wdiff draft-ietf-mpls-ldp-applicability-label-adv-01.txt draft-ietf-mpls-ldp-applicability-label-adv-02.txt

MPLS Working Group Kamran Raza
Internet Draft Sami Boutros
Updates: 5036, 4447 (if approved) 4447, 5918, 6388, 3212 Luca Martini
Intended status: Standards Track Cisco Systems, Inc.
Expires: August 14, 2013 July 19, 2014
Nicolai Leymann
Deutsche Telekom

February 15, 2013

Applicability of LDP

January 20, 2014

Label Advertisement Mode

draft-ietf-mpls-ldp-applicability-label-adv-01.txt

Abstract

An Discipline for LDP speaker negotiates the FECs

draft-ietf-mpls-ldp-applicability-label-adv-02.txt

Abstract

The label advertisement mode with its LDP
peer at the time advertising behavior of session establishment. Although different
applications sharing the same an LDP session may need different modes
of label distribution and advertisement, there is only one type of
label advertisement mode that speaker for a given FEC is negotiated and used per LDP
session. This document clarifies
governed by the use FEC type and not necessarily by the applicability of LDP session's
negotiated label advertisement mode, and categorizes LDP
applications into two broad categories of negotiated mode-bound and
mode-independent applications. The mode. This document updates RFC5036 and
RFC4447 RFC 5036
to remove any ambiguity make that fact clear, as well as updates RFC 3212, RFC 4447,
RFC 5918, and conflict in RFC 6388 by specifying the area of using
correct label advertisement mode
for a given application. all currently defined FECs.

Status of this Memo

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Table of Contents

1. Introduction 3 2
2. Conventions used in this document 3
3. Label Advertisement Mode Applicability 4
3.1. Label Advertisement Mode Negotiation 4
3.2. Mode-based Categorization of LDP Applications 4
3.2.1. Session mode-bound Applications 5
3.2.2. Session mode-independent Applications 5
3.3. Unacceptable label advertisement mode 6
4. Clarification on Mode Applicability 6
4.1. Discipline 3
2.1. Update to RFC-5036 7
4.2. Update to RFC-4447 7
5. 3
2.2. Specification for LDP FECs 4
3. Security Considerations 7
6. 4
4. IANA Considerations 7
7. 4
5. References 7
7.1. 5
5.1. Normative References 7
7.2. 5
5.2. Informative References 8
8. 5
6. Acknowledgments 8 5

1. Introduction

The MPLS architecture [RFC3031] defines two modes of label
advertisement for an LSR:

1. Downstream-on-Demand

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 the time of session establishment
(section 3.5.3 [RFC5036]). To comply with MPLS architecture, establishment.
LDP specification also dictates that only single label advertisement
mode is negotiated, agreed and used for a given LDP session between
two LSRs.

With

The negotiated label advertisement mode defined in RFC 5036 and
carried in the advent of new LDP applications, such as L2VPN [RFC4447],
mLDP [RFC6388], ICCP [ICCP], there are situations when an Initialization message is only indicative. It
indicates how the LDP speakers on a session will advertise labels for
some FECs, but it is shared across more than one application not a rule that restricts the speakers to exchange label
bindings behave
in a specific way. Furthermore, for different some FEC types the advertising
behavior of FEC. Although different applications
sharing the same LDP session may need a different speaker is governed by the FEC type of label
advertisement mode negotiated, there is only one type of label
advertisement mode that is negotiated and agreed at not by
the time of
establishment of LDP session. negotiated behavior.

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 updates [RFC5036] uses the term
"Downstream Unsolicited" to refer to "Unsolicited Downstream". The
LDP specification also uses the terms "label distribution mode" make that fact clear, 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 updates
[RFC3212], [RFC4447], [RFC5036], [RFC5918], and the other proposes
Downstream on Demand, the rules for resolving this difference is:

- If the session is [RFC6388] to indicate
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 each FEC type that has already 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 whether 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 advertisements for the LDP session.

The early LDP applications "Dynamic Label Switching for IP Prefixes"
and "Label-controlled ATM/FR" FEC 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 constrained 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 not. Furthermore, this document specifies
the category of Session
mode-independent application.

3.3. Unacceptable label advertisement mode

The procedures related to unacceptable label advertisement mode, as
defined in RFC-5036 section 3.5.3, continue to apply for any "mode-
bound" FEC/application. For a "mode-independent" FEC/application,
mode negotiation does not apply and hence both LSRs MUST operate in
the mode specified for the given application by the respective
specification.

If a session is jointly shared amongst mode-bound and mode-
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 used for unacceptable mode.

4. Clarification on Mode Applicability all currently defined
LDP FECs.

2. Label Advertisement Discipline

To remove any ambiguity and conflict amongst different
specifications with regards to the use of LDP session's regarding label advertisement mode, we propose an update to
discipline amongst different FEC types sharing a common LDP base specification
RFC-5036 to clarify the applicability of session's negotiated mode.

Furthermore, RFC-4447 session,
this document specifies LDP extensions and procedures to
exchange a label bindings for P2P PW FECs [RFC4447], and dictates the
use of Downstream-Unsolicited mode advertisement disciplines for an LDP session related to
L2VPN PW. FEC
types.

This mode dictation creates a direct conflict in
situations when a PW LDP session is shared with an LDP application
with Downstream-on-Demand mode (such as Label switching Application document introduces following types for IP prefixes). To remove such specifying a conflict, we also propose an
update to label
advertisement discipline for a section of RFC-4447.

4.1. FEC type:

- DU (Downstream Unsolicited)
- DoD (Downstream On Demand)
- As negotiated (DU or DoD)
- Upstream ([RFC6389])
- Not Applicable

2.1. Update to RFC-5036

The section 3.5.3 of [RFC5036] is updated to add following two
statements under the description of "A, Label Advertisement
Discipline":

- The negotiated label advertisement discipline only applies to FEC
label binding advertisement of "Address Prefix" FECs;

- Any new Each document specifying a new defining an LDP FEC MUST must state the applicability
of the negotiated label advertisement discipline for label
binding advertisements for that FEC.

4.2. Update If the negotiated label
advertisement discipline does not apply to the FEC, the
document must also explicitly state the discipline to RFC-4447

The section 3 of [RFC4447] states:

"LDP MUST be used in its downstream unsolicited mode."

Since PW application falls under session mode-independent
application category,
for the FEC.

- This document defines the above statement in [RFC4447] should be
read to mean as follows:

"LDP MUST exchange PW FEC label bindings in downstream unsolicited
manner, independent of 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

Following is the specification of label advertisement mode of
the disciplines to
be used for currently defined LDP session".

5. FEC types.

+------+----------------+--------------------------------+------+
| FEC | FEC Name | Label advertisement discipline |RFC |
| 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 |
+------+----------------+--------------------------------+------+

The above table also lists the RFC (in which given FEC type is
defined), and hence this document updates all the above listed RFCs.

3. Security Considerations

This document specification only clarifies the applicability of 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

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:

- 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

- For the existing FEC types, populate this column with the
values listed under section 2.2.

5. References

7.1.

5.1. Normative References

[RFC5036] L. Andersson, I. Minei, and B. Thomas, "LDP
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.
Heron, "Pseudowire Setup and Maintenance using the Label
Distribution Protocol", RFC 4447, April 2006.

[RFC3031] E. Rosen, A. Viswanathan, and

[RFC5918] R. Callon, "Multiprotocol
Label Switching Architecture", RFC 3031, January 2001.

[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, Asati, I. Minei, and B. Thomas, "Label Distribution
Protocol Typed Wildcard FEC", RFC 2119, March 1997.

7.2. Informative References

[P2MP-PW] S. Boutros, L. Martini, S. Sivabalan, G. Del Vecchio,
Kamite, L. Jin, "Signaling Root-Initiated P2MP PWs using
LDP", draft-ietf-pwe3-p2mp-pw-04.txt, Work in Progress,
March 2012. 5918, August 2010.

[RFC6388] I. Minei, I. Wijnand, Wijnands, K. Kompella, B., and B. Thomas, "LDP
Extensions for P2MP and MP2MP LSPs", RFC 6388, November
2011.

[ICCP] L. Martini, S. Salam, A. Sajassi, and S. Matsushima,
"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. JL. Le Roux, "MPLS Upstream Label
Assignment for LDP", RFC 6389, November 2011.

5.2. Informative References

None.

6. Acknowledgments

We acknowledge the authors of [RFC5036] and [RFC4447] since some of
the text in this document is borrowed from their specification. We
also acknowledge Eric Rosen and Rajiv Asati for their initial review
and
input. input on the document.

This document was prepared using 2-Word-v2.0.template.dot.

Authors' Addresses

Kamran Raza
Cisco Systems, Inc.
2000 Innovation Drive,
Ottawa, ON K2K-3E8, Canada.
E-mail: skraza@cisco.com

Sami Boutros
Cisco Systems, Inc.
3750 Cisco Way,
San Jose, CA 95134, USA.
E-mail: sboutros@cisco.com

Luca Martini
Cisco Systems, Inc.
9155 East Nichols Avenue, Suite 400,
Englewood, CO 80112, USA.
E-mail: lmartini@cisco.com

Nicolai Leymann
Deutsche Telekom AG,
Winterfeldtstrasse 21,
Berlin 10781, Germany.
E-mail: N.Leymann@telekom.de