Re: [mpls] Thoughts on Ancillary Data Indicators.
Kireeti Kompella <kireeti.ietf@gmail.com> Mon, 12 July 2021 20:43 UTC
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From: Kireeti Kompella <kireeti.ietf@gmail.com>
Date: Mon, 12 Jul 2021 13:42:49 -0700
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To: Loa Andersson <loa@pi.nu>
Cc: "mpls@ietf.org" <mpls@ietf.org>, "pals-chairs@ietf.org" <pals-chairs@ietf.org>, "spring-chairs@ietf.org" <spring-chairs@ietf.org>, "mpls-chairs@ietf.org" <mpls-chairs@ietf.org>, DetNet Chairs <detnet-chairs@ietf.org>
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Subject: Re: [mpls] Thoughts on Ancillary Data Indicators.
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Hi Loa, See inline. On Thu, Jul 8, 2021 at 2:11 AM Loa Andersson <loa@pi.nu> wrote: > Design Team, > > We have discussed how to carry ancillary data in in an MPLS packet and > how to include indicators on the presences of such data in the label > stack since the design team started. I think we have some convergence > and that it is time to float an idea that could be the basis for a > consensus. Please note that the actual consensus call will be made on > the mpls wg mailing list, while this is for discussion preparing such a > consensus call in the design team. > > The proposals we have for indicators often rely on assignment of a base > special purpose label. The number of such labels are limited. > > I think we can agree on the following: > > - We want to limit the number of new assignments of base special purpose > labels as much as possible > > - We have a standardized associated channel, the GAL/GACH. We are not > going to change the associated channel. The associated will remain as > specified in RFC 5586. The ACH is found immediately after the label > carrying the Bottom of Stack (BoS) bit. > > - We therefore need a (base) special purpose label to serve as the > forwarding action indicator carrier. > The proposal in draft-kompella-mpls-mspl4fa does this, and at the same time, collapses the requests of 5 or 6 SPLs to a single SPL. - It is attractive to "re-purpose" the ELI to also fill the role as a > general (generic?) forwarding action indicator. This may be done by > using the TTL and TC fields of the ELI as flags indicating which > service is requested. > While I'd be happy if this was possible, backward compatibility MUST be maintained without compromising functionality. > However, in order to do this it must be shown that there is no > potential interference between the normal service supplied by the > ELI/EL and the services indicated by the flags. > > - If we can't demonstrate the non-interference then we should assign > specific forwarding indicator action base special purpose label and > leave the ELI/EL unchanged. > > - The flag field of the re-purposed ELI of the the specially assigned > forwarding action indicator label must be made extendable. These > labels "only" have 11 bits (8 bit TTL and 3 bit TC fields) that can > be used as flags. Already in the very preliminary discussions we have > had so far are almost using all the 11 bits, making the it necessary > to make the indicator extendable. > Actually, the draft already had such an extension in place; the details have been fleshed out a bit better in the new version (just posted). The bit fields have changed as a consequence of my chat with Haoyu; some have been removed, but more added, so all 11 bits have been used up. So the extension header will be needed. The -01 draft is clearer than the -00 draft on several fronts, and lists issues needing resolution. I'm sure more will come up after the MPLS WG meeting. Cheers, Kireeti. > /Loa > > > > -- > > Loa Andersson email: loa@pi.nu > Senior MPLS Expert loa.pi.nu@gmail.com > Bronze Dragon Consulting phone: +46 739 81 21 64 > > _______________________________________________ > mpls mailing list > mpls@ietf.org > https://www.ietf.org/mailman/listinfo/mpls >
- [mpls] Thoughts on Ancillary Data Indicators. Loa Andersson
- Re: [mpls] Thoughts on Ancillary Data Indicators. Jeffrey (Zhaohui) Zhang
- Re: [mpls] Thoughts on Ancillary Data Indicators. bruno.decraene
- Re: [mpls] Thoughts on Ancillary Data Indicators. John E Drake
- Re: [mpls] Thoughts on Ancillary Data Indicators. Haoyu Song
- Re: [mpls] Thoughts on Ancillary Data Indicators. Loa Andersson
- Re: [mpls] Thoughts on Ancillary Data Indicators. Jeffrey (Zhaohui) Zhang
- Re: [mpls] Thoughts on Ancillary Data Indicators. Kireeti Kompella
- Re: [mpls] Thoughts on Ancillary Data Indicators. Kireeti Kompella
- Re: [mpls] Thoughts on Ancillary Data Indicators. bruno.decraene
- Re: [mpls] Thoughts on Ancillary Data Indicators. Haoyu Song