Re: [ippm] New Version Notification for draft-ahuang-ippm-dex-timestamp-ext-00.txt

Haoyu,

Sorry for being late to the party, but Alex mentioned your reply (below) 
in another thread and I felt like I needed to answer this.

Actually, I don't think the limitation can be relaxed. The reason is 
simple: backward compatibility with existing implementations. Let's say 
we do as you suggest (i.e., one bit for two 4-byte fields, which means 
one bit for one 8-byte field). In that case, you would break existing 
implementations since they do not implement the new flag yet. As per 
RFC9326:

"An IOAM node that receives a DEX Option-Type with an unknown flag set 
to 1 MUST ignore the corresponding optional field."

So, existing implementations would skip 4 bytes for each unimplemented 
extension-flag to be compliant with the RFC (and to be forward 
compatible with future extension-flags). Which is definitely not what 
you want. This is exactly why consistency is required from the start, 
and it MUST be a 4-byte field (and so for all extension-flags, even new 
ones).

Thanks,
Justin

On 2/16/23 18:51, Haoyu Song wrote:
> As long as the optional fields are of fixed length (better to be 4 
> octets aligned) there will be no ambiguity. My personal opinion is that 
> the limitation can be relaxed.
> 
> Haoyu
> 
> *From:* Alex Huang Feng <alex.huang-feng@insa-lyon.fr>
> *Sent:* Thursday, February 16, 2023 2:01 AM
> *To:* Haoyu Song <haoyu.song@futurewei.com>
> *Cc:* ippm@ietf.org; Pierre Francois <pierre.francois@insa-lyon.fr>
> *Subject:* Re: [ippm] New Version Notification for 
> draft-ahuang-ippm-dex-timestamp-ext-00.txt
> 
> Hi Haoyu,
> 
> Thanks for your feedback.
> 
> I actually agree with your statement but the only reason I did it using 
> 2 bits is because in IOAM DEX (RFC9326) section 3.2, there is a 
> statement saying each Optional field is 4 octets long:
> 
> *Optional fields:*
> 
> The optional fields, if present, reside after the Reserved field. The 
> order of the optional fields is according to the order of the respective 
> bits, starting from the most significant bit, that are enabled in the 
> Extension-Flags field. Each optional field is 4 octets long.
> 
> There is no MUST in the section, so I did not know how to interpret 
> this. Maybe you have more insights on this.
> 
> Cheers,
> 
> Alex
> 
> 
> 
>     On 15 Feb 2023, at 18:47, Haoyu Song <haoyu.song@futurewei.com
>     <mailto:haoyu.song@futurewei.com>> wrote:
> 
>     Hi Alex,
> 
>     This method allows the direct delay measurement in data plane which
>     could be useful for some applications. The extension is also simple
>     and straightforward.
>     I have just one concern: the timestamp seconds and fraction are
>     defined as two optional field and the timestamp seconds could be the
>     only field used. However, I don't think it would be useful for delay
>     measurement if only the seconds appears. So maybe it's more
>     reasonable to consider them both as just one timestamp field and
>     save a flag bit.
> 
>     Thanks,
>     Haoyu
> 
>     -----Original Message-----
>     From: ippm <ippm-bounces@ietf.org <mailto:ippm-bounces@ietf.org>> On
>     Behalf Of Alex Huang Feng
>     Sent: Wednesday, February 15, 2023 3:30 AM
>     To:ippm@ietf.org <mailto:ippm@ietf.org>
>     Cc: Pierre Francois <pierre.francois@insa-lyon.fr
>     <mailto:pierre.francois@insa-lyon.fr>>
>     Subject: Re: [ippm] New Version Notification for
>     draft-ahuang-ippm-dex-timestamp-ext-00.txt
> 
>     Dear IPPM WG,
> 
>     I would like to present this draft which addresses a missing
>     timestamp in the IOAM Direct Export (DEX) option header.
> 
>     This timestamp extension allows computing the delay between the
>     encapsulation node and the transit or decapsulation node in IOAM DEX
>     Option.
> 
>     On behalf of the authors, I would like to request your feedback on
>     this draft.
> 
>     Cheers,
>     Alex
> 
> 
> 
>         On 15 Feb 2023, at 12:27, internet-drafts@ietf.org
>         <mailto:internet-drafts@ietf.org> wrote:
> 
> 
>         A new version of I-D, draft-ahuang-ippm-dex-timestamp-ext-00.txt
>         has been successfully submitted by Alex Huang Feng and posted to the
>         IETF repository.
> 
>         Name:draft-ahuang-ippm-dex-timestamp-ext
>         Revision:00
>         Title:Timestamp extension for In Situ Operations,
>         Administration, and Maintenance (IOAM) Direct Export
>         Document date:2023-02-15
>         Group:Individual Submission
>         Pages:6
>         URL:
>         https://nam11.safelinks.protection.outlook.com/?url=https%3A%2F%2Fwww.ietf.org%2Farchive%2Fid%2Fdraft-ahuang-ippm-dex-timestamp-ext-00.txt&data=05%7C01%7Chaoyu.song%40futurewei.com%7Cfd4793f6908340b88ac308db0f47ff29%7C0fee8ff2a3b240189c753a1d5591fedc%7C1%7C0%7C638120574175820201%7CUnknown%7CTWFpbGZsb3d8eyJWIjoiMC4wLjAwMDAiLCJQIjoiV2luMzIiLCJBTiI6Ik1haWwiLCJXVCI6Mn0%3D%7C3000%7C%7C%7C&sdata=2iaKat5H9LbLvGCML2Cwrgr14pCivah5y4mH%2BNIgKkA%3D&reserved=0 <https://nam11.safelinks.protection.outlook.com/?url=https%3A%2F%2Fwww.ietf.org%2Farchive%2Fid%2Fdraft-ahuang-ippm-dex-timestamp-ext-00.txt&data=05%7C01%7Chaoyu.song%40futurewei.com%7C7c4ae2c016124a1556b508db1004d9e9%7C0fee8ff2a3b240189c753a1d5591fedc%7C1%7C0%7C638121385272151587%7CUnknown%7CTWFpbGZsb3d8eyJWIjoiMC4wLjAwMDAiLCJQIjoiV2luMzIiLCJBTiI6Ik1haWwiLCJXVCI6Mn0%3D%7C3000%7C%7C%7C&sdata=vTJCUjqB43pv079CLXwoz08%2F6eUd8KHu3BkZsib02F0%3D&reserved=0>
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> 
> 
>         Abstract:
>           This document extends the In Situ Operations, Administration, and
>           Maintenance (IOAM) Direct Export option type to support
>         timestamping
>           by adding and defining two optional timestamp fields and
>           corresponding flags.
> 
> 
> 
> 
> 
>         The IETF Secretariat
> 
> 
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