[ippm] Re: comment on draft-ietf-ippm-hybrid-two-step

Greg Mirsky <gregimirsky@gmail.com> Thu, 26 September 2024 18:14 UTC

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From: Greg Mirsky <gregimirsky@gmail.com>
Date: Thu, 26 Sep 2024 11:14:20 -0700
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To: Vasilenko Eduard <vasilenko.eduard=40huawei.com@dmarc.ietf.org>, IETF IPPM WG <ippm@ietf.org>
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Subject: [ippm] Re: comment on draft-ietf-ippm-hybrid-two-step
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Hi Eduard,
thank you for your interest in our work. I hope that you don't mind
bringing our discussion to the IPPM WG mailing list. Please find my notes
below tagged GIM>>.

Regards,
Greg

On Thu, Sep 26, 2024 at 1:15 AM Vasilenko Eduard <vasilenko.eduard=
40huawei.com@dmarc.ietf.org> wrote:

> Hi Guru,
>
> Section 5 (Operationaal Considerations
> <https://datatracker.ietf.org/doc/html/draft-ietf-ippm-hybrid-two-step-02#name-operationaal-considerations>)
> is too general for me.
>
> IMHO: it would be a problem for HTS to detect follow-up packets on
> downstream intermediate nodes.
>
GIM>> There are several data plane demultiplexing techniques. For example,
a well-known destination port number in IPvX.

> What you put now is effectively “all transit nodes should become stateful
> on the limited number of states”.
>
> It is not good for routers and especially switches.
>
GIM>> A follow-up technique is broadly used in many protocols. For
example, IEEE Std 1588-2008 and RFC 8169
<https://datatracker.ietf.org/doc/rfc8169/>. Furthermore, the RFC 9341
<https://datatracker.ietf.org/doc/rfc9341/> "Alternate Marking Method"
implicitly creates a state in a transit node that supports that hybrid
performance measurement method. Also, IOAM-DEX
<https://datatracker.ietf.org/doc/rfc9326/> might be deployed with stateful
behavior.

> IMHO: you need something like IPv6 HbH attached to follow-up packet to
> make HTS friendly for routers and switches.
>
> It should be a value specified by IANA specifically for HTS, not the
> combinations of the particular 5-tuple.
>
GIM>> Thank you for the suggestion. We plan to have separate specifications
for data planes to describe the application of HTS, e.g., in IPv6 and MPLS.

>
>
> As I understand you properly, you are in general proposing to convert
> routers (and switches?) to “partially stateful devices”,
>
> because the intermediate node should memorize latency (mostly queuing) for
> the last “trigger packet” to record it later into the closest “follow-up
> packet” that would follow.
>
> Stateful devices (IPS, FW, LB) are typically 3x expensive to routers, 5x
> to switches.
>
> “Partially stateful” devices (like you propose) should not be the same
> expensive.
>
> I do not have a clue what be an additional cost if 1% of traffic is
> stateful? If 10%?
>
> Reminder, x% may be from 10^8 flows for 1.6Tbps interface. Hence, asking
> 1% flows to memorize may convert to 10^6 table.
>
> IHMO: cost estimation is important for what you propose.
>
> It was always dangerous to be even partially stateful.
>
GIM>> HTS is an optional mechanism. Vendors may choose to implement it, and
operators might decide to deploy HTS.

>
>
> Best Regards
>
> Eduard Vasilenko
>
> Senior Architect
>
> Network Algorithm Laboratory
>
> Tel: +7(985) 910-1105
>
>
>