LDP FEC Advertisement: Label Advertisement Discipline for LDP Forwarding Equivalence Classes (FECs)
Clarifies that the kind of FEC, not just the session's negotiated mode, decides how an LDP speaker advertises labels.
Raza, K., Boutros, S., Martini, L., and N. Leymann, "Label Advertisement Discipline for LDP Forwarding Equivalence Classes (FECs)", RFC 7358, DOI 10.17487/RFC7358, October 2014, <https://www.rfc-editor.org/info/rfc7358>.
@misc{rfc7358,
series = {Request for Comments},
number = 7358,
howpublished = {RFC 7358},
publisher = {RFC Editor},
doi = {10.17487/RFC7358},
url = {https://www.rfc-editor.org/info/rfc7358},
author = {K. Raza and S. Boutros and L. Martini and N. Leymann},
title = {{Label Advertisement Discipline for LDP Forwarding Equivalence Classes (FECs)}},
pagetotal = 8,
year = 2014,
month = oct,
} RFC text
Contents
Internet Engineering Task Force (IETF) K. Raza
Request for Comments: 7358 S. Boutros
Updates: 3212, 4447, 5036, 5918, 6388, 7140 L. Martini
Category: Standards Track Cisco Systems, Inc.
ISSN: 2070-1721 N. Leymann
Deutsche Telekom
October 2014
Label Advertisement Discipline
for LDP Forwarding Equivalence Classes (FECs)
Abstract
The label advertising behavior of an LDP speaker for a given
Forwarding Equivalence Class (FEC) is governed by the FEC type and
not necessarily by the LDP session's negotiated label advertisement
mode. This document updates RFC 5036 to make that fact clear. It
also updates RFCs 3212, 4447, 5918, 6388, and 7140 by specifying the
label advertisement mode for all currently defined LDP FEC types.
Status of This Memo
This is an Internet Standards Track document.
This document is a product of the Internet Engineering Task Force
(IETF). It represents the consensus of the IETF community. It has
received public review and has been approved for publication by the
Internet Engineering Steering Group (IESG). Further information on
Internet Standards is available in Section 2 of RFC 5741.
Information about the current status of this document, any errata,
and how to provide feedback on it may be obtained at
http://www.rfc-editor.org/info/rfc7358.
Copyright Notice
Copyright (c) 2014 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
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
carefully, as they describe your rights and restrictions with respect
to this document. Code Components extracted from this document must
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
2. Label Advertisement Discipline ..................................3
2.1. Update to RFC 5036 .........................................3
2.2. Specification for LDP FECs .................................4
3. Security Considerations .........................................4
4. IANA Considerations .............................................4
5. References ......................................................6
5.1. Normative References .......................................6
5.2. Informative References .....................................7
Acknowledgments ....................................................8
Authors' Addresses .................................................8
1. Introduction
The Label Distribution Protocol (LDP) [RFC5036] allows label
advertisement mode negotiation at the time of session establishment.
The LDP specification also dictates that only a single label
advertisement mode be negotiated, agreed upon, and used for a given
LDP session between two Label Switching Routers (LSRs).
The negotiated label advertisement mode defined in RFC 5036 and
carried in the LDP Initialization message is only indicative. It
indicates how the LDP speakers on a session will advertise labels for
some Forwarding Equivalence Classes (FECs), but it is not a rule that
restricts the speakers to behave in a specific way. Furthermore, for
some FEC types the advertising behavior of the LDP speaker is
governed by the FEC type and not by the negotiated behavior.
This document updates [RFC5036] to make that fact clear. It also
updates [RFC3212], [RFC4447], [RFC5918], [RFC6388], and [RFC7140] to
indicate, for each FEC type that has already been defined, whether
the label binding advertisements for the FEC are constrained by the
negotiated label advertisement mode or not. Furthermore, this
document specifies the label advertisement mode to be used for all
currently defined FECs.
2. Label Advertisement Discipline
To remove any ambiguity and conflict regarding a label advertisement
discipline among different FEC types sharing a common LDP session,
this document specifies a label advertisement discipline for FEC
types.
This document introduces the following types for specifying a label
advertisement discipline for a FEC type:
- DU (Downstream Unsolicited)
- DoD (Downstream on Demand)
- As negotiated (DU or DoD)
- Upstream ([RFC6389])
- Not applicable
- Unknown
2.1. Update to RFC 5036
Section 3.5.3 of [RFC5036] is updated to add the following two
statements under the description of "A, Label Advertisement
Discipline":
- Each document defining an LDP FEC must state the applicability of
the negotiated label advertisement discipline for label binding
advertisements for that FEC. If the negotiated label
advertisement discipline does not apply to the FEC, the document
must also explicitly state the discipline to be used for the FEC.
- This document defines the label advertisement discipline for the
following FEC types:
+----------+----------+--------------------------------+
| FEC Type | FEC Name | Label Advertisement Discipline |
+----------+----------+--------------------------------+
| 0x01 | Wildcard | Not applicable |
| 0x02 | Prefix | As negotiated (DU or DoD) |
+----------+----------+--------------------------------+
2.2. Specification for LDP FECs
The label advertisement discipline for currently defined LDP FEC
types is listed in Section 4.
This document updates the respective RFCs in which these FECs are
introduced and defined.
3. Security Considerations
This document only clarifies the applicability of an LDP session's
label advertisement mode and hence does not add any LDP security
mechanics and considerations to those already defined in the LDP
specification [RFC5036].
4. IANA Considerations
This document mandates the specification of a label advertisement
discipline for each defined FEC type and hence IANA's "Forwarding
Equivalence Class (FEC) Type Name Space" registry under IANA's "Label
Distribution Protocol (LDP) Parameters" registry has been extended as
follows:
- Added a new column titled "Label Advertisement Discipline" with
the following possible values:
o DU
o DoD
o As negotiated (DU or DoD)
o Upstream
o Not applicable
o Unknown
- Made this document an additional reference for the registry itself
and for all affected registrations.
- Kept other columns of the registry in place and populated as they
were.
For the currently assigned FEC types, the updated registry looks
like:
+=====+====+===============+==============+===========+============+
|Value|Hex | Name |Label | Reference |Notes/ |
| | | |Advertisement | |Registration|
| | | |Discipline | |Date |
+=====+====+===============+==============+===========+============+
| 0 |0x00|Reserved | | | |
+-----+----+---------------+--------------+-----------+------------+
| 1 |0x01|Wildcard |Not applicable| [RFC5036] | |
| | | | | [RFC7358] | |
+-----+----+---------------+--------------+-----------+------------+
| 2 |0x02|Prefix |As negotiated | [RFC5036] | |
| | | |(DU or DoD) | [RFC7358] | |
+-----+----+---------------+--------------+-----------+------------+
| 4 |0x04|CR-LSP |DoD | [RFC3212] | |
| | | | | [RFC7358] | |
+-----+----+---------------+--------------+-----------+------------+
| 5 |0x05|Typed Wildcard |Not applicable| [RFC5918] | |
| | |FEC Element | | [RFC7358] | |
+-----+----+---------------+--------------+-----------+------------+
| 6 |0x06|P2MP |DU | [RFC6388] | |
| | | | | [RFC7358] | |
+-----+----+---------------+--------------+-----------+------------+
| 7 |0x07|MP2MP-up |DU | [RFC6388] | |
| | | | | [RFC7358] | |
+-----+----+---------------+--------------+-----------+------------+
| 8 |0x08|MP2MP-down |DU | [RFC6388] | |
| | | | | [RFC7358] | |
+-----+----+---------------+--------------+-----------+------------+
| 9 |0x09|HSMP-upstream |DU | [RFC7140] | 2014-01-09 |
| | | | | [RFC7358] | |
+-----+----+---------------+--------------+-----------+------------+
| 10 |0x0A|HSMP-downstream|DU, Upstream | [RFC7140] | 2014-01-09 |
| | | | | [RFC7358] | |
+-----+----+---------------+--------------+-----------+------------+
| 128 |0x80|PWid |DU | [RFC4447] | |
| | |FEC Element | | [RFC7358] | |
+-----+----+---------------+--------------+-----------+------------+
| 129 |0x81|Generalized |DU | [RFC4447] | |
| | |PWid | | [RFC7358] | |
| | |FEC Element | | | |
+-----+----+---------------+--------------+-----------+------------+
| 130 |0x82|P2MP PW |Upstream | [P2MP-PW] | 2009-06-03 |
| | |Upstream | | [RFC7358] | |
| | |FEC Element | | | |
+-----+----+---------------+--------------+-----------+------------+
+-----+----+---------------+--------------+-----------+------------+
| 131 |0x83|Protection |DU |[FAST-PROT]| 2010-02-26 |
| | |FEC Element | | [RFC7358] | |
+-----+----+---------------+--------------+-----------+------------+
| 132 |0x84|P2MP PW |DU | [P2MP-PW] | 2014-04-04 |
| | |Downstream | | [RFC7358] | |
| | |FEC Element | | | |
+-----+----+---------------+--------------+-----------+------------+
5. References
5.1. Normative References
[RFC3212] Jamoussi, B., Ed., Andersson, L., Callon, R., Dantu, R.,
Wu, L., Doolan, P., Worster, T., Feldman, N., Fredette,
A., Girish, M., Gray, E., Heinanen, J., Kilty, T., and A.
Malis, "Constraint-Based LSP Setup using LDP", RFC 3212,
January 2002, <http://www.rfc-editor.org/info/rfc3212>.
[RFC4447] Martini, L., Ed., Rosen, E., El-Aawar, N., Smith, T., and
G. Heron, "Pseudowire Setup and Maintenance Using the
Label Distribution Protocol (LDP)", RFC 4447, April 2006,
<http://www.rfc-editor.org/info/rfc4447>.
[RFC5036] Andersson, L., Ed., Minei, I., Ed., and B. Thomas, Ed.,
"LDP Specification", RFC 5036, October 2007,
<http://www.rfc-editor.org/info/rfc5036>.
[RFC5918] Asati, R., Minei, I., and B. Thomas, "Label Distribution
Protocol (LDP) 'Typed Wildcard' Forward Equivalence Class
(FEC)", RFC 5918, August 2010,
<http://www.rfc-editor.org/info/rfc5918>.
[RFC6388] Wijnands, IJ., Ed., Minei, I., Ed., Kompella, K., and B.
Thomas, "Label Distribution Protocol Extensions for
Point-to-Multipoint and Multipoint-to-Multipoint Label
Switched Paths", RFC 6388, November 2011,
<http://www.rfc-editor.org/info/rfc6388>.
[RFC6389] Aggarwal, R. and JL. Le Roux, "MPLS Upstream Label
Assignment for LDP", RFC 6389, November 2011,
<http://www.rfc-editor.org/info/rfc6389>.
[RFC7140] Jin, L., Jounay, F., Wijnands, IJ., and N. Leymann, "LDP
Extensions for Hub and Spoke Multipoint Label Switched
Path", RFC 7140, March 2014,
<http://www.rfc-editor.org/info/rfc7140>.
5.2. Informative References
[FAST-PROT] Shen, Y., Aggarwal, R., Henderickx, W., and Y. Jiang,
"PW Endpoint Fast Failure Protection", Work in Progress,
draft-ietf-pwe3-endpoint-fast-protection-01, July 2014.
[P2MP-PW] Sivabalan, S., Ed., Boutros, S., Ed., Martini, L.,
Konstantynowicz, M., Del Vecchio, G., Nadeau, T., Jounay,
F., Niger, P., Kamite, Y., Jin, L., Vigoureux, M.,
Ciavaglia, L., Delord, S., and K. Raza, "Signaling
Root-Initiated Point-to-Multipoint Pseudowire using LDP",
Work in Progress, draft-ietf-pwe3-p2mp-pw-04, March 2012.
Acknowledgments
We acknowledge Eric Rosen and Rajiv Asati for their initial review
and input on the document.
Authors' Addresses
Kamran Raza
Cisco Systems, Inc.
2000 Innovation Drive
Ottawa, ON K2K-3E8
Canada
EMail: skraza@cisco.com
Sami Boutros
Cisco Systems, Inc.
3750 Cisco Way
San Jose, CA 95134
United States
EMail: sboutros@cisco.com
Luca Martini
Cisco Systems, Inc.
9155 East Nichols Avenue, Suite 400
Englewood, CO 80112
United States
EMail: lmartini@cisco.com
Nicolai Leymann
Deutsche Telekom AG
Winterfeldtstrasse 21
Berlin 10781
Germany
EMail: N.Leymann@telekom.de
AI ELI5
On this page
§1Why the Mode Is Only a Hint
The Label Distribution Protocol (LDP, RFC 5036) lets two Label Switching Routers (LSRs) negotiate a label advertisement mode when a session starts. Only a single mode is negotiated, agreed upon and used for a given session, and it is carried in the LDP Initialization message.
RFC 7358 points out that this negotiated mode is only indicative. It says how the speakers will advertise labels for some Forwarding Equivalence Classes (FECs), but it is not a rule that restricts them to a specific behavior. For some FEC types, the advertising behavior is governed by the FEC type and not by the negotiated behavior.
The document makes that fact clear by updating RFC 5036. It also updates RFC 3212, RFC 4447, RFC 5918, RFC 6388 and RFC 7140 to say, for each FEC type they define, whether label binding advertisements are constrained by the negotiated mode.
When two routers meet, they agree on a general way to share numbered tags. But for some kinds of traffic the kind itself already says how tags must be shared, so the first agreement is just a hint.
§2The Six Discipline Types
Several FEC types can share one LDP session. To remove ambiguity and conflict among them, the RFC defines a label advertisement discipline for each FEC type. It introduces six values for that discipline:
- DU (Downstream Unsolicited)
- DoD (Downstream on Demand)
- As negotiated (DU or DoD)
- Upstream, which refers to RFC 6389
- Not applicable
- Unknown
The text does not add new advertisement behavior. It only names the discipline that already applies to each FEC type.
It makes a short list of labels, like sticky notes, that say how each kind of traffic gets its tags: by one method, by another, by whatever the routers agreed, or not at all.
§2.1The Update to RFC 5036
Section 3.5.3 of RFC 5036, under the description of the label advertisement discipline, gains two statements. First, each document that defines an LDP FEC must state whether the negotiated label advertisement discipline applies to label binding advertisements for that FEC. If it does not apply, the document must also explicitly state the discipline to be used for the FEC.
Second, RFC 7358 itself defines the discipline for two FEC types from RFC 5036: the Wildcard FEC (type 0x01) is Not applicable, and the Prefix FEC (type 0x02) is As negotiated (DU or DoD).
Section 2.2 adds that the disciplines for the other currently defined FEC types are listed in the IANA section, and that the document updates the respective RFCs in which those FECs were introduced.
From now on, whoever invents a new kind of traffic has to say how its tags are shared. The RFC also fills in the answer for the two oldest kinds.
§4The Updated IANA Registry
The IANA registry called "Forwarding Equivalence Class (FEC) Type Name Space", under the "Label Distribution Protocol (LDP) Parameters" registry, was extended. A new column titled "Label Advertisement Discipline" was added, taking the six values above. RFC 7358 was made an additional reference for the registry and for all affected registrations, and the other columns were kept as they were.
The resulting table covers the assigned FEC types. Most are DU: P2MP, MP2MP-up, MP2MP-down, HSMP-upstream, PWid, Generalized PWid, Protection and P2MP PW Downstream. CR-LSP is DoD. HSMP-downstream is listed as DU, Upstream, and P2MP PW Upstream as Upstream. Only the Prefix FEC is As negotiated, while Wildcard and Typed Wildcard are Not applicable.
The official list of traffic kinds got one new column that says how each kind hands out tags.
- 0x01Wildcard — Not applicable
- 0x02Prefix — As negotiated (DU or DoD)
- 0x04CR-LSP — DoD
- 0x05Typed Wildcard FEC Element — Not applicable
- 0x06P2MP — DU
- 0x07MP2MP-up — DU
- 0x08MP2MP-down — DU
- 0x09HSMP-upstream — DU
- 0x0AHSMP-downstream — DU, Upstream
- 0x80PWid FEC Element — DU
- 0x81Generalized PWid FEC Element — DU
- 0x82P2MP PW Upstream FEC Element — Upstream
- 0x83Protection FEC Element — DU
- 0x84P2MP PW Downstream FEC Element — DU
§3Security Considerations
The RFC only clarifies when an LDP session's label advertisement mode applies. It therefore adds no LDP security mechanics and no new considerations beyond those already defined in the LDP specification, RFC 5036.
Nothing new is being sent or locked, only explained, so no new safety rules are needed.