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Versions: (draft-raza-mpls-ldp-ip-pw-capability) 00 01 02 03 04 05 06 07 08 09 RFC 7473

MPLS Working Group                                           Kamran Raza
Internet Draft                                              Sami Boutros
Intended Status: Standards Track
Expires: July 17, 2015                               Cisco Systems, Inc.

                                                        January 18, 2015


  Controlling State Advertisements Of Non-negotiated LDP Applications

              draft-ietf-mpls-ldp-ip-pw-capability-09.txt


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Abstract

  There is no capability negotiation done for Label Distribution
  Protocol (LDP) applications that setup Label Switched Paths (LSPs) for
  IP prefixes or that signal Point-to-point (P2P) Pseudowires (PWs) for
  Layer 2 Virtual Private Networks (L2VPNs). When an LDP session comes
  up, an LDP speaker may unnecessarily advertise its local state for
  such LDP applications even when the peer session is established for
  some other applications like Multipoint LDP (mLDP) or Inter-Chassis
  Communication Protocol (ICCP). This document defines a solution by
  which an LDP speaker announces to its peer its disinterest in such
  non-negotiated applications, thus disabling the unnecessary
  advertisement of corresponding application state, which would have
  otherwise be advertised over the established LDP session.


Table of Contents

   1. Introduction  . . . . . . . . . . . . . . . . . . . . . . . . .  3
   2. Conventions used in this document . . . . . . . . . . . . . . .  4
   3. Non-negotiated LDP applications . . . . . . . . . . . . . . . .  4
     3.1. Non-interesting State . . . . . . . . . . . . . . . . . . .  4
       3.1.1. Prefix-LSPs   . . . . . . . . . . . . . . . . . . . . .  5
       3.1.2. P2P-PWs   . . . . . . . . . . . . . . . . . . . . . . .  5
   4. Controlling State Advertisement . . . . . . . . . . . . . . . .  5
     4.1. State Advertisement Control Capability  . . . . . . . . . .  5
     4.2. Capabilities Procedures . . . . . . . . . . . . . . . . . .  8
       4.2.1. State Control Capability in an Initialization message .  8
       4.2.2. State Control capability in a Capability message  . . .  9
   5. Applicability Statement . . . . . . . . . . . . . . . . . . . .  9
   6. Operational Examples  . . . . . . . . . . . . . . . . . . . . . 11
     6.1. Disabling Prefix-LSPs and P2P-PWs on an ICCP session  . . . 11
     6.2. Disabling Prefix-LSPs on a L2VPN/PW T-LDP session . . . . . 11
     6.3. Disabling Prefix-LSPs dynamically on an estab. LDP session  11
     6.4. Disabling Prefix-LSPs on an mLDP-only session . . . . . . . 12
     6.5. Disabling IPv4 or IPv6 Prefix-LSPs on a dual-stack LSR  . . 12
   7. Security Considerations . . . . . . . . . . . . . . . . . . . . 13
   8. IANA Considerations . . . . . . . . . . . . . . . . . . . . . . 13
   9. References  . . . . . . . . . . . . . . . . . . . . . . . . . . 13
     9.1.  Normative References . . . . . . . . . . . . . . . . . . . 13
     9.2.  Informative References . . . . . . . . . . . . . . . . . . 13
   10. Acknowledgments  . . . . . . . . . . . . . . . . . . . . . . . 14
   Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 14







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1. Introduction

  LDP Capabilities specification [RFC5561] introduced a mechanism to
  negotiate LDP capabilities for a given feature between peer Label
  Switching Routers (LSRs). The capability mechanism insures that no
  unnecessary state is exchanged between peer LSRs unless the
  corresponding feature capability is successfully negotiated between
  the peers.

  Newly defined LDP features and applications, such as Typed Wildcard
  Forwarding Equivalence Class (FEC) [RFC5918], Inter-Chassis
  Communication Protocol [RFC7275], mLDP [RFC6388], and L2VPN Point-to-
  multipoint (P2MP) PW [P2MP-PW] make use of LDP capabilities framework
  for their feature negotiation. However, the earlier LDP application to
  establish LSPs for IP unicast prefixes, and application to signal
  L2VPN P2P PW [RFC4447] [RFC4762] allowed LDP speakers to exchange
  application state without any capability negotiation, thus causing
  unnecessary state advertisement when a given application is not
  enabled on one of the LDP speakers participating in a given session.
  For example, when bringing up and using an LDP peer session with a
  remote Provider Edge (PE) LSR for purely ICCP signaling reasons, an
  LDP speaker may unnecessarily advertise labels for IP (unicast)
  prefixes to this ICCP related LDP peer.

  Another example of unnecessary state advertisement can be cited when
  LDP is to be deployed in an IP dual-stack environment. For instance,
  an LSR that is locally enabled to setup LSPs for both IPv4 and IPv6
  prefixes may advertise (address and label) bindings for both IPv4 and
  IPv6 address families towards an LDP peer that is interested in IPv4
  bindings only. In this case, the advertisement of IPv6 bindings to the
  peer is unnecessary, as well as wasteful, from the point of view of
  LSR memory/CPU and network resource consumption.

  To avoid this unnecessary state advertisement and exchange, currently
  an operator is typically required to configure and define filtering
  policies on the LSR, which introduces unnecessary operational overhead
  and complexity for such deployments.

  This document defines an LDP Capabilities [RFC5561] based solution by
  which an LDP speaker may announce to its peer(s) its disinterest (or
  non-support) for state to setup IP Prefix LSPs and/or to signal L2VPN
  P2P PW at the time of session establishment. This capability helps in
  avoiding unnecessary state advertisement for such feature
  applications. This document also states the mechanics to dynamically
  disable or enable the state advertisement for such applications during
  the session lifetime. The non-interesting state of an application
  depends on the type of application and is described later in section
  3.1.



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2. 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 in RFC-2119 [RFC2119].

  The term "IP" in this document refers to both IPv4 and IPv6 unicast
  address families.

3. Non-negotiated LDP applications

  For the applications that existed prior to the definition of LDP
  Capabilities framework [RFC5561], an LDP speaker typically advertises,
  without waiting for any capabilities exchange and negotiation, its
  corresponding application state to its peers after the session
  establishment. These early LDP applications include:

     o IPv4/IPv6 Prefix LSPs Setup
     o L2VPN P2P FEC128 and FEC129 PWs signaling

   This document onward uses following shorthand terms for these earlier
   LDP applications:

     o "Prefix-LSPs": Refers to an application that sets up LDP LSPs
       corresponding to IP routes/prefixes by advertising label
       bindings for Prefix FEC (as defined in RFC-5036).

     o "P2P-PWs": Refers to an application that signals FEC 128 and/or
       FEC 129 L2VPN P2P Pseudowires using LDP (as defined in RFC-4447).

   To disable unnecessary state exchange for such LDP applications over
   an established LDP session, a new capability is being introduced in
   this document. This new capability controls the advertisement of
   application state and enables an LDP speaker to notify its peer its
   disinterest in the state of one or more of these "Non-negotiated" LDP
   applications at the time of session establishment. Upon receipt of
   such capability, the receiving LDP speaker, if supporting the
   capability, disables the advertisement of the state related to the
   application towards the sender of the capability. This new capability
   can also be sent later in a Capability message to either disable a
   previously enabled application's state advertisement or to enable a
   previously disabled application's state advertisement.

3.1. Non-interesting State

   A non-interesting state of a non-negotiated LDP application:
     - is the application state which is of a no interest to an LSR and
       need not be advertised to the LSR;



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     - need not be advertised in any of the LDP protocol messages;
     - is dependent on application type and specified accordingly.

3.1.1 Prefix-LSPs

   For Prefix-LSPs application type, the non-interesting state refers to
   any state related to IP Prefix FEC (such as FEC label bindings, LDP
   Status). This document, however, does not classify IP address
   bindings (advertised via ADDRESS message) as a non-interesting state
   and allows the advertisement of IP Address bindings. The reason for
   this allowance is that an LSR typically uses peer IP address(es) to
   map an IP routing nexthop/address to an LDP peer for their
   functionality. For example, mLDP [RFC6388] uses peer's IP address(es)
   to determine its upstream LSR to reach Root node as well as to select
   forwarding interface towards its downstream LSR. Hence in an mLDP-
   only network, while it is desirable to disable advertisement of label
   bindings for IP (unicast) Prefixes, disabling advertisement of IP
   address bindings will break mLDP functionality. Similarly, other LDP
   applications may also depend on learnt peer IP address and hence this
   document does not put IP address binding into a non-interesting state
   category to facilitate such LDP applications.

3.1.2 P2P-PWs

   For P2P-PWs application type, the non-interesting state refers to any
   state related to P2P PW FEC128/FEC129 (such as FEC label bindings,
   MAC [address] withdrawal, and LDP PW Status). From now onward in this
   document, the term "state" will mean to refer to the "non-interesting
   state" for an application, as defined in this section.

4. Controlling State Advertisement

   To control advertisement of non-interesting state related to non-
   negotiated LDP applications defined in section 3, a new capability
   TLV is defined as follows.

4.1. State Advertisement Control Capability

   The "State Advertisement Control Capability" is a new Capability
   Parameter TLV defined in accordance with section 3 of LDP
   Capabilities specification [RFC5561]. The format of this new TLV is
   as follows:









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    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|State Adv. Ctrl. Cap (IANA)|           Length              |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |S|  Reserved   |                                               |
   +-+-+-+-+-+-+-+-+
   |                                                               |
   ~            State Advertisement Control Element(s)             ~
   |                                                               |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   Figure 1: Format of an "State Advertisement Control Capability" TLV

   The value of the U-bit for the TLV MUST be set to 1 so that a
   receiver MUST silently ignore this TLV if unknown to it, and continue
   processing the rest of the message. Whereas, The value of F-bit MUST
   be set to 0. Once advertised, this capability cannot be withdrawn;
   thus S-bit MUST be set to 1 in an Initialization and Capability
   message.

   The capability data associated with this State Advertisement Control
   (SAC) Capability TLV is one or more State Advertisement Control
   Elements, where each element indicates enabling/disabling of
   advertisement of non-interesting state for a given application. The
   format of a SAC Element is defined as follows:

                              0 1 2 3 4 5 6 7
                             +-+-+-+-+-+-+-+-+
                             |D| App |Unused |
                             +-+-+-+-+-+-+-+-+

        Figure 2: Format of "State Advertisement Control Element"

   Where:
   D bit: Controls the advertisement of the state specified in "App"
          field:
           1: Disable state advertisement
           0: Enable state advertisement
          When sent in an Initialization message, D bit MUST be set
          to 1.

   App: Defines the legacy application type whose state advertisement
        is to be controlled. The value of this field is defined as
        follows:

         1: IPv4 Prefix-LSPs (LSPs for IPv4 prefixes)
         2: IPv6 Prefix-LSPs (LSPs for IPv6 prefixes)
         3: FEC128 P2P-PW (L2VPN PWid FEC signaling)



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         4: FEC129 P2P-PW (L2VPN Generalized PWid FEC signaling)

         Any other value in this field MUST be treated as an error.

   Unused: MBZ on transmit and ignored on receipt.

   The "Length" field of SAC Capability TLV (in octets) is computed as
   following:
     Length (in octets) = 1 + number of SAC elements
   For example, if there are two SAC elements present, then the Length
   field is set to 3 octets. A receiver of this capability TLV can
   deduce the number of elements present in the TLV by using the Length
   field.

   From now onward, this document uses the term "element" to refer to a
   SAC Element.

   As described earlier, SAC Capability TLV MAY be included by an LDP
   speaker in an Initialization message to signal to its peer LSR that
   state exchange for one or more application(s) need to be disabled on
   the given peer session. This TLV can also be sent later in a
   Capability message to selectively enable or disable these
   applications. If there are more than one elements present in a SAC
   Capability TLV, the elements MUST belong to distinct app types and
   the an app type MUST NOT appear more than once. If a receiver
   receives such a malformed TLV, it SHOULD discard this TLV and
   continue processing rest of the message. If an LSR receives a message
   with a SAC capability TLV containing an element with "App" field set
   to a value other than defined above, the receiver MUST ignore and
   discard the element and continue processing the rest of the TLV.

   To control more than one application state, a sender LSR can either
   send a single capability TLV in a message with multiple elements
   present, or can send separate messages with capability TLV specifying
   one or more elements. A receiving LSR, however, MUST treat each
   incoming capability TLV with an element corresponding to a given
   application type as an update to its existing policy for the given
   type.

   To understand capability updates from an example, let us consider 2
   LSRs, S (LDP speaker) and P (LDP peer), both of which support all the
   non-negotiated applications listed earlier. By default, these LSR
   will advertise state for these applications, as configured, to their
   peer as soon as an LDP session is established. Now assume that P
   receives from S a SAC capability in an Initialization message with
   "IPv6 Prefix-LSPs" and "FEC129 P2P-PW" applications disabled. This
   updates P's outbound policy towards S to advertise state related to
   only IPv4 Prefix-LSPs and FEC128 P2P-PW applications.  Later, P
   receives another capability update from S via a Capability message
   with "IPv6 Prefix-LSPs" enabled and "FEC128 P2P-PWs" disabled. This



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   results in P's outbound policy towards S to advertise both IPv4 and
   IPv6 Prefix-LSPs application state, and disable both FEC128 and
   FEC129 P2P-PWs signaling. Finally, P receives another update from S
   via a Capability message that specifies to disable all four non-
   negotiated applications state, resulting in P outbound policy towards
   S to block/disable state for all these applications, and only
   advertise state for any other application, as applicable.

4.2. Capabilities Procedures

   The SAC capability conveys the desire of an LSR to disable the
   receipt of unwanted/unnecessary state from its LDP peer. This
   capability is unilateral and unidirectional in nature, and a
   receiving LSR is not required to send a similar capability TLV in an
   Initialization or Capability message towards the sender of this
   capability. This unilateral behavior conforms to the procedures
   defined in the Section 6 of LDP Capabilities [RFC5561].

   After this capability is successfully negotiated (i.e. sent by an LSR
   and received/understood by its peer), then the receiving LSR MUST NOT
   advertise any state related to the disabled applications towards the
   capability sending LSR until and unless these application states are
   explicitly enabled again via a capability update. Upon receipt of a
   capability update to disable an enabled application [state] during
   the lifetime of a session, the receiving LSR MUST also withdraw from
   the peer any previously advertised state corresponding to the
   disabled application.

   If a receiving LDP speaker does not understand the SAC capability
   TLV, then it MUST respond to the sender with "Unsupported TLV"
   notification as described in LDP Capabilities [RFC5561]. If a
   receiving LDP speaker does not understand or does not support an
   application specified in an application control element, it SHOULD
   silently ignore/skip such an element and continue processing rest of
   the TLV.

4.2.1. State Control Capability in an Initialization message

   LDP Capabilities [RFC5561] framework dictates that the S-bit of
   capability parameter in an Initialization message MUST be set to 1
   and SHOULD be ignored on receipt.

   An LDP speaker determines (e.g. via some local configuration or
   default policy) if it needs to disable Prefix-LSPs and/or P2P-PWs
   applications with a peer LSR. If there is a need to disable, then the
   SAC TLV needs to be included in the Initialization message with
   respective SAC elements included with their D bit set to 1.




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   An LDP speaker that supports the SAC capability MUST interpret the
   capability TLV in a received Initialization message such that it
   disables the advertisement of the application state towards the
   capability sending LSR for Prefix-LSPs and/or P2P-PWs applications if
   their SAC element's D bit is set to 1.

4.2.2. State Control capability in a Capability message

   If the LDP peer supports "Dynamic Announcement Capability" [RFC5561],
   then an LDP speaker may send SAC capability in a Capability message
   towards the peer. Once advertised, these capabilities cannot be
   withdrawn and hence the S-bit of the TLV MUST be set to 1 when sent
   in a Capability message.

   An LDP speaker may decide to send this TLV towards an LDP peer if one
   or more of its Prefix-LSPs and/or P2P-PWs applications get disabled,
   or if previously disabled application gets enabled again. In this
   case, the LDP speaker constructs the TLV with appropriate SAC
   element(s) and sends the corresponding capability TLV in a Capability
   message.

   Upon receipt of this TLV in a Capability message, the receiving LDP
   speaker reacts in the same manner as it reacts upon the receipt of
   this TLV in an Initialization message. Additionally, the peer
   withdraws/advertises the application state from/to the capability
   sending LDP speaker according to the capability update.

5. Applicability Statement

   The procedures defined in this document may result in disabling
   announcement of label bindings for IP Prefixes and/or P2P PW FECs,
   and hence should be used with caution and discretion. This document
   recommends that this new SAC capability and its procedures SHOULD be
   enabled on an LSR only via a configuration knob. This knob could
   either be a global LDP knob or be implemented per LDP neighbor.
   Hence, it is recommended that an operator SHOULD enable this
   capability and its associated procedures on an LSR towards a neighbor
   only if it is known that such bindings advertisement and exchange
   with the neighbor is unnecessary and wasteful.

   Following table summarizes a non-exhaustive list of typical LDP
   session types on which this new SAC capability and its procedures are
   expected to be applied to disable advertisement of non-interesting
   state:







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    +===============================+================================+
    | Session Type(s)               | Non-interesting State          |
    +===============================+================================+
    | P2P-PW FEC128-only            | IP Prefix LSPs + P2P-PW FEC129 |
    |-------------------------------|--------------------------------|
    | P2P-PW only (FEC128/129)      | IP Prefix LSPs                 |
    |-------------------------------|--------------------------------|
    | IPv4-only on a Dual-Stack LSR | IPv6 Prefix LSPs + P2P-PW      |
    |-------------------------------|--------------------------------|
    | IPv6-only on a Dual-Stack LSR | IPv4 Prefix LSPs + P2P-PW      |
    |-------------------------------|--------------------------------|
    | mLDP-only                     | IP Prefix LSPs + P2P-PW        |
    |-------------------------------|--------------------------------|
    | ICCP-only                     | IP Prefix LSPs + P2P-PW        |
    +-------------------------------+--------------------------------+

   It is to be noted that if an application state needs changing after
   session initialization (e.g. to enable previously disabled
   application or to disable previously enabled application), the
   procedures defined in this document expect LSR peers to support LDP
   "Dynamic Announcement" Capability to announce the change in SAC
   capability via LDP Capability message. However, if any of the peering
   LSR does not support this capability, the alternate option is to
   force reset the LDP session to advertise the new SAC capability
   accordingly during the following session initialization.

   Following are some more important points that an operator need to
   consider regarding the applicability of this new capability and
   associated procedures defined in this document:

   - An operator SHOULD disable Prefix-LSPs state on any Targeted LDP
     (T-LDP) session that is established for ICCP-only and/or PW-only
     purposes.

   - An operator MUST NOT disable Prefix-LSPs state on any T-LDP session
     that is established for remote LFA FRR [RLFA] reasons.

   - In a remote LFA FRR [RLFA] enabled network, it is RECOMMENDED to
     not disable Prefix-LSPs state on a T-LDP session even if the
     current session type is PW-only and/or ICCP-only. This is
     recommended because any remote/T-LDP neighbor could potentially be
     picked as a remote LFA PQ node.

   - This capability SHOULD be enabled for Prefix-LSPs in the
     scenarios when it is desirable to disable (or enable)
     advertisement of "all" the prefix label bindings. For scenarios
     when a "subset" of bindings need to be filtered, the existing
     filtering procedures pertaining to label binding announcement
     should be used.



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   - It is allowed to use label advertisement filtering policies in
     conjunction with the procedures defined in this document for
     Prefix-LSPs. In such cases, the label bindings will be announced
     as per the label filtering policy for the given neighbor when
     Prefix-LSP application is enabled.


6. Operational Examples

6.1. Disabling Prefix-LSPs and P2P-PWs on an ICCP session

   Consider two PE routers, LSR1 and LSR2, which understand/support SAC
   capability TLV, and have an established LDP session to exchange ICCP
   state related to dual-homed devices connected to these LSRs. Let us
   assume that both LSRs are provisioned not to exchange any state for
   Prefix-LSPs (IPv4/IPv6) and P2P-PWs (FEC128/129) application.

   To indicate their disinterest in these applications, the LSRs will
   include a SAC capability TLV (with 4 SAC elements corresponding to
   these 4 applications with D bit set to 1 for each one) in the
   Initialization message. Upon receipt of this TLV in Initialization
   message, the receiving LSR will disable the advertisement of
   IPv4/IPv6 label bindings, as well as P2P PW FEC128/129 signaling,
   towards its peer after session establishment.

6.2. Disabling Prefix-LSPs on a L2VPN/PW T-LDP session

   Now, consider LSR1 and LSR2 have an established T-LDP session for
   P2P-PWs application to exchange label bindings for FEC 128/129. Given
   that there is no need to exchange IP label bindings amongst the PE
   LSRs over a PW T-LDP session in most typical deployments, let us
   assume that LSRs are provisioned to disable IPv4/IPv6 Prefix-LSPs
   application state on the given PW session.

   To indicate their disinterest in Prefix-LSPs application over a PW T-
   LDP session, the LSRs will follow/apply the same procedures as
   described in previous section. As a result, only P2P-PWs related
   state will be exchanged between these LSRs over this T-LDP session.

6.3. Disabling Prefix-LSPs dynamically on an established LDP session

   Assume that LSRs from previous sections were initially provisioned to
   exchange both Prefix-LSPs and P2P-PWs state over the session between
   them, and also support "Dynamic Announcement" Capability [RFC5561].
   Now, assume that LSR1 is dynamically provisioned to disable
   (IPv4/IPv6) Prefix-LSPs over T-LDP session with LSR2. In this case,
   LSR1 will send SAC capability TLV in a Capability message towards
   LSR2 with application control elements defined for IPv4 and IPv6



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   Prefix-LSPs with D bit set to 1. Upon receipt of this TLV, LSR2 will
   disable Prefix-LSPs application state(s) towards LSR1 and withdraw
   all previously advertised application state from LSR1. To withdraw
   label bindings from its peer, LSR2 MAY use a single Prefix FEC Typed
   Wildcard Label Withdraw message [RFC5918] if the peer supports Typed
   Wildcard FEC capability.

   This dynamic disability of Prefix-LSPs application does not impact
   L2VPN P2P-PWs application on the given session, and both LSRs should
   continue to exchange PW Signaling application related state.

6.4. Disabling Prefix-LSPs on an mLDP-only session

   Now assume that LSR1 and LSR2 have formed an LDP session to exchange
   mLDP state only. In typical deployments, LSR1 and LSR2 also exchange
   bindings for IP (unicast) prefixes upon mLDP session, which is
   unnecessary and wasteful for an mLDP-only LSR.

   Using the procedures defined earlier, an LSR can indicate its
   disinterest in Prefix-LSPs application state to its peer upon session
   establishment time or dynamically later via LDP capabilities update.

   Reference to section 3.1, the peer disables the advertisement of any
   state related to IP Prefix FECs, but still advertises IP address
   bindings that are required for the correct operation of mLDP.

6.5. Disabling IPv4 or IPv6 Prefix-LSPs on a dual-stack LSR

   In IP dual-stack scenarios, LSR2 may advertise unnecessary state
   (e.g. IPv6 prefix label bindings) towards peer LSR1 corresponding to
   IPv6 Prefix-LSPs application once a session is established mainly for
   exchanging state for IPv4. The similar scenario also applies when
   advertising IPv4 Prefix-LSPs state on a session meant for IPv6. The
   SAC capability and its procedures defined in this document can help
   to avoid such unnecessary state advertisement.

   Consider IP dual-stack environment where LSR2 is enabled for Prefix-
   LSPs application for both IPv4 and IPv6, but LSR1 is enabled for (or
   interested in) only IPv4 Prefix-LSPs. To avoid receiving unwanted
   state advertisement for IPv6 Prefix-LSPs application from LSR2, LSR1
   can send SAC capability with element for IPv6 Prefix-LSPs with D bit
   set to 1 in the Initialization message towards LSR2 at the time of
   session establishment. Upon receipt of this capability, LSR2 will
   disable all IPv6 label binding advertisement towards LSR1. If IPv6
   Prefix-LSPs application is later enabled on LSR1, LSR1 can update the
   capability by sending SAC capability in a Capability message towards
   LSR2 to enable this application dynamically.




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7. Security Considerations

   The proposal introduced in this document does not introduce any new
   security considerations beyond that already apply to the base LDP
   specification [RFC5036] and [RFC5920].

8. IANA Considerations

   This document defines a new LDP capability parameter TLV. IANA is
   requested to assign the lowest available value after 0x0500 from "TLV
   Type Name Space" in the "Label Distribution Protocol (LDP)
   Parameters" registry as the new code point for the new LDP capability
   TLV code point.

   +-----+---------------------+---------------+-----------------------+
   |Value| Description         | Reference     |Notes/Registration Date|
   +-----+---------------------+---------------+-----------------------+
   | TBA | State Advertisement | This document |                       |
   |     | Control Capability  |               |                       |
   +-----+---------------------+---------------+-----------------------+

9. References

9.1  Normative References

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

   [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>.


9.2  Informative References

   [RFC4447]  Martini, L., Ed., Rosen, E., El-Aawar, N., Smith, T., and
              G. Heron, "Pseudowire Setup and Maintenance Using the
              Label Distribution Protocol (LDP)", RFC 4447, April 2006,
              <http://www.rfc-editor.org/info/rfc4447>.

   [RFC4762]  Lasserre, M., Ed., and V. Kompella, Ed., "Virtual Private
              LAN Service (VPLS) Using Label Distribution Protocol (LDP)
              Signaling", RFC 4762, January 2007, <http://www.rfc-



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              editor.org/info/rfc4762>.

   [RFC5918]  Asati, R., Minei, I., and B. Thomas, "Label Distribution
              Protocol (LDP) 'Typed Wildcard' Forward Equivalence Class
              (FEC)", RFC 5918, August 2010, <http://www.rfc-
              editor.org/info/rfc5918>.

   [RFC5920]  Fang, L., Ed., "Security Framework for MPLS and GMPLS
              Networks", RFC 5920, July 2010, <http://www.rfc-
              editor.org/info/rfc5920>.

   [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, November 2011, <http://www.rfc-
              editor.org/info/rfc6388>.

   [RFC7275]  Martini, L., Salam, S., Sajassi, A., Bocci, M.,
              Matsushima, S., and T. Nadeau, "Inter-Chassis
              Communication Protocol for Layer 2 Virtual Private Network
              (L2VPN) Provider Edge (PE) Redundancy", RFC 7275, June
              2014, <http://www.rfc-editor.org/info/rfc7275>.

   [P2MP-PW]  Martini, L. et. al, "Signaling Root-Initiated Point-to-
              Multipoint Pseudowires using LDP", draft-ietf-pwe3-p2mp-
              pw-04.txt, Work in Progress, March 2012.

   [RLFA]     Bryant, S., Filsfils, C., Previdi, S., Shand, M., So, N.,
              "Remote LFA FRR", draft-ietf-rtgwg-remote-lfa-10, Work in
              Progress, January 2015.

10. Acknowledgments

   The authors would like to thank Eric Rosen and Alexander Vainshtein
   for their review and valuable comments. We also acknowledge Karthik
   Subramanian and IJsbrand Wijnands for bringing up mLDP use case.

Authors' Addresses

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

   Sami Boutros
   Cisco Systems, Inc.
   3750 Cisco Way,
   San Jose, CA 95134, USA.
   E-mail: sboutros@cisco.com



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