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Versions: (draft-farrel-mpls-rsvpte-attributes) 00 01 02 03 04 05 RFC 4420

Network Working Group                          Adrian Farrel (Editor)
Internet Draft                                     Old Dog Consulting
Category: Standards Track
Expires: May 2004                               Dimitri Papadimitriou
                                                              Alcatel

                                                Jean-Philippe Vasseur
                                                  Cisco Systems, Inc.

                                                        November 2003


  Encoding of Attributes for  Multiprotocol Label Switching (MPLS)
         Label Switched Path (LSP) Establishment Using RSVP-TE

             draft-ietf-mpls-rsvpte-attributes-00.txt


Status of this Memo

   This document is an Internet-Draft and is in full
   conformance with all provisions of Section 10 of RFC 2026
   [RFC2026].

   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."

   The list of current Internet-Drafts can be accessed at
   http://www.ietf.org/ietf/1id-abstracts.txt.

   The list of Internet-Draft Shadow Directories can be
   accessed at http://www.ietf.org/shadow.html.

Abstract

   Multiprotocol Label Switching (MPLS) Label Switched Paths (LSPs) may
   be established using the Resource Reservation Protocol Traffic
   Engineering extensions (RSVP-TE). This protocol includes an object
   (the SESSION_ATTRIBUTE object) which carries a flags field used to
   indicate options and attributes of the LSP. That flags field has
   eight bits allowing for eight options to be set.

   Recent proposals in many documents that extend RSVP-TE for signaling
   additional features and function for MPLS LSPs have suggested uses
   for each of the previously unused bits.

   This document defines a new object for RSVP-TE messages that allows
   the signaling of further attribute bits and also the carriage of
   arbitrary attribute parameters. This makes RSVP-TE easily extensible
   to support new requirements.


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1. Introduction and Problem Statement

   Multiprotocol Label Switching (MPLS) Label Switched Paths (LSPs)
   [RFC3031] may be established using the RSVP-TE signaling protocol
   [RFC3209]. This protocol uses the Path message to request that a LSP
   be set up. The Path message includes the SESSION_ATTRIBUTE object
   which carries a flags field used to indicate desired options and
   attributes of the LSP.

   The flags field in the SESSION_ATTRIBUTE object has eight bits. Just
   three of those bits are assigned in [RFC3209]. A further two bits are
   assigned in [FRR] for fast re-reroute functionality leaving only
   three bits available. Several recent proposals and Internet Drafts
   have demonstrated that there is a high demand for the use of the
   other three bits. Some, if not all, of those proposals are likely to
   go forward as RFCs resulting in depletion or near depletion of the
   flags field and a consequent difficulty in signaling new options and
   attributes that may be developed in the future.

   This document defines a new object for RSVP-TE messages that allows
   the signaling of further attributes bits. The new object is
   constructed from TLVs, and a new TLV is defined to carry up to thirty
   two new attributes bits. Because of the nature of the TLV
   construction the object is flexible and allows the future definition
   of:
   - further sets of thirty two bits if more flags are needed to carry
     yet more attributes
   - arbitrary options and attributes parameters carried as individual
     TLVs.

   It is noted that that some options and attributes do not need to be
   acted on by all Label Switched Routers (LSRs) along the path of the
   LSP. In particular, these options and attributes may apply only to
   key LSRs on the path such as the ingress and egress. Special transit
   LSRs, such as AS Border Routers (ASBRs) may also fall into this
   category. This means that the new options and attributes should be
   signaled transparently, and only examined at those points that need
   to act on them.

   On the other hand, other options and attributes may require action
   at all transit LSRs along the path of the LSP. Inability to support
   the required attributes by one of those transit LSRs may require the
   LSR to refuse the establishment of the LSP.

   These considerations are particularly important in the context
   backwards compatibility. In general, it should be possible to provide
   new MPLS services across a legacy network without upgrading those
   LSRs that do not need to participate actively in the new services.

   RSVP includes a way for unrecognized objects to be forwarded by
   transit nodes without them refusing the protocol message and with the
   objects being stripped from the protocol message (see [RFC2205]
   section 3.10). This extends to RSVP-TE and provides a good way to
   ensure that only those LSRs that understand a particular object
   examine it.



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   This document distinguishes between options and attributes that are
   only required at key LSRs along the path of the LSP, and those that
   must be acted on by every LSR along the LSP. Two LSP Attributes
   objects are defined in this document: the first may be passed
   transparently by LSRs that do not recognize it, the second must cause
   LSP setup failure with the generation of a PathErr message if an LSR
   does not recognize it.

   Comments on this document should be made direct to the MPLS mailing
   list at mpls@uu.net.

1.1 Applicability to Generalized MPLS

   The RSVP-TE signaling protocol also forms the basis of a signaling
   protocol for Generalized MPLS (GMPLS) as described in [RFC3471] and
   [RFC3473]. The extensions described in this document are intended to
   be equally applicable to MPLS and GMPLS.

1.2 A Rejected Alternate Solution

   A rejected alternate solution was to define a new C-Type for the
   existing SESSION_ATTRIBUTE object. This new C-Type could allow a
   larger Flags field and address the immediate problem.

   This solution was rejected because:

   - A C-Type is not backward compatible with deployed implementations
     that expect to see a C-Type of 1 or 7. It is important that any
     solution be capable of carrying new attributes transparently
     across legacy LSRs if those LSRs are not required to act on the
     attributes.

   - Support for arbitrary attributes parameters through TLVs would
     have meant a significant change of substance to the existing
     object.

1.3 Protocol Developments Without an Explicit Need

   [This section to be removed if this draft proceeds towards an RFC.
    References in this section are not intended to be normative.]

   It is unusual and inadvised for the IETF to accept a speculative
   change to a protocol without an explicit need. That is, in this case,
   although there is an obvious problem identified, there is no existing
   Working Group proposal that requires further option bits. For today,
   the existing protocol objects are adequate.

   There are, however, several Internet Drafts that propose additional
   attributes associated with LSP setup. These include [CRANKBACK],
   [REOPT] and [INTER-AS]. In view of the likelihood of one or more of
   these drafts advancing to RFC, and considering the probable
   requirement to be able to signal further options and attributes for
   other purposes in the very near future, it is proposed that this
   document be debated within the MPLS Working Group so that a solution
   will be available should the need arise.



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   Further, the lack of a considered approach to handle the shortage of
   SESSION_ATTRIBUTE flags might give rise to a range of diverse
   solutions each developed within the context of a single protocol
   extension. Clearly a single coherent solution is better.

   [This section to be removed if this draft proceeds towards an RFC.]

2. Terminology

   This document uses terminology from the MPLS architecture document
   [RFC3031] and from the RSVP-TE protocol specification [RFC3209] which
   inherits from the RSVP specification [RFC2205].

   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 [6].

3. Attributes TLVs

   Attributes carried by the new objects defined in this document are
   encoded within TLVs. One or more TLVs may be present in each object.
   There are no ordering rules for TLVs and no interpretation should be
   placed on the order in which TLVs are received.

   Each TLV is 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
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |             Type              |           Length              |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                                                               |
   //                            Value                            //
   |                                                               |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

      Type

         The identifier of the TLV.

      Length

         The length of the value field in bytes. Thus if no value
         field is present the length field contains the value zero.
         Each value field must be zero padded at the end to take it
         up to a four byte boundary - the padding is not included in
         the length so that a one byte value would be encoded in an
         eight byte TLV with length field set to one.

      Value

         The data for the TLV padded as described above.






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3.1 Attributes Flags TLV

   This document defines only one TLV type value. Type 1 indicates the
   Attributes Flags TLV. Other TLV types may be defined in future with
   type values assigned by IANA.

   The Attributes Flags TLV value field is a 32 bit array of flags
   numbered from the MSB as bit zero. The length field for this TLV is
   set to 4.

   Unassigned bits are considered as reserved and MUST be set to zero
   on transmission and ignored on receipt.

   No bits are defined in this document. The assignment of bits is
   managed by IANA.

4. LSP_ATTRIBUTES Object

   The LSP_ATTRIBUTES object is used to signal attributes required in
   support of an LSP, or to indicate the nature or use of an LSP where
   that information is not required to be acted on by all transit LSRs.
   Specifically, if an LSR does not support the object, it forwards it
   unexamined and unchanged. This facilitates the exchange of attributes
   across legacy networks that do not support this new object.

   This object effectively extends the flags field in the SESSION_
   ATTRIBUTE object and allows for the future inclusion of more complex
   objects through TLVs.

   The LSP_ATTRIBUTES object class is TBD of the form 11bbbbbb. This
   C-Num value (see section 7) ensures that LSRs that do not recognize
   the object pass it on transparently.

   One C-Type is defined, C-Type = 1 for LSP Attributes.

   This object is optional and may be placed on Path messages to convey
   additional information about the desired attributes of the LSP.

4.1 Format

   LSP_ATTRIBUTES class = TBD, C-Type = 1

    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
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                                                               |
   //                       Attributes TLVs                       //
   |                                                               |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   The Attributes TLVs are encoded as described in section 3.







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4.2 Generic Processing Rules

   An LSR that does not support this object will pass it on unaltered
   because of the C-Num.

   An LSR that does support this object, but does not recognize a TLV
   type code carried in this object, or recognizes the TLV but does not
   support the attribute MUST act as specified in the document that
   defines the TLV.

   An LSR that supports the Attributes Flags TLV, but does not
   recognize a bit set in the Attributes Flags TLV MUST forward the
   object unchanged.

   An LSR that supports the Attributes Flags TLV and recognizes a bit
   that is set but does not support the indicated attribute MUST act as
   specified in the document that defines the bit.

5. LSP_REQUIRED_ATTRIBUTES Object

   The LSP_REQUIRED_ATTRIBUTES object is used to signal attributes
   required in support of a LSP, or to indicate the nature or use of
   a LSP where that information MUST be inspected at each transit LSR.
   Specifically, each transit LSR MUST examine the attributes in the
   LSP_REQUIRED_ATTRIBUTES object and MUST NOT forward the object
   transparently.

   This object effectively extends the flags field in the SESSION_
   ATTRIBUTE object and allows for the future inclusion of more complex
   objects through TLVs. It complements the LSP_ATTRIBUTES object.

   The LSP_REQUIRED_ATTRIBUTES object class is TBD of the form 0bbbbbbb.
   This C-Num value (see section 7) ensures that LSRs that do not
   recognize the object reject the LSP setup effectively saying that
   they do not support the attributes requested. This means that this
   object should only be used for attributes that require support at
   some transit LSRs and so require examination at all transit LSRs. See
   section 4 for how end-to-end and selective attributes are signaled.

   One C-Type is defined, C-Type = 1 for LSP Required Attributes.

   This object is optional and may be placed on Path messages to convey
   additional information about the desired attributes of the LSP.

5.1 Format

   LSP_REAQUIRED_ATTRIBUTES class = TBD, C-Type = 1

    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
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                                                               |
   //                      Attributes TLVs                        //
   |                                                               |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   The Attributes TLVs are encoded as described in section 3.

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5.2 Generic Processing Rules

   An LSR that does not support this object will use a PathErr to reject
   the Path message based on the C-Num using the error code "Unknown
   Object Class".

   An LSR that does not recognize a TLV type code carried in this object
   MUST reject the Path message using a PathErr with Error Code
   "Unknown Attributes TLV" and Error Value set to the value of the
   unknown TLV type code.

   An LSR that does not recognize a bit set in the Attributes Flags
   TLV MUST reject the Path message using a PathErr with Error Code
   "Unknown Attributes Bit" and Error Value set to the bit number of
   the unknown bit in the Attributes Flags (that is a number between 0
   and 32).

   An LSR that recognizes an attribute, however encoded, but which does
   not support that attribute MUST act according to the behavior
   specified in the document that defines that specific attribute.

6. Message Formats

   The LSP_ATTRIBUTES object and the LSP_REQUIRED_ATTRIBUTES object MAY
   be carried in a Path message.

   The order of objects in RSVP-TE messages is recommended, but
   implementations must be capable of receiving the objects in any
   meaningful order. The LSP_ATTRIBUTES object and LSP_REQUIRED_
   ATTRIBUTES objects are RECOMMENDED to be placed immediately after the
   SESSION_ATTRIBUTE object if it is present, or otherwise immediately
   after the LABEL_REQUEST object.

   If both the LSP_ATTRIBUTES object and the LSP_REQUIRED_ATTRIBUTES
   object are present, the LSP_REQUIRED_ATTRIBUTES object is RECOMMENDED
   to be placed first.

   LSRs should be prepared to receive these objects in any order in any
   position within a Path message. Subsequent instances of these objects
   within a Path message SHOULD be ignored.

7. IANA Considerations

7.1 New RSVP C-Nums and C-Types

   Two new RSVP C-Nums are defined in this document and should be
   assigned by IANA.

   o LSP_ATTRIBUTES object

     The C-Num should be of the form 11bbbbbb so that LSRs that do not
     recognize the object will ignore the object but forward it,
     unexamined and unmodified, in all messages resulting from this
     message.




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     One C-Type is defined for this object and should be assigned by
     IANA.

     o LSP Attributes TLVs

       Recommended C-Type value 1.

   o LSP_REQUIRED_ATTRIBUTES object

     The C-Num should be of the form 0bbbbbbb so that LSRs that do not
     recognize the object will reject the message that carries it with
     an "Unknown Object Class" error.

     One C-Type is defined for this object and should be assigned by
     IANA.

     o LSP Required Attributes TLVs

       Recommended C-Type value 1.

7.2 New TLV Space

   The two new objects referenced above are constructed from TLVs. Each
   TLV includes a 16-bit type identifier (the T-field). The same T-field
   values are applicable to both objects.

   IANA is requested to manage the space of TLV type identifiers as
   follows:

   - TLV Type
   - TLV Name
   - Whether allowed on LSP_ATTRIBUTES object
   - Whether allowed on LSP_REQUIRED_ATTRIBUTES object.

   This document defines one TLV type as follows:
   - TLV Type = 1
   - TLV Name = LSP Attributes Flags
   - allowed on LSP_ATTRIBUTES object
   - allowed on LSP_REQUIRED_ATTRIBUTES object.

7.3 Attributes Flags

   This document provides 32 new attributes bit flags for use in other
   documents that specify new RSVP-TE attributes. These flags are
   present in the LSP Attributes Flags TLV referenced in the previous
   section.

   IANA is requested to manage the space of attributes bit flags
   numbering them in the usual IETF notation starting at zero.

7.4 SESSION_ATTRIBUTE Flags Field

   This document does not make any alterations to the definition of the
   existing SESSION_ATTRIBUTE object nor to the definition of meanings
   assigned to the flags in the Flags field of that object. These flags
   are assigned meanings in various other RFCs and Internet Drafts.


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   It is suggested that IANA manage the allocation of meaning to the
   bits in the Flags field of the SESSION_ATTRIBUTE object to prevent
   accidental double allocation of any one bit.

7.5 New Error Codes

   This document defines the following new error codes and error values.
   Numeric values should be assigned by IANA.

   Error Code                     Error Value
   "Unknown Attributes TLV"       Identifies the unknown TLV type code.
   "Unknown Attributes Bit"       Identifies the unknown Attribute Bit.

8. Security Considerations

   This document adds two new objects to the RSVP Path message as used
   in MPLS and GMPLS signaling. It does not introduce any new direct
   security issues and the reader is referred to the security
   considerations expressed in [RFC2205], [RFC3209] and [RFC3473].

   It is of passing note that any signaling request that indicates the
   functional preferences or attributes of an MPLS LSP may provide
   anyone with unauthorized access to the contents of the message with
   information about the LSP that an administrator may wish to keep
   secret. Although this document adds new objects for signaling desired
   LSP attributes, it does not contribute to this issue which can
   only be satisfactorily handled by encrypting the content of the
   signaling message.

9. Acknowledgements

   Credit to the OSPF Working Group for inspiration from their solution
   to a similar problem.

   Thanks to Rahul Aggarwal for his careful review and support of this
   work. Thanks also to Raymond Zhang for his input.

10. Intellectual Property Consideration

   The IETF takes no position regarding the validity or scope
   of any intellectual property or other rights that might be
   claimed to pertain to the implementation or use of the
   technology described in this document or the extent to
   which any license under such rights might or might not be
   available; neither does it represent that it has made any
   effort to identify any such rights.  Information on the
   IETF's procedures with respect to rights in standards-track
   and standards-related documentation can be found in BCP-11.
   Copies of claims of rights made available for publication
   and any assurances of licenses to be made available, or the
   result of an attempt made to obtain a general license or
   permission for the use of such proprietary rights by
   implementors or users of this specification can be obtained
   from the IETF Secretariat.




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   The IETF invites any interested party to bring to its
   attention any copyrights, patents or patent applications, or
   other proprietary rights which may cover technology that may
   be required to practice this standard.  Please address the
   information to the IETF Executive Director.

11. Normative References

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

   [RFC2205]     Braden, R. (Ed.), Zhang, L., Berson, S., Herzog, S.
                 and S. Jamin, "Resource ReserVation Protocol --
                 Version 1 Functional Specification", RFC 2205,
                 September 1997.

   [RFC3209]     Awduche, D., Berger, L., Gan, D., Li, T.,
                 Srinivasan, V. and G. Swallow, "RSVP-TE: Extensions
                 to RSVP for LSP Tunnels", RFC 3209, December 2001.

   [RFC3471]     Berger, L. (Editor), "Generalized Multi-Protocol Label
                 Switching (GMPLS) Signaling Functional Description",
                 RFC 3471, January 2003.

   [RFC3473]     Berger, L. (Editor), "Generalized MPLS Signaling -
                 RSVP-TE Extensions", RFC 3473 January 2003.

   [FRR]         Pan, P. (Ed.), "Fast Reroute Extensions to RSVP-TE for
                 LSP Tunnels", <draft-ietf-mpls-rsvp-lsp-fastreroute-03
                 .txt>, Internet Draft, work in progress.

12. Informative References

   [RFC2026]     Bradner, S., "The Internet Standards Process
                 -- Revision 3", RFC 2026, October 1996.

   [RFC3031]     Rosen, E., Viswanathan, A., and Callon, R.,
                 "Multiprotocol Label Switching
                 Architecture", RFC 3031, January 2001.

   [INTER-AS]    Vasseur, JP., Zhang, R., "Inter-AS MPLS Traffic
                 Engineering", <draft-vasseur-inter-as-te-01.txt>,
                 Internet Draft, work in progress.

   [OSPF-CAPS]   Lindem, A., Shen, N., Aggarwal, R., Shaffer, S.,
                 Vasseur, JP., "Extensions to OSPF for Advertising
                 Optional Router Capabilities", <draft-ietf-ospf-cap-
                 00.txt>, Internet Draft, work in progress.

   [REOPT]       Vasseur, JP., Ikejiri, Y., "Reoptimization of MPLS
                 Traffic Engineering loosely routed explicit LSP path",
                 <draft-vasseur-mpls-loose-path-reopt-02.txt>, Internet
                 Draft, work in progress.





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13. Authors' Addresses

   Adrian Farrel
   Old Dog Consulting
   Phone:  +44 (0) 1978 860944
   EMail:  adrian@olddog.co.uk

   Dimitri Papadimitriou (Alcatel)
   Fr. Wellesplein 1,
   B-2018 Antwerpen, Belgium
   Phone:  +32 3 240-8491
   EMail:  dimitri.papadimitriou@alcatel.be

   Jean Philippe Vasseur
   Cisco Systems, Inc.
   300 Apollo Drive
   Chelmsford, MA 01824
   300 Beaver Brook Road
   Boxborough , MA - 01719
   USA
   Email: jpv@cisco.com

14. Full Copyright Statement

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   Reserved.

   This document and translations of it may be copied and
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