Network Working Group Kamran Raza Internet Draft Sami Boutros Updates: 5036, 4447 (if approved) Luca Martini Intended status: Standards Track Expires: December 31, 2011 Cisco Systems, Inc. July 1, 2011 Applicability of LDP Label Advertisement Mode draft-raza-mpls-ldp-applicability-label-adv-00.txt Abstract An LDP speaker negotiates the label advertisement mode with its LDP peer at the time of session establishment. Although different applications sharing the same LDP session may need different modes of label distribution and advertisement, there is only one type of label advertisement mode that is negotiated and used per LDP session. This document clarifies the use and the applicability of session's negotiated label advertisement mode, and categorizes LDP applications into two broad categories of negotiated mode-bound and mode-independent applications. This document proposal and clarification thus updates [RFC5036] and [RFC4447]. Status of this Memo This Internet-Draft is submitted in full conformance with the provisions of BCP 78 and BCP 79. Internet-Drafts are working documents of the Internet Engineering Task Force (IETF), its areas, and its working groups. Note that other groups may also distribute working documents as Internet- Drafts. Internet-Drafts are draft documents valid for a maximum of six months and may be updated, replaced, or obsoleted by other documents at any time. It is inappropriate to use Internet-Drafts as reference material or to cite them other than as "work in progress." The list of current Internet-Drafts can be accessed at http://www.ietf.org/ietf/1id-abstracts.txt The list of Internet-Draft Shadow Directories can be accessed at http://www.ietf.org/shadow.html This Internet-Draft will expire on December 31, 2011. Raza, et. al Expires December 2011 [Page 1] Internet-Draft Applicability of LDP Label Advertisement Mode July 2011 Copyright Notice Copyright (c) 2011 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 3 2. Conventions used in this document 3 3. Label Advertisement Mode Applicability 4 3.1. Label Advertisement Mode Negotiation 4 3.2. LDP Applications Categorization 4 3.2.1. Session mode-bound Applications 5 3.2.2. Session mode-independent Applications 5 3.3. Update to RFC-5036 6 3.4. Update to RFC-4447 6 4. Future Work 6 5. Security Considerations 6 6. IANA Considerations 7 7. References 7 7.1. Normative References 7 7.2. Informative References 7 8. Acknowledgments 7 Raza, et. al Expires December 2011 [Page 2] Internet-Draft Applicability of LDP Label Advertisement Mode July 2011 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 unsolicitedly to LSR peers that have not explicitly requested them. The MPLS architecture [RFC3031] also specifies that on any given label distribution adjacency, the upstream LSR and the downstream LSR must agree to using a single label advertisement mode. Label Distribution Protocol (LDP) [RFC5036] allows label advertisement mode negotiation at the session establishment time (section 3.5.3 [RFC5036]). To comply with MPLS architecture, LDP specification also dictates that only one label advertisement mode is agreed and used on a given LDP session between two LSRs. With the advent of new applications, such as L2VPN [RFC4447], mLDP [MLDP], ICCP [ICCP], running on top of LDP, there are situations when an LDP session is shared across more than one application to exchange label bindings for different type of FECs. Although different applications sharing the same LDP session may need 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 session's label advertisement mode for each application using the session. It also categorizes LDP applications into two broad categories of negotiated mode-bound and mode-independent applications. This document proposal and clarification thus updates [RFC5036] and [RFC4447]. 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]. Raza, et. al Expires December 2011 [Page 3] Internet-Draft Applicability of LDP Label Advertisement Mode July 2011 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", as well as uses the terms "label distribution" and "label advertisement" interchangeably. This document also uses these terms interchangeably. 3. Label Advertisement Mode Applicability 3.1. Label Advertisement Mode Negotiation Label advertisement mode is negotiated between participating 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 [RFC5036]. 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 LSRs must use the same mode for label binding exchange. 3.2. LDP Applications Categorization At the time of standardization of LDP base specification RFC-3036, the earlier applications 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: . L2VPN P2P PW ([RFC4447]) Raza, et. al Expires December 2011 [Page 4] Internet-Draft Applicability of LDP Label Advertisement Mode July 2011 . L2VPN P2MP PW ([P2MP-PW]) . mLDP ([MLDP]) . ICCP ([ICCP]) We divide these LDP applications into two broad categories from label advertisement mode usage point of view: 1. Session mode-bound Applications (i.e. use the negotiated label advertisement mode) 2. Session mode-independent Applications (i.e. do not care about the negotiated label advertisement mode) 3.2.1. Session mode-bound Applications The FEC label binding exchange for such LDP applications MUST use the negotiated label advertisement mode. The early LDP applications "Dynamic Label Switching for IP Prefixes" and "Label-controlled ATM/FR" fall into this category. 3.2.2. Session mode-independent Applications The FEC label binding, or any other application data, exchange for such LDP applications 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 their respective specifications. For example, [MLDP] 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, fall into this category of LDP application. 3.2.2.1. Upstream Label Assignment As opposed to downstream assigned label advertisement defined by [RFC3031], [LDP-UPSTREAM] specification defines new mode of label advertisement where label advertisement and distribution occurs for upstream assigned labels. As stated in earlier section 3.1 of this document, [RFC5036] only allows specifying Downstream-Unsolicited or Downstream-on-Demand mode. This means that any LDP application that requires upstream Raza, et. al Expires December 2011 [Page 5] Internet-Draft Applicability of LDP Label Advertisement Mode July 2011 assigned label advertisement also falls under the category of Session mode-independent application. 3.3. Update to RFC-5036 For clarification reasons, 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 document specifying a new FEC SHOULD state the applicability of the negotiated label advertisement discipline for that FEC. 3.4. Update to RFC-4447 [RFC4447] specifies LDP extensions and procedures to exchange label bindings for P2P PW FECs. 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, 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 the negotiated label advertisement mode of the LDP session." 4. Future Work This document only clarifies the existing behavior for LDP label advertisement mode for different applications without defining any protocol extensions. In future, a new LDP capability [RFC5561] based mechanism can be defined to signal/negotiate label advertisement mode per FEC/application. 5. 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 LDP specification [RFC5036]. Raza, et. al Expires December 2011 [Page 6] Internet-Draft Applicability of LDP Label Advertisement Mode July 2011 6. IANA Considerations None. 7. References 7.1. Normative References [RFC5036] Andersson, L., Menei, I., and Thomas, B., Editors, "LDP Specification", RFC 5036, September 2007. [RFC3031] Rosen, E., Viswanathan, A., and Callon, R., "Multiprotocol Label Switching Architecture", RFC 3031, January 2001. 7.2. Informative References [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. [P2MP-PW] Boutros, S., Martini, L., Sivabalan, S., Del Vecchio, G., Kamite, Jin, L., "Signaling Root-Initiated P2MP PWs using LDP", draft-ietf-pwe3-p2mp-pw-02.txt, Work in Progress, March 2011. [MLDP] Minei, I., Kompella, K., Wijnands, I., and Thomas, B., "LDP Extensions for Point-to-Multipoint and Multipoint-to- Multipoint Label Switched Paths", draft-ietf-mpls-ldp-p2mp -14.txt, Work in Progress, June 2011. [ICCP] Martini, L., Salam, S., Sajassi, A., and Matsushima, S., "Inter-Chassis Communication Protocol for L2VPN PE Redundancy", draft-ietf-pwe3-iccp-05.txt, Work in Progress, April 2011. [UPSTREAM-LDP] Aggarwal, R., and Le Roux, J.L., "MPLS Upstream Label Assignment for LDP", draft-ietf-mpls-ldp-upstream-10.txt, Work in Progress, February 2011. [RFC5561] Thomas, B., Raza, K., Aggarwal, S., Aggarwal, R., and Le Roux, JL., "LDP Capabilities", RFC 5561, July 2009. 8. Acknowledgments The authors would like to acknowledge Eric Rosen and Rajiv Asati for their review and input. Raza, et. al Expires December 2011 [Page 7] Internet-Draft Applicability of LDP Label Advertisement Mode July 2011 This document was prepared using 2-Word-v2.0.template.dot. Authors' Addresses Kamran Raza Cisco Systems, Inc. 2000 Innovation Drive, Kanata, 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 Raza, et. al Expires December 2011 [Page 8]