Network Working Group Rajiv Asati Internet Draft Cisco Systems, Inc. Expiration Date: May 2008 Pradosh Mohapatra Cisco Systems, Inc. Bob Thomas Cisco Systems, Inc. Emily Chen Huawei Technologies Co., Ltd. November 2007 LDP End-of-LIB draft-asati-mpls-ldp-end-of-lib-01.txt Status of this Memo By submitting this Internet-Draft, each author represents that any applicable patent or other IPR claims of which he or she is aware have been or will be disclosed, and any of which he or she becomes aware will be disclosed, in accordance with Section 6 of 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. Asati, et al. [Page 1] Internet Draft draft-asati-mpls-ldp-end-of-lib-01.txt November 2007 Copyright Notice Copyright (C) The IETF TRUST (2007). Abstract 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 its labels. These include session establishment when LDP-IGP sync is in use and session re-establishment following loss of an LDP session when LDP graceful restart is in use. 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 ............... 3 4 Signaling Completion of Label Advertisement ........ 4 5 Usage Guidelines ................................... 5 5.1 IGP-Sync ........................................... 5 5.2 LDP Graceful Restart ............................... 6 5.3 Wildcard Label Request ............................. 6 5.4 Missing Expected End-of-LIB Notifications .......... 7 6 IANA Considerations ................................ 7 7 Security Considerations ............................ 7 8 References ......................................... 7 9 Author Information ................................. 8 10 Intellectual Property Statement .................... 9 11 Full Copyright Statement ........................... 9 Asati, et al. [Page 2] Internet Draft draft-asati-mpls-ldp-end-of-lib-01.txt November 2007 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 its labels. For example, when an LDP speaker is using LDP-IGP synchronization procedures [LDPSynch] 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 [LDPCap] at session establishment time for informing a peer that an LDP speaker is capable of handling Notification messages that carry unrecognized Status Codes. 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]. 3. Unrecognized Notification Capability An LDP speaker MAY include a Capability Parameter [LDPCap] in an Initialization message to inform a peer that it ignores Notification Messages that carry a Status 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: Asati, et al. [Page 3] Internet Draft draft-asati-mpls-ldp-end-of-lib-01.txt November 2007 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 | +-+-+-+-+-+-+-+-+ where: U and F bits: As specified by RFC5036. 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 MAY signal completion of its label advertisements to a peer by means of a Notification message if its peer had advertised the Unrecognized Notification capability during session establishment. 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. End-of-LIB is a new Status Code. - 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 unless its peer had advertised the Unrecognized Notification capability during session establishment. Asati, et al. [Page 4] Internet Draft draft-asati-mpls-ldp-end-of-lib-01.txt November 2007 5. Usage Guidelines The FEC's known to an LDP speaker and the labels the speaker has bound to those FEC's 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 judgement call the LDP speaker makes. The following guidelines may be useful. An LDP speaker is assumed to "know" a set of FEC's. 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. 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 it should send the peer an End-of-LIB Notification. The following considers each of these situations in turn. 5.1. IGP-Sync LDP-IGP Sync is a mechanism directly connected LDP speakers may use to delay using the link connecting them for IP traffic until the labels required to support IP over MPLS traffic on the link have been learned. 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 Asati, et al. [Page 5] Internet Draft draft-asati-mpls-ldp-end-of-lib-01.txt November 2007 Notification after it completes advertisement of its IP label bindings to the peer. The LDP speaker may use an End-of-LIB Notification from a directly connected peer to determine when the peer has completed its label advertisements for IP prefixes. After the speaker has exchanged End-of-LIB Notifications with the peer the speaker should consider LDP to be fully operational for the link to the peer and should signal the IGP to start advertising the link with normal cost. 5.2. LDP Graceful Restart LDP Graceful Restart helps 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 for a pre-agreed upon period using forwarding state installed prior to the restart. During that period 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. When the period elapses any remaining stale forwarding state is removed by the router. Receipt of the 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 resources it requires without having to wait until the timeout occurs. 5.3. Wildcard Label Request When an LDP speaker receives a Label Request message for a Typed Wildcard FEC 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. Asati, et al. [Page 6] Internet Draft draft-asati-mpls-ldp-end-of-lib-01.txt November 2007 5.4. Missing Expected End-of-LIB Notifications There is no guarantee that an LDP speaker will receive End-of-LIB Notifications from a peer in a situation where it may be used. Therefore, in situations where the End-of-LIB Notification may be used an implementation SHOULD NOT depend on the receipt of the notification. To deal with the possibility of missing notifications an LDP speaker may time out receipt of an expected End-of-LIB Notification, and if the timeout occurs may behave as if it had received the notification. 6. IANA Considerations This draft introduces a new LDP Status Code and a new LDP Capability both of which require IANA assignment. 7. Security Considerations No security considerations beyond those that apply to the base LDP specification and described in [RFC5036] apply to signaling the End- of-LIB condition as described in this document. 8. References Normative References [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC2119, March 1997. [RFC5036] Andersson, L., Ed., Minei, I., Ed., and Thomas, B., Ed., "LDP Specification", RFC 5036, October 2007. [LDPCap] Thomas, B., Aggarwal, S., Aggarwal, R., Le Roux, J.L., "LDP Capabilities", draft-ietf-mpls-ldp-capabilities-00, Work in Progress, May 2007. [TypedWC] Thomas, B., Minei, I., "LDP Typed Wildcard FEC", draft- ietf-mpls-ldp-typed-wildcard-01, Work in Progress, May 2007. Asati, et al. [Page 7] Internet Draft draft-asati-mpls-ldp-end-of-lib-01.txt November 2007 Informative References [LDPSynch] Jork, M., Atlas, A., Fang, L., "LDP IGP Synchronization", draft-ietf-mpls-igp-sync-00,, Work in Progress, September 2007. [RFC3478] Leelanivas, M., Rekhter, Y., Aggarwal, R., "Graceful Restart Mechanism for Label Distribution Protocol", February 2003. 9. Author Information Rajiv Asati Cisco Systems, Inc. Mail Stop RTP6P/2/1 7025-6 Kit Creek Road PO Box 14987 Research Triangle Park , NORTH CAROLINA 27709-4987 Email: rajiva@cisco.com Pradosh Mohapatra Cisco Systems, Inc. Mail Stop SJC15/3/3 3750 Cisco Way San Jose , CALIFORNIA 95134 Email: pmohapat@cisco.com Bob Thomas Cisco Systems, Inc. 1414 Massachusetts Ave. Boxborough MA 01719 Email: rhthomas@cisco.com Emily Chen Huawei Technologies Co., Ltd. NO.5 Streat, Shangdi Information Haidian Beijing China Email: chenying220@huawei.com Asati, et al. [Page 8] Internet Draft draft-asati-mpls-ldp-end-of-lib-01.txt November 2007 10. 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The IETF invites any interested party to bring to its attention any copyrights, patents or patent applications, or other proprietary rights that may cover technology that may be required to implement this standard. Please address the information to the IETF at ietf- ipr@ietf.org. 11. Full Copyright Statement Copyright (C) The IETF Trust (2007). This document is subject to the rights, licenses and restrictions contained in BCP 78, and except as set forth therein, the authors retain all their rights. This document and the information contained herein are provided on an "AS IS" basis and THE CONTRIBUTOR, THE ORGANIZATION HE/SHE REPRESENTS OR IS SPONSORED BY (IF ANY), THE INTERNET SOCIETY, THE IETF TRUST AND THE INTERNET ENGINEERING TASK FORCE DISCLAIM ALL WARRANTIES, EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF THE INFORMATION HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED WARRANTIES OF MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE. 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