/=0xFF/g. Also applies to Figure 31 
and Figure 42.

s10: The discussion I think effectively covers issues of privacy 
inherited both from SNMP/MiBs and IPFIX but it might be worth putting in 
the 'P word' and expanding a bit more on this subject to make it clear 
that accessing MiB objects  via IPFIX opens up a whole new opportunity 
for privacy violations.