MPLS Working Group Rajiv Asati Internet Draft Cisco Systems Intended status: Standards Track Expires: Feb 2010 Pradosh Mohapatra Cisco Systems Emily Chen Huawei Technologies Bob Thomas August 28, 2009 Signaling LDP Label Advertisement Completion draft-ietf-mpls-ldp-end-of-lib-04.txt Status of this Memo This Internet-Draft is submitted to IETF in full conformance with the provisions of BCP 78 and BCP 79. This document may contain material from IETF Documents or IETF Contributions published or made publicly available before November 10, 2008. The person(s) controlling the copyright in some of this material may not have granted the IETF Trust the right to allow modifications of such material outside the IETF Standards Process. Without obtaining an adequate license from the person(s) controlling the copyright in such materials, this document may not be modified outside the IETF Standards Process, and derivative works of it may not be created outside the IETF Standards Process, except to format it for publication as an RFC or to translate it into languages other than English. 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 Asati, et al. Expires Feb 28, 2010 [Page 1] Internet-Draft draft-ietf-mpls-ldp-end-of-lib August 2009 This Internet-Draft will expire on Feb 28, 2010. Copyright Notice Copyright (c) 2009 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 in effect on the date of publication of this document (http://trustee.ietf.org/license-info). Please review these documents carefully, as they describe your rights and restrictions with respect to this document. Abstract There are situations following Label Distribution Protocol (LDP) session establishment where it would be useful for an LDP speaker to know when its peer has advertised all of its labels. The LDP specification provides no mechanism for an LDP speaker to notify a peer when it has completed its initial label advertisements to that peer. This document specifies means for an LDP speaker to signal completion of its initial label advertisements following session establishment. Table of Contents 1. Introduction...................................................3 2. Specification Language.........................................3 3. Unrecognized Notification Capability...........................4 4. Signaling Completion of Label Advertisement....................4 4.1. Missing Expected End-of-LIB Notifications.................5 5. Usage Guidelines...............................................6 5.1. LDP-IGP Sync..............................................7 5.2. LDP Graceful Restart......................................7 5.3. Wildcard Label Request....................................8 6. Security Considerations........................................8 7. IANA Considerations............................................8 8. Acknowledgments................................................9 Asati, et al. Expires Feb 28, 2010 [Page 2] Internet-Draft draft-ietf-mpls-ldp-end-of-lib August 2009 9. References....................................................10 9.1. Normative References.....................................10 9.2. Informative References...................................10 Author's Addresses...............................................11 1. Introduction There are situations following LDP session establishment where it would be useful for an LDP speaker to know when its peer has advertised all of the labels from its Label Information Base (LIB). For example, when an LDP speaker is using LDP-IGP synchronization procedures [RFC5443], it would be useful for the speaker to know when its peer has completed advertisement of its IP label bindings. Similarly, after an LDP session is re-established when LDP Graceful Restart [RFC3478] is in effect, it would be helpful for each peer to signal the other after it has advertised all its label bindings. The LDP specification [RFC5036] provides no mechanism for an LDP speaker to notify a peer when it has completed its initial label advertisements to that peer. This document specifies use of a Notification message with the "End- of-LIB" Status Code for an LDP speaker to signal completion of its label advertisements following session establishment. RFC5036 implicitly assumes that new Status Codes will be defined over the course of time. However, it does not explicitly define the behavior of an LDP speaker which does not understand the Status Code in a Notification message. To avoid backward compatibility issues this document specifies use of the LDP capability mechanism [RFC5561] at session establishment time for informing a peer that an LDP speaker is capable of handling a Notification message that carries an unrecognized Status Code. 2. Specification Language 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]. Asati, et al. Expires Feb 28, 2010 [Page 3] Internet-Draft draft-ietf-mpls-ldp-end-of-lib August 2009 3. Unrecognized Notification Capability An LDP speaker MAY include a Capability Parameter [RFC5561] in the Initialization message to inform a peer that it ignores Notification Messages that carry a Status Type-Length-Value (TLV) with a non-fatal Status Code unknown to it. The Capability Parameter for the Unrecognized Notification capability is a TLV with the following format: 0 1 2 3 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ |U|F| Unrecog Notif (IANA) | Length | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ |S| Reserved | +-+-+-+-+-+-+-+-+ Figure 1 Unrecognized Notification Capability format Where: U and F bits: MUST be 1 and 0 respectively as per section 3 of LDP Capabilities [RFC5561]. Unrecog Notif: TLV code point to be assigned by IANA. S-bit: MUST be 1 (indicates that capability is being advertised). Upon receiving a Notification with an unrecognized Status Code an LDP speaker MAY generate a console or system log message for trouble shooting purposes. 4. Signaling Completion of Label Advertisement An LDP speaker that conforms to this specification SHOULD signal completion of its label advertisements to a peer by means of a Notification message, if its peer has advertised the Unrecognized Notification capability during session establishment. The LDP speaker Asati, et al. Expires Feb 28, 2010 [Page 4] Internet-Draft draft-ietf-mpls-ldp-end-of-lib August 2009 SHOULD send the Notification message (per Forwarding Equivalence Class (FEC) Type) to a peer even if the LDP speaker had zero Label bindings to advertise to that peer. Such a Notification message MUST carry: - A status TLV (with TLV E- and F-bits set to zero) that carries an "End-of-LIB" Status Code (value to be assigned by IANA). - A FEC TLV with the Typed Wildcard FEC Element [TypedWC] that identifies the FEC type for which initial label advertisements have been completed. In terms of Section 3.5.1 of RFC5036, this TLV is an "Optional Parameter" of the Notification message. An LDP speaker MUST NOT send a Notification which carries a Status TLV with the End-of-LIB Status Code to a peer unless the peer had advertised the Unrecognized Notification capability during session establishment. This applies to any LDP peers discovered via either basic discovery or extended discovery mechanism (per section 2.4 of [RFC5036]). 4.1. Missing Expected End-of-LIB Notifications There is no guarantee that an LDP speaker will receive (or send) End- of-LIB Notification from (or to) a peer even if the LDP speaker has signaled the 'Unrecognized Notification' capability (section 3). Although it is expected that an LDP speaker supporting Unrecognized Notification Capability would support sending and receiving End-of- LIB Notication, it is not mandatory by definition. Please note that this is not a concern since the LDP speaker would simply ignore the received Notification with End-of-LIB status code (or any status code) that is not recognized or supported, by definition. To deal with the possibility of missing End-of-LIB Notifications after the LDP session establishment, an LDP speaker MAY time out receipt of an expected End-of-LIB Notification. An LDP speaker SHOULD start a per-peer internal timer, called 'EOL Notification' timer (the default value of 60 seconds is RECOMMENDED, though the value of this timer SHOULD be configurable) immediately following the LDP session establishment. Asati, et al. Expires Feb 28, 2010 [Page 5] Internet-Draft draft-ietf-mpls-ldp-end-of-lib August 2009 This timer is reset by the subsequent label advertisement, and stopped by the End-of-LIB Notification message. Lacking any label advertisement from the peer, the timer would expire, resulting in the LDP speaker to behave as if it had received the End-of-LIB notification from the peer. If the End-of-LIB Notification message is received after the timer expires, then the message SHOULD be ignored. 5. Usage Guidelines The FECs known to an LDP speaker and the labels the speaker has bound to those FECs may change over the course of time. This makes determining when an LDP speaker has advertised "all" of its label bindings for a given FEC type an issue. Ultimately, this determination is a judgment call the LDP speaker makes. The following guidelines may be useful. An LDP speaker is assumed to "know" a set of FECs. Depending on a variety of criteria, such as: - The label distribution control mode in use (Independent or Ordered); - The set of FEC's to which the speaker has bound local labels; - Configuration settings which may constrain which label bindings the speaker may advertise to peers; the speaker can determine the set of bindings for a given FEC type that it is permitted to advertise to a given peer. LDP-IGP Sync, LDP Graceful Restart, and the response to a Wildcard Label Request [TypedWC] are situations that would benefit from End- of-LIB Notification. In these situations, after an LDP speaker completes its label binding advertisements to a peer, sending an End- of-LIB Notification to the peer makes their outcome deterministic. The following subsections further explain each of these situations one by one. Asati, et al. Expires Feb 28, 2010 [Page 6] Internet-Draft draft-ietf-mpls-ldp-end-of-lib August 2009 5.1. LDP-IGP Sync The LDP-IGP Synchronization [RFC5443] specifies a mechanism by which directly connected LDP speakers may delay the use of the link between them, for transit IP traffic forwarding until the labels required to support IP over MPLS traffic forwarding have been distributed and installed. Without an End-of-LIB Notification, the speaker must rely on some heuristic to determine when it has received all of its peer's label bindings. The heuristic chosen could cause LDP to signal the IGP too soon in which case the likelihood that traffic will be dropped increases, or too late in which case traffic is kept on sub-optimal paths longer than necessary. Following session establishment, with a directly connected peer that has advertised the Unrecognized Notification capability, an LDP speaker using LDP-IGP Sync may send the peer an End-of-LIB Notification after it completes advertisement of its IP label bindings to the peer. Similarly, the LDP speaker may use the End-of- LIB Notification received from a directly connected peer to determine when the peer has completed advertisement of its label bindings for IP prefixes. After receiving the notification, the LDP speaker should consider LDP to be fully operational for the link and signal the IGP to start advertising the link with normal cost. 5.2. LDP Graceful Restart LDP Graceful Restart [RFC3478] helps to reduce the loss of MPLS traffic caused by the restart of a router's LDP component. It defines procedures that allow routers capable of preserving MPLS forwarding state across the restart to continue forwarding MPLS traffic using forwarding state installed prior to the restart for a configured time period. The current behavior without End-of-LIB Notification is as follows: the restarting router and its peers consider the preserved forwarding state to be usable but stale until it is refreshed by receipt of new label advertisements following re-establishment of new LDP sessions or until the time period expires. When the time period expires, any remaining stale forwarding state is removed by the router. Receiving End-of-LIB Notification from a peer in an LDP Graceful Restart scenario enables an LDP speaker to stop using stale forwarding information learned from that peer and to recover the Asati, et al. Expires Feb 28, 2010 [Page 7] Internet-Draft draft-ietf-mpls-ldp-end-of-lib August 2009 resources it requires without having to wait until the time period expiry. The time period expiry can still be used if the End-of-LIB- Notification message is not received. 5.3. Wildcard Label Request When an LDP speaker receives a Label Request message for a Typed Wildcard FEC (e.g. a particular FEC element type) from a peer it determines the set of bindings, it is permitted to advertise the peer for the FEC type specified by the request. Assuming the peer had advertised the Unrecognized Notification capability at session initialization time, the speaker should send the peer an End-of-LIB Notification for the FEC type when it completes advertisement of the permitted bindings. As in the previous applications, receipt of the Notification eliminates uncertainty as to when the peer has completed its advertisements of label bindings for the requested Wildcard FEC Element Type. 6. Security Considerations No security considerations beyond those that apply to the base LDP specification [RFC5036] and further described in [MPLSsec] apply to signaling the End-of-LIB condition as described in this document. 7. IANA Considerations This draft introduces a new LDP Status Code and a new LDP Capability both of which require IANA assignment - The 'End-of-LIB' status code requires a code point from the Status Code Name Space. [RFC5036] partitions the Status Code Name Space into 3 regions: IETF Consensus region, First Come First Served region, and Private Use region. The authors recommend that a code point from the IETF Consensus range be assigned to the 'End-of- LIB' status code. The 'Unrecognized Notification' Capability requires a code point from the TLV Type name space. [RFC5036] partitions the TLV TYPE name space into 3 regions: IETF Consensus region, First Come Asati, et al. Expires Feb 28, 2010 [Page 8] Internet-Draft draft-ietf-mpls-ldp-end-of-lib August 2009 First Served region, and Private Use region. The authors recommend that a code point from the IETF Consensus range be assigned to the 'Unrecognized Notification' Capability. 8. Acknowledgments The authors would like to recognize Kamran Raza, who helped to formulate this draft. The authors would like to thank Ina Minei, Alia Atlas, Yakov Rekhter, Loa Andersson and Luyuan Fang for their valuable feedback and contribution. This document was prepared using 2-Word-v2.0.template.dot. Asati, et al. Expires Feb 28, 2010 [Page 9] Internet-Draft draft-ietf-mpls-ldp-end-of-lib August 2009 9. References 9.1. Normative References [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, March 1997. [RFC5036] Andersson, L., Doolan, P., Feldman, N., Fredette, A. and Thomas, B., "LDP Specification", RFC 5036, January 2001. [RFC5561] Thomas, B., Aggarwal, S., Aggarwal, R., Le Roux, J.L., "LDP Capabilities", RFC5561, May 2007. [TypedWC] Thomas, B., Minei, I., "LDP Typed Wildcard FEC", draft- ietf-mpls-ldp-typed-wildcard-03, Work in Progress, March 2008. 9.2. Informative References [RFC5443] Jork, M., Atlas, A., Fang, L., "LDP IGP Synchronization", RFC5443, Dec 2007. [RFC3478] Leelanivas, M., Rekhter, Y., Aggarwal, R., "Graceful Restart Mechanism for Label Distribution Protocol", February 2003. [MPLSsec] Fang, L., "Security Framework for MPLS and GMPLS Networks", draft-ietf-mpls-mpls-and-gmpls-security-framework-06, Work in Progress, July 13 2009. Asati, et al. Expires Feb 28, 2010 [Page 10] Internet-Draft draft-ietf-mpls-ldp-end-of-lib August 2009 Author's Addresses Rajiv Asati Cisco Systems, 7025-6 Kit Creek Rd, RTP, NC, 27709-4987 Email: rajiva@cisco.com Pradosh Mohapatra Cisco Systems, 3750 Cisco Way, San Jose, CA, 95134 Email: pmohapat@cisco.com Bob Thomas Email: bobthomas@alum.mit.edu Emily Chen Huawei Technologies No.5 Street, Shangdi Information, Haidian, Beijing, China Email: chenying220@huawei.com Asati, et al. Expires Feb 28, 2010 [Page 11]