wdiff rfc7274.original rfc7274.txt

Network Working Group
Internet Engineering Task Force (IETF) K. Kompella
Internet-Draft
Request for Comments: 7274 Juniper Networks
Updates: 3032, 3038, 3209, 3811, 4182, 4928, 5331, L. Andersson
5586, 5921, 5960, 6391, 6478, 6790 (if approved) Huawei
A. Farrel
Intended status:
Category: Standards Track A. Farrel
ISSN: 2070-1721 Juniper Networks
Expires: Septmeber 18, 2014 March 18,
June 2014

Allocating and Retiring Special Purpose Special-Purpose MPLS Labels
draft-ietf-mpls-special-purpose-labels-06

Abstract

Some MPLS labels have been allocated for specific purposes. A block
of labels (0-15) has been set aside to this end, and end; these labels are
commonly called "reserved labels". They will be called "special "special-
purpose labels" in this document.

As there are only 16 of these special purpose special-purpose labels, caution is
needed in the allocation of new special purpose labels, yet special-purpose labels; yet, at the
same time allow time, forward progress should be allowed when one is called for.

This memo defines new procedures to follow in for the allocation and retirement of special purpose
special-purpose labels, as well as a method to extend the special special-
purpose label space. space and a description of how to handle extended
special-purpose labels in the data plane. Finally, this memo renames
the IANA registry for these special-purpose labels to "Special Purpose "Special-Purpose MPLS
Label Values", Values" and creates a new one registry called the "Extended Special Purpose
Special-Purpose MPLS Label Values" registry.

This document updates a number of previous RFCs that used use the term
"reserved label". Specifically, this document updates RFC RFCs 3032, RFC
3038, RFC 3209, RFC 3811, RFC 4182, RFC 4928, RFC 5331, RFC 5586, RFC 5921, RFC 5960, RFC 6391, RFC 6478, and RFC
6790.

Status of this This Memo

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

Internet-Drafts are working documents an Internet Standards Track document.

This document is a product of the Internet Engineering Task Force
(IETF). Note that other groups may also distribute
working documents as Internet-Drafts. The list It represents the consensus of current Internet-
Drafts is at http://datatracker.ietf.org/drafts/current/.

Internet-Drafts are draft documents valid the IETF community. It has
received public review and has been approved for a maximum publication by the
Internet Engineering Steering Group (IESG). Further information on
Internet Standards is available in Section 2 of six months RFC 5741.

Information about the current status of this document, any errata,
and how to provide feedback on it may be updated, replaced, or obsoleted by other documents obtained 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 September 18, 2014.
http://www.rfc-editor.org/info/rfc7274.

This document is subject to BCP 78 and the IETF Trust's Legal
Provisions Relating to IETF Documents
(http://trustee.ietf.org/license-info) in effect on the date of
publication of this document. Please review these documents
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described in the Simplified BSD License.

Table of Contents

1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3 ....................................................3
1.1. Conventions used . . . . . . . . . . . . . . . . . . . . . 3 Used in This Document ..........................3
2. Questions . . . . . . . . . . . . . . . . . . . . . . . . . . 4 .......................................................3
3. Answers . . . . . . . . . . . . . . . . . . . . . . . . . . . 5 .........................................................4
3.1. Extended Special Purpose Special-Purpose MPLS Label Values . . . . . . . . 6 .................5
3.2. Process for Retiring Special Purpose Special-Purpose Labels . . . . . . . 7 ................6
4. Updated RFCs . . . . . . . . . . . . . . . . . . . . . . . . . 8 ....................................................7
5. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 9 .............................................8
6. Security Considerations . . . . . . . . . . . . . . . . . . . 10 .........................................8
7. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 10 .................................................9
8. References . . . . . . . . . . . . . . . . . . . . . . . . . . 11 ......................................................9
8.1. Normative References . . . . . . . . . . . . . . . . . . . 11 .......................................9
8.2. Informational Informative References . . . . . . . . . . . . . . . . . 12
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 13 ....................................10

1. Introduction

The specification of the MPLS Label Stack Encoding for Multi-Protocol
Label Switching (MPLS) specification [RFC3032] defined four special purpose
special-purpose label values (0 to 3), 3) and set aside values 4 through
15 for future use. These labels have special significance in both
the control and the data plane. Since then, three further values
have been allocated (values 7, 13, and 14 in [RFC6790], [RFC5586] [RFC5586],
and [RFC3429], respectively), leaving nine unassigned values from the
original space of sixteen.

While the allocation of three out of the remaining twelve special special-
purpose label values in the space of about 12 years is not in itself
a cause for concern, the scarcity of special purpose special-purpose labels is.
Furthermore, many of the special purpose special-purpose labels require special
processing by forwarding hardware, changes to which are often
expensive,
expensive and sometimes impossible. Thus, documenting a newly
allocated special purpose special-purpose label value is important.

This memo outlines some of the issues in allocating and retiring
special purpose
special-purpose label values, values and defines mechanisms to address these.
This memo also extends the space of special purpose special-purpose labels.

1.1. Conventions used Used in This Document

The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in [RFC2119].

Two new acronyms are introduced:

XL The Extension Label Label. A label that indicates that an extended special
purpose
special-purpose label follows.

ESPL An Extended Special Purpose Special-Purpose Label. A Special Purpose Label special-purpose label that
is placed in the label stack after the Extension Label. The
combination of XL and ESPL might be regarded as a new form of
"compound label" comprising more than one consecutive entry in
the label stack.

2. Questions

In re-appraising MPLS special purpose special-purpose labels, the following questions
come to mind:

1. What allocation policies should be applied by IANA for the
allocation of special purpose special-purpose labels? Should Early Allocation
[RFC7120] be allowed? Should there be labels for Experimental
Use experimental
use or Private Use private use [RFC5226]?
2. What documentation is required for special purpose special-purpose labels
allocated henceforth?

3. Should a special purpose special-purpose label ever be retired? What criteria
are relevant here? Can a retired special purpose special-purpose label ever be
re-allocated for a different purpose? What procedures and time
frames are appropriate?

4. The special purpose special-purpose label value of 3 (the "Implicit Null Label", NULL Label"
[RFC3032]) is only used in signaling, never in the data plane.
Could it (and should it) be used in the data plane? If so, how
and for what purpose?

5. What is a feasible mechanism to extend the space of special special-
purpose labels, labels should this become necessary?

6. Should extended special purpose special-purpose labels be used for load
balancing?

3. Answers

This section provides answers to the questions posed in the previous
section.

A. Allocation of special purpose special-purpose MPLS labels is via "Standards
Action".

B. The IANA registry will be renamed "Special Purpose "Special-Purpose MPLS
Labels". Label
Values".

C. Early allocation may be allowed on a case-by-case basis.

D. The current space of 16 special purpose special-purpose labels is too small
for setting aside values for experimental or private use.
However, the extended special purpose labels "Extended Special-Purpose MPLS Label Values"
registry created by this document has enough space, and this
document defines a range for experimental use.

2. A Standards Track RFC must accompany a request for allocation of
Standards Action special purpose special-purpose labels, as per [RFC5226].

3. The retirement of a special purpose special-purpose MPLS label value must follow
a strict and well-documented process. This is necessary since we
must avoid orphaning the use of this label value in existing
deployments. This process is detailed in Section 3.2.

4. For now, the use of the "implicit null label" (label "Implicit NULL Label" (value 3) in the
data plane will not be allowed. If this decision is revisited
later, an accompanying Standards Track RFC that details the use
of the label, a discussion of possible sources of confusion
between signaling and data plane, and mitigation thereof shall be
required.

5. A special purpose special-purpose label (the "extension" label, "Extension Label", XL, label value 15) is
set aside for the purpose of extending the space of special special-
purpose labels. Further details are described in Section 3.1.

6. [RFC6790] says that special purpose special-purpose labels MUST NOT be used for
load balancing. The same logic applies to extended special special-
purpose labels (ESPLs). Thus, this document specifies that ESPLs
MUST NOT be used for load balancing. It is noted that existing
implementations would violate this, as they do not recognize XL
as anything other than a single Special Purpose Label special-purpose label and will
not expect an ESPL to follow. The consequence is that if ESPLs
are used in some packets of a flow, these packets may be
delivered on different paths and so could be re-ordered.
However, it is important to specify the correct behavior for
future implementations, hence the use of "MUST NOT".

A further question that needed to be settled in this regard was
whether a "regular" special purpose special-purpose label retains its meaning if it
follows the XL. The answer to this question is provided in
Section 3.1.

3.1. Extended Special Purpose Special-Purpose MPLS Label Values

The XL MUST be followed by another label L (and thus MUST have the
bottom-of-stack bit clear). L MUST be interpreted as an ESPL and
interpreted as defined in a new registry created by this document
(see Section 5). Whether or not L has the bottom-of-stack bit set
depends on whether other labels follow L. The XL only assigns
special meaning to L. A label after L (if any) is parsed as usual, usual
and thus may be a regular label or a special purpose special-purpose label; if the
latter, it may be the XL, XL and thus followed by another ESPL.

The label value 15 is set aside as the XL as shown in Section 5.

Values 0-6 and 8-15 0-15 of the Extended Special Purpose "Extended Special-Purpose MPLS Label Values"
registry are set aside as reserved; these reserved. Furthermore, values 0-6 and 8-15
MUST NOT appear in the data plane.
If plane following an XL; an LSR encounters such ESPL values it 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 treat drop the packet as
malformed and discard it per [RFC3031]. packet.

Label 7 (when received) retains its meaning as ELI Entropy Label
Indicator (ELI) whether a regular
special purpose 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 insert
inserts an entropy label label, it MUST insert the ELI as a regular special purpose
special-purpose label, not as an ESPL.

3.1.1. Forwarding Packets with Extended Special Purpose Special-Purpose Labels

If an LSR encounters the XL at the top of stack and it doesn't
understand extension labels, it SHOULD MUST drop the packet as specified for
the handling of any unknown an invalid incoming label according to [RFC3031]. If
an LSR encounters an ESPL at the top of stack (after the XL) and that it
does not understand the ESPL, understand, it SHOULD MUST drop the packet, again following the procedures for unknown labels as set out in [RFC3031].
same procedure. In either case, the LSR MAY log the event, but such
logging MUST be rate-
limited. rate-limited.

An LSR SHOULD NOT make forwarding decisions on labels not at the top
of stack. For load balancing load-balancing decisions, see Answer 6 of in Section 3.

3.1.2. Choosing a New Special Purpose Special-Purpose Label

When allocating a new Special Purpose Label, special-purpose label, protocol designers
should consider whether they could use an Extended Special Purpose
Label. extended special-purpose
label. Doing so would help to preserve the scarce resources of
"normal" Special Purpose Labels special-purpose labels for use in cases where minimizing the
size of the label stack size is particularly important.

3.2. Process for Retiring Special Purpose Special-Purpose Labels

While the following process is defined for the sake of completeness,
note that retiring special purpose special-purpose labels is difficult. It is
recommended that this process be used sparingly.

a. A label value that has been assigned from the "Special Purpose "Special-Purpose
MPLS Label Values" registry may be deprecated by IETF consensus
with review by the MPLS working group (or designated experts if
the working group or a successor does not exist). An RFC with at
least Informational status is required.

The RFC will direct the IANA to mark the label value as "deprecated"
in the registry, registry but will not release it at this stage.

Deprecating means that no further specifications using the
deprecated value will be documented.

At the same time time, this is an indication to vendors not to include
the deprecated value in new implementations, implementations and to operators to
avoid including it in new deployments.

b. 12 Twelve months after the RFC deprecating the label value is
published, an IETF-wide survey may be conducted to determine if
the deprecated label value is still in use. If the survey
indicates that the deprecated label value is in use, the survey
may be repeated after a further an additional 6 months.

c. 24 months after the RFC that deprecated the label value was
published and if If the survey indicates that a deprecated label value is not in
use, 24 months after the RFC that deprecated the label value was
published, publication may be requested of an IETF Standards
Track Internet-Draft that retires the deprecated the label value.
This document will request that IANA to release the label value for
future use and assignment.

4. Updated RFCs

The following RFCs contain references to the term "reserved labels":

o [RFC3032] ("MPLS Label Stack Encoding"), Encoding")
o [RFC3038] ("VCID Notification over ATM link for LDP")
o [RFC3209] ("Extensions ("RSVP-TE: Extensions to RSVP for LSP Tunnels")
o [RFC3811] ("MPLS TC MIB") ("Definitions of Textual Conventions (TCs) for
Multiprotocol Label Switching (MPLS) Management")
o [RFC4182] ("Removing a Restriction on the use of MPLS") MPLS Explicit
NULL")
o [RFC4928] ("Avoiding ECMP Equal Cost Multipath Treatment in MPLS
Networks")
o [RFC5331], [RFC5586] ("G-ACh [RFC5331] ("MPLS Upstream Label Assignment and GAL") Context-Specific
Label Space")
o [RFC5921] [RFC5586] ("MPLS Generic Associated Channel")
o [RFC5921] ("A Framework for MPLS in Transport Profile Framework") Networks")
o [RFC5960] ("MPLS-TP ("MPLS Transport Profile Data Plane Architecture")
o [RFC6391] ("FAT-PW") ("Flow-Aware Transport of Pseudowires over an MPLS
Packet Switched Network")
o [RFC6478] ("Pseudowire Status for Static Pseudowires")
o [RFC6790] ("MPLS Entropy Labels"). Labels")

All such references should be read as "special purpose "special-purpose labels".

5. IANA Considerations

This document requests

IANA to make has made the following changes and additions to its registration
of MPLS Labels. labels.

1. Change Changed the name of the "Multiprotocol Label Switching
Architecture (MPLS) Label Values" registry to the "Special
Purpose "Special-Purpose
MPLS Label Values".

2. Change Changed the allocations allocation policy for the "Special Purpose "Special-Purpose MPLS Label
Values" registry to Standards Action.

3. Assign label Assigned value 15 from the "Special Purpose "Special-Purpose MPLS Label Values"
registry, naming it the "extension label", "Extension Label" and citing this
document as the reference.

4. Create Created a new registry called the "Extended Special Purpose Special-Purpose MPLS
Label Values" registry. The ranges registration procedure is Standards
Action, and allocation policies the ranges for this registry are as follows shown in Table 1
(using terminology from [RFC5226]). Early allocation following
the policy defined in [RFC7120] is allowed only for those values
assigned by Standards Action.

+---------------------+---------------------------------------------+
| Range | Allocation Policy |
+---------------------+---------------------------------------------+
| 0 - 15 | Reserved. Not Never to be allocated. made available for |
| | allocation. |
| | |
| 16 - 239 | Standards Action Unassigned |
| | |
| 240 - 255 | Reserved for Experimental Use |
| | |
| 256 - 1048575 | Reserved. Not to be allocated made available for |
| | allocation without a new Standards Track |
| | Standards Track RFC to define an allocation |
| | policy. |
+---------------------+---------------------------------------------+

Table 1

6. Security Considerations

This document does not make a large change to the operation of the
MPLS data plane plane, and security considerations are largely unchanged
from those specified in the MPLS architecture Architecture [RFC3031] and in the
MPLS and GMPLS Security Framework [RFC5920].

However, it should be noted that increasing the label stack can cause
packet fragmentation and may also make packets unprocessable by some
implementations. This document provides a protocol-legal way to
increase the label stack through the insertion of additional
{XL,ESPL} pairs at a greater rate than insertion of single "rogue"
labels. This might provide a way to attack some nodes in a network
that can only process label stacks of a certain size without
violating the protocol rules.

This document also describes events that may cause an LSR to issue
event logs at a per-packet rate. It is critically important that
implementations rate-limit such logs.

7. Acknowledgments

Thanks to Pablo Frank and Lizhong Jin for useful discussions. Thanks
to Curtis Villamizar, Mach Chen, Alia Atlas, Eric Rosen, Maria
Napierala, Roni Even, Stewart Bryant, John Drake, Andy Malis, and Tom
Yu for useful comments.

8. References

8.1. Normative References

[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.

[RFC3031] Rosen, E., Viswanathan, A., and R. Callon, "Multiprotocol
Label Switching Architecture", RFC 3031, January 2001.

[RFC3032] Rosen, E., Tappan, D., Fedorkow, G., Rekhter, Y.,
Farinacci, D., Li, T., and A. Conta, "MPLS Label Stack
Encoding", RFC 3032, January 2001.

[RFC3038] Nagami, K., Katsube, Y., Demizu, N., Esaki, H., and P.
Doolan, "VCID Notification over ATM link for LDP", RFC
3038, January 2001.

[RFC3209] Awduche, D., Berger, L., Gan, D., Li, T., Srinivasan, V.,
and G. Swallow, "RSVP-TE: Extensions to RSVP for LSP
Tunnels", RFC 3209, December 2001.

[RFC3811] Nadeau, T. T., Ed., and J. Cucchiara, Ed., "Definitions of
Textual Conventions (TCs) for Multiprotocol Label
Switching (MPLS) Management", RFC 3811, June 2004.

[RFC4182] Rosen, E., "Removing a Restriction on the use of MPLS
Explicit NULL", RFC 4182, September 2005.

[RFC4928] Swallow, G., Bryant, S., and L. Andersson, "Avoiding Equal
Cost Multipath Treatment in MPLS Networks", BCP 128, RFC
4928, June 2007.

[RFC5226] Narten, T. and H. Alvestrand, "Guidelines for Writing an
IANA Considerations Section in RFCs", BCP 26, RFC 5226,
May 2008.

[RFC5331] Aggarwal, R., Rekhter, Y., and E. Rosen, "MPLS Upstream
Label Assignment and Context-Specific Label Space", RFC
5331, August 2008.

[RFC5960] Frost, D., Ed., Bryant, S., Ed., and M. Bocci, Ed., "MPLS
Transport Profile Data Plane Architecture", RFC 5960,
August 2010.

[RFC6391] Bryant, S., Ed., Filsfils, C., Drafz, U., Kompella, V.,
Regan, J., and S. Amante, "Flow-Aware Transport of
Pseudowires over an MPLS Packet Switched Network", RFC
6391, November 2011.

[RFC6478] Martini, L., Swallow, G., Heron, G., and M. Bocci,
"Pseudowire Status for Static Pseudowires", RFC 6478, May
2012.

[RFC6790] Kompella, K., Drake, J., Amante, S., Henderickx, W., and
L. Yong, "The Use of Entropy Labels in MPLS Forwarding",
RFC 6790, November 2012.

[RFC7120] Cotton, M., "Early IANA Allocation of Standards Track Code
Points", BCP 100, RFC 7120, January 2014.

8.2. Informational Informative References

[RFC3429] Ohta, H., "Assignment of the 'OAM Alert Label' for
Multiprotocol Label Switching Architecture (MPLS)
Operation and Maintenance (OAM) Functions", RFC 3429,
November 2002.

[RFC5586] Bocci, M., Ed., Vigoureux, M., Ed., and S. Bryant, Ed.,
"MPLS Generic Associated Channel", RFC 5586, June 2009.

[RFC5920] Fang, L., Ed., "Security Framework for MPLS and GMPLS
Networks", RFC 5920, July 2010.

[RFC5921] Bocci, M., Ed., Bryant, S., Ed., Frost, D., Ed., Levrau,
L., and L. Berger, "A Framework for MPLS in Transport
Networks", RFC 5921, July 2010.

Authors' Addresses

Kireeti Kompella
Juniper Networks
1194 N. Mathilda Ave
Sunnyvale, CA 94089
US

Email:

EMail: kireeti.kompella@gmail.com

Loa Andersson
Huawei

Email:

EMail: loa@mail01.huawei.com

Adrian Farrel
Juniper Networks

Email:

EMail: adrian@olddog.co.uk