MPLS Working Group Rajiv Asati Internet Draft Cisco Systems Intended status: Standards Track Expires:
MarchJune 2009 Pradosh Mohapatra Cisco Systems Bob Thomas Emily Chen Huawei Technologies September 15,December 29, 2008 LDP End-of-LIB draft-ietf-mpls-ldp-end-of-lib-01.txtdraft-ietf-mpls-ldp-end-of-lib-02.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 This Internet-Draft will expire on March 15, 2007.June 29, 2009. Copyright Notice Copyright (C) The IETF Trust (2008). 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...................................................2 2. Specification Language.........................................3 3. Unrecognized Notification Capability...........................3 4. Signaling Completion of Label Advertisement....................4 5. Usage Guidelines...............................................5 5.1. IGP-Sync..................................................5LDP-IGP Sync..............................................5 5.2. LDP Graceful Restart......................................6 5.3. Wildcard Label Request....................................7 5.4. Missing Expected End-of-LIB Notifications.................7 6. Security Considerations........................................7 7. IANA Considerations............................................7 8. Acknowledgments................................................8 9. References.....................................................9 9.1. Normative References......................................9 9.2. Informative References....................................9 Author's Addresses...............................................10 Intellectual Property Statement..................................10 Disclaimer of Validity...........................................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 its labels. For example, when an LDP speaker is using LDP-IGP synchronization procedures [LDPSync], 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 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]. 3. Unrecognized Notification Capability An LDP speaker MAY include a Capability Parameter [LDPCap] in the 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: 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: Should be set 1 and 0 respectively as per section 4 of LDP Capabilities [LDPCap]. 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. The LDP speaker MAY send the Notification message (per 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(with TLV E- and F-bits set to zerozero) that carries an "End-of-LIB" Status Code.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]). 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 judgement 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. 5.1. LDP-IGP Sync The LDP-IGP Synchronization [LDPSync] 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 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. 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 even if the LDP speaker has signaled its capability. Therefore, an implementation SHOULD NOT depend on the receipt of such a 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, it may behave as if it had received the notification. If the End-of-LIB Notification message is received after the time-out occurs, then the message should be ignored. 6. Security Considerations No security considerations beyond those that apply to the base LDP specification [RFC5036] and further described in [RFC5036][MPLSsec] apply to signaling the End- of-LIBEnd-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.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 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 thank Ina Minei, Alia Atlas, Yakov Rekhter, Loa Andersson and Luyuan Fang for their valuable feedback and contribution. The authors would like to recognize Kamran Raza, who helped to formulate this draft. This document was prepared using 2-Word-v2.0.template.dot. 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. [LDPCap] Thomas, B., Aggarwal, S., Aggarwal, R., Le Roux, J.L., "LDP Capabilities", draft-ietf-mpls-ldp-capabilities-02, Work in Progress, 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 [LDPSync] Jork, M., Atlas, A., Fang, L., "LDP IGP Synchronization", draft-ietf-mpls-ldp-igp-sync-02, Work in Progress, June 2008. [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-04, Work in Progress, Nov 2008. Author's Addresses Rajiv Asati Cisco Systems, 7025-6 Kit Creek Rd, RTP, NC, 27709-4987 Email: firstname.lastname@example.org Pradosh Mohapatra Cisco Systems, 3750 Cisco Way, San Jose, CA, 95134 Email: email@example.com Bob Thomas Email: firstname.lastname@example.org Emily Chen Huawei Technologies No.5 Street, Shangdi Information, Haidian, Beijing, China Email: email@example.com Intellectual Property Statement The IETF takes no position regarding the validity or scope of any Intellectual Property Rights or other rights that might be claimed to pertain to the implementation or use of the technology described in this document or the extent to which any license under such rights might or might not be available; nor does it represent that it has made any independent effort to identify any such rights. Information on the procedures with respect to rights in RFC documents can be found in BCP 78 and BCP 79. 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