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rfc:rfc8237

Internet Engineering Task Force (IETF) L. Martini Request for Comments: 8237 Monoski LLC Category: Standards Track G. Swallow ISSN: 2070-1721 SETC

                                                         E. Bellagamba
                                                              Ericsson
                                                          October 2017
           MPLS Label Switched Path (LSP) Pseudowire (PW)
              Status Refresh Reduction for Static PWs

Abstract

 This document describes a method for generating an aggregated
 pseudowire (PW) status message transmitted for a statically
 configured PW on a Multiprotocol Label Switching (MPLS) Label
 Switched Path (LSP) to indicate the status of one or more PWs carried
 on the LSP.
 The method for transmitting the PW status information is not new;
 however, this protocol extension allows a Service Provider (SP) to
 reliably monitor the individual PW status while not overwhelming the
 network with multiple periodic status messages.  This is achieved by
 sending a single cumulative summary status verification message for
 all the PWs grouped in the same LSP.

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 in Section 2 of RFC 7841.
 Information about the current status of this document, any errata,
 and how to provide feedback on it may be obtained at
 https://www.rfc-editor.org/info/rfc8237.

Martini, et al. Standards Track [Page 1] RFC 8237 MPLS LSP PW Status Refresh Reduction October 2017

Copyright Notice

 Copyright (c) 2017 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
 (https://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.

Martini, et al. Standards Track [Page 2] RFC 8237 MPLS LSP PW Status Refresh Reduction October 2017

Table of Contents

 1. Introduction ....................................................3
    1.1. Requirements Language ......................................4
    1.2. Terminology ................................................4
    1.3. Notational Conventions .....................................5
 2. PW Status Refresh Reduction Protocol ............................5
    2.1. Protocol States ............................................5
         2.1.1. INACTIVE ............................................5
         2.1.2. STARTUP .............................................6
         2.1.3. ACTIVE ..............................................6
    2.2. Timer Value Change Transition Procedure ....................6
 3. PW Status Refresh Reduction Procedure ...........................7
 4. PW Status Refresh Reduction Message Encoding ....................8
 5. PW Status Refresh Reduction Control Messages ...................11
    5.1. Notification Message ......................................12
    5.2. PW Configuration Message ..................................12
         5.2.1. MPLS-TP Tunnel ID ..................................13
         5.2.2. PW ID Configured List ..............................14
         5.2.3. PW ID Unconfigured List ............................15
 6. PW Provisioning Verification Procedure .........................15
    6.1. PW ID List Advertising and Processing .....................16
 7. Security Considerations ........................................16
 8. IANA Considerations ............................................17
    8.1. PW Status Refresh Reduction Message Types .................17
    8.2. PW Configuration Message Sub-TLVs .........................17
    8.3. PW Status Refresh Reduction Notification Codes ............18
    8.4. PW Status Refresh Reduction Message Flags .................18
    8.5. G-ACh Registry Allocation .................................19
    8.6. Guidance for Designated Experts ...........................19
 9. References .....................................................19
    9.1. Normative References ......................................19
    9.2. Informative References ....................................20
 Authors' Addresses ................................................20

1. Introduction

 When PWs use a Multiprotocol Label Switching (MPLS) network as the
 Packet Switched Network (PSN), they are set up using static label
 assignment per Section 4 of [RFC8077], and the PW status information
 is propagated using the method described in [RFC6478].  There are two
 basic modes of operation described in [RFC6478], Section 5.3:
 (1) periodic retransmission of non-zero status messages and (2) a
 simple acknowledgment of PW status (Section 5.3.1 of [RFC6478]).  The
 LSP-level protocol described below applies to the case when

Martini, et al. Standards Track [Page 3] RFC 8237 MPLS LSP PW Status Refresh Reduction October 2017

 PW status is acknowledged immediately with a requested refresh value
 of zero (no refresh).  In this case, the PW status refresh reduction
 protocol is necessary for several reasons, such as the following:
   i. The PW status refresh reduction protocol greatly increases the
      scalability of the PW status protocol by reducing the amount of
      messages that a Provider Edge (PE) needs to periodically send to
      its neighbors.
  ii. The PW status refresh reduction protocol will detect a remote PE
      restart.
 iii. If the local state is lost for some reason, the PE needs to be
      able to request a status refresh reduction from the remote PE.
  iv. The PW status refresh reduction protocol can optionally detect a
      remote PE provisioning change.

1.1. Requirements Language

 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
 "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and
 "OPTIONAL" in this document are to be interpreted as described in
 BCP 14 [RFC2119] [RFC8174] when, and only when, they appear in all
 capitals, as shown here.

1.2. Terminology

 FEC: Forwarding Equivalence Class
 LDP: Label Distribution Protocol
 LSP: Label Switched Path
 MS-PW: Multi-Segment Pseudowire
 PE: Provider Edge
 PW: Pseudowire
 S-PE: Switching Provider Edge Node of MS-PW
 SS-PW: Single-Segment Pseudowire
 T-PE: Terminating Provider Edge Node of MS-PW

Martini, et al. Standards Track [Page 4] RFC 8237 MPLS LSP PW Status Refresh Reduction October 2017

1.3. Notational Conventions

 All multiple-word atomic identifiers use underscores ("_") between
 the words to join the words.  Many of the identifiers are composed of
 a concatenation of other identifiers.  These are expressed using
 double-colon ("::") notation.
 Where the same identifier type is used multiple times in a
 concatenation, they are qualified by a prefix joined to the
 identifier by a dash ("-").  For example, Src-Node_ID is the Node_ID
 of a node referred to as "Src" ("Src" is short for "source").
 The notation does not define an implicit ordering of the information
 elements involved in a concatenated identifier.

2. PW Status Refresh Reduction Protocol

 The PW status refresh reduction protocol consists of a simple message
 that is sent at the LSP level, using the MPLS Generic Associated
 Channel (G-ACh) [RFC5586].
 For a particular LSP where the PW status refresh reduction protocol
 is enabled, a PE using this protocol MUST send the PW status refresh
 reduction Message as soon as a PW is configured on that LSP.  The
 message is then retransmitted at a locally configured interval
 indicated in the Refresh Timer field.  If no acknowledgment is
 received, the protocol does not reach the ACTIVE state
 (Section 2.1.3), and the PE SHOULD NOT send any PW status messages
 with a Refresh Timer of zero as described in [RFC6478],
 Section 5.3.1.
 It is worth noting that no relationship exists between the locally
 configured timer for the PW status refresh reduction protocol and the
 individual PW status Refresh Timers.

2.1. Protocol States

 The protocol can be in three possible states: INACTIVE, STARTUP, and
 ACTIVE.

2.1.1. INACTIVE

 This state is entered when the protocol is turned off.  This state is
 also entered if all PWs on a specific LSP are deprovisioned.

Martini, et al. Standards Track [Page 5] RFC 8237 MPLS LSP PW Status Refresh Reduction October 2017

2.1.2. STARTUP

 In this state, the PE transmits periodic PW status refresh reduction
 Messages with the Ack Session ID (Section 4) set to 0.  The PE
 remains in this state until a PW status refresh message is received
 with the correct local Session ID in the Ack Session ID field.  State
 can transition from the STARTUP state to the ACTIVE or INACTIVE
 state.

2.1.3. ACTIVE

 This state is entered once the PE receives a PW status refresh
 reduction Message with the correct local Session ID in the Ack
 Session ID field within 3.5 times the Refresh Timer field value of
 the last PW status refresh reduction Message transmitted.  This state
 is immediately exited in the following scenarios:
   i. A valid PW status refresh reduction Message is not received
      within 3.5 times the current Refresh Timer field value (assuming
      that a timer transition procedure is not in progress).
      New state: STARTUP.
  ii. A PW status refresh reduction Message is received with the wrong
      Ack Session ID field value or a zero Ack Session ID field value.
      New state: STARTUP.
 iii. All PWs using the particular LSP are deprovisioned, or the
      protocol is disabled.
      New state: INACTIVE.

2.2. Timer Value Change Transition Procedure

 If a PE needs to change the value of the Refresh Timer field while
 the PW status refresh reduction protocol is in the ACTIVE state, the
 following procedure must be followed:
   i. A PW status refresh reduction Message is transmitted with the
      new timer value.
  ii. If the new value is greater than the original one, the PE will
      operate according to the new timer value immediately.

Martini, et al. Standards Track [Page 6] RFC 8237 MPLS LSP PW Status Refresh Reduction October 2017

 iii. If the new value is smaller than the original one, the PE will
      operate according to the original timer value for a period
      3.5 times the original timer value or until the first valid PW
      status refresh reduction Message is received.
      A PE receiving a PW status refresh reduction Message with a new
      timer value will immediately acknowledge the new value via a PW
      status refresh reduction Message and will start operating
      according to the new timer value.

3. PW Status Refresh Reduction Procedure

 When the PW status refresh reduction protocol on a particular LSP is
 in the ACTIVE state, the PE can send all PW status messages, for PWs
 on that LSP, with a Refresh Timer value of zero.  This greatly
 decreases the amount of messages that the PE needs to transmit to the
 remote PE because once the PW status message for a particular PW is
 acknowledged, further repetitions of that message are no longer
 necessary.
 To further reduce the amount of possible messages when an LSP starts
 forwarding traffic, care should be taken to permit the PW status
 refresh reduction protocol to reach the ACTIVE state quickly, and
 before the first PW status Refresh Timer expires.  This can be
 achieved by using a PW status refresh reduction Message Refresh Timer
 value that is much smaller than the PW status message Refresh Timer
 value in use (Section 5.3.1 of [RFC6478]).
 If the PW status refresh reduction protocol session is terminated by
 entering the INACTIVE state or the STARTUP state, the PE MUST
 immediately resend all the previously sent PW status messages for
 that particular LSP for which the session was terminated.  In this
 case, the Refresh Timer value MUST NOT be set to 0 and MUST be set
 according to the local policy of the PE router.  Implementations MUST
 take care to avoid flooding the remote PE with a large number of PW
 status messages at once.  If the PW status refresh reduction protocol
 session is terminated for administrative reasons and the local PE can
 still communicate with the remote PE, the local PE SHOULD pace the
 transmission of PW status messages to the remote PE.

Martini, et al. Standards Track [Page 7] RFC 8237 MPLS LSP PW Status Refresh Reduction October 2017

4. PW Status Refresh Reduction Message Encoding

 The packet containing the PW status refresh reduction Message is
 encoded as follows (omitting link-layer information):
     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
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |               MPLS LSP (tunnel) Label Stack Entry             |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |                              GAL                              |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |0 0 0 1|Version|   Reserved    | 0x29 PW OAM Message           |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |          Session ID           |         Ack Session ID        |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |         Refresh Timer         |     Total Message Length      |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |         Checksum              |    Message Sequence Number    |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    | Last Received Sequence Number | Message Type  |U|C|   Flags   |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |                                                               |
    ~                     Control Message Body                      ~
    |                                                               |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 This message contains the following fields:
  • MPLS LSP (tunnel) Label Stack Entry
       The label stack is explained in [RFC3031].
  • GAL
       The G-ACh Label (GAL) and the next 4 octets (including the PW
       OAM Message field as the Channel Type) are explained in
       Section 2.1 of [RFC5586].
  • PW OAM Message
       This field indicates the Channel Type in the G-ACh header, as
       described in Section 2.1 of [RFC5586].

Martini, et al. Standards Track [Page 8] RFC 8237 MPLS LSP PW Status Refresh Reduction October 2017

  • Session ID
       A non-zero locally selected session number that is not
       preserved if the local PE restarts.
       In order to get a locally unique Session ID, the recommended
       choice is to perform a CRC-16 ("CRC" stands for "Cyclic
       Redundancy Check"), giving as input the following data:
       |YY|MM|DD|HHMMSSLLL|
       Where:
       YY = the last two decimal digits of the current year
       MM = the two decimal digits of the current month
       DD = the two decimal digits of the current day
       HHMMSSLLL = the decimal digits of the current time,
          expressed in hours (HH), minutes (MM), seconds (SS), and
          milliseconds (LLL)
       If the calculation results in an already-existing Session ID, a
       unique Session ID can be generated by adding 1 to the result
       until the Session ID is unique.  Any other method to generate a
       locally unique Session ID is also acceptable.
  • Ack Session ID
       The Acknowledgment Session ID received from the remote PE.
  • Refresh Timer
       A non-zero unsigned 16-bit integer value greater than or equal
       to 10, expressed in milliseconds, that indicates the desired
       refresh interval.  The default value of 30000 is RECOMMENDED.
  • Total Message Length
       Total length in octets of the Checksum, Message Type, Flags,
       Message Sequence Number, and Control Message Body.  A value of
       zero means that no control message is present and, therefore,
       that no Checksum or subsequent fields are present either.

Martini, et al. Standards Track [Page 9] RFC 8237 MPLS LSP PW Status Refresh Reduction October 2017

  • Checksum
       A 16-bit field containing the one's complement of the one's
       complement sum of the entire message (including the G-ACh
       header), with the Checksum field replaced by zero for the
       purpose of computing the checksum.  An all-zero value means
       that no checksum was transmitted.  Note that when the checksum
       is not computed, the header of the bundle message will not be
       covered by any checksum.
  • Message Sequence Number
       An unsigned 16-bit integer that is started from 1 when the
       protocol enters the ACTIVE state.  The sequence number wraps
       back to 1 when the maximum value is reached.  The value 0 is
       reserved and MUST NOT be used.
  • Last Received Message Sequence Number
       The sequence number of the last message received.  If no
       message has yet been received during this session, this field
       is set to 0.
  • Message Type
       The type of control message that follows.  Control message
       types are allocated in this document and by IANA.
  • (U) Unknown flag bit
       Upon receipt of an unknown message or TLV, if U is clear (0),
       a notification message with code "Unknown TLV (U-Bit=0)"
       (code 0x4) MUST be sent to the remote PE, and the keepalive
       session MUST be terminated by entering the STARTUP state; if
       U is set (1), the unknown message, or message containing an
       unknown TLV, MUST be acknowledged and silently ignored, and the
       following messages, or TLVs, if any, processed as if the
       unknown message or TLV did not exist.  In this case, the PE MAY
       send back a single notification message per keepalive session
       with code "Unknown TLV (U-Bit=1)".  This last step is OPTIONAL.
  • (C) Configuration flag bit
       The C-Bit is used to signal the end of PW configuration
       transmission.  If it is set, the sending PE has finished
       sending all of its current configuration information.

Martini, et al. Standards Track [Page 10] RFC 8237 MPLS LSP PW Status Refresh Reduction October 2017

  • Flags
       The remaining 6 bits of PW status refresh reduction Message
       Flags to be allocated by IANA.  These unallocated bits MUST be
       set to 0 on transmission and ignored on reception.
  • Control Message Body
       The Control Message Body is defined in Section 5 and is
       specific to the type of message.
 It should be noted that the Checksum, Message Sequence Number, Last
 Received Message Sequence Number, Message Type, Flags, and Control
 Message Body are OPTIONAL.  The Total Message Length field is used to
 parse how many optional fields are included.  Hence, all optional
 fields that precede a specific field that needs to be included in a
 specific implementation MUST be included if that optional field is
 also included.
 If any of the above values are outside the specified range, a
 notification message is returned with code "PW configuration not
 supported", and the message is ignored.

5. PW Status Refresh Reduction Control Messages

 PW status refresh reduction Control Messages consist of the Checksum,
 Message Sequence Number, Last Received Message Sequence Number,
 Message Type, Flags, and Control Message Body.
 When a PW status refresh reduction Control Message needs to be sent,
 the system can attach it to a scheduled PW status refresh reduction
 Message or send one ahead of time.  In any case, PW status refresh
 reduction Control Messages always piggyback on normal messages.
 A PW status refresh reduction Message is also called a PW status
 refresh reduction Control Message if it contains a control message
 construct.
 There can only be one control message construct per PW status refresh
 reduction Message.  If the U-Bit is set and a PE receiving the PW
 status refresh reduction Message does not understand the control
 message, the control message MUST be silently ignored.  However, the
 Message Sequence Number MUST still be acknowledged by sending a Null
 Notification message back with the appropriate value in the Last
 Message Received field.  If a control message is not acknowledged
 after 3.5 times the value of the Refresh Timer, a fatal notification
 -- "Unacknowledged control message" -- MUST be sent, and the PW
 status refresh reduction session MUST be terminated.

Martini, et al. Standards Track [Page 11] RFC 8237 MPLS LSP PW Status Refresh Reduction October 2017

 If a PE does not want or need to send a control message, the Checksum
 and all subsequent fields MUST NOT be sent, and the Total Message
 Length field is then set to 0.

5.1. Notification Message

 The most common use of the notification message is to acknowledge the
 reception of a message by indicating the received Message Sequence
 Number in the Last Received Sequence Number field.  The notification
 message is encoded 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
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |         Checksum              |    Message Sequence Number    |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    | Last Received Sequence Number |  Type=0x01    |U|C|   Flags   |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |                      Notification Code                        |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 The message type is set to 0x01, and the U-Bit is treated as
 described in Section 4.  The Notification Codes are 32-bit quantities
 assigned by IANA (see the IANA Considerations section).  Notification
 codes are considered either "Error codes" or simple notifications.
 If the Notification Code is an Error code as indicated in the IANA
 allocation registry, the keepalive session MUST be terminated by
 entering the STARTUP state.
 When there is no notification information to be sent, the
 notification code is set to 0 to indicate a "Null Notification".  The
 C-Bit MUST always be set to 0 in this type of message.  The remaining
 6 bits of PW status refresh reduction Message Flags are to be
 allocated by IANA.  These unallocated bits MUST be set to 0 on
 transmission and ignored on reception.

5.2. PW Configuration Message

 The PW status refresh reduction TLVs are informational TLVs that
 allow the remote PE to verify certain provisioning information.  This
 message contains a series of sub-TLVs, in no particular order, that
 contain PW and LSP configuration information.  The message has no
 preset length limit; however, its total length will be limited by the
 transport network's Maximum Transmission Unit (MTU).  PW status
 refresh reduction Messages MUST NOT be fragmented.  If a sender has
 more configuration information to send than will fit into one PW
 Configuration Message, it may send additional messages carrying
 additional TLVs.

Martini, et al. Standards Track [Page 12] RFC 8237 MPLS LSP PW Status Refresh Reduction October 2017

     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
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |         Checksum              |    Message Sequence Number    |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    | Last Received Sequence Number |  Type=0x02    |U|C|   Flags   |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    ~                                                               ~
    |                PW Configuration Message Sub-TLVs              |
    ~                                                               ~
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 The PW Configuration Message type is set to 0x02.  For this message,
 the U-Bit is set to 1, as processing of these messages is OPTIONAL.
 The C-Bit is used to signal the end of PW configuration transmission.
 If it is set, the sending PE has finished sending all of its current
 configuration information.  The PE transmitting the configuration
 MUST set the C-Bit on the last PW Configuration Message when all
 current PW configuration information has been sent.
 PW Configuration Message sub-TLVs have the following generic 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        |  Length       |        Value                  |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    ~                                                               ~
    |                      Value (Continued)                        |
    ~                                                               ~
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

5.2.1. MPLS-TP Tunnel ID

 This TLV contains the MPLS-TP Tunnel ID ("MPLS-TP" stands for "MPLS
 Transport Profile").  When the configuration message is used for a
 particular keepalive session, the MPLS-TP Tunnel ID sub-TLV MUST be
 sent at least once.

Martini, et al. Standards Track [Page 13] RFC 8237 MPLS LSP PW Status Refresh Reduction October 2017

 The MPLS-TP Tunnel ID is encoded 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
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |   Type=0x01   |  Length=20    |      MPLS-TP Tunnel ID        |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    ~                                                               ~
    |           MPLS-TP Tunnel ID (Continued) (20 octets)           |
    ~                                                               ~
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 The MPLS point-to-point tunnel ID is defined in [RFC6370].  The
 coding used by the node that is the source of a message is:
    Src-Global_Node_ID::Src-Tunnel_Num::Dst-Global_Node_ID::
    Dst-Tunnel_Num
 Note that a single tunnel ID is enough to identify the tunnel and the
 source end of the message.

5.2.2. PW ID Configured List

 This OPTIONAL sub-TLV contains a list of the provisioned PWs on
 the LSP.
     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=0x02   |    Length     |         PW Path ID            |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |                                                               |
    |                      PW Path ID (Continued)                   |
    ~                                                               ~
    |                                                               |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 The PW Path ID is a 32-octet PW path identifier [RFC6370].  The
 coding used by the node that is the source of a message is:
    AGI::Src-Global_ID::Src-Node_ID::Src-AC_ID::
    Dst-Global_ID::Dst-Node_ID::Dst-AC_ID
 The number of PW Path IDs in the TLV will be inferred by the length
 of the TLV, up to a maximum of 8.  The procedure for processing this
 TLV will be described in Section 6.

Martini, et al. Standards Track [Page 14] RFC 8237 MPLS LSP PW Status Refresh Reduction October 2017

5.2.3. PW ID Unconfigured List

 This OPTIONAL sub-TLV contains a list of the PWs that have been
 deprovisioned on the LSP.  Note that sending the same PW address in
 both the PW ID Configured List sub-TLV and the PW ID Unconfigured
 List sub-TLV in the same configuration message constitutes a fatal
 session error.  If this error occurs, an error notification message
 is returned with the Error code "PW Configuration TLV conflict", and
 the session is terminated by entering the STARTUP state.
     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=0x03   |    Length     |         PW Path ID            |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |                                                               |
    |                      PW Path ID (Continued)                   |
    ~                                                               ~
    |                                                               |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 The PW Path ID is a 32-octet PW path identifier as defined in
 Section 5.2.2.
 The number of PW Path IDs in the TLV will be inferred by the length
 of the TLV, up to a maximum of 8.

6. PW Provisioning Verification Procedure

 The advertisement of the PW Configuration Message is OPTIONAL.
 A PE that desires to use the PW Configuration Message to verify the
 configuration of PWs on a particular LSP should advertise its PW
 configuration to the remote PE on LSPs that have active keepalive
 sessions.  When a PE receives PW configuration information using this
 protocol and it does not support processing the information or is not
 willing to process it, it MUST acknowledge all the PW Configuration
 Messages with the notification code "PW configuration not supported".
 In this case, the information in the PW Configuration Message is
 silently ignored.  If a PE receives such a notification, it SHOULD
 stop sending PW Configuration Messages for the duration of the PW
 status refresh reduction keepalive session.

Martini, et al. Standards Track [Page 15] RFC 8237 MPLS LSP PW Status Refresh Reduction October 2017

 If PW configuration information is received, it is used to verify the
 accuracy of the local configuration information against the remote
 PE's configuration information.  If a configuration mismatch is
 detected, where a particular PW is configured locally but not on the
 remote PE, the following actions SHOULD be taken:
   i. The local PW MUST be considered in "Not Forwarding" state
      (Section 6.3.2 of [RFC8077]).
  ii. The PW Attachment Circuit status is set to reflect the PW fault.
 iii. An alarm SHOULD be raised to a network management system.
  iv. A notification message with the notification code "PW
      configuration mismatch" MUST be sent to the remote PE.  Only one
      such message is REQUIRED per configuration message even if the
      configuration message is split into multiple configuration
      messages due to individual message-size restrictions on a
      particular link.  Upon receipt of such a message, the receiving
      PE MAY raise an alarm to a network management system.  This
      alarm MAY be cleared when the configuration is updated.

6.1. PW ID List Advertising and Processing

 When configuration messages are advertised on a particular LSP, the
 PE sending the messages needs to checkpoint the configuration
 information sent by setting the C-Bit when all currently known
 configuration information has been sent.  This process allows the
 receiving PE to immediately proceed to verify all the currently
 configured PWs on that LSP, eliminating the need for a long waiting
 period.
 If a new PW is added to a particular LSP, the PE MUST place the
 configuration verification of this PW on hold for a period of at
 least 30 seconds.  This is necessary to minimize false-positive
 events of misconfiguration due to the ends of the PW being slightly
 out of sync.

7. Security Considerations

 The security considerations discussed in [RFC6478] are adequate for
 the mechanism described in this document, since the operating
 environment is almost identical to the one where this protocol would
 be deployed.  It should also be noted that since this protocol is
 designed to be deployed between two adjacent PEs connected by a
 physical link, it is not possible to misdirect or inject traffic
 without compromising the PW transport link itself.

Martini, et al. Standards Track [Page 16] RFC 8237 MPLS LSP PW Status Refresh Reduction October 2017

8. IANA Considerations

 The registries in this section have been created or updated as
 appropriate in the "Pseudowire Name Spaces (PWE3)" registry or the
 "Generic Associated Channel (G-ACh) Parameters" registry.  For the
 allocation ranges designated as "vendor-proprietary extensions", the
 respective IANA registry contains the vendor name in brackets at the
 end of the Description field.

8.1. PW Status Refresh Reduction Message Types

 IANA has set up the "PW Status Refresh Reduction Control Messages"
 registry.  This registry contains 8-bit values.  Type values 1 and 2
 are defined in this document.  Type values 3 through 64 and 128
 through 254 are to be assigned by IANA using the "Expert Review"
 policy defined in [RFC8126].  Type values 65 through 127, 0, and 255
 are to be allocated using the "IETF Review" policy defined in
 [RFC8126].
 The Type values are assigned as follows:
    Type   Message Description
    ----   ------------------------
    0x01   Notification message
    0x02   PW Configuration Message

8.2. PW Configuration Message Sub-TLVs

 IANA has set up the "PW Status Refresh Reduction Configuration
 Message Sub-TLVs" registry.  This registry contains 8-bit values.
 Type values 1 through 3 are defined in this document.  Type values 4
 through 64 and 128 through 254 are to be assigned by IANA using the
 "Expert Review" policy defined in [RFC8126].  Type values 65 through
 127, 0, and 255 are to be allocated using the "IETF Review" policy
 defined in [RFC8126].
 The Type values are assigned as follows:
    Sub-TLV Type    Description
    ------------    -----------------------
    0x01            MPLS-TP Tunnel ID
    0x02            PW ID Configured List
    0x03            PW ID Unconfigured List

Martini, et al. Standards Track [Page 17] RFC 8237 MPLS LSP PW Status Refresh Reduction October 2017

8.3. PW Status Refresh Reduction Notification Codes

 IANA has set up the "PW Status Refresh Reduction Notification Codes"
 registry.  This registry contains 32-bit values.  Type values 0
 through 7 are defined in this document.  Type values 8 through 65536
 and 134,217,729 through 4,294,967,294 are to be assigned by IANA
 using the "Expert Review" policy defined in [RFC8126].  Type values
 65537 through 134,217,728, 0, and 4,294,967,295 are to be allocated
 using the "IETF Review" policy defined in [RFC8126].
 For each value assigned, IANA should also track whether the value
 constitutes an error as described in Section 5.1.  When values are
 assigned by IETF Review, the settings in the "Error?" column must be
 documented in the RFC that requests the allocation.  For
 "Expert Review" assignments, the settings in the "Error?" column must
 be made clear by the requester at the time of assignment.
 The Type values are assigned as follows:
    Code          Error?    Description
    ----------    ------    ------------------------------
    0x00000000    No        Null Notification
    0x00000001    No        PW configuration mismatch
    0x00000002    Yes       PW Configuration TLV conflict
    0x00000003    No        Unknown TLV (U-Bit=1)
    0x00000004    Yes       Unknown TLV (U-Bit=0)
    0x00000005    No        Unknown Message Type
    0x00000006    No        PW configuration not supported
    0x00000007    Yes       Unacknowledged control message

8.4. PW Status Refresh Reduction Message Flags

 IANA has set up the "PW Status Refresh Reduction Message Flags"
 registry.  This is an 8-bit registry, with the first two most
 significant bits allocated by this document as follows:
    Bit Position  Name    Description
    ------------  ----    ----------------------
         0        U       Unknown flag bit
         1        C       Configuration flag bit
 The remaining bits are to be allocated using the "IETF Review" policy
 defined in [RFC8126].

Martini, et al. Standards Track [Page 18] RFC 8237 MPLS LSP PW Status Refresh Reduction October 2017

8.5. G-ACh Registry Allocation

 IANA maintains a registry called "MPLS Generalized Associated Channel
 (G-ACh) Types (including Pseudowire Associated Channel Types)".  IANA
 has allocated a new value as follows:
    Value     Description                     Reference
    -----     ---------------------------     ---------
    0x29      PW Status Refresh Reduction     RFC 8237

8.6. Guidance for Designated Experts

 In all cases of review by the Designated Expert (DE) described here,
 the DE is expected to ascertain the existence of suitable
 documentation (a specification) as described in [RFC8126] and to
 verify that the document is permanently and publicly available.  The
 DE is also expected to check that the clarity of purpose and use of
 the requested code points fit the general architecture and intended
 purpose of the respective message or TLV.  Lastly, the DE should
 check that any assignment does not duplicate or conflict with work
 that is active or already published within the IETF.

9. References

9.1. 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,
            <https://www.rfc-editor.org/info/rfc2119>.
 [RFC3031]  Rosen, E., Viswanathan, A., and R. Callon, "Multiprotocol
            Label Switching Architecture", RFC 3031,
            DOI 10.17487/RFC3031, January 2001,
            <https://www.rfc-editor.org/info/rfc3031>.
 [RFC6370]  Bocci, M., Swallow, G., and E. Gray, "MPLS Transport
            Profile (MPLS-TP) Identifiers", RFC 6370,
            DOI 10.17487/RFC6370, September 2011,
            <https://www.rfc-editor.org/info/rfc6370>.
 [RFC6478]  Martini, L., Swallow, G., Heron, G., and M. Bocci,
            "Pseudowire Status for Static Pseudowires", RFC 6478,
            DOI 10.17487/RFC6478, May 2012,
            <https://www.rfc-editor.org/info/rfc6478>.

Martini, et al. Standards Track [Page 19] RFC 8237 MPLS LSP PW Status Refresh Reduction October 2017

 [RFC8077]  Martini, L., Ed., and G. Heron, Ed., "Pseudowire Setup and
            Maintenance Using the Label Distribution Protocol (LDP)",
            STD 84, RFC 8077, DOI 10.17487/RFC8077, February 2017,
            <https://www.rfc-editor.org/info/rfc8077>.
 [RFC8126]  Cotton, M., Leiba, B., and T. Narten, "Guidelines for
            Writing an IANA Considerations Section in RFCs", BCP 26,
            RFC 8126, DOI 10.17487/RFC8126, June 2017,
            <https://www.rfc-editor.org/info/rfc8126>.
 [RFC8174]  Leiba, B., "Ambiguity of Uppercase vs Lowercase in
            RFC 2119 Key Words", BCP 14, RFC 8174,
            DOI 10.17487/RFC8174, May 2017,
            <https://www.rfc-editor.org/info/rfc8174>.

9.2. Informative References

 [RFC5586]  Bocci, M., Ed., Vigoureux, M., Ed., and S. Bryant, Ed.,
            "MPLS Generic Associated Channel", RFC 5586,
            DOI 10.17487/RFC5586, June 2009,
            <https://www.rfc-editor.org/info/rfc5586>.

Authors' Addresses

 Luca Martini
 Monoski LLC
 Email: lmartini@monoski.com
 George Swallow
 Southend Technical Center
 Email: swallow.ietf@gmail.com
 Elisa Bellagamba
 Ericsson EAB
 Torshamnsgatan 48
 16480, Stockholm
 Sweden
 Email: elisa.bellagamba@gmail.com

Martini, et al. Standards Track [Page 20]

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