MPLS Working Group
Internet Engineering Task Force (IETF) L. Andersson
Internet-Draft
Request for Comments: 9017 Bronze Dragon Consulting
Updates: 3032, 7274 (if approved) K. Kompella
Intended status:
Category: Standards Track Juniper Networks
Expires: July 25, 2021
ISSN: 2070-1721 A. Farrel
Old Dog Consulting
January 21,
April 2021
Special Purpose
Special-Purpose Label terminology
draft-ietf-mpls-spl-terminology-06 Terminology
Abstract
This document discusses and recommends a terminology that may be used
when MPLS Special Purpose Special-Purpose Labels (SPL) (SPLs) are specified and documented.
This document applies that terminology change to the relevant IANA
registry and also clarifies the use of the Entropy Label Indicator
(7) when immediately preceded by the Extension Label (15).
This document updates RFC 7274 RFCs 3032 and RFC 3032. 7274.
Status of This Memo
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provisions of BCP 78 and BCP 79.
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This Internet-Draft will expire on July 25, 2021.
https://www.rfc-editor.org/info/rfc9017.
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
1.1. Terminology . . . . . . . . . . . . . . . . . . . . . . . 3
2. Background . . . . . . . . . . . . . . . . . . . . . . . . . 3
2.1. GMPLS Special Purpose Special-Purpose Labels . . . . . . . . . . . . . . 3
3. Terminology and Abbreviations . . . . . . . . . . . . . . . . 3
4. Clarification on Handling of the Entropy Label Indicator . . 5
5. Security Considerations . . . . . . . . . . . . . . . . . . . 6
6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 6
7. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 6
8. Contributors . . . . . . . . . . . . . . . . . . . . . . . . 6
9. References . . . . . . . . . . . . . . . . . . . . . . . . . 6
9.1.
7.1. Normative References . . . . . . . . . . . . . . . . . . 7
9.2.
7.2. Informative References . . . . . . . . . . . . . . . . . 7
Acknowledgements
Contributors
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 7
1. Introduction
RFC 7274 [RFC7274] made some changes to the terminology used for MPLS
Special Purpose Labels,
Special-Purpose Labels but did not define consistent terminology.
One thing that RFC 7274 did was to deprecate the use of the term
"reserved labels" when describing a range of labels allocated from a
registry maintained by IANA. The term "Reserved" in such a registry
means "set aside, not to be used", but that range of labels was
available for allocation according to the policies set out in that
registry. The name "Special Purpose "Special-Purpose Labels" was introduced in RFC
7274 in place of the previous term, and the abbreviation SPL "SPL" was
recommended.
At the time of writing the first draft version of this document, the
IETF was in the process of allocating the very first SPLs from the
Extended SPL (eSPL) range [RFC8595]. This document discusses and
recommends terminology and abbreviations to be used when talking
about and documenting Special Purpose Special-Purpose Labels.
This document updates RFC 3032 [RFC3032] and RFC 7274 [RFC7274] in
that it changes the terminology for both Base SPLs (previously
referred to simply as "Special-Purpose Labels") and Extended SPLs.
This document applies that terminology change to the relevant IANA
registry and also clarifies the use of the Entropy Label Indicator
(7) when immediately preceded by the Extension Label (15).
1.1. Terminology
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.
2. Background
Two sets of SPLs are defined for use in MPLS:
* The range of 0-15, Base Special Purpose 0-15 (Base Special-Purpose Labels (bSPLs), (bSPLs) as described
in this document) is specified in RFC 3032 [RFC3032].
* The range 0-1048575 of eSPLs is specified in RFC 7274 [RFC7274].
* the
- The values 0-15 have been reserved and are never to be allocated
* the
allocated.
- The values 16-239 are available for allocation
* the allocation.
- The values 240-255 are for experimental use
* the use.
- The values 256-1048575 are currently not available for
allocation. A standard track Standards Track RFC will would be needed to allocate
any labels from change
this range. rule, and that RFC would need to define the ranges that
are made available for allocation and the registration policy
for those ranges.
2.1. GMPLS Special Purpose Special-Purpose Labels
Note that IANA maintains a registry that is called "Special Purpose "Special-Purpose
Generalized Label Values". Labels in that registry have special
meaning when present in certain signalling signaling objects, are 32 bits long,
and are not to be confused with MPLS forwarding plane forwarding-plane labels. This
document does not make any changes to the GMPLS registry or to how
labels from that registry are described.
3. Terminology and Abbreviations
Prior to the publication of this document, IANA maintains maintained a name
space for 'Special-Purpose "Special-Purpose Multiprotocol Label Switching (MPLS) Label Values'
Values" code points [SPL-NAME-SPACE]. Within this name space space, there
are two registries. One is was called the
'Special-Purpose "Special-Purpose MPLS Label Values'
Values" registry [bSPL]. The other is was called 'Extended Special-Purpose the "Extended Special-
Purpose MPLS Label Values' Values" registry [eSPL].
The difference in the name of the name space and the first registry
is only that the MPLS abbreviation is expanded. This document makes
no change to the name of the name space itself (i.e., "Special-
Purpose Multiprotocol Label Switching (MPLS) Label Values"). This
document changes the name of the first registry to 'Base Special-Purpose "Base Special-
Purpose MPLS Label Values', Values" but leaves the name of the latter registry
unchanged as 'Extended "Extended Special-Purpose MPLS Label Values'. Values".
The following conventions will be used in specifications and when
talking about SPLs.
o
* Collectively, the two (unrelated) ranges (0-15 and 16-1048575) are
known as Special Purpose Labels (SPL).
o Special purpose labels "Special-Purpose Labels" (SPLs).
* SPLs from the range 0-15 are called Base Special
Purpose Labels (bSPL).
o Special purpose labels "Base Special-Purpose Labels"
(bSPLs).
* SPLs from the range 16-1048575 are called
Extended Special "Extended Special-
Purpose Labels (eSPL). Labels" (eSPLs). (Note that the reserved values 0-15 from
the 'Extended "Extended Special-Purpose MPLS Label Values' Values" registry do not
need a name name, as they are not available for allocation and MUST NOT
be used.)
o
* The combination of the Extension Label (XL) (value 15 15, which is a
bSPL,
bSPL and which is also called the xSPL) "xSPL") and an eSPL is called a
Composite Special Purpose Label
"Composite Special-Purpose Label" (cSPL).
This results in a label stacks such as the illustrative examples shown in Figure Figures 1
and Figure 2.
0 31
| MPLS Label Stack entry |
+--------+--------+--------+--------+
| MPLS Label Stack entry |
+--------+--------+--------+--------+
bSPL | Base SPL |
+--------+--------+--------+--------+
| MPLS Label Stack entry (cont.) |
Figure 1: Example of Label Stack
0 31
| MPLS Label Stack entry |
+--------+--------+--------+--------+
| MPLS Label Stack entry |
+--------+--------+--------+--------+
xSPL | Extension Label (XL) | <--+
+--------+--------+--------+--------+ |--- cSPL
eSPL | Extended SPL | <--+
+--------+--------+--------+--------+
| MPLS Label Stack entry (cont.) |
Figure 2: Example of Label Stack
4. Clarification on Handling of the Entropy Label Indicator
Section 3.1 of [RFC7274] contains two paragraphs that describe the
handling of the Entropy Label Indicator (label 7). These paragraphs
have introduced some confusion about whether the Entropy Label
Indicator can be present when immediately preceded by the Extension
Label. This document updates [RFC7274] by replacing those paragraphs
as follows.
OLD
| Values 0-15 of the "Extended Special-Purpose MPLS Label Values"
| registry are set aside as reserved. Furthermore, values 0-6 and
| 8-15 MUST NOT appear in the data plane following an XL; an LSR
| processing a packet with an XL at the top of the label stack
| followed by a label with value 0-6 or 8-15 MUST drop the packet.
|
| Label 7 (when received) retains its meaning as Entropy Label
| Indicator (ELI) whether a regular special-purpose label or an
| ESPL; this is because of backwards compatibility with existing
| implemented and deployed code and hardware that looks for the ELI
| without verifying if the previous label is XL or not. However,
| when an LSR inserts an entropy label, it MUST insert the ELI as a
| regular special-purpose label, not as an ESPL.
NEW
| Values 0-15 of the "Extended Special-Purpose MPLS Label Values"
| registry are set aside as reserved. Furthermore, an
| implementation MUST NOT place a label with a value in the range
| 0-15 in the label stack immediately following an XL; an LSR
| processing a packet with an XL at the top of the label stack
| immediately followed by a label with a value in the range 0-15
| MUST drop the packet.
|
| When inspecting a label stack to find an Entropy Label Indicator
| (ELI - -- label 7) 7), a pre-existing preexisting implementation may fail to inspect
| the previous label, label and so thus not notice that it is an XL. Such
| systems can continue to process the entropy information and
| forward the packet when the previous label is an XL without
| causing harm. However, the packet will be dropped when the XL
| reaches the top of the stack at another LSR.
END
5. Security Considerations
The
This document describes the terminology to be used when describing
and specifying the use of SPLs. It does not effect the affect forwarding in the
MPLS data plane, nor does it have any effect on how LSPs Label Switched
Paths are established by an MPLS control plane or by a centralized
controller.
This document does not aim to describe existing implementations of
SPLs or potential vulnerabilities of SPLs.
6. IANA Considerations
IANA is requested to change has changed the name of the registry that today is once called "Special-Purpose "Special-
Purpose MPLS Label Values" is changed to now be called "Base
Special- Purpose Special-Purpose
MPLS Label Values".
7. Acknowledgements
We like to thank Values" [bSPL].
IANA has also updated the Routing Directorate reviwer Eric Gray for a
detailed, careful and insightful review, and Tom Petch "Base Special-Purpose MPLS Label Values"
registry by changing the description for pointing
out several issues of clarity.
8. Contributors
The following people contributed text value 15 from "Extension
Label" to "Extension Label (XL)" and also adding this document:
Stewart Bryant
Futurewei Technologies Inc.
Email: stewart.bryant@gmail.com
9. document as a
reference.
+=======+======================+====================+
| Value | Description | Reference |
+=======+======================+====================+
| 15 | Extension Label (XL) | RFC 7274, RFC 9017 |
+-------+----------------------+--------------------+
Table 1: Updated Entry for Value 15 in the "Base
Special-Purpose MPLS Label Values" Registry
7. References
9.1.
7.1. Normative References
[bSPL] "Special-Purpose IANA, "Base Special-Purpose MPLS Label Values",
<https://www.iana.org/assignments/mpls-label-values/mpls-
label-values.xhtml#special-purpose/>.
<https://www.iana.org/assignments/mpls-label-values/>.
[eSPL] IANA, "Extended Special-Purpose MPLS Label Values",
<https://www.iana.org/assignments/mpls-label-values/mpls-
label-values.xhtml#extended/>.
<https://www.iana.org/assignments/mpls-label-values/>.
[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>.
[RFC3032] Rosen, E., Tappan, D., Fedorkow, G., Rekhter, Y.,
Farinacci, D., Li, T., and A. Conta, "MPLS Label Stack
Encoding", RFC 3032, DOI 10.17487/RFC3032, January 2001,
<https://www.rfc-editor.org/info/rfc3032>.
[RFC7274] Kompella, K., Andersson, L., and A. Farrel, "Allocating
and Retiring Special-Purpose MPLS Labels", RFC 7274,
DOI 10.17487/RFC7274, June 2014,
<https://www.rfc-editor.org/info/rfc7274>.
[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>.
[SPL-NAME-SPACE]
IANA, "Special-Purpose Multiprotocol Label Switching
(MPLS) Label Values", <https://www.iana.org/assignments/mpls-
label-values/mpls-label-values.xhtml/>.
9.2.
<https://www.iana.org/assignments/mpls-label-values/>.
7.2. Informative References
[RFC8595] Farrel, A., Bryant, S., and J. Drake, "An MPLS-Based
Forwarding Plane for Service Function Chaining", RFC 8595,
DOI 10.17487/RFC8595, June 2019,
<https://www.rfc-editor.org/info/rfc8595>.
Acknowledgements
We would like to thank the Routing Directorate reviewer, Eric Gray,
for a detailed, careful, and insightful review, and Tom Petch for
pointing out several issues of clarity.
Contributors
The following individual contributed text to this document:
Stewart Bryant
Futurewei Technologies Inc.
Email: stewart.bryant@gmail.com
Authors' Addresses
Loa Andersson
Bronze Dragon Consulting
Email: loa@pi.nu
Kireeti Kompella
Juniper Networks
Email: kireeti@juniper.net
Adrian Farrel
Old Dog Consulting
Email: adrian@olddog.co.uk