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2 MPLS Working Group L. Andersson
3 Internet-Draft Bronze Dragon Consulting
4 Updates: 3032, 7274 (if approved) K. Kompella
5 Intended status: Standards Track Juniper Networks
6 Expires: March 28, 2021 A. Farrel
7 Old Dog Consulting
8 September 24, 2020
10 Special Purpose Label terminology
11 draft-ietf-mpls-spl-terminology-04
13 Abstract
15 This document discusses and recommends a terminology that may be used
16 when MPLS Special Purpose Labels (SPL) are specified and documented.
18 This document applies that terminology change to the relevant IANA
19 registry and also clarifies the use of the Entropy Label Indicator
20 (7) when immediately preceded by the Extension Label (15).
22 This document updates RFC 7274 and RFC 3032.
24 Status of This Memo
26 This Internet-Draft is submitted in full conformance with the
27 provisions of BCP 78 and BCP 79.
29 Internet-Drafts are working documents of the Internet Engineering
30 Task Force (IETF). Note that other groups may also distribute
31 working documents as Internet-Drafts. The list of current Internet-
32 Drafts is at https://datatracker.ietf.org/drafts/current/.
34 Internet-Drafts are draft documents valid for a maximum of six months
35 and may be updated, replaced, or obsoleted by other documents at any
36 time. It is inappropriate to use Internet-Drafts as reference
37 material or to cite them other than as "work in progress."
39 This Internet-Draft will expire on March 28, 2021.
41 Copyright Notice
43 Copyright (c) 2020 IETF Trust and the persons identified as the
44 document authors. All rights reserved.
46 This document is subject to BCP 78 and the IETF Trust's Legal
47 Provisions Relating to IETF Documents
48 (https://trustee.ietf.org/license-info) in effect on the date of
49 publication of this document. Please review these documents
50 carefully, as they describe your rights and restrictions with respect
51 to this document. Code Components extracted from this document must
52 include Simplified BSD License text as described in Section 4.e of
53 the Trust Legal Provisions and are provided without warranty as
54 described in the Simplified BSD License.
56 Table of Contents
58 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
59 1.1. Terminology . . . . . . . . . . . . . . . . . . . . . . . 3
60 2. Background . . . . . . . . . . . . . . . . . . . . . . . . . 3
61 2.1. GMPLS Special Purpose Labels . . . . . . . . . . . . . . 3
62 3. Terminology and Abbreviations . . . . . . . . . . . . . . . . 3
63 4. Clarification on Use of Entropy Label Indicator . . . . . . . 5
64 5. Security Considerations . . . . . . . . . . . . . . . . . . . 6
65 6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 6
66 7. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 6
67 8. Contributors . . . . . . . . . . . . . . . . . . . . . . . . 6
68 9. References . . . . . . . . . . . . . . . . . . . . . . . . . 7
69 9.1. Normative References . . . . . . . . . . . . . . . . . . 7
70 9.2. Informative References . . . . . . . . . . . . . . . . . 7
71 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 7
73 1. Introduction
75 RFC 7274 [RFC7274] made some changes to the terminology used for MPLS
76 Special Purpose Labels, but did not define consistent terminology.
78 One thing that RFC 7274 did was to deprecate use of the term
79 "reserved labels" when describing a range of labels allocated from a
80 registry maintained by IANA. The term "Reserved" in such a registry
81 means "set aside, not to be used", but that range of labels was
82 available for allocation according to the policies set out in that
83 registry. The name "Special Purpose Labels" was introduced in RFC
84 7274 in place of the previous term, and the abbreviation SPL was
85 recommended.
87 At the time of writing the first version of this document, the IETF
88 was in the process of allocating the very first SPLs from the
89 Extended SPL (eSPL) range [RFC8595]. This document discusses and
90 recommends terminology and abbreviations to be used when talking
91 about and documenting Special Purpose Labels.
93 This document updates RFC 3032 [RFC3032] and RFC 7274 [RFC7274] in
94 that it changes the terminology for both Base SPLs and Extended SPLs.
96 This document applies that terminology change to the relevant IANA
97 registry and also clarifies the use of the Entropy Label Indicator
98 (7) when immediately preceded by the Extension Label (15).
100 1.1. Terminology
102 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
103 "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and
104 "OPTIONAL" in this document are to be interpreted as described in BCP
105 14 [RFC2119] [RFC8174] when, and only when, they appear in all
106 capitals, as shown here.
108 2. Background
110 Two sets of SPLs are defined for use in MPLS:
112 The range of 0-15, Base Special Purpose Labels (bSPLs), is
113 specified in RFC 3032 [RFC3032].
115 The range 0-1048575 of eSPLs is specified in RFC 7274 [RFC7274].
117 * the values 0-15 have been reserved never to be allocated
119 * the values 16-239 are available for allocation
121 * the values 240-255 are for experimental use
123 * the values 256-1048575 are currently not available for
124 allocation. A standard track RFC will be needed to allocate
125 any labels from this range.
127 2.1. GMPLS Special Purpose Labels
129 Note that IANA maintains a registry called "Special Purpose
130 Generalized Label Values". Labels in that registry have special
131 meaning when present in certain signalling objects, are 32 bits long,
132 and are not to be confused with MPLS forwarding plane labels. This
133 document does not make any changes to the GMPLS registry or to how
134 labels from that registry are described.
136 3. Terminology and Abbreviations
138 IANA maintains a name space for 'Special-Purpose Multiprotocol Label
139 Switching (MPLS) Label Values' code points [SPL-NAME-SPACE]. Within
140 this name space there are two registries. One is called the
141 'Special-Purpose MPLS Label Values' registry [bSPL]. The other is
142 called 'Extended Special-Purpose MPLS Label Values' registry [eSPL].
144 The difference in the name of the name space and the first registry
145 is only that the MPLS abbreviation is expanded. This document
146 changes the name of the first registry to 'Base Special-Purpose MPLS
147 Label Values', but leaves the name of the latter registry unchanged
148 as 'Extended Special-Purpose MPLS Label Values'.
150 The following conventions will be used in specifications and when
151 talking about SPLs.
153 o Collectively, the two (unrelated) ranges (0-15 and 16-1048575) are
154 known as Special Purpose Labels (SPL).
156 o Special purpose labels from the range 0-15 are called Base Special
157 Purpose Labels (bSPL).
159 o Special purpose labels from the range 16-1048575 are called
160 Extended Special Purpose Labels (eSPL). (Note that the reserved
161 values 0-15 from the 'Extended Special-Purpose MPLS Label Values'
162 registry do not need a name as they are not available for
163 allocation and MUST NOT be used.)
165 This results in a label stacks such as the illustrative examples
166 shown in Figure 1 and Figure 2.
168 0 31
169 | MPLS Label Stack entry |
170 +--------+--------+--------+--------+
171 | MPLS Label Stack entry |
172 +--------+--------+--------+--------+
173 bSPL | Base SPL |
174 +--------+--------+--------+--------+
175 | MPLS Label Stack entry (cont.) |
177 Figure 1: Example of Label Stack
179 0 31
180 | MPLS Label Stack entry |
181 +--------+--------+--------+--------+
182 | MPLS Label Stack entry |
183 +--------+--------+--------+--------+
184 xSPL | Extension Label (XL) | <--+
185 +--------+--------+--------+--------+ |--- cSPL
186 eSPL | Extended SPL | <--+
187 +--------+--------+--------+--------+
188 | MPLS Label Stack entry (cont.) |
190 Figure 2: Example of Label Stack
192 4. Clarification on Use of Entropy Label Indicator
194 Section 3.1 of [RFC7274] contains two paragraphs that describe the
195 use of the Entropy Label Indicator (label 7). These paragraphs have
196 introduced some confusion about whether the Entropy Label Indicator
197 can be present when immediately preceded by the Extension Label.
198 This document updates [RFC7274] by replacing those paragraphs as
199 follows.
201 OLD
203 Values 0-15 of the "Extended Special-Purpose MPLS Label Values"
204 registry are set aside as reserved. Furthermore, values 0-6 and
205 8-15 MUST NOT appear in the data plane following an XL; an LSR
206 processing a packet with an XL at the top of the label stack
207 followed by a label with value 0-6 or 8-15 MUST drop the packet.
209 Label 7 (when received) retains its meaning as Entropy Label
210 Indicator (ELI) whether a regular special-purpose label or an
211 ESPL; this is because of backwards compatibility with existing
212 implemented and deployed code and hardware that looks for the ELI
213 without verifying if the previous label is XL or not. However,
214 when an LSR inserts an entropy label, it MUST insert the ELI as a
215 regular special-purpose label, not as an ESPL.
217 NEW
219 Values 0-15 of the "Extended Special-Purpose MPLS Label Values"
220 registry are set aside as reserved. Furthermore, an
221 implementation MUST NOT place a label with value 0-15 in the label
222 stack immediately following an XL; an LSR processing a packet with
223 an XL at the top of the label stack immediately followed by a
224 label with value 0-15 MUST drop the packet.
226 When inspecting a label stack to find an Entropy Label Indicator
227 (ELI - label 7) a pre-existing implementation may fail to inspect
228 the previous label, and so not notice that it is an XL. Such
229 systems can continue to process the entropy information and
230 forward the packet when the previous label is an XP without
231 causing harm. However, the packet will be dropped when the XL
232 reaches the top of the stack at another LSR.
234 END
236 5. Security Considerations
238 The document describes the terminology to be used when describing and
239 specifying the use of SPLs. It does not effect the forwarding in the
240 MPLS data plane, nor does it have any effect on how LSPs are
241 established by an MPLS control plane or by a centralized controller.
243 This document does not aim to describe existing implementations of
244 SPLs or potential vulnerabilities of SPLs.
246 6. IANA Considerations
248 IANA is requested to change the name of the registry that today is
249 called "Special-Purpose MPLS Label Values" is changed to "Base
250 Special- Purpose MPLS Label Values".
252 7. Acknowledgements
254 We like to thank the Routing Directorate reviwer Eric Gray for a
255 detailed, careful and insightful review, and Tom Petch for pointing
256 out several issues of clarity.
258 8. Contributors
260 The following people contributed text to this document:
262 Stewart Bryant
263 Futurewei Technologies Inc.
265 Email: stewart.bryant@gmail.com
267 Figure 3
269 9. References
271 9.1. Normative References
273 [bSPL] "Special-Purpose MPLS Label Values",
274 .
277 [eSPL] "Extended Special-Purpose MPLS Label Values",
278 .
281 [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
282 Requirement Levels", BCP 14, RFC 2119,
283 DOI 10.17487/RFC2119, March 1997,
284 .
286 [RFC3032] Rosen, E., Tappan, D., Fedorkow, G., Rekhter, Y.,
287 Farinacci, D., Li, T., and A. Conta, "MPLS Label Stack
288 Encoding", RFC 3032, DOI 10.17487/RFC3032, January 2001,
289 .
291 [RFC7274] Kompella, K., Andersson, L., and A. Farrel, "Allocating
292 and Retiring Special-Purpose MPLS Labels", RFC 7274,
293 DOI 10.17487/RFC7274, June 2014,
294 .
296 [RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC
297 2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174,
298 May 2017, .
300 [SPL-NAME-SPACE]
301 "Special-Purpose Multiprotocol Label Switching (MPLS)
302 Label Values", .
305 9.2. Informative References
307 [RFC8595] Farrel, A., Bryant, S., and J. Drake, "An MPLS-Based
308 Forwarding Plane for Service Function Chaining", RFC 8595,
309 DOI 10.17487/RFC8595, June 2019,
310 .
312 Authors' Addresses
313 Loa Andersson
314 Bronze Dragon Consulting
316 Email: loa@pi.nu
318 Kireeti Kompella
319 Juniper Networks
321 Email: kireeti@juniper.net
323 Adrian Farrel
324 Old Dog Consulting
326 Email: adrian@olddog.co.uk