Re: [mpls] Indicators in the stack and ancillary data after the BoS

[[e-mail]]

[+ authors of draft-song-mpls-eh-indicator]

> From: mpls [mailto:[e-mail]] On Behalf Of Loa Andersson
> 
> Jeffrey,
> 
> 
> On 17/06/2021 17:01, Jeffrey (Zhaohui) Zhang wrote:
> > Hi Loa,
> >
> >> but I'd like to see the DT address multiple indicators in the stack and multiple
> sets of ancillary data after the BoS.
> >
> > I think the earlier emails of this email thread were talking about multiple indicators
> in the stack; for multiple set of ancillary data after the BoS, either the extended
> ACH or the proposed MPLS/generic extension headers or a merge of those
> proposals should be able to handle it. This is alluded to the DataAfterBOS wiki
> page.
> 
> hmm - yes partly, but there are several indicators proposed in several
> drafts
> 
>   draft-gandhi-mpls-ioam-sr has an E"E indicaor and an HBH indicator
> 
>   draft-kompella-mpls-mspl4fa make use of TC field and TTL of a special
> purpose label (FAI) as indicators
> 
>   there has also been discussion about putting more than one GAL in the
> stack, i.e. differerent GALs pointing to different ACHs.
> 
>   draft-many-mpls-multiple-gal proposes to add a copy of the GAL higher
> uop the stack so that LSRs with a too shallow maximun readable depth
> might reach the GAL
> 
>   there has also been discussion about putting more than one GAL in the
> stack, i.e. differerent GALs pointing to different ACHs.
> 
>   draft-song-mpls-eh-indicator have a list of potential indicators, that
> is also telling if the EH should be processed on every EH capable node
> or "just" at ingress and egress

The following draft proposes a way to carry indicators.
https://datatracker.ietf.org/doc/html/draft-decraene-mpls-slid-encoded-entropy-label-id#section-2

It's short (less than one page) and backward compatible for LSR & LER.

Referring to table 5 of draft-song-mpls-eh-indicator it also
-  does not require additional label assuming Entropy Label is already used for load balancing 
-  does not require an additional scarce resource (Special-Purpose MPLS Label value)
- allows location freedom
- does not need control plane extension

Could the authors of draft-song-mpls-eh-indicator update their table 5 in order to include the above draft?

Thanks,
Regards,
--Bruno
 
> 
> The FAI might put ancillary data after the BoS.
> 
> I think we need to have a comprehensive discussion
> 
> - first what we want to have
> - second how when re-direct by an indicator we find the
>    ancillary data that belongs to that indicator.
> 
> /Loa
> 
> 
> 
> 
> >
> > Thanks.
> >
> > Jeffrey
> >
> > -----Original Message-----
> > From: Loa Andersson <[e-mail]>
> > Sent: Thursday, June 17, 2021 10:46 AM
> > To: Jeffrey (Zhaohui) Zhang <[e-mail]>; Alexander Vainshtein
> <[e-mail]>; Stewart Bryant <[e-mail]>
> > Cc: [e-mail]
> > Subject: Re: [mpls] [EXTERNAL] Indicators in the stack and ancillary data after
> the BoS
> >
> > [External Email. Be cautious of content]
> >
> >
> > DT,
> >
> > Responded to Jeffrey's mail, but it is intended to address the entire
> > discussion.
> >
> > There seem to be enough issues to sort out around the GAL/ACH pair, and
> > I was worried about a set of other indicators and the data that they
> > might want to put "after the BoS". So far I have seen no real effort to
> > address the interference's this might lead to.
> >
> > Further inline
> >
> >
> > On 17/06/2021 16:15, Jeffrey (Zhaohui) Zhang wrote:
> >> Hi,
> >>
> >> It’s not clear how we could put a GAL not at a BoS:
> >>
> >>      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
> >>
> >>      |                              ACH                              |
> >>
> >>      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
> >>
> >>      |                         ACH TLV Header                        |
> >>
> >>      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
> >>
> >>      |                                                               ~
> >>
> >>      ~                     zero or more ACH TLVs                     ~
> >>
> >>      ~                                                               |
> >>
> >>      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
> >>
> >>      |                                                               ~
> >>
> >>      ~                        G-ACh Message                          ~
> >>
> >>      ~                                                               |
> >>
> >>      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
> >>
> >>                         Figure 2: G-ACh Packet Payload
> >>
> >> If the GAL does not have S-bit set, wouldn’t a transit LSR treat any
> >> 4-ocet field (i.e. those in the above Figure) after that GAL as a
> >> label+TOS+S+TTL? If that 4-octet field has the S-bit set, the transit
> >> LSR will think the label stack ends there even though that’s just part
> >> of the ACH.
> >>
> >> Or are you saying that a GAL not at the BoS will not have the ACH
> >> following it?
> >
> > Well, as far as I understand a GAL which does not have the NoS-bit set
> > will have other labels after itself. The BoS-bit will be found deeper
> > down stack and the ACH will immediately fo9llow the BoS.
> >
> > Yes there are issues here, but I'd like to see the DT address multiple
> > indicators in the stack and multiple sets of ancillary data after the BoS.
> >
> > I think we need to nail down the relevant questiuons first, and start
> > working on solutions after that.
> >
> > /Loa
> >>
> >> Jeffrey
> >>
> >> *From:*mpls <[e-mail]> *On Behalf Of *Alexander Vainshtein
> >> *Sent:* Thursday, June 17, 2021 5:07 AM
> >> *To:* Stewart Bryant <[e-mail]>
> >> *Cc:* [e-mail]
> >> *Subject:* Re: [mpls] [EXTERNAL] Indicators in the stack and ancillary
> >> data after the BoS
> >>
> >> *[External Email. Be cautious of content]*
> >>
> >> Stewart,
> >>
> >> I fully agree with your statement that “an old implementation that
> >> received a ToS GAL not at BoS would at best throw an exception or worst
> >> be unpredictable”.
> >>
> >> Regarding your statement “it is OK to have multiple GALs and GALs not at
> >> BoS IFF the creator of the LSP ensured that all LSRs on the LSP,
> >> including ECMP and FRR paths that found the GAL at ToS were known to be
> >> able to process it correctly”:
> >>
> >>   1. I fully agree with this statement as a general restriction
> >>   2. Quite a lot of things have to be done in order to make this
> >>      restriction work including at least:
> >>
> >>       1. The definition of correct processing of GAL at ToS but not at
> >>          BoS must be provided
> >>       2. Advertisement of ability to process GAL not at BoS correctly in
> >>          IGP and BGP must be defined
> >>       3. Ability to set up network-wide paths that only cross nodes that
> >>          process GAL correctly must be provided for different techniques
> >>          (RSVP-TE, SR-TE, FlexAlgo. BGP-LU etc.)
> >>
> >> It is still possible that, after all this work, we shall find out  that
> >> the benefits of supporting GAL at ToS but not BoS will be only available
> >> in the networks where all the nodes support the new functionality
> >> because presence of non-supporting nodes imposes too many restrictions
> >> on connectivity and/or resilience.
> >>
> >> Regards,
> >>
> >> Sasha
> >>
> >> Office: [phone]
> >>
> >> Cell:      [phone]
> >>
> >> Email: [e-mail]
> <mailto:[e-mail]>
> >>
> >> *From:*Stewart Bryant <[e-mail]
> >> <mailto:[e-mail]>>
> >> *Sent:* Thursday, June 17, 2021 10:36 AM
> >> *To:* Alexander Vainshtein <[e-mail]
> >> <mailto:[e-mail]>>
> >> *Cc:* Stewart Bryant <[e-mail]
> >> <mailto:[e-mail]>>; [e-mail]
> >> <mailto:[e-mail]>; [e-mail] <mailto:[e-mail]>
> >> *Subject:* Re: [mpls] [EXTERNAL] Indicators in the stack and ancillary
> >> data after the BoS
> >>
> >>      On 17 Jun 2021, at 07:45, Alexander Vainshtein
> >>      <[e-mail]
> >>      <mailto:[e-mail]>> wrote:
> >>
> >>      While that might be the case, I think that the Open DT may give it a
> >>      try and investigate how the existing systems will handle GAL being
> >>      not the BoS label.
> >>
> >>      */[[Sasha]] Great minds think alike! One useful step could be
> >>      collecting the known actual behavior of popular implementations in
> >>      this case, say, by running a survey among the vendors – what do you
> >>      think?/*
> >>
> >> That is actually a considerable amount of work that will take a while.
> >>
> >> It seems to me that an old implementation that received a ToS GAL not at
> >> BoS would at best throw an exception or worst be unpredictable.
> >>
> >> The original assumed processing model is to take the context of the PW
> >> label or PW+FAT label, discover the GAL and then process the GAL in the
> >> context of the PW label.
> >>
> >> When we extended GAL to apply to LSPs we again had the model that the
> >> GAL operated in the context of the LSP label that preceded it for
> >> context. It was still BoS.
> >>
> >> Putting the GAL further up the stack is a new behaviour.
> >>
> >> If it arrives at an LSR that knows the new semantic all is good.
> >>
> >> If it arrives at an LSR that does not know the new semantic then
> >>
> >> a) An error has occurred either in setting up the LSP, or in forwarding.
> >>
> >> b) The behaviour at the receiving node is unpredictable, but in any well
> >> written implementation should just result in the packet being dropped
> >> and counted as with any other Mal-formed packet.
> >>
> >> So I would think that it is OK to have multiple GALs and GALs not at BoS
> >> IFF the creator of the LSP ensured that all LSRs on the LSP, including
> >> ECMP and FRR paths that found the GAL at ToS were known to be able to
> >> process it correctly.
> >>
> >> A GAL not at BoS and not at ToS should not be inspected or processed by
> >> any LSR that did not know what it was doing, and to attempt to precess
> >> it would be a violation of the normal MPLS processing model.
> >>
> >> - Stewart
> >>
> >>
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> >
> > --
> >
> > Loa Andersson                        email: [e-mail]
> > Senior MPLS Expert                          [e-mail]
> > Bronze Dragon Consulting             phone: [phone]
> >
> > Juniper Business Use Only
> >
> 
> --
> 
> Loa Andersson                        email: [e-mail]
> Senior MPLS Expert                          [e-mail]
> Bronze Dragon Consulting             phone: [phone]
> 
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