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 <[email protected]> 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:[email protected]] > *Sent:* Thursday, November 16, 2017 10:26 PM > *To:* John E Drake <[email protected]>; Ext - [email protected] < > [email protected]>; [email protected] > *Cc:* [email protected]; > [email protected]; [email protected]; [email protected]; [email protected] > *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:[email protected] <[email protected]>] *On > Behalf Of *John E Drake > *Sent:* Thursday, November 16, 2017 8:00 PM > *To:* Ext - [email protected] <[email protected]>; > [email protected] > *Cc:* [email protected]; > [email protected]; [email protected]; [email protected]; [email protected] > *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:[email protected] <[email protected]>] *On > Behalf Of *[email protected] > *Sent:* Thursday, November 16, 2017 4:44 AM > *To:* [email protected] > *Cc:* [email protected]; > [email protected]; [email protected]; [email protected]; [email protected] > *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:[email protected] <[email protected]>] *Im > Auftrag von *Adrian Farrel > *Gesendet:* Donnerstag, 16. November 2017 06:35 > *An:* 'Mach Chen' <[email protected]>; 'Jeff Tantsura' < > [email protected]>; 'Robert Raszuk' <[email protected]> > *Cc:* 'draft-hegde-spring-traffic-accounting-for-sr-paths' < > [email protected]>; 'spring' < > [email protected]>; 'Zafar Ali (zali)' <[email protected]>; 'mpls' < > [email protected]> > *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 > > > > _______________________________________________ > mpls mailing list > [email protected] > https://www.ietf.org/mailman/listinfo/mpls > >
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