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Internet Engineering Task Force (IETF) R. Asati Request for Comments: 5918 Cisco Systems Category: Standards Track I. Minei ISSN: 2070-1721 Juniper Networks

                                                             B. Thomas
                                                           August 2010

         Label Distribution Protocol (LDP) 'Typed Wildcard'
                  Forward Equivalence Class (FEC)

Abstract

 The Label Distribution Protocol (LDP) specification for the Wildcard
 Forward Equivalence Class (FEC) element has several limitations.
 This document addresses those limitations by defining a Typed
 Wildcard FEC Element and associated procedures.  In addition, it
 defines a new LDP capability to address backward compatibility.

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/rfc5918.

Asati, et al. Standards Track [Page 1] RFC 5918 LDP 'Typed Wildcard' FEC August 2010

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 document authors.  All rights reserved.

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Table of Contents

 1. Introduction ....................................................3
 2. Specification Language ..........................................4
 3. The Typed Wildcard FEC Element ..................................4
 4. Procedures for the Typed Wildcard FEC Element ...................5
 5. Typed Wildcard FEC Capability ...................................6
 6. Typed Wildcard FEC Element for Prefix FEC Element ...............7
 7. Typed Wildcard FEC Element for Host and Wildcard FEC Elements ...8
 8. IANA Considerations .............................................8
 9. Security Considerations .........................................8
 10. Acknowledgments ................................................9
 11. References .....................................................9
    11.1. Normative References ......................................9
    11.2. Informative References ....................................9

Asati, et al. Standards Track [Page 2] RFC 5918 LDP 'Typed Wildcard' FEC August 2010

1. Introduction

 LDP [RFC5036] distributes labels for Forwarding Equivalence Classes
 (FECs).  LDP uses FEC TLVs in LDP messages to specify FECs.  An LDP
 FEC TLV includes one or more FEC elements.  A FEC element includes a
 FEC type and an optional type-dependent value.

 RFC 5036 specifies two FEC types (Prefix and Wildcard), and other
 documents specify additional FEC types; e.g., see [RFC4447] and
 [MLDP].

 As specified by RFC 5036, the Wildcard FEC Element refers to all FECs
 relative to an optional constraint.  The only constraint RFC 5036
 specifies is one that limits the scope of the Wildcard FEC Element to
 "all FECs bound to a given label".

 The RFC 5036 specification of the Wildcard FEC Element has the
 following deficiencies that limit its utility:

 1) The Wildcard FEC Element is untyped.  There are situations where
    it would be useful to be able to refer to all FECs of a given type
    (as another constraint).

 2) Use of the Wildcard FEC Element is limited to Label Withdraw and
    Label Release messages only.  There are situations where it would
    be useful to have a Wildcard FEC Element, with type constraint, in
    Label Request messages.

 This document:

addresses the above limitations by defining a Typed Wildcard FEC

Element and procedures for its use.

specifies use of the LDP capability mechanism [RFC5561] at

session establishment time for informing a peer that an LDP

      speaker is capable of handling the Typed Wildcard FEC.

specifies use of the Typed Wildcard FEC Element in a Label

Request message.

specifies the Typed Wildcard FEC Element for the Prefix FEC

Element specified by RFC 5036.

 Note that this document does not change procedures specified for the
 LDP Wildcard FEC Element by RFC 5036.

Asati, et al. Standards Track [Page 3] RFC 5918 LDP 'Typed Wildcard' FEC August 2010

2. Specification Language

 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 [RFC2119].

 LDP   - Label Distribution Protocol

 FEC   - Forwarding Equivalence Class

 TLV   - Type Length Value

 LSR   - Label Switching Router

3. The Typed Wildcard FEC Element

 The Typed Wildcard FEC Element refers to all FECs of the specified
 type that meet the constraint.  It specifies a 'FEC Element Type' and
 an optional constraint, which is intended to provide additional
 information.

 The format of the Typed Wildcard FEC Element is:

    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 2
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    | Typed (0x05)  | FEC Element   | Len FEC Type  |               |
    | Wildcard      | Type          | Info          |               |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+               |
    |                                                               |
    ~          Additional FEC Type-specific Information             ~
    |                  (Optional)                                   |
    |                                               +-+-+-+-+-+-+-+-+
    |                                               |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

                     Figure 1: Typed Wildcard FEC Element

 Where:

    Typed Wildcard: One-octet FEC Element Type (0x05).

    FEC Element Type: One-octet FEC Element Type that specifies the
       FEC Element Type to be wildcarded.  Please see Section 3.4.1 of
       RFC 5036.

Asati, et al. Standards Track [Page 4] RFC 5918 LDP 'Typed Wildcard' FEC August 2010

          Any (future) document specifying a new FEC Element Type (not
          defined in RFC 5036) should prescribe whether typed
          wildcarding is needed for that FEC Element Type.

    Len FEC Type Info:  One octet that specifies the length in octets
       of the FEC Type Specific information field.  It MUST be set to
       0 if there is no Additional FEC Type-specific Information.

    Additional FEC Type-specific Information (Optional): Additional
       information that is specific to the FEC Element Type and that
       is required to fully specify the Typed Wildcard.  If this field
       is absent, then all FECs of the specified FEC Type would be
       matched.

          Any (future) document specifying Typed wildcarding for any
          FEC Element Type should also specify the length and format
          of Additional FEC Type Specific Information, if included.

 This document specifies one FEC Element Type instance (e.g., Prefix
 FEC) for the 'Typed Wildcard FEC Element' in Section 6.

4. Procedures for the Typed Wildcard FEC Element

 When a FEC TLV contains a Typed Wildcard FEC Element, the Typed
 Wildcard FEC Element MUST be the only FEC Element in the TLV.  If an
 LDP speaker receives a FEC TLV containing a Typed Wildcard FEC
 Element and any other FEC elements, then the LDP speaker should
 ignore the other FEC elements and continue processing as if the
 message only contains the Typed Wildcard FEC Element.

 An LDP implementation that supports the Typed Wildcard FEC Element
 MUST support its use in Label Request, Label Withdraw, and Label
 Release messages.

 An LDP implementation that supports the Typed Wildcard FEC Element
 MUST support it for every FEC Element Type defined in [RFC5036].

 Receipt of a Label Request message with a FEC TLV containing a Typed
 Wildcard FEC Element is interpreted as a request to send one or more
 Label Mappings for all FECs of the type specified by the FEC Element
 Type field in the Typed Wildcard FEC Element encoding.

 An LDP implementation that supports the Typed Wildcard FEC Element
 MUST support the following constraints whenever a Typed Wildcard FEC
 appears in a Label Withdraw or Label Release message:

Asati, et al. Standards Track [Page 5] RFC 5918 LDP 'Typed Wildcard' FEC August 2010

 1) If the message carries an optional Label TLV, the Typed Wildcard
    FEC Element refers to all FECs of the specified FEC type bound to
    the specified label.

 2) If the message has no Label TLV, the Typed Wildcard FEC Element
    refers to all FECs of the specified FEC type.

 Backwards compatibility with a router not supporting the Typed
 Wildcard FEC element is ensured by the FEC procedures defined in RFC
 5036.  Quoting from RFC 5036:

    If it [an LSR] encounters a FEC Element type it cannot decode, it
    SHOULD stop decoding the FEC TLV, abort processing the message
    containing the TLV, and send an "Unknown FEC" Notification message
    to its LDP peer signaling an error.

 A router receiving a FEC TLV containing a Typed Wildcard FEC element
 for either a FEC Element Type that it doesn't support or for a FEC
 Element Type that doesn't support the use of wildcarding, MUST stop
 decoding the FEC TLV, abort processing the message containing the
 TLV, and send an "Unknown FEC" Notification message to its LDP peer
 to signal an error.

 A router receiving a FEC TLV containing a Typed Wildcard FEC element
 MAY also leverage mechanisms defined in [RFC5919] (say, if it had
 zero label binding for the requested FEC type, etc.).

5. Typed Wildcard FEC Capability

 As noted above, RFC 5036 FEC procedures provide for backward
 compatibility with an LSR not supporting the Typed Wildcard FEC
 Element.  However, they don't provide means for an LSR that wishes to
 use the Typed Wildcard FEC Element to determine whether a peer
 supports it other than to send a message that uses the FEC Element
 and to wait and see how the peer responds.

 An LDP speaker that supports the Typed Wildcard FEC Element MUST
 inform its peers of the support by including a Typed Wildcard FEC
 Element Capability Parameter [RFC5561] in its Initialization messages
 only.

 The Capability Parameter for the Typed Wildcard FEC capability is a
 TLV with the following format:

Asati, et al. Standards Track [Page 6] RFC 5918 LDP 'Typed Wildcard' FEC August 2010

    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|Typed WCard FEC Cap(0x050B)|            Length             |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |S| Reserved    |
    +-+-+-+-+-+-+-+-+

                Figure 2: Typed Wildcard FEC Capability Format

 Where:

    U and F bits: MUST be 1 and 0, respectively, as per Section 3 of
       LDP Capabilities [RFC5561].

    Typed WCard FEC Cap: 0x050B

    Length: Two octets.  It MUST be set to 0x0001.

    S-bit: MUST be 1 (indicates that capability is being advertised).

6. Typed Wildcard FEC Element for Prefix FEC Element

 RFC 5036 defines the Prefix FEC Element, but it does not specify a
 Typed Wildcard for it.  This section specifies the Typed Wildcard FEC
 Element for Prefix FEC Elements.

 The format of the Prefix FEC Typed Wildcard FEC Element ("Prefix FEC
 Wildcard" for short), based on Figure 1, is:

    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 2
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    | Typed Wcard   | Type = Prefix |   Len = 2     |  Address...   |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    | ...Family     |
    +-+-+-+-+-+-+-+-+

         Figure 3: Format of Prefix FEC Element Using Typed Wildcard

 Where:

    FEC Element Type: "Prefix" FEC Element (0x02, per RFC 5036).

    Len FEC Type Info: Two octets.  It MUST be set to 0x0002.

    Address Family: Two-octet quantity containing a value from the
       "ADDRESS FAMILY NUMBERS" registry on http://www.iana.org.

Asati, et al. Standards Track [Page 7] RFC 5918 LDP 'Typed Wildcard' FEC August 2010

 The procedures described in Section 4 apply to the Prefix FEC
 Wildcard processing.

7. Typed Wildcard FEC Element for Host and Wildcard FEC Elements

 There is no need to specify Typed Wildcard FEC Elements for the Host
 FEC Element specified by [RFC3036], nor for the Wildcard FEC Element
 specified by RFC 5036.  The [RFC3036] Host FEC Element has been
 removed from RFC 5036, and the Wildcard FEC Element is untyped by
 definition.

 In other words, the 'FEC Element Type' field in 'Typed Wildcard FEC
 Element' MUST NOT be either 0x01 or 0x03.

8. IANA Considerations

 This document introduces a new LDP FEC Element Type and a new LDP
 Capability, both of which have been assigned by IANA.

    IANA has assigned a 'Typed Wildcard FEC Element' code point (0x05)
    from the LDP FEC Type Name Space.  [RFC5036] partitions the FEC
    Type Name Space into 3 regions:  IETF Consensus region, First Come
    First Served region, and Private Use region.  The code point 0x05
    is from the IETF Consensus range.

    IANA has assigned a 'Typed Wildcard FEC Capability' code point
    (0x050B) from the TLV Type name space.  [RFC5036] partitions the
    TLV TYPE name space into 3 regions:  IETF Consensus region, Vendor
    Private Use region, and Experimental Use region.  The code point
    0x050B is from the IETF Consensus range.

9. Security Considerations

 No security considerations beyond those that apply to the base LDP
 specification [RFC5036] and that are further described in [RFC5920]
 apply to use of the Typed Wildcard FEC Elements as described in this
 document.

 One could deduce that the security exposure is reduced by this
 document, since an LDP speaker using the Typed Wildcard FEC Element
 could use a single message to request, withdraw, or release all the
 label mappings of a particular type (a particular Address Family
 Identifier (AFI), for example), whereas an LDP speaker using the
 Wildcard FEC Element, as defined in the base LDP specification
 [RFC5036], could use a single message to request, withdraw, or
 release all the label mappings of all types (all AFIs, for example).

Asati, et al. Standards Track [Page 8] RFC 5918 LDP 'Typed Wildcard' FEC August 2010

10. Acknowledgments

 The authors would like to thank Yakov Rekhter for suggesting that the
 limitations of the Wildcard FEC be addressed.  Also, thanks to Adrian
 Farrel, Kamran Raza, and Richard L. Barnes for extensive review of
 this document.

11. References

11.1. Normative References

 [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
            Requirement Levels", BCP 14, RFC 2119, March 1997.

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

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

11.2. Informative References

 [RFC3036]  Andersson, L., Doolan, P., Feldman, N., Fredette, A., and
            B. Thomas, "LDP Specification", RFC 3036, January 2001.

 [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.

 [RFC5919]  Asati, R., Mohapatra, P., Minei, I., and B. Thomas,
            "Signaling LDP Label Advertisement Completion", RFC 5919,
            August 2010.

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

 [MLDP]     Minei, I., Ed., Kompella, K., Wijnands, I., Ed., and B.
            Thomas, "Label Distribution Protocol Extensions for Point-
            to-Multipoint and Multipoint-to-Multipoint Label Switched
            Paths", Work in Progress, July 2010.

Asati, et al. Standards Track [Page 9] RFC 5918 LDP 'Typed Wildcard' FEC August 2010

Authors' Addresses

 Rajiv Asati
 Cisco Systems
 7025-6 Kit Creek Rd.
 Research Triangle Park, NC  27709-4987
 EMail: rajiva@cisco.com

 Ina Minei
 Juniper Networks
 1194 North Mathilda Ave.
 Sunnyvale, CA  94089
 EMail: ina@juniper.net

 Bob Thomas
 EMail: bobthomas@alum.mit.edu

Asati, et al. Standards Track [Page 10]