draft-ietf-mpls-ldp-applicability-label-adv-01.txt   draft-ietf-mpls-ldp-applicability-label-adv-02.txt 
MPLS Working Group Kamran Raza MPLS Working Group Kamran Raza
Internet Draft Sami Boutros Internet Draft Sami Boutros
Updates: 5036, 4447 (if approved) Luca Martini Updates: 5036, 4447, 5918, 6388, 3212 Luca Martini
Intended status: Standards Track Cisco Systems, Inc. Intended status: Standards Track Cisco Systems, Inc.
Expires: August 14, 2013 Expires: July 19, 2014
Nicolai Leymann Nicolai Leymann
Deutsche Telekom Deutsche Telekom
February 15, 2013 January 20, 2014
Applicability of LDP Label Advertisement Mode Label Advertisement Discipline for LDP FECs
draft-ietf-mpls-ldp-applicability-label-adv-01.txt draft-ietf-mpls-ldp-applicability-label-adv-02.txt
Abstract Abstract
An LDP speaker negotiates the label advertisement mode with its LDP The label advertising behavior of an LDP speaker for a given FEC is
peer at the time of session establishment. Although different governed by the FEC type and not necessarily by the LDP session's
applications sharing the same LDP session may need different modes negotiated label advertisement mode. This document updates RFC 5036
of label distribution and advertisement, there is only one type of to make that fact clear, as well as updates RFC 3212, RFC 4447,
label advertisement mode that is negotiated and used per LDP RFC 5918, and RFC 6388 by specifying the label advertisement mode
session. This document clarifies the use and the applicability of for all currently defined FECs.
session's negotiated label advertisement mode, and categorizes LDP
applications into two broad categories of negotiated mode-bound and
mode-independent applications. The document updates RFC5036 and
RFC4447 to remove any ambiguity and conflict in the area of using
correct label advertisement mode for a given application.
Status of this Memo Status of this Memo
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Copyright Notice Copyright Notice
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Table of Contents Table of Contents
1. Introduction 3 1. Introduction 2
2. Conventions used in this document 3 2. Label Advertisement Discipline 3
3. Label Advertisement Mode Applicability 4 2.1. Update to RFC-5036 3
3.1. Label Advertisement Mode Negotiation 4 2.2. Specification for LDP FECs 4
3.2. Mode-based Categorization of LDP Applications 4 3. Security Considerations 4
3.2.1. Session mode-bound Applications 5 4. IANA Considerations 4
3.2.2. Session mode-independent Applications 5 5. References 5
3.3. Unacceptable label advertisement mode 6 5.1. Normative References 5
4. Clarification on Mode Applicability 6 5.2. Informative References 5
4.1. Update to RFC-5036 7 6. Acknowledgments 5
4.2. Update to RFC-4447 7
5. Security Considerations 7
6. IANA Considerations 7
7. References 7
7.1. Normative References 7
7.2. Informative References 8
8. Acknowledgments 8
1. Introduction 1. Introduction
The MPLS architecture [RFC3031] defines two modes of label Label Distribution Protocol (LDP) [RFC5036] allows label
advertisement for an LSR: advertisement mode negotiation at the time of session establishment.
LDP specification also dictates that only single label advertisement
1. Downstream-on-Demand mode is negotiated, agreed and used for a given LDP session between
two LSRs.
2. Unsolicited Downstream
The "Downstream-on-Demand" mode requires an LSR to explicitly
request the label binding for FECs from its peer, whereas
"Unsolicited Downstream" mode allows an LSR to distribute the label
binding for FECs to LSR peers that have not explicitly requested
them. The MPLS architecture also specifies that on any given label
distribution adjacency, the upstream LSR and the downstream LSR must
agree to use a single label advertisement mode.
Label Distribution Protocol (LDP) [RFC5036] allows label
advertisement mode negotiation at time of session establishment
(section 3.5.3 [RFC5036]). To comply with MPLS architecture, LDP
specification also dictates that only single label advertisement
mode is agreed and used for a given LDP session between two LSRs.
With the advent of new LDP applications, such as L2VPN [RFC4447],
mLDP [RFC6388], ICCP [ICCP], there are situations when an LDP
session is shared across more than one application to exchange label
bindings for different types of FEC. Although different applications
sharing the same LDP session may need a different type of label
advertisement mode negotiated, there is only one type of label
advertisement mode that is negotiated and agreed at the time of
establishment of LDP session.
This document clarifies the use and the applicability of label
advertisement mode of a session for each application using the
session. It also categorizes LDP applications into two broad
categories of mode-bound and mode-independent applications.
The document also suggests an update to RFC-5036 and RFC-4447 to
remove any ambiguity and conflict in the area of using correct label
advertisement mode for a given LDP application.
2. Conventions 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 RFC-2119 [RFC2119].
The unqualified term "mode" used in document refers to "label
advertisement mode".
Please also note that LDP specification [RFC5036] uses the term
"Downstream Unsolicited" to refer to "Unsolicited Downstream". The
LDP specification also uses the terms "label distribution mode" and
"label advertisement mode" interchangeably. Like LDP specification
document, this document also uses these terms interchangeably.
3. Label Advertisement Mode Applicability
3.1. Label Advertisement Mode Negotiation
Label advertisement mode is negotiated between LSR peers at the time
of session establishment. The label advertisement mode is specified
in LDP Initialization message's "Common Session Parameter" TLV by
setting A-bit (Label Advertisement Discipline bit) to 1 or 0 for
Downstream-on-Demand or Downstream-Unsolicited modes respectively.
The negotiation of the A-bit is specified in section 3.5.3 of
[RFC5036] as follows:
"If one LSR proposes Downstream Unsolicited and the other proposes
Downstream on Demand, the rules for resolving this difference is:
- If the session is for a label-controlled ATM link or a
label- controlled Frame Relay link, then Downstream on Demand
MUST be used.
- Otherwise, Downstream Unsolicited MUST be used."
Once label advertisement mode has been negotiated and agreed, both
LSR peers must use the same mode for label binding exchange.
3.2. Mode-based Categorization of LDP Applications
The earlier applications, defined and identified at the time of
standardization of LDP base specification RFC-3036, using LDP to
exchange their FEC bindings were:
. Dynamic Label Switching for IP Prefixes
. Label-controlled ATM/FR
Since then, several new applications have emerged that use LDP to
signal their FEC bindings and/or application data. These include:
. L2VPN P2P PW ([RFC4447])
. L2VPN P2MP PW ([P2MP-PW])
. mLDP ([RFC6388])
. ICCP ([ICCP])
We divide the LDP applications into two broad categories from label
advertisement mode usage point of view:
1. Session mode-bound Applications
2. Session mode-independent Applications
3.2.1. Session mode-bound Applications
We define a "session mode-bound application" to be an application
which uses the negotiated label advertisement mode. This means that
the FEC-label binding exchange for such an LDP application MUST use
the label advertisement mode negotiated for the LDP session.
The early LDP applications "Dynamic Label Switching for IP Prefixes"
and "Label-controlled ATM/FR" are included into this category.
3.2.2. Session mode-independent Applications
We define a "session mode-independent application" to be an
application which does not care about the negotiated label
advertisement mode. This means that the FEC-label binding, or any
other application data, exchange for such an LDP application does
not care about, nor tied to the "negotiated" label advertisement
mode of the session; rather, the information exchange is driven by
the application need and procedures as described by its
specification document. For example, [RFC6388] specifies procedures
to advertise P2MP FEC label binding in an unsolicited manner,
irrespective of the negotiated label advertisement mode of the
session.
The applications, PW (P2P and P2MP), MLDP, and ICCP, are included
into this category of LDP applications.
3.2.2.1. Upstream Label Assignment
As opposed to downstream assigned label advertisement defined by
[RFC3031], [RFC6389] specification defines new mode of label
advertisement where label advertisement and distribution occurs for
upstream assigned labels.
As stated earlier in this document, LDP base specification RFC-5036
only allows specifying Downstream-Unsolicited or Downstream-on-Demand
mode. This means that any LDP application that requires upstream
assigned label advertisement also falls under the category of Session
mode-independent application.
3.3. Unacceptable label advertisement mode 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 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.
The procedures related to unacceptable label advertisement mode, as This document updates [RFC5036] to make that fact clear, and updates
defined in RFC-5036 section 3.5.3, continue to apply for any "mode- [RFC3212], [RFC4447], [RFC5036], [RFC5918], and [RFC6388] to indicate
bound" FEC/application. For a "mode-independent" FEC/application, for each FEC type that has already been defined whether the label
mode negotiation does not apply and hence both LSRs MUST operate in binding advertisements for the FEC are constrained by the negotiated
the mode specified for the given application by the respective label advertisement mode or not. Furthermore, this document specifies
specification. the label advertisement mode to be used for all currently defined
LDP FECs.
If a session is jointly shared amongst mode-bound and mode- 2. Label Advertisement Discipline
independent FEC/applications, session will not be established if the
label advertisement mode is unacceptable (between the LSRs) for a
given mode-bound FEC/application type. This is inline with RFC-5036
section 3.5.3 specification for unacceptable mode.
4. Clarification on Mode Applicability To remove any ambiguity and conflict regarding label advertisement
discipline amongst different FEC types sharing a common LDP session,
this document specifies a label advertisement disciplines for FEC
types.
To remove any ambiguity and conflict amongst different This document introduces following types for specifying a label
specifications with regards to the use of LDP session's label advertisement discipline for a FEC type:
advertisement mode, we propose an update to LDP base specification
RFC-5036 to clarify the applicability of session's negotiated mode.
Furthermore, RFC-4447 specifies LDP extensions and procedures to - DU (Downstream Unsolicited)
exchange label bindings for P2P PW FECs [RFC4447], and dictates the - DoD (Downstream On Demand)
use of Downstream-Unsolicited mode for an LDP session related to - As negotiated (DU or DoD)
L2VPN PW. This mode dictation creates a direct conflict in - Upstream ([RFC6389])
situations when a PW LDP session is shared with an LDP application - Not Applicable
with Downstream-on-Demand mode (such as Label switching Application
for IP prefixes). To remove such a conflict, we also propose an
update to a section of RFC-4447.
4.1. Update to RFC-5036 2.1. Update to RFC-5036
The section 3.5.3 of [RFC5036] is updated to add following two The section 3.5.3 of [RFC5036] is updated to add following two
statements under the description of "A, Label Advertisement statements under the description of "A, Label Advertisement
Discipline": Discipline":
- The negotiated label advertisement discipline only applies to FEC - Each document defining an LDP FEC must state the applicability
label binding advertisement of "Address Prefix" FECs; 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.
- Any new document specifying a new FEC MUST state the - This document defines the label advertisement discipline for
applicability of the negotiated label advertisement discipline for the following FEC types:
that FEC.
4.2. Update to RFC-4447 +----------+----------+--------------------------------+
| FEC Type | FEC Name | Label advertisement discipline |
+----------+----------+--------------------------------+
| 0x01 | Wildcard | Not applicable |
| 0x02 | Prefix | As negotiated (DU or DoD) |
+----------+----------+--------------------------------+
The section 3 of [RFC4447] states: 2.2. Specification for LDP FECs
"LDP MUST be used in its downstream unsolicited mode." Following is the specification of label advertisement disciplines to
be used for currently defined LDP FEC types.
Since PW application falls under session mode-independent +------+----------------+--------------------------------+------+
application category, the above statement in [RFC4447] should be | FEC | FEC Name | Label advertisement discipline |RFC |
read to mean as follows: | Type | | | |
+------+----------------+--------------------------------+------+
| 0x01 | Wildcard | Not applicable | 5036 |
| 0x02 | Prefix | As negotiated (DU or DoD) | 5036 |
| 0x04 | CR-LSP | DoD | 3212 |
| 0x05 | Typed Wildcard | Not applicable | 5918 |
| 0x06 | P2MP | DU | 6388 |
| 0x07 | MP2MP-up | DU | 6388 |
| 0x08 | MP2MP-down | DU | 6388 |
| 0x80 | PWid | DU | 4447 |
| 0x81 | Gen. PWid | DU | 4447 |
+------+----------------+--------------------------------+------+
"LDP MUST exchange PW FEC label bindings in downstream unsolicited The above table also lists the RFC (in which given FEC type is
manner, independent of the negotiated label advertisement mode of defined), and hence this document updates all the above listed RFCs.
the LDP session".
5. Security Considerations 3. Security Considerations
This document specification only clarifies the applicability of LDP This document specification only clarifies the applicability of LDP
session's label advertisement mode, and hence does not add any LDP session's label advertisement mode, and hence does not add any LDP
security mechanics and considerations to those already defined in security mechanics and considerations to those already defined in
the LDP specification [RFC5036]. the LDP specification [RFC5036].
6. IANA Considerations 4. IANA Considerations
None. This document mandates the specification of a label advertisement
discipline for each defined FEC type, and hence extends IANA's
"Forwarding Equivalence Class (FEC) Type Name Space" registry under
IANA's "Label Distribution Protocol (LDP) Parameters" as follows:
7. References - Add a new column titled "Label advertisement discipline" with
following possible values:
o DU
o DoD
o As negotiated (DU or DoD)
o Upstream
o Not applicable
7.1. Normative References - For the existing FEC types, populate this column with the
values listed under section 2.2.
5. References
5.1. Normative References
[RFC5036] L. Andersson, I. Minei, and B. Thomas, "LDP [RFC5036] L. Andersson, I. Minei, and B. Thomas, "LDP
Specification", RFC 5036, September 2007. Specification", RFC 5036, September 2007.
[RFC3212] B. Jamoussi, et al., "Constraint-Based LSP Setup using
LDP", RFC 3212, January 2002
[RFC4447] L. Martini, Editor, E. Rosen, El-Aawar, T. Smith, G. [RFC4447] L. Martini, Editor, E. Rosen, El-Aawar, T. Smith, G.
Heron, "Pseudowire Setup and Maintenance using the Label Heron, "Pseudowire Setup and Maintenance using the Label
Distribution Protocol", RFC 4447, April 2006. Distribution Protocol", RFC 4447, April 2006.
[RFC3031] E. Rosen, A. Viswanathan, and R. Callon, "Multiprotocol [RFC5918] R. Asati, I. Minei, and B. Thomas, "Label Distribution
Label Switching Architecture", RFC 3031, January 2001. Protocol Typed Wildcard FEC", RFC 5918, August 2010.
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
7.2. Informative References
[P2MP-PW] S. Boutros, L. Martini, S. Sivabalan, G. Del Vecchio, [RFC6388] I. Minei, I. Wijnands, K. Kompella, and B. Thomas, "LDP
Kamite, L. Jin, "Signaling Root-Initiated P2MP PWs using Extensions for P2MP and MP2MP LSPs", RFC 6388, November
LDP", draft-ietf-pwe3-p2mp-pw-04.txt, Work in Progress, 2011.
March 2012.
[RFC6388] I. Minei, I. Wijnand, K. Kompella, B., "LDP Extensions for [RFC6389] R. Aggarwal, and JL. Le Roux, "MPLS Upstream Label
P2MP and MP2MP LSPs", RFC 6388, November 2011. Assignment for LDP", RFC 6389, November 2011.
[ICCP] L. Martini, S. Salam, A. Sajassi, and S. Matsushima, 5.2. Informative References
"Inter-Chassis Communication Protocol for L2VPN PE
Redundancy", draft-ietf-pwe3-iccp-09.txt, Work in
Progress, July 2012.
[RFC6389] R. Aggarwal, and J.L. Le Roux, "MPLS Upstream Label None.
Assignment for LDP", RFC 6389, November 2011.
8. Acknowledgments 6. Acknowledgments
We acknowledge the authors of [RFC5036] and [RFC4447] since some of We acknowledge Eric Rosen and Rajiv Asati for their initial review
the text in this document is borrowed from their specification. We and input on the document.
also acknowledge Eric Rosen and Rajiv Asati for their review and
input.
This document was prepared using 2-Word-v2.0.template.dot. This document was prepared using 2-Word-v2.0.template.dot.
Authors' Addresses Authors' Addresses
Kamran Raza Kamran Raza
Cisco Systems, Inc. Cisco Systems, Inc.
2000 Innovation Drive, 2000 Innovation Drive,
Ottawa, ON K2K-3E8, Canada. Ottawa, ON K2K-3E8, Canada.
E-mail: skraza@cisco.com E-mail: skraza@cisco.com
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