Re: [IPFIX] draft-ietf-opsawg-ipfix-fixes: tcpOptions/ipv4Options bit mappings

[Andrew Feren <[e-mail]>]

Hi Paul,

I’m coming in a little late on this, but I took a few days to scan the many thousands of pcaps I’ve collected from customers over the last 20 years and look at existing exporter and collector implementations that I have access too.  Based on what I have found there may be no complaints because no one has implemented it.  I was unable to find a single use of either ipv4Options(208) or tcpOptions(209) in the wild.  Looking at the RFCs and errata it is hard to see how anyone could have implemented these IEs without many questions.

I asked myself how I would have implemented this if I had to make a decision based on what exists and came to the same conclusions you did in https://mailarchive.ietf.org/arch/msg/ipfix/v9ywSgTeYzataQnhMG-x7SxLo0U/.  If others reach the same conclusions my inclination is to make a 3rd and, hopefully final, errata attempt.  As a collector developer I’m sympathetic to the option to deprecate these IEs and try again, but I feel like a careful errata may be OK in this case.

-Andrew

From: IPFIX <[e-mail]> on behalf of Aitken, Paul <paitken=[e-mail]>
Date: Thursday, September 21, 2023 at 4:55 PM
To: [e-mail] <[e-mail]>, opsawg <[e-mail]>, Benoit Claise <[e-mail]>
Cc: [e-mail] <[e-mail]>
Subject: Re: [IPFIX] draft-ietf-opsawg-ipfix-fixes: tcpOptions/ipv4Options bit mappings
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Med, no-one else has reported problems with these elements in the last 15 years. So what do you want to achieve?

We should not update the registry without first understanding what has already been implemented. The best we can hope for is that existing implementations show consensus on the encoding. If so, then we should ensure that the IPFIX registry and errata align with the implementations.

If there's no consensus then it would be better to create new elements and deprecate the existing ones. But it's not worth creating new elements unless they would be broadly deployed.

P.

On 20/09/2023 15:12, [e-mail]<mailto:[e-mail]> wrote:
Hi Paul, all,

I digged into ipfix archives to see the discussion that happened around these errata and when scrolling I found this message:
https://mailarchive.ietf.org/arch/msg/ipfix/v9ywSgTeYzataQnhMG-x7SxLo0U/ [mailarchive.ietf.org]<https://urldefense.com/v3/__https:/mailarchive.ietf.org/arch/msg/ipfix/v9ywSgTeYzataQnhMG-x7SxLo0U/__;!!OSsGDw!M5ZqkW9HRmWiKi1m5ic3WY8jsxZ45KQaLkjwDuXEsMATOM758Px86B3PFsAdY1QMsKrL16GYBWpn0jnJUvJb6MlP$> but no follow-up.

This confirms my initial assessment that a fix is needed.

Cheers,
Med

De : BOUCADAIR Mohamed INNOV/NET
Envoyé : mardi 19 septembre 2023 15:02
À : 'Aitken, Paul' <[e-mail]><mailto:[e-mail]>; opsawg <[e-mail]><mailto:[e-mail]>; Benoit Claise <[e-mail]><mailto:[e-mail]>
Objet : RE: draft-ietf-opsawg-ipfix-fixes: tcpOptions/ipv4Options bit mappings

Hi Paul,

Yes, that’s what I was referring to in my previous messages when I said “FWIW, (1) is what was followed in RFC5102 but changed since then by errata.”.

I’m having trouble with that errata as I don’t understand why the reversal was only made at the octet level and not the full IE + how to link that with “Option number X is mapped to bit X”.

Thank you.

Cheers,
Med

De : Aitken, Paul <[e-mail]<mailto:[e-mail]>>
Envoyé : mardi 19 septembre 2023 12:13
À : BOUCADAIR Mohamed INNOV/NET <[e-mail]<mailto:[e-mail]>>; opsawg <[e-mail]<mailto:[e-mail]>>; Benoit Claise <[e-mail]<mailto:[e-mail]>>
Objet : Re: draft-ietf-opsawg-ipfix-fixes: tcpOptions/ipv4Options bit mappings

Med, this figure originally appeared in section 5.8.8 of draft-ietf-ipfix-info-13, -14, and RFC 5102 with the bits in this order:

              0     1     2     3     4     5     6     7

          +-----+-----+-----+-----+-----+-----+-----+-----+

          |   0 |   1 |   2 |   3 |   4 |   5 |   6 |   7 |  ...

          +-----+-----+-----+-----+-----+-----+-----+-----+

The bits were reversed by this errata: https://www.rfc-editor.org/errata/eid2946 [rfc-editor.org]<https://urldefense.com/v3/__https:/www.rfc-editor.org/errata/eid2946__;!!OSsGDw!M5ZqkW9HRmWiKi1m5ic3WY8jsxZ45KQaLkjwDuXEsMATOM758Px86B3PFsAdY1QMsKrL16GYBWpn0jnJUlDjvWkS$>

Also see https://www.rfc-editor.org/errata/eid1739 [rfc-editor.org]<https://urldefense.com/v3/__https:/www.rfc-editor.org/errata/eid1739__;!!OSsGDw!M5ZqkW9HRmWiKi1m5ic3WY8jsxZ45KQaLkjwDuXEsMATOM758Px86B3PFsAdY1QMsKrL16GYBWpn0jnJUqK4eb1D$>

P.
On 19/09/2023 09:49, [e-mail]<mailto:[e-mail]> wrote:
Hi all,

The description of these IEs says that “Options are mapped to bits according to their option numbers. Option number X is mapped to bit X”, however the drawing does not reflect that (tcpOptions):

        0     1     2     3     4     5     6     7
    +-----+-----+-----+-----+-----+-----+-----+-----+
    |   7 |   6 |   5 |   4 |   3 |   2 |   1 |   0 |  ...
    +-----+-----+-----+-----+-----+-----+-----+-----+

        8     9    10    11    12    13    14    15
    +-----+-----+-----+-----+-----+-----+-----+-----+
... |  15 |  14 |  13 |  12 |  11 |  10 |   9 |   8 |...
    +-----+-----+-----+-----+-----+-----+-----+-----+

       16    17    18    19    20    21    22    23
    +-----+-----+-----+-----+-----+-----+-----+-----+
... |  23 |  22 |  21 |  20 |  19 |  18 |  17 |  16 |...
    +-----+-----+-----+-----+-----+-----+-----+-----+

                          . . .

       56    57    58    59    60    61    62    63
    +-----+-----+-----+-----+-----+-----+-----+-----+
... |  63 |  62 |  61 |  60 |  59 |  58 |  57 |  56 |
    +-----+-----+-----+-----+-----+-----+-----+-----+

I suspect that the confusion is rooted in the interpretation of “bit X”: as (1) “bit position X” or the resulting (2) “binary value”:

  1.  If (1) is followed, then bit#0 would be mapped to option 0, bit#1 to option 1, and so on. This logic is followed, e.g., for ipv6ExtensionHeaders.
  2.  If (2) is followed, then bit#63 would be mapped to option 0, bit#62 to option 1, and so on.

In both cases, the drawing is not aligned with the narrative text. We may either consider updating the drawing or the text.

Which change is likely to have less impact on existing implementations? FWIW, (1) is what was followed in RFC5102 but changed since then by errata.

Thank you.

Cheers,
Med

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