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rfc:rfc6667

Internet Engineering Task Force (IETF) K. Raza Request for Comments: 6667 S. Boutros Category: Standards Track C. Pignataro ISSN: 2070-1721 Cisco Systems

                                                             July 2012
    LDP 'Typed Wildcard' Forwarding Equivalence Class (FEC) for
               PWid and Generalized PWid FEC Elements

Abstract

 The "Typed Wildcard Forwarding Equivalence Class (FEC) Element"
 defines an extension to the Label Distribution Protocol (LDP) that
 can be used when requesting, withdrawing, or releasing all label
 bindings for a given FEC Element type is desired.  However, a Typed
 Wildcard FEC Element must be individually defined for each FEC
 Element type.  This specification defines the Typed Wildcard FEC
 Elements for the Pseudowire Identifier (PWid) (0x80) and Generalized
 PWid (0x81) FEC Element types.

Status of This Memo

 This is an Internet Standards Track document.
 This document is a product of the Internet Engineering Task Force
 (IETF).  It represents the consensus of the IETF community.  It has
 received public review and has been approved for publication by
 the Internet Engineering Steering Group (IESG).  Further
 information on Internet Standards is available in Section 2 of
 RFC 5741.
 Information about the current status of this document, any
 errata, and how to provide feedback on it may be obtained at
 http://www.rfc-editor.org/info/rfc6667.

Copyright Notice

 Copyright (c) 2012 IETF Trust and the persons identified as the
 document authors.  All rights reserved.
 This document is subject to BCP 78 and the IETF Trust's Legal
 Provisions Relating to IETF Documents
 (http://trustee.ietf.org/license-info) in effect on the date of
 publication of this document.  Please review these documents
 carefully, as they describe your rights and restrictions with respect
 to this document.  Code Components extracted from this document must

Raza, et al. Standards Track [Page 1] RFC 6667 PWid and Gen. PWid Typed Wildcard FEC July 2012

 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.
 This document may not be modified, and derivative works of it may not
 be created, except to format it for publication as an RFC or to
 translate it into languages other than English.

Table of Contents

 1. Introduction ....................................................2
 2. Typed Wildcard for PW FEC Elements ..............................3
 3. Applicability Statement .........................................4
 4. Operation .......................................................4
    4.1. PW Consistency Check .......................................5
    4.2. PW Graceful Shutdown .......................................5
    4.3. Wildcard PW Status .........................................5
    4.4. Typed Wildcard MAC Withdrawal in VPLS ......................6
 5. Security Considerations .........................................6
 6. Acknowledgments .................................................7
 7. References ......................................................7
    7.1. Normative References .......................................7
    7.2. Informative References .....................................7

1. Introduction

 An extension to the Label Distribution Protocol (LDP) [RFC5036]
 defines the general notion of a "Typed Wildcard Forwarding
 Equivalence Class (FEC) Element" [RFC5918].  This can be used when
 requesting, releasing, or withdrawing all label bindings for a given
 type of FEC Element is desired.  However, a Typed Wildcard FEC
 Element must be individually defined for each type of FEC Element.
 [RFC4447] defines the "PWid FEC Element" and "Generalized PWid FEC
 Element", but does not specify the Typed Wildcard format for these
 elements.  This document specifies the format of the Typed Wildcard
 FEC Element for the "PWid FEC Element" and "Generalized PWid FEC
 Element".  The procedures for Typed Wildcard processing for PWid and
 Generalized PWid FEC Elements are the same as described in [RFC5918]
 for any Typed Wildcard FEC Element type.
 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].

Raza, et al. Standards Track [Page 2] RFC 6667 PWid and Gen. PWid Typed Wildcard FEC July 2012

2. Typed Wildcard for PW FEC Elements

 The format of the Typed Wildcard FEC Element for PWid and Generalized
 PWid is specified as:
     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
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |Typed Wcard=0x5| Type=PW FEC   |   Len = 2     |R|   PW type   |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |    . . .      |
    +-+-+-+-+-+-+-+-+
          Figure 1: Format of Typed Wildcard FEC Element for
                         PW FEC Element Types
 Where:
    Typed Wcard (one octet): Typed Wildcard FEC Element type (0x05)
         as specified in [RFC5918].
    [FEC Element] Type (one octet): PW FEC Element type:
       PWid: (type 0x80 [RFC4447])
       Generalized PWid: (type 0x81 [RFC4447])
    Len [FEC Type Info] (one octet):  Two. (There is additional
         FEC info to scope the Typed Wildcard.)
    R bit (Reserved bit): MUST be set to ZERO on transmit and ignored
         on receipt.
    PW type (15-bits): PW type as specified in [RFC4447].  This field
         is used to scope the wildcard FEC operation to limit all PWs
         of a given type.  This MUST be set to "Wildcard" type
         (0x7FFF), as defined in [IANA-PWE3], when referring PWs of
         all types (see Section 4 for its usage).
 [RFC4447] defines the "PW Grouping ID TLV" that can be used for
 wildcard withdrawal or status messages related to Generalized PWid
 FECs.  When the Typed Wildcard FEC for Generalized PWid FEC element
 is in use, the "PW Grouping ID TLV" MUST NOT be present in the same
 message.  If present, the receiving Label Switching Router (LSR) MUST
 ignore this TLV silently and process the rest of the message.

Raza, et al. Standards Track [Page 3] RFC 6667 PWid and Gen. PWid Typed Wildcard FEC July 2012

3. Applicability Statement

 The Typed Wildcard FEC Elements defined in this document for the PWid
 and Generalized PWid FEC Elements provide a finer degree of
 granularity when compared to the wildcard FEC mechanics defined in
 [RFC5036].
 The PWid FEC Element as defined in [RFC4447] contains a Group ID
 field.  This field is defined as an arbitrary 32-bit value that
 represents a group of PWs and is used to create groups in the PW
 space, including potentially a single group of all PWs for a given
 FEC Element type.  This grouping enables an LSR to send "wildcard"
 label withdrawals and/or status notification messages corresponding
 to a PW group upon physical port failures.  Similarly, [RFC4447]
 defines the "PW Grouping ID TLV" used in the same fashion for the
 Generalized PWid FEC Element.
 The PWid Typed Wildcard FEC Elements defined in this document help us
 achieve similar functionality as the "Group ID" field or "PW Grouping
 ID TLV" for label withdrawal and status notification messages.
 Additionally, the Typed Wildcard procedures [RFC5918] provide a more
 generalized and comprehensive solution by allowing:
 1. Typed Wildcard Label Request messages
 2. Label TLVs in label messages to further constrain the wildcard to
    all FECs of the specified FEC type [and its specific filter] that
    are also bound to the specified label.
 This document allows use of the Typed Wildcard PW FEC Element in any
 LDP message that specifies a FEC TLV as a mandatory or optional
 parameter of the message.  In addition to LDP label messages, this
 also applies to notification messages (containing PW Status) and
 Address Withdraw (for MAC address withdrawal [RFC4762]) messages in
 the context of LDP PW signaling.  When a Typed Wildcard PW FEC
 Element is used in an Address Withdraw message for Virtual Private
 LAN Service (VPLS) Media Access Control (MAC) address withdrawal, the
 MAC List TLV MUST contain an empty list.

4. Operation

 The use of Typed Wildcard FEC Elements for PW can be useful under
 several scenarios.  This section describes some use cases to
 illustrate their application.  The following use cases consider two
 LSR nodes, A and B, with an LDP session between them to exchange
 Layer 2 Virtual Private Network (L2VPN) PW bindings.

Raza, et al. Standards Track [Page 4] RFC 6667 PWid and Gen. PWid Typed Wildcard FEC July 2012

4.1. PW Consistency Check

 A user may request a control-plane consistency check at LSR A for the
 Generalized PWid FEC bindings that it learned from LSR B over the LDP
 session.  To perform this consistency check, LSR A marks all its
 learned Generalized PWid FEC bindings from LSR B as stale, and then
 sends a Label Request message towards LSR B for the Typed Wildcard
 FEC Element for Generalized PWid FEC Element type with the PW type
 set to "Wildcard" (0x7FFF).  Upon receipt of such a request, LSR B
 replays its database related to the Generalized PWid FEC Element
 using one or more Label Mapping messages.  As a PW binding is
 received at LSR A, the associated binding state is marked as
 refreshed (not stale).  When replay completes for the Generalized
 PWid FEC type, LSR B marks the end of its replay by sending an
 End-of-LIB notification [RFC5919] corresponding to the Generalized
 PWid FEC Element type.  Upon receipt of this notification at LSR A,
 any remaining stale PW binding of the Generalized PWid FEC type
 learned from the peer LSR B is cleaned up and removed from the
 database.  This completes the consistency check with LSR B at LSR A
 for Generalized PWid FEC type.

4.2. PW Graceful Shutdown

 It may be desirable to perform shutdown/removal of existing PW
 bindings advertised towards a peer in a graceful manner -- i.e., all
 advertised PW bindings are to be removed from a peer without session
 flap.  For example, to request a graceful delete of the PWid FEC and
 Generalized PWid FEC bindings at LSR A learned from LSR B, LSR A
 would send a Label Withdraw message towards LSR B with Typed Wildcard
 FEC Elements pertaining to the PWid FEC Element (with PW type set to
 0x7FFF) and Generalized PWid FEC Element (with PW type set to
 0x7FFF).  Upon receipt of such a message, LSR B would delete all PWid
 and Generalized PWid bindings learned from LSR A.  Afterwards, LSR B
 would send Label Release messages corresponding to received Label
 Withdraw messages with the Typed FEC Element.

4.3. Wildcard PW Status

 The Typed Wildcard FEC Elements for PW FECs can be very useful to
 convey PW status amongst LSRs.  The Provider Edge (PE) devices can
 send the "PW Status TLV" in an LDP Notification message to indicate
 PW status (i.e., a Pseudowire Status Code denoting, for example, a
 particular fault) to their remote peers [RFC4447].  In case of a
 global failure affecting all PWs, an LSR typically sends one PW
 Status LDP Notification message per PW.  This per-PW-Status message
 has scalability implications in a large-scale network with a large
 number of PWs.

Raza, et al. Standards Track [Page 5] RFC 6667 PWid and Gen. PWid Typed Wildcard FEC July 2012

 Using Typed Wildcard FEC Element for a given type of PW FEC Element,
 the LSR will need to send only one PW Status Notification message
 with the Typed Wildcard PW FEC specified to notify about the common
 status applicable to all PWs as scoped by the PW Typed Wildcard FEC.

4.4. Typed Wildcard MAC Withdrawal in VPLS

 [RFC4762] defines a pseudowire-based solution to implement Virtual
 Private LAN Service (VPLS).  Section 6.2 of RFC 4762 describes MAC
 Withdrawal procedures and extensions in a VPLS environment.  These
 procedures use the LDP Address Withdraw message containing the FEC
 TLV (with the PW FEC element corresponding to the VPLS instance) and
 MAC List TLV (to specify addresses to be withdrawn).  The procedures
 described in RFC 4762 also allow MAC address withdrawal wildcarding
 for a given VPLS instance.
 Using RFC 4762 procedures, a PE LSR can withdraw all MAC addresses
 for a given VPLS instance by sending an Address Withdraw message with
 a VPLS instance corresponding to the PW FEC element in a FEC TLV, and
 a MAC List TLV with an empty list of addresses.  If there is more
 than one VPLS instance on a given PE LSR node, separate Address
 Withdraw messages need to be sent by the PE LSR if it wishes to
 withdraw MAC addresses for all or a subset of VPLS instances upon
 some global failure or configuration.  Per-PW (VPLS instance) MAC
 Withdraw message may have some scalability implications in a large-
 scale network.
 As stated in Section 3, this document allows use of the Typed
 Wildcard PW FEC in Address Withdraw messages corresponding to VPLS
 MAC Withdrawal.  The use of PW Typed Wildcard FEC enhances the scope
 of MAC withdrawal beyond just a single VPLS instance and allows a PE
 node to wildcard withdraw all MAC addresses for:
    o  all VPLS instances; or
    o  all VPLS instances corresponding to a given PW type.

5. Security Considerations

 No new security considerations beyond those that apply to
 specifications [RFC5036], [RFC4447], [RFC4762], [RFC5918], and
 [RFC5920] apply to the use of the PW Typed Wildcard FEC Element types
 described in this document.

Raza, et al. Standards Track [Page 6] RFC 6667 PWid and Gen. PWid Typed Wildcard FEC July 2012

6. Acknowledgments

 The authors would like to thank Eric Rosen, Reshad Rahman, Siva
 Sivabalan, and Zafar Ali for their review and valuable comments.  We
 also acknowledge Daniel Cohn for suggesting use of the Typed Wildcard
 PW FEC for VPLS MAC withdrawal.
 This document was prepared using 2-Word-v2.0 template.dot.

7. References

7.1. Normative References

 [RFC5036]   Andersson, L., Ed., Minei, I., Ed., and B. Thomas, Ed.,
             "LDP Specification", RFC 5036, October 2007.
 [RFC5918]   Asati, R., Minei, I., and B. Thomas, "Label Distribution
             Protocol (LDP) 'Typed Wildcard' Forward Equivalence Class
             (FEC)", RFC 5918, August 2010.
 [RFC5919]   Asati, R., Mohapatra, P., Chen, E., and B. Thomas,
             "Signaling LDP Label Advertisement Completion", RFC 5919,
             August 2010.
 [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.
 [RFC4762]   Lasserre, M., Ed., and V. Kompella, Ed., "Virtual Private
             LAN Service (VPLS) Using Label Distribution Protocol
             (LDP) Signaling", RFC 4762, January 2007.
             [RFC2119]   Bradner, S., "Key words for use in RFCs to
             Indicate Requirement Levels", BCP 14, RFC 2119, March
             1997.

7.2. Informative References

 [RFC5920]   Fang, L., Ed., "Security Framework for MPLS and GMPLS
             Networks", RFC 5920, July 2010.
 [IANA-PWE3] Internet Assigned Numbers Authority, "Pseudo Wires Name
             Spaces (PWE3)",
             http://www.iana.org/assignments/pwe3-parameters, May
             2011.

Raza, et al. Standards Track [Page 7] RFC 6667 PWid and Gen. PWid Typed Wildcard FEC July 2012

Authors' Addresses

 Kamran Raza
 Cisco Systems, Inc.
 2000 Innovation Drive
 Ottawa ON K2K-3E8
 Canada
 EMail: skraza@cisco.com
 Sami Boutros
 Cisco Systems, Inc.
 3750 Cisco Way
 San Jose, CA 95134
 USA
 EMail: sboutros@cisco.com
 Carlos Pignataro
 Cisco Systems, Inc.
 7200 Kit Creek Road
 Research Triangle Park, NC 27709-4987
 USA
 EMail: cpignata@cisco.com

Raza, et al. Standards Track [Page 8]

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