Re: [IPv6] 6MAN: looking for feedback to draft-eckert-6man-qos-exthdr-discuss (Re: New Version Notification for ...)

[Tom Herbert <[e-mail]>]

On Wed, Mar 6, 2024 at 2:54 AM Tim Chown
<Tim.Chown=[e-mail]> wrote:
>
> Hi,
>
> On 5 Mar 2024, at 18:31, Tom Herbert <tom=[e-mail]> wrote:
>
> On Tue, Mar 5, 2024 at 6:41 AM Tim Chown
> <Tim.Chown=[e-mail]> wrote:
>
> <snip>
>
>
> And that is similar in spirit to what the CERN experiments are doing with flow label semantics, which would/could be HbH header information if then insertion penalty were not so high.
>
>
> Hi Tim,
>
> The CERN experiment might be okay as an experiment, but overloading
> the twenty bit information of flow label is neither scalable nor
> standardizable. This is especially true for those proposals that want
> to set some bits differently within the same flow and expect that
> routers will ignore those bits for ECMP hash.
>
>
> The flow label is big enough for the science use case; it’s split into experiment (community), activity (application area) and has 5 bits for entropy.  The use case is just understanding which experiments and activities are consuming capacity on expensive links.
>
> As suggested at the SFO IETF we’d like to use HbH, as there’s far richer metadata that could also be included than fits in 20 bits.
>
> I am interested in what you mean by " if then insertion penalty were
> not so high".
>
>
> Inserting the HbH reduces throughput, which is important for large scale data transfers. There’s an example in the paper Eric Vyncke published recently that shows it’s significant - https://netdevconf.info/0x17/docs/netdev-0x17-paper40-talk-paper.pdf.  Our experience is similar, but we have hooked up the person who did Eric’s implementation with the one who did ours to look again. Setting the flow label I recall reduced performance by something like 0.5%.

HI Tim,

The minimum size of the extension header is eight bytes so that's 0.5%
overhead (is that the number you're referring to?). With a 9K MTU that
drops to 0.09%. In comparison to other forms of wire overhead, like
encapsulation or even IPv6 itself, EH overhead can be insignificant
(or not depending on the format of the extension header :-) ). Also
the Netdev paper describes using eBPF to set extension headers, that's
not the most efficient way to do it. Much better to set them on the
socket (still working to get full Linux support for that).

Tom

>
> Tim
>
> Tom
>
>
>
> https://www.ietf.org/archive/id/draft-cc-v6ops-wlcg-flow-label-marking-02.html
>
> And there are others, each doing something slightly different, when we’d ideally have one EH to rule them all.
>
> Tim
>
>
> Right now this is a discussion draft not intended to become RFC because it's my impression that the
> 6MAN community might benefit from some useful summary of how DetNet (and potentially other WGs) might
> use this work, but this would not be part of a final spec draft, and likewise i have a wide range of
> open questions instead of answers, and i included those questions into the draft seeking for feedback from
> 6MAN.
>
> Overall, i didn't want to go down a possible rabbit hole of working on details of the spec if it just
> turns out to involve insurmountable IETF process obtacles to go this route. For example, we could continue to
> standardize all advanced forwarding functions only into MPLS and ignore IPv6 as DetNet has done so far
> (*mumble ;-).
>
> The lack of such extension headers has IMHO held back innovation into better (stateless) QoS, especially
> in many controlled networks since at least 25 years, for example when draft-stoica-diffserv-dps
> was abandomed because it was too painfull trying to get to through all the IETF IPv6 bureaucracy -
> for just one algorithm, when there are so many that would deserve experimentation in specific
> networks. But given the good recent/ongoing work for example into  I-D.ietf-6man-hbh-processing,
> i would hope that we're closer now to actually wanting our extensibility of IPv6 actually be used
> by the industry (instead of all this happening only in MPLS).
>
> With DetNet we are too in the situation that we have multiple candidates on the table and IMHO
> it will not be very useufl trying to run a lottery for a single "winner" and standardize just that.
>
> I have seen a lot more success in the industry by just letting different algorithms compete with
> each othrer in products and let the market decide. That was quite a lot happening in e.g.: packet
> scheduling in routers at least since the end of the 90th when in my impression every new
> hardware forwarding router implemented it's own new packet scheduler based on the just hired lead
> engineers PhD thesis. And over a period of 20 years, a lot of commonality and industry
> knowledge evolved in that space. For this type of scheduling, this innovation was possible because it did not
> require new packet headers, but just a lot of (ab)use of DSCP and/or more or less horrenduous
> QoS configurations. But for those solutions that do require additional in-packet-QoS metadata,
> we never created a viable method where it was easy for the  innovators/implementers to concentrate
> on the novelties of the algorithm in question and get all the knucklehead "how to packetize and what generic
> requirements/functionalities" be provided as much as possible by an existing framework/RFC.
>
> So, i'd be very happy to find interest to help progress this work, aka: writing something
> that ultimately would become a draft-ietf-6man-common-qos-exthr or the like. I have tentatively
> asked for a slot for IETF119 6MAN to present and get feedback, if you think that would be time well
> spent, pls. chime in.
>
> Cheers
>   Toerless, for the authors
>
> On Mon, Mar 04, 2024 at 12:30:53PM -0800, [e-mail] wrote:
>
> A new version of Internet-Draft draft-eckert-6man-qos-exthdr-discuss-00.txt
> has been successfully submitted by Toerless Eckert and posted to the
> IETF repository.
>
> Name:     draft-eckert-6man-qos-exthdr-discuss
> Revision: 00
> Title:    Considerations for common QoS IPv6 extension header(s)
> Date:     2024-03-04
> Group:    Individual Submission
> Pages:    27
> URL:      https://www.ietf.org/archive/id/draft-eckert-6man-qos-exthdr-discuss-00.txt
> Status:   https://datatracker.ietf.org/doc/draft-eckert-6man-qos-exthdr-discuss/
> HTMLized: https://datatracker.ietf.org/doc/html/draft-eckert-6man-qos-exthdr-discuss
>
>
> Abstract:
>
>  This document is written to start a discussion and collect opinions
>  and ansers to questions raised in this document on the issue of
>  defining IPv6 extension headers for DETNET-WG functionality with
>  IPv6.
>
>
>
> The IETF Secretariat
>
>
> --------------------------------------------------------------------
> IETF IPv6 working group mailing list
> [e-mail]
> Administrative Requests: https://www.ietf.org/mailman/listinfo/ipv6
> --------------------------------------------------------------------
>
>
> --------------------------------------------------------------------
> IETF IPv6 working group mailing list
> [e-mail]
> Administrative Requests: https://www.ietf.org/mailman/listinfo/ipv6
> --------------------------------------------------------------------
>
>
>