MPLS Working Group                                          Kamran Raza
Internet Draft                                             Sami Boutros
Intended status: Standards Track
Expires: February 17, August 18, 2013                                  Cisco Systems

                                                        August 18, 2012

                                                      February 19, 2013

               Disabling IPoMPLS and P2P PW LDP Applications



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   Currently, no LDP capability is exchanged for LDP applications like
   IP label switching Label Switching and L2VPN P2P PW signaling. When an LDP session
   comes up, an LDP speaker may unnecessarily advertise its local state
   for such LDP applications even when the peer session may be
   established for some other applications like ICCP. This document
   proposes a solution by which an LDP speaker announces to its peer its
   disinterest in such non-negotiated application. applications. This, in turn,
   disables the advertisement of corresponding application state, which
   would have otherwise be advertised by default, over the established
   LDP session.

Table of Contents

  1. Introduction                                                      3
  2. Conventions used in this document                                 4
  3. Non-negotiated LDP applications                                   4
  4. Controlling State Exchange for Non-negotiated LDP Applications    5
     4.1. Application Control Capability                               5
  5. Capabilities Procedures                                           7
     5.1. Application Control Capability in an Initialization message 7  8
     5.2. Application Control capability in a Capability message       8
  6. Operational Examples                                              8
     6.1. Disabling IPoMPLS and P2P PW application apps. on an ICCP session 8        9
     6.2. Disabling IPoMPLS application on a L2VPN/PW T-LDP session    9
     6.3. Disabling IPoMPLS appl. dynamically app.dynamically on an estab. IP/PW session 9
     6.4. Disabling unwanted state advert. advertisement by an IP a dual-stack LSR  10
  7. Security Considerations                                          10
  8. IANA Considerations                                              10
  9. Conclusions                                                     11
  10. References                                                       11
     9.1. Normative References                                        11
     9.2. Informative References                                      11
  10. Acknowledgments                                                 12

1. Introduction

  LDP Capabilities [RFC5561] introduced a mechanism to negotiate LDP
  capabilities for a given feature amongst peer 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.

  While new LDP features and applications, such as Typed Wildcard FEC
  [RFC5918], Inter-Chassis Communication Protocol [ICCP], mLDP
  [RFC6388], and L2VPN P2MP PW [P2MP-PW] make use of LDP capabilities
  framework for their feature negotiation, the earlier LDP features and
  applications like IP label switching Label Switching and L2VPN P2P PW signaling
  [RFC4447] [RFC4762] may cause unnecessary state exchange between LDP
  peers speakers to exchange application
  state unnecessarily even when the 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
  PE LSR for purely ICCP signaling purposes, the reasons, an LDP speaker may
  unnecessarily advertise labels for IP (unicast) prefixes to this ICCP
  related LDP peer as per its default behavior.

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

  To avoid this unnecessary state advertisement and exchange, currently
  an operator is typically required to configure and define some sort
  of filtering policies on the box LSR for exchanging LDP state exchange, applications
  state, which introduces operational overhead and complexity.

  This document proposes an LDP Capabilities [RFC5561] based solution
  by which an LDP speaker may announce to its peer(s) its disinterest
  (or non-
  support/disability) to its peer non-support/disability) for IP Label Switching and/or L2VPN P2P
  PW Signaling application at the time of session establishment. This
  helps avoiding unnecessary state exchange for such feature
  applications. The proposal also states the mechanics to dynamically
  disable or enable such an application dynamically during the session lifetime.
  The document introduces a new LDP capability to implement this

2. Conventions used in this document

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   document are to be interpreted as described in RFC-2119 [RFC2119].

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

   This document uses shorthand terms "IPoMPLS" to refer to IP Label
   Switching application, and "P2P PW" to refer to L2VPN PW signaling
   for FEC 128 and FEC 129 P2P PWs. Pseudowires.

3. Non-negotiated LDP applications

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

   o  IPv4/IPv6 label switching Label Switching ("IPoMPLS")

   o  L2VPN P2P PW signaling ("P2P PW")

   To disable unnecessary state exchange for such LDP applications, 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 LDP peer its disinterest in 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, MUST disable disables the advertisement
   of any state related to the application towards the sender. Moreover, the sender LSR SHOULD also disable the
   advertisement of corresponding application state towards the peer. This new
     capability can also be sent later in a Capability message to either
   disable these applications, enabled applications or to enable previously disabled
   applications dynamically.

4. Controlling State Exchange for Non-negotiated LDP Applications

   To control advertisement of state related to non-negotiated LDP
   applications, namely IPoMPLS and P2P PW signaling, a new capability
   TLV is defined as follows.

4.1. Application Control Capability

   The "Application 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:

    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| App Control Cap.  (IANA)  |           Length              |
   |S|  Reserved   |                                               |
   |                                                               |
   ~               Application Control Element(s)                  ~
   |                                                               |

      Figure 1: Format of an "Application 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 and
   hence the withdrawn;
   thus S-bit MUST be set to 1 both in an Initialization message and Capability

     The capability data associated with this TLV is one or more
   Application Control Elements, where each element defines indicates
   enabling/disabling of state advertisement for a given application.
   The format of an Application Control Element is defined as follows:

                      0                   1
                      0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5
   |  App  |D|Rsvd1|
                     |AppType|D|Rsvd1|    Rsvd2      |

          Figure 2: Format of an "Application Control Element"



  AppType: Defines the (non-negotiated) application type. The value of
    this field is defined as:
       1: IPv4 Label switching
       2: IPv6 Label switching
       3: P2P PW FEC128 signaling
       4: P2P PW FEC129 signaling
    0, 5-15: Reserved.

   D bit: Controls the advertisement of state for the application as
    follows application:
       1: Disable state advertisement
       0: Enable state advertisement
      When sent in an Initialization message, D bit MUST be set to 1.

   Rsvd1, Rsvd2: Reserved for future use. MBZ on transmit and ignored on

   The "Length" field of "Application Control Capability" TLV depends on
   the number of Application Control Elements present in the TLV. For
   example, if there are two elements present, then the Length field is
   set to 5 octets. A receiver of this capability TLV can deduce number
   of application control elements present in the TLV by using Length


   From now onward, this document uses the term "element" to refer to an
   application control element.
   Application Control Element.

   As described earlier, "Application Control 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 a the given peer session. This TLV can also be sent
   later in a Capability message to selectively enable or disable these
   applications. An "Application Control Capability" TLV MUST contain
   elements with distinct application types and the TLV MUST NOT contain
   the same application type more than once. If a receiver receives such
   a malformed TLV, it SHOULD discard this TLV and continue processing
   rest of the message.

   To control more than one application, 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 message
   capability TLV for a given application type as an incremental update to the its
   existing control. policy for given type.

   To understand capability updates from an example, let us consider 2
   LSR peers, R1 (sender) and R2 (receiver),
   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 applications, as configured, to their
   peer as soon as an LDP session is established. Now assume that R2 P
   receives an Application Control capability in the Initialization
   message with "IPv6 Label switching" and "P2P PW FEC129" applications
   disabled. This updates R2's P's outbound policy towards R1 S to advertise
   state related to only "IPv4 Label switching" and "P2P PW FEC 128"
   applications.  Now, R2  Later, P receives a another capability update from R1 S via
   a Capability message with "IPv6 Label switching" enabled and "P2P PW
   FEC128" disabled. This updates R2's results in P's outbound policy towards R1 S to
   advertise both IPv4 and IPv6 Label switching state, and disable both
   P2P PW FEC128 and FEC 129 signaling. Finally, R2 P receives another
   update from R1 S via a Capability message that specifies to disable all 4
   four non-negotiated applications, resulting R2 P outbound policy towards R1
   S to block/disable state for all these applications, and only
   advertise state for any other application, if present.

  5. Capabilities Procedures

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

   After this capability is successfully negotiated (i.e. sent by a
   sender an LSR
   and received/understood by the receiver), its peer), then both
   participating LSRs the receiving LSR MUST NOT exchange
   advertise any state related to the disabled applications towards the
   capability sending LSR until and unless these applications are
   explicitly enabled again via a capability update.

   If a receiving LDP speaker does not understand the Application
   Control capability TLV, then it MUST respond to the sender with
   "Unsupported TLV" Notification notification as described in LDP Capabilities
   [RFC5561]. Upon receipt of such Notification, the sender MAY still
   continue to block/disable its outbound state advertisement towards
   the peer for the requested disabled applications. 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.

5.1. Application Control Capability in an Initialization message

   LDP Capabilities [RFC5561] dictate 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 they need it needs to disable IPoMPLS and/or P2P PW
   applications with a peer LSR. If there is a need to disable, then the
   "Application Control Capability" TLV needs to be included in the
   Initialization message with respective application control elements
   included with their D bit set to 1.
     An LDP speaker that supports the "Application Control" capability
   MUST interpret the capability TLV in a received Initialization
   message such that it disables the advertisement of the application
   state towards the sender capability sending LSR for IPoMPLS and/or P2P PW
   applications if their application control element's D bit is set to

5.2. Application Control capability in a Capability message

   If the LDP peer supports "Dynamic Announcement Capability" [RFC5561],
   then an LDP speaker may send Application Control 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 any one
   or more of its IPoMPLS and/or P2P PW signaling applications get
   disabled, or if previously disabled application gets enabled again.
   In this case, the LDP speaker constructs the TLV with appropriate
   application control
   elements element(s) and sends the corresponding capability
   TLV in a Capability message. Furthermore, the LDP speaker also withdraws/advertises
   application(s) related state (such as address/label bindings) from/to
   its peer according to the capability update.

   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 receiving
   LDP speaker peer
   withdraws/advertises application state from/to the capability sending peer
   LDP speaker according to the capability update.

6. Operational Examples

6.1. Disabling IPoMPLS and P2P PW applications on an ICCP session

   Consider two PE routers, LSR1 and LSR2, which understand/support
   "Application Control" capability TLV, and have an established LDP
     session due to ICCP application in order to exchange ICCP state related to dual-homed devices
   connected to these LSRs. Let us assume that LSR1 is both LSRs are
   provisioned not to exchange any state for IPoMPLS (IPv4/IPv6) and
   P2P PW (FEC128/129) application with LSR2. application.

   To indicate its their disinterest in these applications, the LSR1 LSRs will
   include an "Application Control" capability TLV (with 4 application
   control 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 LSR2 receiving LSR will
   disable advertisement of IPv4/IPv6 bindings (addresses and labels),
   as well as P2P PW FEC128/129 signaling, towards LSR1 its peer after
   session establishment.

   The LSR1 will also disable similar state advertisement for these
   applications towards LSR2 independently, irrespective of the fact
   whether or not LSR2 could disable the corresponding application
   state advertisement towards LSR1.

6.2. Disabling IPoMPLS application on a L2VPN/PW T-LDP session

   Now, consider LSR1 and LSR2 have an established T-LDP session for
   P2P PW application just to exchange label bindings for FEC 128/129.
   Since in most typical deployments, Given
   that there is no need to exchange IP (v4/v6) address/label bindings
   amongst the PE LSRs, LSRs over a PW T-LDP session in most typical
   deployments, let us assume that LSR1 is LSRs are provisioned to disable
   IPoMPLS (IPv4/IPv6)application on given PW session towards LSR2. session.

   To indicate its their disinterest in IPoMPLS application over PW T-LDP
   session, the LSR1 LSRs will follow/apply the same procedures to disable
   IPv4 and IPv6 label switching as described in previous section.
   Similarly, LSR2 will behave accordingly by disabling As a
   result, only P2P PW related state
   advertisement for IPoMPLS application towards LSR1. will be exchanged between these
   LSRs over this T-LDP session.

6.3. Disabling IPoMPLS application dynamically on an established IP/PW

   Assume that LSRs from previous sections were initially provisioned to
   exchange both IPoMPLS and P2P PW state over the session between them,
   and also support "Dynamic Announcement" Capability [RFC5561]. Now,
   assume that LSR1 is dynamically provisioned to disable IPoMPLS
   (IPv4/IPv6) over T-LDP session with LSR2. In this case, LSR1 will
   first disable its future outbound application state towards LSR2, and
   also withdraw all its previously advertised IPoMPLS state (labels and
   addresses) by sending a single Prefix FEC Typed Wildcard Label
   Withdraw message [RFC5918], and an Address Withdraw message
   respectively towards LSR2. LSR1 will also
   send Application Control capability TLV in a Capability message
   towards LSR2 with application control elements defined for IPv4 and
   IPv6 label switching with D bit set to 1. Upon receipt of this TLV,
     LSR2 will also disable IPoMPLS
   applications application(s) towards LSR1 and withdraw
   all previous IP label/address state using the same mechanics as described earlier for from LSR1. To withdraw label and
   address bindings from its peer, LSR2 MAY use a single Prefix FEC
   Typed Wildcard Label Withdraw message [RFC5918] and an Address
   Withdraw message respectively.

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

6.4. Disabling unwanted state advertisement by an IP dual-stack LSR

   In IP dual-stack scenarios, an LSR2 may advertise unnecessary state
   (label/address bindings) towards peer LSR1 corresponding to IPv6
   label switching application once a session is established mainly for
   exchanging state for IPv4. The similar scenario also applies when
   advertising IPv4 label switching state on a session meant for IPv6.
   The Application Control 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 IPoMPLS
   application for both IPv4 and IPv6, but LSR1 is enabled for (or
   interested in) only IPv4oMPLS. To avoid receiving unwanted state
   advertisement for IPv6oMPLS application from LSR2, LSR1 can send
   "Application Control" capability with element for IPv6 label
   switching 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 and address binding
   advertisement towards LSR1. If IPv6oMPLS is later enabled on LSR1,
   LSR1 can update the capability by sending Application Control
   capability in Capability message towards LSR2 to enable IPv6oMPLS
   application dynamically.

   [LDPv6] specification section 7 also suggests an alternate way to
   avoid the unnecessary state advertisement in the above scenario.

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

  The document defines following a new capability parameter TLV and requests
  following LDP TLV code point assignment by IANA from LDP "TLV Type
  Name Space" registry:

   o  "Application Control Capability" TLV (requested codepoint: 0x50C)

9. Conclusions

   The document proposed a solution using LDP Capabilities [RFC5561]
   mechanics to disable unnecessary state exchange, if/as desired,
   between LDP peers for currently non-negotiated IP/PW LDP

10. References


9.1. Normative References

   [RFC5036] L. Andersson, I. Minei, and B. Thomas, "LDP Specification",
             RFC 5036, September 2007.

   [RFC5561] B. Thomas, K. Raza, S. Aggarwal, R. Aggarwal, and JL. Le
             Roux, "LDP Capabilities", RFC 5561, July 2009.

   [RFC2119] S. Bradner, "Key words for use in RFCs to Indicate
             Requirement Levels", BCP 14, RFC2119, March 1997.


9.2. Informative References

   [RFC5918] R. Asati, I. Minei, and B. Thomas, "Label Distribution
             Protocol Typed Wildcard FEC", RFC 5918, August 2010.

   [RFC4447] L. Martini, E. Rosen, El-Aawar, T. Smith, and G. Heron,
             "Pseudowire Setup and Maintenance using the Label
             Distribution Protocol", RFC 4447, April 2006.

   [RFC4762] M. Lasserre, and V. Kompella,  "Virtual Private LAN Service
             (VPLS) Using Label Distribution Protocol (LDP) Signaling",
             RFC 4762, January 2007.

   [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, October 2011. March 2012.

   [ICCP]    L. Martini, S. Salam, A. Sajassi, and S. Matsushima,
             "Inter-Chassis Communication Protocol for L2VPN PE
             Redundancy", draft-ietf-pwe3-iccp-09.txt, Work in Progress,
             July 2012.

   [RFC6388] I. Minei, I. Wijnand, K. Kompella, and B. Thomas, "LDP
             Extensions for P2MP and MP2MP LSPs", RFC 6388, November

   [LDPv6]   R. Asati, et al., "Updates to LDP for IPv6", draft-ietf-
             mpls-ldp-ipv6-07.txt, Work in Progress, June 2012.

   [RFC5920] L. Fang, et al., "Security Framework for MPLS and GMPLS
             Networks", RFC 5920, July 2010.


10. Acknowledgments

   The authors would like to thank Eric Rosen for his valuable input and

   This document was prepared using

Authors' Addresses

  Kamran Raza
  Cisco Systems, Inc.,
  2000 Innovation Drive,
  Ottawa, ON K2K-3E8, Canada.

  Sami Boutros
  Cisco Systems, Inc.
  3750 Cisco Way,
  San Jose, CA 95134, USA.