Re: [mpls] [spring] redux: Special purpose labels in draft-hegde-spring-traffic-accounting-for-sr-paths

Hi John, et. al,
GAL may be placed anywhere in the stack, not only at the BoS. That was
re-affirmed by RFC 6423 that extended applicability of the GAL to PWs. Thus
GAL indicates that the ACH immediately follows the label stack, i.e. what
ever label has S bit set. Resulting from that, I think, we may set GAL
multiple times in SR-MPLS stack to work around the RLD syndrome. Yes, it is
bump-in-a-wire with ACH.

Regards,
Greg

On Fri, Nov 17, 2017 at 12:02 PM, John E Drake <jdrake@juniper.net> wrote:

> Dave,
>
>
>
> I think the EoS bit is set in the GAL.  I.e., there would be a small fixed
> size identifier between the stack and the payload.  As I indicated it’s
> just a suggestion.
>
>
>
> Yours Irrespectively,
>
>
>
> John
>
>
>
> *From:* David Allan I [mailto:david.i.allan@ericsson.com]
> *Sent:* Thursday, November 16, 2017 10:26 PM
> *To:* John E Drake <jdrake@juniper.net>; Ext - Ruediger.Geib@telekom.de <
> Ruediger.Geib@telekom.de>; adrian@olddog.co.uk
> *Cc:* draft-hegde-spring-traffic-accounting-for-sr-paths@ietf.org;
> spring@ietf.org; zali@cisco.com; robert@raszuk.net; mpls@ietf.org
> *Subject:* RE: [spring] [mpls] redux: Special purpose labels in
> draft-hegde-spring-traffic-accounting-for-sr-paths
>
>
>
> Would not the concept of
>
>
>
> <forwarding labels><GAL><id>(EOS set)<payload>
>
>
>
> Get a bit strange?  We are simply swapping one reserved label for another…
>
>
>
> Dave
>
>
>
> *From:* spring [mailto:spring-bounces@ietf.org <spring-bounces@ietf.org>] *On
> Behalf Of *John E Drake
> *Sent:* Thursday, November 16, 2017 8:00 PM
> *To:* Ext - Ruediger.Geib@telekom.de <Ruediger.Geib@telekom.de>;
> adrian@olddog.co.uk
> *Cc:* draft-hegde-spring-traffic-accounting-for-sr-paths@ietf.org;
> spring@ietf.org; zali@cisco.com; robert@raszuk.net; mpls@ietf.org
> *Subject:* Re: [spring] [mpls] redux: Special purpose labels in
> draft-hegde-spring-traffic-accounting-for-sr-paths
>
>
>
> Ruediger,
>
>
>
> There is also the possibility of using a GAL w/ a new fixed size GACH
> containing the SR Segment List Id.  This is similar to Robert’s suggestion
> of using a VXLAN header.
>
>
>
> Yours Irrespectively,
>
>
>
> John
>
>
>
> *From:* mpls [mailto:mpls-bounces@ietf.org <mpls-bounces@ietf.org>] *On
> Behalf Of *Ruediger.Geib@telekom.de
> *Sent:* Thursday, November 16, 2017 4:44 AM
> *To:* adrian@olddog.co.uk
> *Cc:* draft-hegde-spring-traffic-accounting-for-sr-paths@ietf.org;
> spring@ietf.org; robert@raszuk.net; mpls@ietf.org; zali@cisco.com
> *Subject:* Re: [mpls] [spring] redux: Special purpose labels in
> draft-hegde-spring-traffic-accounting-for-sr-paths
>
>
>
> Adrian,
>
>
>
> to me, there’s no ideal solution. But an analysis may help to find a
> useful solution. There’s a need to collect traffic statistics also for
> packets which don’t follow the shortest end to end path. There’s no simple
> howto, I think.
>
>
>
> For the time being, I’d prefer not to add special labels to the stack.
> What other options are there?
>
> -        Accounting at the router pushing a relevant label stack only.
>
> -        Accounting of an n-label stack.
>
> -        Acoounting of a subset of labels only (e.g. Node-SID Labels and
> Anycast-SID, but not ADJ-SID). The idea is a compromise to limit the number
> of counters be maintained. Consider accounting of the top 2 labels carrying
> global routing information.
>
> -        A special label. Shradda proposes to put such a label into the
> stack. The labels present there prior to the addition are maintained. One
> might think about a single top label which identifies and replaces the
> label stack carrying routing information relevant for the path. That would
> simplify accounting, but it requires suitable IGP functionality.
>
>
>
> None of the options sounds simple. Are there more (and simpler) ones I
> didn’t come upon?
>
>
>
> Regards, Ruediger
>
>
>
> *Von:* spring [mailto:spring-bounces@ietf.org <spring-bounces@ietf.org>] *Im
> Auftrag von *Adrian Farrel
> *Gesendet:* Donnerstag, 16. November 2017 06:35
> *An:* 'Mach Chen' <mach.chen@huawei.com>; 'Jeff Tantsura' <
> jefftant.ietf@gmail.com>; 'Robert Raszuk' <robert@raszuk.net>
> *Cc:* 'draft-hegde-spring-traffic-accounting-for-sr-paths' <
> draft-hegde-spring-traffic-accounting-for-sr-paths@ietf.org>; 'spring' <
> spring@ietf.org>; 'Zafar Ali (zali)' <zali@cisco.com>; 'mpls' <
> mpls@ietf.org>
> *Betreff:* Re: [spring] [mpls] redux: Special purpose labels in
> draft-hegde-spring-traffic-accounting-for-sr-paths
>
>
>
> Let's unpick a couple of things...
>
>
>
> 1. This work is not talking about per-flow accounting, it is talking about
> peer SR-path accounting
>
> 2. ipfix on its own does not cut it because you still have to put a marker
> in the packets
>
> 3. Yes, SR assumes there is no (i.e. zero) state per SR-path in the network
>
> But this third point causes a tension: we want to use SR because it is
> good, but we want to do transit node diagnostics because (frankly) they are
> necessary.
>
> To get the full picture of why they are necessary read the draft, or
> consider ECMP.
>
>
>
> This discussion will not be unfamiliar to those who tried to debug LDP
> networks.
>
>
>
> Adrian
>
>
>
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