Internet DRAFT - draft-andersson-mpls-open-dt-questions
draft-andersson-mpls-open-dt-questions
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.
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This Internet-Draft will expire on November 11, 2021.
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Copyright (c) 2021 IETF Trust and the persons identified as the
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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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