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Versions: (draft-esale-mpls-app-aware-tldp) 00 01 02 03 04 05 06 07 08 09

MPLS Working Group                                         Santosh Esale
INTERNET-DRAFT                                           Raveendra Torvi
Updates: 7473 (if approved)                             Juniper Networks
Intended Status: Proposed Standard                            Luay Jalil
Expires: December 29, 2017                                       Verizon
                                                            Uma Chunduri
                                                                  Huawei
                                                             Kamran Raza
                                                     Cisco Systems, Inc.
                                                           June 27, 2017


                     Application-aware Targeted LDP
                   draft-ietf-mpls-app-aware-tldp-09


Abstract

   Recent targeted Label Distribution Protocol (tLDP) applications such
   as remote loop-free alternate (LFA) and BGP auto discovered
   pseudowire may automatically establish a tLDP session to any Label
   Switching Router (LSR) in a network.  The initiating LSR has
   information about the targeted applications to administratively
   control initiation of the session. However, the responding LSR has no
   such information to control acceptance of this session. This document
   defines a mechanism to advertise and negotiate Targeted Applications
   Capability (TAC) during LDP session initialization.  As the
   responding LSR becomes aware of targeted applications, it may
   establish a limited number of tLDP sessions for certain applications.
   In addition, each targeted application is mapped to LDP Forwarding
   Equivalence Class (FEC) Elements to advertise only necessary LDP FEC-
   label bindings over the session. This document updates RFC 7473 for
   enabling advertisement of LDP FEC-label bindings over the session.

Status of this Memo

   This Internet-Draft is submitted to IETF in full conformance with the
   provisions of BCP 78 and 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."



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   The list of current Internet-Drafts can be accessed at
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Copyright and License Notice

   Copyright (c) 2017 IETF Trust and the persons identified as the
   document authors. All rights reserved.

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   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 Contents

   1  Introduction  . . . . . . . . . . . . . . . . . . . . . . . . .  4
     1.1 Conventions Used in This Document  . . . . . . . . . . . . .  4
     1.2 Terminology  . . . . . . . . . . . . . . . . . . . . . . . .  5
   2. Targeted Application Capability . . . . . . . . . . . . . . . .  5
     2.1 Encoding . . . . . . . . . . . . . . . . . . . . . . . . . .  5
     2.2 Procedures . . . . . . . . . . . . . . . . . . . . . . . . .  6
     2.3 LDP message procedures . . . . . . . . . . . . . . . . . . .  8
       2.3.1 Initialization message . . . . . . . . . . . . . . . . .  8
       2.3.2 Capability message . . . . . . . . . . . . . . . . . . .  9
   3. Targeted Application FEC Advertisement Procedures . . . . . . .  9
   4. Interaction of Targeted Application Capabilities and State
      Advertisement Control Capabilities  . . . . . . . . . . . . . . 10
   5. Use cases . . . . . . . . . . . . . . . . . . . . . . . . . . . 12
     5.1 Remote LFA Automatic Targeted session  . . . . . . . . . . . 12
     5.2 FEC 129 Auto Discovery Targeted session  . . . . . . . . . . 13
     5.3 LDP over RSVP and Remote LFA targeted session  . . . . . . . 13
     5.4 mLDP node protection targeted session  . . . . . . . . . . . 13
   6. Security Considerations . . . . . . . . . . . . . . . . . . . . 14
   7. IANA Considerations . . . . . . . . . . . . . . . . . . . . . . 14
   8. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . . 15
   9. Contributing Authors  . . . . . . . . . . . . . . . . . . . . . 15
   10.  References  . . . . . . . . . . . . . . . . . . . . . . . . . 16



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     10.1  Normative References . . . . . . . . . . . . . . . . . . . 16
     10.2  Informative References . . . . . . . . . . . . . . . . . . 16
   Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 17
















































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1  Introduction

   LDP uses the extended discovery mechanism to establish the tLDP
   adjacency and subsequent session as described in [RFC5036]. A LSR
   initiates extended discovery by sending tLDP Hello to specific
   address. The remote LSR decides to either accept or ignore the tLDP
   Hello based on local configuration only. Targeted LDP application is
   an application that uses tLDP session to exchange information such as
   FEC-Label bindings with a peer LSR in the network. For an application
   such as FEC 128 pseudowire, the remote LSR is configured with the
   source LSR address so that it can use that information to accept or
   ignore given tLDP Hello.

   However, applications such as Remote LFA and BGP auto discovered
   pseudowire automatically initiate asymmetric extended discovery to
   any LSR in a network based on local state only. With these
   applications, the remote LSR is not explicitly configured with the
   source LSR address. So the remote LSR either responds or ignores all
   tLDP Hellos.

   In addition, since the session is initiated and established after
   adjacency formation, the responding LSR has no targeted applications
   information available to choose a session with targeted application
   that it is configured to support. Also, the initiating LSR may employ
   a limit per application on locally initiated automatic tLDP sessions,
   however the responding LSR has no such information to employ a
   similar limit on the incoming tLDP sessions. Further, the responding
   LSR does not know whether the source LSR is establishing a tLDP
   session for configured, automatic or both applications.

   This document proposes and describes a solution to advertise Targeted
   Application Capability (TAC), consisting of a targeted application
   list, during initialization of a tLDP session. It also defines a
   mechanism to enable an new application and disable an old application
   after session establishment. This capability advertisement provides
   the responding LSR with the necessary information to control the
   acceptance of tLDP sessions per application. For instance, an LSR may
   accept all BGP auto discovered tLDP sessions as defined in [RFC6074]
   but may only accept limited number of Remote LFA tLDP sessions as
   defined in [RFC7490]

   Also, the targeted LDP application is mapped to LDP FEC element type
   to advertise specific application FECs only, avoiding the
   advertisement of other unnecessary FECs over a tLDP session.

1.1 Conventions Used in This Document

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",



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   "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and
   "OPTIONAL" in this document are to be interpreted as described in RFC
   2119 [RFC2119] and RFC 8174 [RFC8174] when, and only when, they
   appear in all capitals, as shown here.

1.2 Terminology

   In addition to the terminology defined in [RFC7473], this document
   uses the following terms:


    tLDP    : Targeted LDP
    TAC     : Targeted Application Capability
    TAE     : Targeted Application Element
    TA-Id   : Targeted Application Identifier
    SAC     : State Advertisement Control Capability
    LSR     : Label Switching Router
    mLDP    : Multipoint LDP
    PQ      : Remote-LFA nexthops
    RSVP-TE : RSVP Traffic Engineering
    P2MP    : Point-to-Multipoint
    PW      : Pseudowire
    P2P-PW  : Point-to-point Psuedowire
    MP2MP   : Multipoint-to-Multipoint
    HSMP LSP: Hub and Spoke Multipoint Label Switched Path
    LSP     : Label Switched Path
    MP2P    : Multipoint-to-point
    MPT     : Merge Point

2. Targeted Application Capability

2.1 Encoding

   An LSR MAY advertise that it is capable of negotiating a targeted LDP
   application list over a tLDP session by using the Capability
   Advertisement as defined in [RFC5561] and 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
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |U|F| TLV Code Point            |            Length             |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |S| Reserved    |                                               |
     +-+-+-+-+-+-+-+-+       Capability Data                         |
     |                                               +-+-+-+-+-+-+-+-+
     |                                               |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+



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     This document defines a new optional capability TLV of type TBD1
     called 'Targeted Application Capability (TAC)'. Flag "U" MUST be
     set to 1 to indicate that this capability must be silently ignored
     if unknown. The TAC's Capability Data contains the Targeted
     Application Element (TAE) information encoded as follows:


       Targeted Application Element(TAE)

        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
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |    Targ. Appl. Id             |E|       Reserved              |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

       Targeted Application Identifier (TA-Id):
       a 16 bit Targeted Application Identifier value.

       E-bit: The enable bit indicates whether the sender is
       advertising or withdrawing the TAE. The E-bit value is used as
       follows:

         1 - The TAE is advertising the targeted application.
         0 - The TAE is withdrawing the targeted application.


2.2 Procedures

   At tLDP session establishment time, a LSR MAY include a new
   capability TLV, TAC TLV, as an optional TLV in the LDP Initialization
   message. The TAC TLV's Capability data MAY consist of zero or more
   TAEs each pertaining to a unique TA-Id that a LSR supports over the
   session. If the receiver LSR receives the same TA-Id in more than one
   TAE, it MUST process the first element and ignore the duplicate
   elements. If the receiver LSR receives an unknown TA-Id in the TAE,
   it MUST silently ignore such a TAE and continue processing the rest
   of the TLV.

   If the receiver LSR does not receive the TAC TLV in the
   Initialization message or it does not understand the TAC TLV, the TAC
   negotiation is considered unsuccessful and the session establishment
   proceeds as per [RFC5036]. On the receipt of a valid TAC TLV, an LSR
   MUST generate its own TAC TLV with TAEs consisting of unique TA-Ids
   that it supports over the tLDP session. If there is at least one TAE
   common between the TAC TLV it has received and its own, the session
   MUST proceed to establishment as per [RFC5036]. If not, A LSR MUST
   send a 'Session Rejected/Targeted Application Capability Mis-Match'
   Notification message to the peer and close the session. The



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   initiating LSR SHOULD tear down the corresponding tLDP adjacency
   after sent or receipt of a 'Session Rejected/Targeted Application
   Capability Mis-Match' Notification message to or from the responding
   LSR respectively.

   If both the peers support TAC TLV, an LSR decides to establish or
   close a tLDP session based on the negotiated targeted application
   list. For example, an initiating LSR advertises A, B and C as TA-Ids,
   and the responding LSR advertises C, D and E as TA-Ids. Then the
   negotiated TA-Id as per both the LSRs is C.  Another example, an
   initiating LSR advertises A, B and C as TA-Ids, and the responding
   LSR, which acts as a passive LSR, advertises all the applications -
   A, B, C, D and E - as TA-Ids that it supports over this session. Then
   the negotiated targeted applications as per both the LSRs are A, B
   and C. Finally, If the initiating LSR advertises A, B and C as a TA-
   Ids and the responding LSR advertises D and E as TA-Ids, then the
   negotiated targeted applications as per both the LSRs are none.
   Therefore, if the intersection of the sets of received and sent TA-Id
   is null, then LSR sends 'Session Rejected/Targeted Application
   Capability Mis-Match' Notification message to the peer LSR and closes
   the session.

   When the responding LSR playing the active role [RFC5036] in LDP
   session establishment receives a 'Session Rejected/Targeted
   Application Capability Mis-Match' Notification message, it MUST set
   its session setup retry interval to a maximum value, as such 0xffff.
   The session MAY stay in NON EXISTENT state. When it detects a change
   in the initiating LSR or local LSR configuration pertaining to TAC
   TLV, it MUST clear the session setup back off delay associated with
   the session to re-attempt the session establishment. A LSR detects
   configuration change on the other LSR with the receipt of tLDP Hello
   message that has a higher configuration sequence number than the
   earlier tLDP Hello message.

   When the initiating LSR playing the active role in LDP session
   establishment receives a 'Session Rejected/Targeted Application
   Capability Mis-Match' Notification message, either it MUST close the
   session and tear down the corresponding tLDP adjacency or it MUST set
   its session setup retry interval to a maximum value, as such 0xffff.

   If the initiating LSR decides to tear down the associated tLDP
   adjacency, the session is closed on the initiating as well as the
   responding LSR. It MAY also take appropriate actions. For instance,
   if an automatic session intended to support the Remote LFA
   application is rejected by the responding LSR, the initiating LSR may
   inform the IGP to calculate another PQ node [RFC7490] for the route
   or set of routes. More specific actions are a local matter and
   outside the scope of this document.



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   If the initiating LSR sets the session setup retry interval to
   maximum, the session MAY stay in a non-existent state. When this LSR
   detects a change in the responding LSR configuration or its own
   configuration pertaining to TAC TLV, it MUST clear the session setup
   back off delay associated with the session in order to re-attempt the
   session establishment.

   After a tLDP session has been established with TAC capability, the
   initiating and responding LSR MUST distribute FEC-label bindings for
   the negotiated applications only. For instance, if the tLDP session
   is established for BGP auto discovered pseudowire, only FEC 129 label
   bindings MUST be distributed over the session. Similarly, a LSR
   operating in downstream on demand mode MUST request FEC-label
   bindings for the negotiated applications only.

   If the Targeted Application Capability and Dynamic Capability,
   described in [RFC5561], are negotiated during session initialization,
   TAC MAY be re-negotiated after session establishment by sending an
   updated TAC TLV in LDP Capability message. The updated TAC TLV
   carries TA-Ids with incremental update only. The updated TLV MUST
   consist of one or more TAEs with E-bit set or E-bit off to advertise
   or withdraw the new and old application respectively. This may lead
   to advertisements or withdrawals of certain types of FEC-Label
   bindings over the session or tear down of the tLDP adjacency and
   subsequently the session.

   The Targeted Application Capability is advertised on tLDP session
   only. If the tLDP session changes to link session, a LSR SHOULD
   withdraw it with S bit set to 0. Similarly, if the link session
   changes to tLDP, a LSR SHOULD advertise it via the Capability
   message. If the capability negotiation fails, this may lead to
   destruction of the tLDP session.

   By default, LSR SHOULD accept tLDP hellos in order to then accept or
   reject the tLDP session based on the application information.

   In addition, LSR SHOULD allow the configuration of any TA-Id in order
   to facilitate private TA-Id's usage by a network operator.

2.3 LDP message procedures

2.3.1 Initialization message

  1. The S-bit of the Targeted Application Capability TLV MUST be
     set to 1 to advertise Targeted Application Capability and
     SHOULD be ignored on the receipt as defined in [RFC5561]

  2. The E-bit of the Targeted Application Element MUST be set to 1 to



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     enable Targeted application and SHOULD be ignored on the receipt.

  3. An LSR MAY add State Control Capability by mapping Targeted
     Application Element to State Advertisement Control (SAC) Elements
     as defined in Section 4.

2.3.2 Capability message

  The initiating or responding LSR may re-negotiate the TAC after local
  configuration change with the Capability message.

  1. The S-bit of TAC is set to 1 or 0 to advertise or withdraw it.

  2. After configuration change, If there is no common TAE between
     its new TAE list and peers TAE list, the LSR MUST send a
     'Session Rejected/Targeted Application Capability Mis-Match'
     Notification message and close the session.

  3. If there is a common TAE, a LSR MAY also update SAC Capability
     based on updated TAC as described in section 4 and send the
     updated TAC and SAC capabilities in a Capability message to
     the peer.

  4. A receiving LSR processes the Capability message with TAC TLV.
     If the S-bit is set to 0, the TAC is disabled for the session.

  5. If the S-bit is set to 1, a LSR process a list of TAEs from
     TACs capability data with E-bit set to 1 or 0 to update the
     peer's TAE.

3. Targeted Application FEC Advertisement Procedures

   The targeted LDP application MUST be mapped to LDP FEC element types
   as follows to advertise only necessary LDP FEC-Label bindings over
   the tLDP session.


     Targeted Application     Description              FEC mappings
   +----------------------+------------------------+------------------+
   |LDPv4 Tunneling       | LDP IPv4 over RSVP-TE  | IPv4 prefix      |
   |                      | or other MPLS tunnel   |                  |
   +----------------------+------------------------+------------------+
   |                      |                        |                  |
   |LDPv6 Tunneling       | LDP IPv6 over RSVP-TE  | IPv6 prefix      |
   |                      | or other MPLS tunnel   |                  |
   +----------------------+------------------------+------------------+
   |mLDP Tunneling        | mLDP over RSVP-TE or   | P2MP             |
   |                      | or other MPLS tunnel   | MP2MP-up         |



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   |                      |                        | MP2MP-down       |
   |                      |                        | HSMP-downstream  |
   |                      |                        | HSMP-upstream    |
   +----------------------+------------------------+------------------+
   |                      |                        |                  |
   |LDPv4 Remote LFA      | LDPv4 over LDPv4 or    | IPv4 prefix      |
   |                      | other MPLS tunnel      |                  |
   +----------------------+------------------------+------------------+
   |LDPv6 Remote LFA      | LDPv6 over LDPv6 or    | IPv6 prefix      |
   |                      | other MPLS tunnel      |                  |
   +----------------------+------------------------+------------------+
   |                      |                        |                  |
   |LDP FEC 128 PW        | LDP FEC 128 Pseudowire | PWid FEC Element |
   +----------------------+------------------------+------------------+
   |                      |                        |                  |
   |LDP FEC 129 PW        | LDP FEC 129 Pseudowire | Generalized PWid |
   |                      |                        | FEC Element      |
   +----------------------+------------------------+------------------+
   |                      |                        | FEC types as     |
   |LDP Session Protection| LDP session protection | per protected    |
   |                      |                        | session          |
   +----------------------+------------------------+------------------+
   |LDP ICCP              | LDP Inter-chasis       |                  |
   |                      | control protocol       | None             |
   +----------------------+------------------------+------------------+
   |                      |                        |                  |
   |LDP P2MP PW           | LDP P2MP Pseudowire    | P2MP PW Upstream |
   |                      |                        | FEC Element      |
   +----------------------+------------------------+------------------+
   |                      |                        | P2MP             |
   |mLDP Node Protection  | mLDP node protection   | MP2MP-up         |
   |                      |                        | MP2MP-down       |
   |                      |                        | HSMP-downstream  |
   |                      |                        | HSMP-upstream    |
   +----------------------+------------------------+------------------+
   |                      |                        |                  |
   |IPv4 intra-area FECs  | IPv4 intra-area FECs   | IPv4 prefix      |
   +----------------------+------------------------+------------------+
   |                      |                        |                  |
   |IPv6 intra-area FECs  | IPv6 intra-area FECs   | IPv6 prefix      |
   +----------------------+------------------------+------------------+

   Intra-area FECs : FECs that are on the shortest path tree and not
   leafs of the shortest path tree.

4. Interaction of Targeted Application Capabilities and State
   Advertisement Control Capabilities




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   As described in this document, the set of TAEs negotiated between two
   LDP peers advertising TAC represents the willingness of both peers to
   advertise state information for a set of applications. The set of
   applications negotiated by the TAC mechanism is symmetric between the
   two LDP peers. In the absence of further mechanisms, two LDP peers
   will both advertise state information for the same set of
   applications.

   As described in [RFC7473], State Advertisement Control(SAC) TLV can
   be used by an LDP speaker to communicate its interest or disinterest
   in receiving state information from a given peer for a particular
   application.  Two LDP peers can use the SAC mechanism to create
   asymmetric advertisement of state information between the two peers.

   The TAC negotiation facilitates the awareness of targeted
   applications to both the peers. It enables them to advertise only
   necessary LDP FEC-label bindings corresponding to negotiated
   applications. With the SAC, the responding LSR is not aware of
   targeted applications. Thus it may be unable to communicate its
   interest or disinterest to receive state information from the peer.
   Therefore, when the responding LSR is not aware of targeted
   applications such a remote LFA and BGP auto discovered pseudowires,
   TAC mechanism should be used and when the responding LSR is aware
   (with appropriate configuration) of targeted applications such as FEC
   128 pseudowire, SAC mechanism should be used. Also after TAC
   mechanism makes the responding LSR aware of targeted application, the
   SAC mechanism may be used to communicate its disinterest in receiving
   state information from the peer for a particular negotiated
   application, creating asymmetric advertisements.

   Thus, the TAC mechanism enables two LDP peers to symmetrically
   advertise state information for negotiated targeted applications.
   Further, the SAC mechanism enables both of them to asymmetrically
   disable receipt of state information for some of the already
   negotiated targeted applications. Collectively, both TAC and SAC
   mechanisms can be used to control the FEC-label bindings that are
   advertised over the tLDP session. For instance, suppose the
   initiating LSR establishes a tLDP session to the responding LSR for
   Remote LFA and FEC 129 PW targeted applications with TAC. So each LSR
   advertises the corresponding FEC-Label bindings.  Further, suppose
   the initiating LSR is not the PQ node for responding LSRs Remote LFA
   IGP calculations. In such a case, the responding LSR may use the SAC
   mechanism to convey its disinterest in receiving state information
   for Remote LFA targeted LDP application.

   For a given tLDP session, the TAC mechanism can be used without the
   SAC mechanism, and the SAC mechanism can be used without the TAC
   mechanism. It is useful to discuss the behavior when TAC and SAC



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   mechanisms are used on the same tLDP session. The TAC mechanism MUST
   take precedence over the SAC mechanism with respect to enabling
   applications for which state information will be advertised. For a
   tLDP session using the TAC mechanism, the LDP peers MUST NOT
   advertise state information for an application that has not been
   negotiated in the most recent TAE list (referred to as an un-
   negotiated application).  This is true even if one of the peers
   announces its interest in receiving state information that
   corresponds to the un-negotiated application by sending a SAC TLV.
   In other words, when TAC is being used, SAC cannot and should not
   enable state information advertisement for applications that have not
   been enabled by TAC.

   On the other hand, the SAC mechanism MUST take precedence over the
   TAC mechanism with respect to disabling state information
   advertisements. If an LDP speaker has announced its disinterest in
   receiving state information for a given application to a given peer
   using the SAC mechanism, its peer MUST NOT send state information for
   that application, even if the two peers have negotiated that the
   corresponding application via the TAC mechanism.


   For the purposes of determining the correspondence between targeted
   applications defined in this document and application state as
   defined in [RFC7473] an LSR MUST use the following mappings:

      LDPv4 Tunneling - IPv4 Prefix-LSPs
      LDPv6 Tunneling - IPv6 Prefix-LSPs
      LDPv4 Remote LFA - IPv4 Prefix-LSPs
      LDPv6 Remote LFA - IPv6 Prefix-LSPs
      LDP FEC 128 PW - FEC128 P2P-PW
      LDP FEC 129 PW - FEC129 P2P-PW


   An LSR MUST map Targeted Application to LDP capability as follows:

      mLDP Tunneling - P2MP Capability, MP2MP Capability
                       and HSMP LSP Capability TLV
      mLDP node protection - P2MP Capability, MP2MP Capability
                       and HSMP LSP Capability TLV

5. Use cases

5.1 Remote LFA Automatic Targeted session

   The LSR determines that it needs to form an automatic tLDP session to
   remote LSR based on IGP calculation as described in [RFC7490] or some
   other mechanism, which is outside the scope of this document. The LSR



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   forms the tLDP adjacency and constructs an Initialization message
   with TAC TLV with TAE as Remote LFA during session establishment. The
   receiver LSR processes the LDP Initialization message and verifies
   whether it is configured to accept a Remote LFA tLDP session. If it
   is, it may further verify that establishing such a session does not
   exceed the configured limit for Remote LFA sessions. If all these
   conditions are met, the receiver LSR may respond back with an
   Initialization message with TAC corresponding to Remote LFA, and
   subsequently the session may be established.

   After the session has been established with TAC capability, the
   sender and receiver LSR distribute IPv4 or IPv6 FEC label bindings
   over the session. Further, the receiver LSR may determine that it
   does not need these FEC label bindings. So it may disable the receipt
   of these FEC label bindings by mapping targeted application element
   to state control capability as described in section 4.

5.2 FEC 129 Auto Discovery Targeted session

   BGP auto discovery may determine whether the LSR needs to initiate an
   auto-discovery tLDP session with a border LSR. Multiple LSRs may try
   to form an auto discovered tLDP session with a border LSR. So, a
   service provider may want to limit the number of auto discovered tLDP
   sessions a border LSR can accept. As described in Section 2, LDP may
   convey targeted applications with TAC TLV to border LSR. A border LSR
   may establish or reject the tLDP session based on local
   administrative policy. Also, as the receiver LSR becomes aware of
   targeted applications, it can also employ an administrative policy
   for security. For instance, it can employ a policy to accept all
   auto-discovered session from source-list.

   Moreover, the sender and receiver LSR must exchange FEC 129 label
   bindings only over the tLDP session.

5.3 LDP over RSVP and Remote LFA targeted session

   A LSR may want to establish a tLDP session to a remote LSR for LDP
   over RSVP tunneling and Remote LFA applications. The sender LSR may
   add both these applications as a unique Targeted Application Element
   in the Targeted Application Capability data of a TAC TLV. The
   receiver LSR may have reached a configured limit for accepting Remote
   LFA automatic tLDP sessions, but it may have been configured to
   accept LDP over RSVP tunneling. In such a case, the tLDP session is
   formed for both LDP over RSVP and Remote LFA applications as both
   need same FECs - IPv4 or IPv6 or both.

5.4 mLDP node protection targeted session




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   A merge point LSR may determine that it needs to form automatic tLDP
   session to the upstream point of local repair (PLR) LSR for MP2P and
   MP2MP LSP [RFC6388] node protection as described in the [RFC7715].
   The MPT LSR may add a new targeted LDP application - mLDP protection
   - as a unique TAE in the Targeted Application Capability Data of a
   TAC TLV and send it in the Initialization message to the PLR. If the
   PLR is configured for mLDP node protection and establishing this
   session does not exceed the limit of either mLDP node protection
   sessions or automatic tLDP sessions, the PLR may decide to accept
   this session. Also, the PLR may respond back with the initialization
   message with a TAC TLV that has one of the TAEs as - mLDP protection,
   and the session proceeds to establishment as per [RFC5036].

6. Security Considerations

   The Capability procedure described in this document does not
   introduce any change to LDP Security Considerations section described
   in [RFC5036].

   As described in [RFC5036], DoS attacks via Extended Hellos, which are
   required to establish a tLDP session, can be addressed by filtering
   Extended Hellos using access lists that define addresses with which
   Extended Discovery is permitted.  Further, as described in section
   5.2 of this document, a LSR can employ a policy to accept all auto-
   discovered Extended Hellos from the configured source addresses
   list.

   Also for the two LSRs supporting TAC, the tLDP session is only
   established after successful negotiation of the TAC. The initiating
   and receiving LSR MUST only advertise TA-Ids that they support. In
   other words, what they are configured for over the tLDP session.

7. IANA Considerations

   This document requires the assignment of a new code point for a
   Capability Parameter TLVs from the IANA managed LDP registry "TLV
   Type Name Space", corresponding to the advertisement of the Targeted
   Applications capability. IANA is requested to assign the lowest
   available value after 0x050B.

      Value  Description                       Reference
      -----  --------------------------------  ---------
      TBD1   Targeted Applications capability  [this document]

   This document requires the assignment of a new code point for a
   status code from the IANA managed registry "STATUS CODE NAME SPACE"
   on the Label Distribution Protocol (LDP) Parameters page,
   corresponding to the notification of session Rejected/Targeted



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   Application Capability Mis-Match. IANA is requested to assign the
   lowest available value after 0x0000004B.

      Value E Description                       Reference
      ----- - --------------------------------  ---------
      TBD2  1 Session Rejected/Targeted
              Application Capability Mis-Match  [this document]


   This document also creates a new name space 'the LDP Targeted
   Application Identifier' on the Label Distribution Protocol (LDP)
   Parameters page, that is to be managed by IANA. The range is 0x0001-
   0xFFFE, with the following values requested in this document.


      Value            Description                Reference
      --------         -------------------------  ---------------
      0x0000           Reserved                   [this document]
      0x0001           LDPv4 Tunneling            [this document]
      0x0002           LDPv6 Tunneling            [this document]
      0x0003           mLDP Tunneling             [this document]
      0x0004           LDPv4 Remote LFA           [this document]
      0x0005           LDPv6 Remote LFA           [this document]
      0x0006           LDP FEC 128 PW             [this document]
      0x0007           LDP FEC 129 PW             [this document]
      0x0008           LDP Session Protection     [this document]
      0x0009           LDP ICCP                   [this document]
      0x000A           LDP P2MP PW                [this document]
      0x000B           mLDP Node Protection       [this document]
      0x000C           LDPv4 Intra-area FECs      [this document]
      0x000D           LDPv6 Intra-area FECs      [this document]
      0x0001 - 0x1FFF  Available for assignment
                       by IETF Review
      0x2000 - 0F7FF   Available for assignment
                       as first come first served
      0xF800 - 0xFBFF  Available for private use
      0xFC00 - 0xFFFE  Available for experimental use
      0xFFFF           Reserved                   [this document]

8. Acknowledgments

   The authors wish to thank Nischal Sheth, Hassan Hosseini, Kishore
   Tiruveedhul, Loa Andersson, Eric Rosen, Yakov Rekhter, Thomas
   Beckhaus, Tarek Saad, Lizhong Jin and Bruno Decraene for doing the
   detailed review. Thanks to Manish Gupta and Martin Ehlers for their
   input to this work and many helpful suggestions.

9. Contributing Authors



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   Chris Bowers
   Juniper Networks
   1133 Innovation Way
   Sunnyvale, CA  94089
   USA
   EMail: cbowers@juniper.net

   Zhenbin Li
   Huawei
   Bld No.156 Beiqing Rd
   Beijing  100095
   China
   Email: lizhenbin@huawei.com


10.  References

10.1  Normative References


   [RFC5036]  Andersson, L., Ed., Minei, I., Ed., and B. Thomas, Ed.,
              "LDP Specification", RFC 5036, October 2007,
              <http://www.rfc-editor.org/info/rfc5036>.

   [RFC5561]  Thomas, B., Raza, K., Aggarwal, S., Aggarwal, R., and JL.
              Le Roux, "LDP Capabilities", RFC 5561, July 2009,
              <http://www.rfc-editor.org/info/rfc5561>.

   [RFC7473] Kamran Raza, Sami Boutros, "Controlling State
              Advertisements of Non-negotiated LDP Applications", RFC
              7473, March 2015, <http://www.rfc-
              editor.org/info/rfc7473>.

   [RFC7715] IJ. Wijnands, E. Rosen, K. Raza, J. Tantsura, A. Atlas, Q.
              Zhao, "mLDP Node Protection", RFC 7715, January 2016,
              <http://www.rfc-editor.org/info/rfc7715>.

   [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
              Requirement Levels", BCP 14, RFC 2119, March 1997,
              <http://www.rfc-editor.org/info/rfc2119>.

   [RFC8174] B. Leiba, "Ambiguity of Uppercase vs Lowercase in RFC 2119
              Key Words", BCP 14, RFC8174, May 2017, <http://www.rfc-
              editor.org/info/rfc8174>.

10.2  Informative References

   [RFC7490] S. Bryant, C. Filsfils, S. Previdi, M. Shand, N. So,



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              "Remote Loop-Free Alternate (LFA) Fast Reroute (FRR)",
              April 2015.

   [RFC6074] E. Rosen, B. Davie, V. Radoaca, and W. Luo, "Provisioning,
              Auto-Discovery, and Signaling in Layer 2 Virtual Private
              Networks (L2VPNs)", January 2011.

   [RFC6388] IJ. Wijnands, I. Minei, K. Kompella, B. Thomas, "Label
              Distribution Protocol Extensions for Point-to-Multipoint
              and Multipoint-to-Multipoint Label Switched Paths",
              November 2011.

Authors' Addresses

              Santosh Esale
              Juniper Networks
              1133 Innovation Way
              Sunnyvale, CA  94089
              USA
              EMail: sesale@juniper.net

              Raveendra Torvi
              Juniper Networks
              10 Technology Park Drive
              Westford, MA 01886
              USA
              EMail: rtorvi@juniper.net

              Luay Jalil
              Verizon
              1201 E Arapaho Rd
              Richardson, TX  75081
              USA
              Email: luay.jalil@verizon.com

              Uma Chunduri
              Huawei
              2330 Central Expy
              Santa Clara, CA 95050
              USA
              Email: uma.chunduri@huawei.com

              Kamran Raza
              Cisco Systems, Inc.
              2000 Innovation Drive
              Ottawa, ON K2K-3E8
              Canada
              E-mail: skraza@cisco.com



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