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Versions: 00 01                                                         
MPLS Working Group                                          L. Andersson
Internet-Draft                                  Bronze Dragon Consulting
Intended status: Informational                              May 10, 2021
Expires: November 11, 2021


                    MPLS Open Design Team Questions
               draft-andersson-mpls-open-dt-questions-01

Abstract

   This document is a living document, meaning that during the life
   timme of the MPLS Open Design Team we will put additonal questions/
   issues into the document.  When we find an answer amd a way to
   document the issu it will be removed from this document.

   Ideally when the Design Team is closed this document will be empty,
   or maybe we just add a pointer to where the answer to quesstion is
   documented.  Thus this document will never go on to become an RFCc.

Status of This Memo

   This Internet-Draft is submitted in full conformance with the
   provisions of BCP 78 and BCP 79.

   Internet-Drafts are working documents of the Internet Engineering
   Task Force (IETF).  Note that other groups may also distribute
   working documents as Internet-Drafts.  The list of current Internet-
   Drafts is at https://datatracker.ietf.org/drafts/current/.

   Internet-Drafts are draft documents valid for a maximum of six months
   and may be updated, replaced, or obsoleted by other documents at any
   time.  It is inappropriate to use Internet-Drafts as reference
   material or to cite them other than as "work in progress."

   This Internet-Draft will expire on November 11, 2021.

Copyright Notice

   Copyright (c) 2021 IETF Trust and the persons identified as the
   document authors.  All rights reserved.

   This document is subject to BCP 78 and the IETF Trust's Legal
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   carefully, as they describe your rights and restrictions with respect
   to this document.  Code Components extracted from this document must



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   include Simplified BSD License text as described in Section 4.e of
   the Trust Legal Provisions and are provided without warranty as
   described in the Simplified BSD License.

Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   2
     1.1.  Requirement Language  . . . . . . . . . . . . . . . . . .   2
   2.  Open DT Question List . . . . . . . . . . . . . . . . . . . .   3
     2.1.  Below the BoS . . . . . . . . . . . . . . . . . . . . . .   3
       2.1.1.  Limitations to the ability of LSR's to scan the Label
               Stack . . . . . . . . . . . . . . . . . . . . . . . .   3
       2.1.2.  Does flooding om maximum scanning depth of an LSR
               scale?  . . . . . . . . . . . . . . . . . . . . . . .   3
       2.1.3.  Placeholder, due to duplicate to another section  . .   4
       2.1.4.  First Nibble  . . . . . . . . . . . . . . . . . . . .   4
       2.1.5.  More then on ACH after the BoS  . . . . . . . . . . .   4
       2.1.6.  More then one indicator?  . . . . . . . . . . . . . .   4
       2.1.7.  Multiple types of Indicators in the same stack  . . .   4
       2.1.8.  Comfortable Readable Label Depth  . . . . . . . . . .   4
     2.2.  Above the BoS . . . . . . . . . . . . . . . . . . . . . .   5
       2.2.1.  Resuse the ELI  . . . . . . . . . . . . . . . . . . .   5
       2.2.2.  Using any bSPL  . . . . . . . . . . . . . . . . . . .   5
       2.2.3.  Use of Extended SPLs  . . . . . . . . . . . . . . . .   5
       2.2.4.  Generalized Action Indicator  . . . . . . . . . . . .   5
   3.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .   5
   4.  Acknowledgements  . . . . . . . . . . . . . . . . . . . . . .   6
   5.  Normative References  . . . . . . . . . . . . . . . . . . . .   6
   Author's Address  . . . . . . . . . . . . . . . . . . . . . . . .   6

1.  Introduction

   "Living Documents" are not commonly used in the IETF, but we have
   considered it to be a good way of documenting the state of the issues
   worked on by the design team.

1.1.  Requirement Language

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and
   "OPTIONAL" in this document are to be interpreted as described in BCP
   14 [RFC2119] [RFC8174] when, and only when, they appear in all
   capitals, as shown here.

   For a document that is not intended to become and RFC on the
   Standards Track it might seem moot to have the requirement language
   included, however it might be that a question or an answer to one of




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   the questions might use the BCP 14 language, so to avoid ambiguity we
   left it in

2.  Open DT Question List

2.1.  Below the BoS

   As we start working on this document we just add new questions as we
   define them.  It is possible that later we will try to find a
   grouping af questions based more on technical commonalities.

2.1.1.  Limitations to the ability of LSR's to scan the Label Stack

   Several LSRs have limitations how deep it is possible to scan the
   label stack looking for certain information.  If the info that are
   being looked for is below this depth, is it possible to use these
   LSRs for manadatoy actions?

   The inormation needed for the mandatory action will never be found.

2.1.2.  Does flooding om maximum scanning depth of an LSR scale?

   A remedy for the issues in Section 2.1.1 has been suggested, the
   maximum scanning depth for each LSR in the network should be flooded
   to all othr LSRs and used as a constraint when setting up LSPs.

   Would that scasle satisfactorily.

   Tentative answer:

   Stewart: It is one additional capability field (no more than a byte)
   to flood and I find it hard to imagine that it would not scale.

   The IGPs will need to be slightly updated, RFC 8491 will be a good
   starting point.

   Loa: Flooding will be done by an IGP, which is a small update to the
   IGP.  For networks that is controlled by a network management system
   (centralized controller), the NMS will both knew the scanning
   limitations and establish the LSP.

   Conclusion: Unless we see any further comments, this question is
   closed.








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2.1.3.  Placeholder, due to duplicate to another section

   Duplicate entry, in order to keep section number the duplicate has
   ben replaced by a placeholder.

2.1.4.  First Nibble

   We have indications that when we started to snoop the first nibble
   after the LSE that has the BoS set to find out if the packet carried
   IP (v4 or v6), there was also an agreement that "we" would never put
   anything but 0b0000 or 0b0001 in that first nibble.

   It is off couurse intresting to try to understand the definition of
   "we" but since the aggreement were between the Internet Area and the
   PWE3 working group, it is likely that it will be considered binding
   for the Routing Area.

   Stewart: Can you try to find out more about this and where we stand
   today.

2.1.5.  More then on ACH after the BoS

   Is it possible to have more than one ACH after the BoS.

   If currently not possible do we want to add it?

   How are the ACH's separated and related to the indicator in the label
   stack?

2.1.6.  More then one indicator?

   What happens when you find the first indicator?

   If an LSR is scanning "the entire stack", what happens when the first
   indicator is found?  Is the scanning aborted.

   If an GAL is below an FAI in the stack will it be found?

2.1.7.  Multiple types of Indicators in the same stack

   Is it possible to have multiple types of indicators in the same label
   stack, e.g.  FAI and GAL?

2.1.8.  Comfortable Readable Label Depth

   What is the Readable Label Depth (RLD) that we are comforable with.





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   This is a question that was voiced at a DT meeting, but there were
   not real discussion.

   Here we take the question to mean "What is the minimum RLD that we
   can count on by any LSR when we design functions that need to detect
   action indicators in the label stack?"

2.2.  Above the BoS

   -

2.2.1.  Resuse the ELI

   When using bSPLs for multipurpose - "the useless bit in the bSPL" -
   it was sometimes talked about reusing the ELI (unless this was
   misunderstood).

   Is this still on the agenda?

2.2.2.  Using any bSPL

   Is it possible to use the "useless bits" in any bSPL to indicate
   actions?

   If we do will the corresponding bits. e.g.  MSB in the TTL, mean the
   same thing regardless of in which bSPL it is found?

2.2.3.  Use of Extended SPLs

   Is it possible to use the "useless bits" in an eSPL/cSPL?  It would
   give use more bits to play with.  If the answer to the question in
   Section 2.2.2 is yes the useless bits in the XL would be interpreted
   as in any other indicator, but you have at least 11 new bits in the
   eSPL.

   Maybe allocate an extended FAI-2 from the extended range?

2.2.4.  Generalized Action Indicator

   Could we generalize the FAI (+ FAI-2 ?) to be general mechanism for
   indicating presence of "stuff" after the BoS?

3.  IANA Considerations

   This document does not make any allocations of code points from IANA
   registries.





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4.  Acknowledgements

   -

   -

5.  Normative References

   [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
              Requirement Levels", BCP 14, RFC 2119,
              DOI 10.17487/RFC2119, March 1997,
              <https://www.rfc-editor.org/info/rfc2119>.

   [RFC8174]  Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC
              2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174,
              May 2017, <https://www.rfc-editor.org/info/rfc8174>.

Author's Address

   Loa Andersson
   Bronze Dragon Consulting

   Email: loa@pi.nu




























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