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Internet Engineering Task Force (IETF) IJ. Wijnands, Ed.Request for Comments: 7715 K. RazaCategory: Standards Track Cisco Systems, Inc.ISSN: 2070-1721 A. Atlas Juniper Networks, Inc. J. Tantsura Ericsson Q. Zhao Huawei Technology January 2016Multipoint LDP (mLDP) Node ProtectionAbstract This document describes procedures to support node protection for Point-to-Multipoint and Multipoint-to-Multipoint Label Switched Paths (P2MP and MP2MP LSPs) that have been built by the Multipoint Label Distribution Protocol (mLDP). In order to protect a node N, the Point of Local Repair (PLR) Label Switching Router (LSR) of N must learn the Merge Point (MPT) LSR(s) of node N such that traffic can be redirected to them in case node N fails. Redirecting the traffic around the failed node N depends on existing Point-to-Point (P2P) Label Switched Paths (LSPs). The pre-established LSPs originate from the PLR LSR and terminate on the MPT LSRs while bypassing LSR N.Status of This Memo This is an Internet Standards Track document. This document is a product of the Internet Engineering Task Force (IETF). It represents the consensus of the IETF community. It has received public review and has been approved for publication by the Internet Engineering Steering Group (IESG). Further information on Internet Standards is available inSection 2 of RFC 5741. Information about the current status of this document, any errata, and how to provide feedback on it may be obtained athttp://www.rfc-editor.org/info/rfc7715.Wijnands, et al. Standards Track [Page 1]

RFC 7715                  mLDP Node Protection              January 2016Copyright Notice   Copyright (c) 2016 IETF Trust and the persons identified as the   document authors.  All rights reserved.   This document is subject toBCP 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 Contents1.  Introduction . . . . . . . . . . . . . . . . . . . . . . . . .31.1.  Conventions Used in This Document  . . . . . . . . . . . .31.2.  Terminology  . . . . . . . . . . . . . . . . . . . . . . .42.  PLR Determination  . . . . . . . . . . . . . . . . . . . . . .42.1.  Transit Node Procedure . . . . . . . . . . . . . . . . . .52.2.  MP2MP Root Node Procedure  . . . . . . . . . . . . . . . .62.3.  PLR Information Encoding . . . . . . . . . . . . . . . . .73.  Using the tLDP Session . . . . . . . . . . . . . . . . . . . .94.  Link or Node Failure . . . . . . . . . . . . . . . . . . . . .104.1.  Reconvergence after Node or Link Failure . . . . . . . . .114.1.1.  Node Failure . . . . . . . . . . . . . . . . . . . . .124.1.2.  Link Failure . . . . . . . . . . . . . . . . . . . . .124.1.3.  Switching to New Primary Path  . . . . . . . . . . . .125.  mLDP Capabilities for Node Protection  . . . . . . . . . . . .135.1.  PLR Capability . . . . . . . . . . . . . . . . . . . . . .135.2.  MPT Capability . . . . . . . . . . . . . . . . . . . . . .145.3.  The Protected LSR  . . . . . . . . . . . . . . . . . . . .145.4.  The Node Protection Capability . . . . . . . . . . . . . .156.  Security Considerations  . . . . . . . . . . . . . . . . . . .167.  IANA Considerations  . . . . . . . . . . . . . . . . . . . . .168.  References . . . . . . . . . . . . . . . . . . . . . . . . . .178.1.  Normative References . . . . . . . . . . . . . . . . . . .178.2.  Informative References . . . . . . . . . . . . . . . . . .17   Acknowledgments  . . . . . . . . . . . . . . . . . . . . . . . . .18   Contributors . . . . . . . . . . . . . . . . . . . . . . . . . . .18   Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . .19Wijnands, et al.             Standards Track                    [Page 2]

RFC 7715                  mLDP Node Protection              January 20161.  Introduction   This document describes procedures to support node protection for   Point-to-Multipoint and Multipoint-to-Multipoint Label Switched Paths   (P2MP and MP2MP LSPs) that have been built by the Multipoint Label   Distribution Protocol (mLDP) [RFC6388].  In order to protect a node   N, the Point of Local Repair (PLR) LSR of N must learn the Merge   Point (MPT) LSR(s) of node N such that traffic can be redirected to   them in case node N fails.  Redirecting the traffic around the failed   node N depends on existing P2P LSPs.  The pre-established LSPs   originate from the PLR LSR and terminate on the MPT LSRs while   bypassing LSR N.  The procedures to set up these P2P LSPs are outside   the scope of this document, but one can imagine using techniques   based on the Resource Reservation Protocol for Traffic Engineering   (RSVP-TE) [RFC5420] or Label Distribution Protocol (LDP) Loop-Free   Alternate (LFA) [RFC5286] to accomplish this.   The solution described in this document notifies the PLR(s) of the   MPT LSR(s) via signaling using a Targeted LDP (tLDP) session   [RFC7060].  By having a tLDP session with the PLR, no additional   procedures need to be defined in order to support Make-Before-Break   (MBB), Graceful Restart (GR), and Typed Wildcard Forwarding   Equivalence Class (FEC).  All this is achieved at the expense of   having additional tLDP sessions between each MPT and PLR LSR.   In order to allow a node to be protected against failure, the LSRs   providing the PLR and the MPT functionality as well as the protected   node MUST support the functionality described in this document.  LDP   capability negotiation [RFC5561] is used to signal the availability   of the functionality between the participating nodes; these nodes   MUST support capability negotiation.1.1.  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 inRFC 2119 [RFC2119].   The term "node" is used to refer to an LSR; "node" and "LSR" are used   interchangeably in this document.  The terms "PLR" and "MPT" are used   as shorthand to refer to "PLR LSR" and "MPT LSR", respectively.Wijnands, et al.             Standards Track                    [Page 3]

RFC 7715 mLDP Node Protection January 20161.2. Terminology mLDP: Multipoint LDP PLR: Point of Local Repair The LSR that redirects the traffic to one or more Merge Point LSRs. MPT: Merge Point The LSR that merges the backup LSP with the primary LSP. Note, there can be multiple MPT LSRs for a single MP-LSP node protection. tLDP: Targeted LDP MP LSP: Multi-Point LSP Either a P2MP or MP2MP LSP. root node: The root of either a P2MP or MP2MP LSP as defined in [RFC6388].2. PLR Determination In order for an MPT to establish a tLDP session with a PLR, it first has to learn the PLR for a particular MP LSP. It is the responsibility of the protected node N to advertise the address of the PLR to the MPT. The PLR address for an MP LSP on node N is the address of the upstream LDP peer, but only when node N is NOT the root node of the MP2MP LSP. If the upstream LDP peer is unable to function as PLR, the procedures in this document do not apply and are out of the scope. If node N is the root node, the procedures are slightly different as described inSection 2.2. The procedures that follow assume that all the participating nodes (N, PLRs, MPTs) are enabled (e.g., by a user configuration) to support and implement the PLR determination feature. The procedures as documented in this RFC require the protected node to be directly connected to the PLR and MPT nodes. This is because mLDP depends on unicast routing to determine the upstream LSR and unicast routing (by default) only has information about the next hop and not beyond that. Support for non-directly connected PLR and MPT nodes is outside the scope of this document.Wijnands, et al. Standards Track [Page 4]

RFC 7715 mLDP Node Protection January 20162.1. Transit Node Procedure Below are the procedures for when the protected node is a transit node along the path to the root. root ^ | (LSR1) . | . . | . . (N) . . / \ . . / \. (LSR2) (LSR3) | | N: The node being protected. ...: Backup LSPs from LSR1 to LSR2 and LSR3. Figure 1 Node N uses the root address of the MP LSP to determine the upstream LSR for a given MP LSP following the procedures as documented inSection 2.4.1.1 of [RFC6388]. The upstream LSR in Figure 1 is LSR1 because it is the first hop along the shortest path to reach the root address. After determining the upstream LSR, node N (which has the node protection feature enabled) MUST advertise the address of LSR1 as the PLR address to the downstream members of the MP LSP (i.e., LSR2 and LSR3) if the given downstream member has announced support for node protection (seeSection 5 regarding capability negotiation). For the format and encoding of PLR address information, seeSection2.3. Note, in order for the protected traffic to reach nodes LSR2 and LSR3, LSR1 MUST have two unidirectional LSPs to LSR2 and LSR3, bypassing node N. The procedures for setting up these LSPs are outside the scope of this document.Wijnands, et al. Standards Track [Page 5]

RFC 7715 mLDP Node Protection January 20162.2. MP2MP Root Node Procedure Below are the procedures for when the protected node is the root of an MP2MP LSP. Consider figure 2 below. | (LSR1) . | . . | . . (N) . root . / \ . . / \. (LSR2)....(LSR3) | | N: The MP2MP root node being protected. ...: Backup LSPs between LSR1, LSR2, and LSR3. Figure 2 Assume that LSR1, LSR2, and LSR3 are all members of an MP2MP LSP for which N is the root node. Since N is the root of the MP2MP LSP, there is no upstream LSR and no 'single' PLR LSR for protecting node N. In order to protect node N, all the directly connected members of the MP2MP must participate in protecting node N by acting both as PLR and MPT LSR. An LSR will act as MPT for traffic coming from the other LSR(s) and it will act as PLR for traffic it is sending to the other LSR(s). Since node N knows the members of the MP2MP LSP, it will advertise the member list to its directly connected members, excluding the member it is sending to. For example, node N will advertise list {LSR3,LSR1} to LSR2 excluding LSR2 from it. Instead of advertising a single PLR when node N is not the root, a list of PLRs is advertised using the procedures documented inSection 2.3. It should be noted that the MP2MP root node protection mechanism doesn't replace the Root Node Redundancy (RNR) procedures as described inSection 7 of [RFC6388]. The node protection procedures in this document will help in restoring traffic for the existing MP2MP LSPs after node failure, but a new root node has to be elected eventually in order to allow new MP2MP LSPs to be created. Note, in order for the protected traffic to be exchanged between nodes LSR1, LSR2, and LSR3, bidirectional LSPs have to exist between the LSRs, bypassing node N. The procedures for setting up these LSPs are outside the scope of this document.Wijnands, et al. Standards Track [Page 6]

RFC 7715                  mLDP Node Protection              January 20162.3.  PLR Information Encoding   The upstream LSR address is conveyed via an LDP Notification message   with an MP Status TLV, where the MP Status TLV contains a new "PLR   Status Value Element" that specifies the address of the PLR.   The new "PLR Status Value Element" is encoded as described below.   PLR Status Element:    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   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+   | Type =  2     |           Length              |  Addr Family  |   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+   | Addr Fam cont | Num PLR entry |                               |   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+                               +   |                                                               |   |                         PLR entry (1 or more)                 ~   |                                                               |   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+   Where      Type: PLR Status Value Element (Type 2).      Length: The Length field is an unsigned integer that encodes the      length of the Status Value following the Length field.  The      encoded Length varies based on the Addr Family and the number of      PLR entries.      Addr Family: Two-octet quantity containing a value from IANA's      "Address Family Numbers" registry [AFI] that encodes the address      family for the PLR address encoded in the PLR entry.      Num PLR entry: Element as an unsigned integer followed by the      number of "PLR entry" fields in the format specified below.Wijnands, et al.             Standards Track                    [Page 7]

RFC 7715                  mLDP Node Protection              January 2016   The format of a "PLR Entry" is as follows:    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   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+   |A|        Reserved             |       PLR address             |   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+   ~                  PLR address (cont)                           ~   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+   Where      A bit: 0 = Withdraw, 1 = Add.      Reserved: 15 bits; MUST be zero on transmit and ignored on      receipt.      PLR address: PLR address encoded according to the Address Family      field encoded in the PLR Status Value Element.  Note that the      length of the PLR address field is specific to the Address Family      that is encoded.   The size of a "PLR Entry" is the 2 octets ("A bit + Reserved") + PLR   address length.  The length of the PLR address is dependent on the   Address Family as encoded in the PLR Status Value Element.  The size   of a "PLR entry" is 6 octets and 18 octets, respectively, for an IPv4   PLR address and an IPv6 PLR address.   If the PLR address on N changes for a given MP LSP, N needs to   trigger a new PLR Status to update the MPT(s).  Node N can advertise   or withdraw a given PLR from its PLR set by setting the A bit to 1 or   0 respectively in the corresponding PLR entry.  Removing a PLR   address is likely due to a link failure; see the procedures as   documented inSection 4.1.  To remove all PLR addresses belonging to   the encoded Address Family, an LSR N MUST encode a PLR Status Value   Element with no PLR entry and the "Num PLR entry" field MUST be set   to zero.   Both the PLR Status and an MP FEC TLV [RFC5036] MUST be included in   the LDP Notification message so that a receiver is able to associate   the PLR Status with the MP LSP.Wijnands, et al.             Standards Track                    [Page 8]

RFC 7715 mLDP Node Protection January 20163. Using the tLDP Session The receipt of a PLR MP Status (with PLR addresses) for an MP LSP on a receiving LSR makes it an MPT for node protection. If not already established, the MPT LSR MUST establish a tLDP session with all of the learned PLR addresses using the procedures as documented in [RFC7060]. Using Figure 1 as the reference topology, let us assume that both LSR2 and LSR3 are MPTs and have established a tLDP session with the PLR being LSR1. Assume that both LSR2 and LSR3 have a FEC <R,X> with an upstream LSR N and label Ln assigned to FEC towards N. The MPTs will create a secondary upstream LSR for the FEC <R,X> (using the received PLR address) and assign label Lpx to it. The MPTs will do that for each PLR address that was learned for the MP LSP. In this example, the MPTs will have a FEC <R,X> with two local labels associated with it. Label Ln that was assigned to N using the normal mLDP procedures, and Label Lpx that was assigned to PLR (LSR1) for the purpose of node protection. Note, when the protected node is an MP2MP root node, there will be an upstream LSR for each PLR address that was advertised along with a unique Label Lpx. The receipt of a FEC Label Mapping alone over the tLDP session from MPT on a PLR conveys the label information but does not convey the node being protected. The information about a protected node is known to the MPT LSR and needs to be communicated to the PLR as well. For this reason, the FEC Label Mapping (FEC <R,X> : Lpx) sent by the MPT over the tLDP session to the PLR MUST include a Status TLV with an MP Status and a new LDP MP Status Value Element called the "Protected Node Status Value Element". This new value element is used to specify the address of the node being protected. The "Protected Node Status Value Element" has 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 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Type = 3 | Length | Addr Family | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Addr Fam cont | Node address ~ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Type : Protected Node Status Value Element (Type 3). Length: The Length field is an unsigned integer that encodes the length of the Status Value following the Length field. The encoded Length varies based on the Address Family and is 6 octets for Address Family + IPv4 address and 18 octets for Address Family + IPv6 address.Wijnands, et al. Standards Track [Page 9]

RFC 7715                  mLDP Node Protection              January 2016      Addr Family: Two-octet quantity containing a value from IANA's      "Address Family Numbers" registry [AFI] that encodes the address      family for the node address.      Node address: Protected node address encoded according to the      Address Family field.   When a PLR receives a Label Mapping for FEC <R,X> that includes a   Protected Node Status, it will only use that label binding once the   Node advertised in the Status value becomes unreachable.  If the LSP   is an MP2MP LSP, the PLR would have assigned a Label Mapping for the   upstream MP2MP FEC Element to the MPT ([RFC6388], Section 3) for FEC   <R,X>.  This label binding on the MPT MUST only be used once node N   becomes unreachable.   The procedures to determine if a node is unreachable is a local   decision and not spelled out in this document.  Typically, link   failure or Bidirectional Forwarding Detection (BFD) can be used to   determine and detect node unreachability.4.  Link or Node Failure   Consider the following topology:                           root                            ^                            |                        . (LSR1)                      .   / |  .                     .  (M) |   .                     .    \ |    .                      .    (N)   .                       .   /  \  .                        . /    \.                      (LSR2)  (LSR3)                         |      |               N: The node being protected.               M: The backup node to protect link LSR1 - N.               ...: Backup LSPs from LSR1 to LSR2 and LSR3.                              Figure 3   Assume that LSR1 is the PLR for protected node N and that LSR2 and   LSR3 are MPTs for node N.  When LSR1 discovers that node N is   unreachable, it cannot immediately determine whether it is the link   from LSR1 to N or the actual node N that has failed.  In Figure 3,Wijnands, et al.             Standards Track                   [Page 10]

RFC 7715                  mLDP Node Protection              January 2016   the link between LSR1 and N is also protected using Fast Reroute   (FRR) [RFC4090] link protection via node M.  LSR1 MAY simultaneously   invoke both link protection via node M to N using redirection of the   traffic and node protection directly to LSR1 and LSR2.  If only the   link failed, LSR2 and LSR3 will receive the packets twice due to the   two protection mechanisms.  To prevent duplicate packets being   forwarded to the receivers on the tree, LSR2 and LSR3 need to   determine from which upstream node they should accept the packets.   This can be either from the primary upstream LSR N or from the   secondary upstream LSR1, but never both at the same time.  The   selection between the primary upstream LSR or (one or more) secondary   upstream LSRs (on LSR2 and LSR3) is based on the reachability of the   protected node N.  As long as N is reachable from an MPT, the MPT   should accept and forward the MPLS packets from N.  Once N becomes   unreachable, the LSPs from secondary upstream PLR LSRs (LSR1 in our   example) are activated.  Note that detecting if N is unreachable is a   local decision and not spelled out in this document.   Typically, link failure or BFD can be used to determine and detect   node unreachability.4.1.  Reconvergence after Node or Link Failure   Consider the following topology:                           root                            ^                         _  |                      /.  (LSR1)                     /.   /. |  .\                    /.  (M). |   .\                  (P).    \. |    .\                    \.     ( N )   .(Q)                     \.   /     \   ./                      \. /       \ ./                     (LSR2)     (LSR3)                        |          |               N: The node being protected.               M: The backup node to protect link 'LSR1 - N'.               P and Q: The nodes on the new primary path after                  failure of node N.               ...: P2P backup LSPs.                               Figure 4Wijnands, et al.             Standards Track                   [Page 11]

RFC 7715 mLDP Node Protection January 2016 Assume that LSR1 has detected that node N is unreachable and invoked both the link protection and node protection procedures as described in this example. LSR1 is acting as PLR and sending traffic over both the backup P2P LSP to node N (via M) and the P2P LSPs directly to LSR2 and LSR3, acting as MPT LSRs. The sequence of events is dependent on whether the link from LSR1 to N has failed or node N itself has failed. The nodes downstream from the protected node (and participating in node protection) MUST have the capability to determine that the protected node has become unreachable. Otherwise, the procedures below cannot be applied.4.1.1. Node Failure If node N failed, both LSR2 and LSR3 will have changed the primary upstream LSR to the secondary upstream LSR (LSR1) due to node N being unreachable. With that, the label bindings previously assigned to LSR1 will be activated on the MPTs (LSR2 and LSR3) and the label binding to N will be disabled. Traffic is now switched over to the label bindings that were installed for node protection.4.1.2. Link Failure If the link 'LSR1 - N' has failed, both LSR2 and LSR3 will not change the primary upstream LSR because node N is still reachable. LSR2 and LSR3 will receive traffic over two different bindings, the primary label binding assigned to node N (due to link protection via node M) as well as over the binding assigned to LSR1 for the node protection. Since the secondary upstream LSRs have not been activated, the traffic received due to node protection will be dropped. Node N will reconverge and update LSR2 and LSR3 (Section 2.3) with the information that the PLR address (LSR1) is no longer applicable and must be removed. In response, LSR2 and LSR3 MUST send a Label Withdraw to LSR1 to withdraw the label binding. This will stop the traffic being forwarded over the backup P2P LSPs for node protection. LSR1 will respond back with a Label Release as soon as the binding has been removed.4.1.3. Switching to New Primary Path The network will eventually reconverge and a new best path to the root will be found by LSR2 and LSR3. LSR2 will find that P is its new primary upstream LSR to reach the root and LSR3 will find Q. Note that although the current active upstream LSR can either be node N or LSR1 (depending on link or node failure), it does not matter for the following procedures. Both LSR2 and LSR3 SHOULD use the Make- Before-Break (MBB) procedures as described inSection 8 of [RFC6388] to switch to the new primary upstream node. As soon as the new primary upstream LSRs P and Q are activated, a Label Withdraw messageWijnands, et al. Standards Track [Page 12]

RFC 7715 mLDP Node Protection January 2016 MUST be sent to the old upstream LSR. Note that an upstream LSR switchover from a tLDP neighbor to a directly connected LDP neighbor is no different compared to switching between two directly connected neighbors. After the Label Withdraw message has been received by LSR1 or node N, forwarding will stop and a Label Release will be sent. When it is determined that after reconvergence there is no more interest in the tLDP session between the MPT and the PLR, the tLDP session MAY be taken down. It is possible that having no more interest in the tLDP session is temporarily due to link flapping. In order to avoid the tLDP session from flapping, it is RECOMMENDED to apply a delay before tearing down the session. Determining the delay is a local implementation matter. If the operator is not concerned with the tLDP session flapping and/or other procedures are in place to avoid this altogether, there is no need to apply the delay.5. mLDP Capabilities for Node Protection In order to describe the capabilities of the participating LSRs, this document is organizing it per role in the network, i.e., Point of Local Repair (PLR), Merge Point (MPT), and protected node (as depicted in Figure 1).5.1. PLR Capability A PLR node should handle the following conditions: 1. Accept an incoming tLDP session from the MPT LSR. 2. Support the receipt of a "Protected Node Status Value Element" status in an MP Status TLV over tLDP session. 3. Upon node failure detection, capable of switching traffic towards one or more MPT(s) over a P2P LSP (bypassing N) using the labels previously advertised for MP LSPs over the tLDP session. An LSR capable of performing these actions will advertise itself as PLR capable in the Node Protection Capability (seeSection 5.4). This is a unidirectional capability announced from PLR to the protected LSR.Wijnands, et al. Standards Track [Page 13]

RFC 7715 mLDP Node Protection January 20165.2. MPT Capability An MPT node should handle the following conditions; 1. Support the receipt of "PLR Status Value Element" in an MP Status TLV from a protected node N. 2. Support to transmit "Protected Node Status Value Element" in an MP Status TLV to a PLR. An LSR capable of performing these actions will advertise itself as MPT capable in the Node Protection Capability (seeSection 5.4). This is a unidirectional capability from MPT to the protected LSR.5.3. The Protected LSR A protected node should handle the following conditions: 1. Determine the PLR and MPT capability for directly connected upstream and downstream LSRs for a given MP FEC. 2. Support transmitting of "PLR Status Value Element" in an MP Status TLV to one or more downstream MPT LSRs. The protected LSR does not advertise any capability for mLDP Node Protection because it does not need to receive any of the defined MP Status values as described above. However, the protected node does play an important role in the signaling and setup of the node protection. For a given FEC, the protected node can only send PLR information to a downstream LSR if the PLR has signaled the PLR capability and the downstream LSR has signaled the MPT capability. When the downstream LSR (acting as MPT) receives the PLR Status, it can implicitly infer that the advertised LSR(s) are PLR capable. The MPT LSR can now proceed with setting up a tLDP session with the PLR(s) and MP LSP node protection signaling.Wijnands, et al. Standards Track [Page 14]

RFC 7715                  mLDP Node Protection              January 20165.4.  The Node Protection Capability   We define a single capability "MP Node Protection Capability" to   announce the PLR and MPT capability.   The format of the capability parameter TLV is as follows:    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| Type = 0x0972             |           Length = 2          |   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+   |S| Reserved    |P|M| Reserved  |   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+   Where      U/F bits: MUST be set to 1 and 0, respectively (as per [RFC5561]).      Type: MP Node Protection Capability (Type = 0x0972).      Length: Unsigned integer; MUST be set to 2.      S bit: Set to 1 to announce and 0 to withdraw the capability (as      per [RFC5561]).      P bit: Set to 1 to indicate the PLR is capable of MP LSP node      protection.      M bit: Set to 1 to indicate the MPT is capable of MP LSP node      protection.      Reserved: MUST be zero on transmit and ignored on receipt.   The above capability can be sent in an LDP Initialization message to   announce capability at the session establishment time, or it can be   sent in an LDP Capability message to dynamically update (announce or   withdraw) its capability towards its peer using procedures specified   in [RFC5561].   An LSR that supports the PLR functionality LSR MAY send this   capability to its downstream MP peers with P bit set; whereas, an LSR   that supports the MPT functionality MAY send this capability to its   upstream peer with M bit set.  Moreover, an LSR that supports both   the PLR and MPT functionality MAY sent this capability to its peers   with both P and M bit set.Wijnands, et al.             Standards Track                   [Page 15]

RFC 7715                  mLDP Node Protection              January 20166.  Security Considerations   The procedures in this document add two new TLVs to existing LDP   messages.  Those TLVs can be protected by the mechanisms that are   used to protect LDP messages as described in [RFC6388] and [RFC5920].   If it were possible to attack the mechanisms described in this   document, an LSR (a PLR or a MPT) could be induced to support a large   number of tLDP sessions and set up an even larger number of LSPs.   The security mechanisms described in [RFC6388] and [RFC5920] are   believed to be adequate, but an implementation could provide   additional protection by counting such protection sessions and LSPs   and producing a log message to the operator if a threshold is   crossed.7.  IANA Considerations   IANA has allocated the following two new code points from the "LDP MP   Status Value Element type" registry within the "Label Distribution   Protocol (LDP) Parameters" registry.      Value | Name                                   | Reference      ------+----------------------------------------+-----------         2  | PLR Status Value Element               | this doc      ------+----------------------------------------+-----------         3  | Protected Node Status Value Element    | this doc   IANA has assigned the following new code point for a new Capability   Parameter TLV.  The code point has been assigned from the IETF   Consensus range of the "TLV Type Name Space" registry within the   "Label Distribution Protocol (LDP) Parameters" registry.      Value | Description                   | Reference | Notes/Reg Date      ------+-------------------------------+-----------+---------------      0x0972| MP Node Protection Capability | this doc  |Wijnands, et al.             Standards Track                   [Page 16]

RFC 7715                  mLDP Node Protection              January 20168.  References8.1.  Normative References   [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate              Requirement Levels",BCP 14,RFC 2119,              DOI 10.17487/RFC2119, March 1997,              <http://www.rfc-editor.org/info/rfc2119>.   [RFC5036]  Andersson, L., Ed., Minei, I., Ed., and B. Thomas, Ed.,              "LDP Specification",RFC 5036, DOI 10.17487/RFC5036,              October 2007, <http://www.rfc-editor.org/info/rfc5036>.   [RFC6388]  Wijnands, IJ., Ed., Minei, I., Ed., Kompella, K., and B.              Thomas, "Label Distribution Protocol Extensions for Point-              to-Multipoint and Multipoint-to-Multipoint Label Switched              Paths",RFC 6388, DOI 10.17487/RFC6388, November 2011,              <http://www.rfc-editor.org/info/rfc6388>.   [RFC5561]  Thomas, B., Raza, K., Aggarwal, S., Aggarwal, R., and JL.              Le Roux, "LDP Capabilities",RFC 5561,              DOI 10.17487/RFC5561, July 2009,              <http://www.rfc-editor.org/info/rfc5561>.   [RFC7060]  Napierala, M., Rosen, E., and IJ. Wijnands, "Using LDP              Multipoint Extensions on Targeted LDP Sessions",RFC 7060,              DOI 10.17487/RFC7060, November 2013, <http://www.rfc-editor.org/info/rfc7060>.   [AFI]      IANA, "Address Family Numbers",              <http://www.iana.org/assignments/address-family-numbers>.8.2.  Informative References   [RFC4090]  Pan, P., Ed., Swallow, G., Ed., and A. Atlas, Ed., "Fast              Reroute Extensions to RSVP-TE for LSP Tunnels",RFC 4090,              DOI 10.17487/RFC4090, May 2005,              <http://www.rfc-editor.org/info/rfc4090>.   [RFC5286]  Atlas, A., Ed., and A. Zinin, Ed., "Basic Specification              for IP Fast Reroute: Loop-Free Alternates",RFC 5286,              DOI 10.17487/RFC5286, September 2008,              <http://www.rfc-editor.org/info/rfc5286>.Wijnands, et al.             Standards Track                   [Page 17]

RFC 7715                  mLDP Node Protection              January 2016   [RFC5420]  Farrel, A., Ed., Papadimitriou, D., Vasseur, JP., and A.              Ayyangarps, "Encoding of Attributes for MPLS LSP              Establishment Using Resource Reservation Protocol Traffic              Engineering (RSVP-TE)",RFC 5420, DOI 10.17487/RFC5420,              February 2009, <http://www.rfc-editor.org/info/rfc5420>.   [RFC5920]  Fang, L., Ed., "Security Framework for MPLS and GMPLS              Networks",RFC 5920, DOI 10.17487/RFC5920, July 2010,              <http://www.rfc-editor.org/info/rfc5920>.Acknowledgments   The authors thank Nagendra Kumar, Duan Hong, Martin Vigoureux, Kenji   Fujihira, Loa Andersson, and Ben Campbell for their comments on this   document.  Also, many thanks to Elwyn Davies and Adrian Farrel for   the detailed review and contribution to this document.Contributors   The following individual contributed to this document:   Eric Rosen   Juniper Networks, Inc.   10 Technology Park Drive   Westford, MA  01886   United States   Email: erosen@juniper.netWijnands, et al.             Standards Track                   [Page 18]

RFC 7715                  mLDP Node Protection              January 2016Authors' Addresses   IJsbrand Wijnands (editor)   Cisco Systems, Inc.   De kleetlaan 6a   Diegem  1831   Belgium   Email: ice@cisco.com   Kamran Raza   Cisco Systems, Inc.   2000 Innovation Drive   Ottawa, Ontario K2K-3E8   Canada   Email: skraza@cisco.com   Alia Atlas   Juniper Networks, Inc.   10 Technology Park Drive   Westford, MA  01886   United States   Email: akatlas@juniper.net   Jeff Tantsura   Ericsson   300 Holger Way   San Jose, CA  95134   United States   Email: jeff.tantsura@ericsson.com   Quintin Zhao   Huawei Technology   125 Nagog Technology Park   Acton, MA  01719   United States   Email: quintin.zhao@huawei.comWijnands, et al.             Standards Track                   [Page 19]

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