





Internet Engineering Task Force (IETF)                     X. Zhang, Ed.
Request for Comments: 8359                           Huawei Technologies
Updates: 3471, 3473, 6205                                 V. Beeram, Ed.
Category: Standards Track                               Juniper Networks
ISSN: 2070-1721                                               I. Bryskin
                                                     Huawei Technologies
                                                           D. Ceccarelli
                                                                Ericsson
                                                     O. Gonzalez de Dios
                                                              Telefonica
                                                              March 2018


                    Network-Assigned Upstream Label

Abstract

   This document discusses a Generalized Multi-Protocol Label Switching
   (GMPLS) Resource reSerVation Protocol with Traffic Engineering
   (RSVP-TE) mechanism that enables the network to assign an upstream
   label for a bidirectional Label Switched Path (LSP).  This is useful
   in scenarios where a given node does not have sufficient information
   to assign the correct upstream label on its own and needs to rely on
   the downstream node to pick an appropriate label.  This document
   updates RFCs 3471, 3473, and 6205 as it defines processing for a
   special label value in the UPSTREAM_LABEL object.

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 7841.

   Information about the current status of this document, any errata,
   and how to provide feedback on it may be obtained at
   https://www.rfc-editor.org/info/rfc8359.











Zhang, et al.                Standards Track                    [Page 1]

RFC 8359             Network Assigned Upstream-Label          March 2018


Copyright Notice

   Copyright (c) 2018 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
   (https://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
   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.

Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   2
   2.  Requirements Language . . . . . . . . . . . . . . . . . . . .   3
   3.  Unassigned Upstream Label . . . . . . . . . . . . . . . . . .   3
     3.1.  Procedures  . . . . . . . . . . . . . . . . . . . . . . .   4
     3.2.  Backwards Compatibility . . . . . . . . . . . . . . . . .   5
   4.  Use-Case: Wavelength Setup for IP over Optical Networks . . .   5
     4.1.  Initial Setup . . . . . . . . . . . . . . . . . . . . . .   6
     4.2.  Wavelength Change . . . . . . . . . . . . . . . . . . . .   7
   5.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .   7
   6.  Security Considerations . . . . . . . . . . . . . . . . . . .   7
   7.  References  . . . . . . . . . . . . . . . . . . . . . . . . .   8
     7.1.  Normative References  . . . . . . . . . . . . . . . . . .   8
     7.2.  Informative References  . . . . . . . . . . . . . . . . .   9
   Acknowledgements  . . . . . . . . . . . . . . . . . . . . . . . .   9
   Contributors  . . . . . . . . . . . . . . . . . . . . . . . . . .   9
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  10

1.  Introduction

   A functional description of the Generalized Multi-Protocol Label
   Switching (GMPLS) signaling extensions for setting up a bidirectional
   Label Switched Path (LSP) is provided in [RFC3471].  The GMPLS
   Resource reSerVation Protocol with Traffic Engineering (RSVP-TE)
   extensions for setting up a bidirectional LSP are specified in
   [RFC3473].  The bidirectional LSP setup is indicated by the presence
   of an UPSTREAM_LABEL object in the Path message.  As per the existing
   setup procedure outlined for a bidirectional LSP, each upstream node
   must allocate a valid upstream label on the outgoing interface before
   sending the initial Path message downstream.  However, there are
   certain scenarios (see Section 4) where it is not desirable or
   possible for a given node to pick the upstream label on its own.



Zhang, et al.                Standards Track                    [Page 2]

RFC 8359             Network Assigned Upstream-Label          March 2018


   This document defines the protocol mechanism to be used in such
   scenarios.  This mechanism enables a given node to offload the task
   of assigning the upstream label for a given bidirectional LSP to
   nodes downstream in the network.  It is meant to be used only for
   bidirectional LSPs that assign symmetric labels at each hop along the
   path of the LSP.  Bidirectional Lambda Switch Capable (LSC) LSPs use
   symmetric lambda labels (format specified in [RFC6205]) at each hop
   along the path of the LSP.

   As per the bidirectional LSP setup procedures specified in [RFC3471]
   and [RFC3473], the UPSTREAM_LABEL object must indicate a label that
   is valid for forwarding.  This document updates that by allowing the
   UPSTREAM_LABEL object to indicate a special label that isn't valid
   for forwarding.  As per the bidirectional LSC LSP setup procedures
   specified in [RFC6205], the LABEL_SET object and the UPSTREAM_LABEL
   object must contain the same label value.  This document updates that
   by allowing the UPSTREAM_LABEL object to carry a special label value
   that is different from the one used in the LABEL_SET object.

2.  Requirements Language

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and
   "OPTIONAL" in this document are to be interpreted as described in
   BCP 14 [RFC2119] [RFC8174] when, and only when, they appear in all
   capitals, as shown here.

3.  Unassigned Upstream Label

   This document defines a special label value -- "0xFFFFFFFF" (for a
   4-octet label) -- to indicate an Unassigned Upstream Label.  Similar
   "all-ones" patterns are expected to be used for labels of other
   sizes.

       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
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1|
      |                              ...                              |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

         Figure 1: Unassigned UPSTREAM_LABEL - "all-ones" Pattern

   The presence of this value in the UPSTREAM_LABEL object of a Path
   message indicates that the upstream node has not assigned an upstream
   label on its own and has requested the downstream node to provide a
   label that it can use in both the forward and reverse directions.




Zhang, et al.                Standards Track                    [Page 3]

RFC 8359             Network Assigned Upstream-Label          March 2018


   The presence of this value in the UPSTREAM_LABEL object of a Path
   message MUST also be interpreted by the receiving node as a request
   to mandate symmetric labels for the LSP.

3.1.  Procedures

   The scope of the procedures is limited to the exchange and processing
   of messages between an upstream node and its immediate downstream
   node.  The Unassigned Upstream Label is used by an upstream node when
   it is not in a position to pick the upstream label on its own.  In
   such a scenario, the upstream node sends a Path message downstream
   with an Unassigned Upstream Label and requests the downstream node to
   provide a symmetric label.  If the upstream node desires to make the
   downstream node aware of its limitations with respect to label
   selection, it MUST specify a list of valid labels via the LABEL_SET
   object as specified in [RFC3473].

   In response, the downstream node picks an appropriate symmetric label
   and sends it via the LABEL object in the Resv message.  The upstream
   node would then start using this symmetric label for both directions
   of the LSP.  If the downstream node cannot pick the symmetric label,
   it MUST issue a PathErr message with a "Routing Problem/Unacceptable
   Label Value" indication.  If the upstream node that signals an
   Unassigned Upstream Label receives a label with the "all-ones"
   pattern or any other unacceptable label in the LABEL object of the
   Resv message, it MUST issue a ResvErr message with a "Routing
   Problem/Unacceptable Label Value" indication.

   The upstream node will continue to signal the Unassigned Upstream
   Label in the Path message even after it receives an appropriate
   symmetric label in the Resv message.  This is done to make sure that
   the downstream node would pick a different symmetric label if and
   when it needs to change the label at a later time.  If the upstream
   node receives an unacceptable changed label, then it MUST issue a
   ResvErr message with a "Routing Problem/Unacceptable Label Value"
   indication.















Zhang, et al.                Standards Track                    [Page 4]

RFC 8359             Network Assigned Upstream-Label          March 2018


                  +----------+                    +------------+
               ---| Upstream |--------------------| Downstream |---
                  +----------+                    +------------+

                              Path
                               Upstream Label (Unassigned)
                               Label-Set (L1, L2 ... Ln)
                              ------------------->

                              Resv
                               Label (Assigned - L2)
                              <-------------------

                       Figure 2: Signaling Sequence

3.2.  Backwards Compatibility

   If the downstream node is running an implementation that doesn't
   support the semantics of an Unassigned UPSTREAM LABEL, it will either
   (a) reject the special label value and generate an error as specified
   in Section 3.1 of [RFC3473] or (b) accept it and treat it as a valid
   label.

   If the behavior that is exhibited is (a), then there are no backwards
   compatibility concerns.  If the behavior that is exhibited is (b),
   then the downstream node will send a label with the "all-ones"
   pattern in the LABEL object of the Resv message.  In response, the
   upstream node will issue a ResvErr message with a "Routing Problem/
   Unacceptable Label Value" indication.

4.  Use-Case: Wavelength Setup for IP over Optical Networks

   Consider the network topology depicted in Figure 3.  Nodes A and B
   are client IP routers that are connected to an optical Wavelength
   Division Multiplexing (WDM) transport network.  F and I represent WDM
   nodes.  The transponder sits on the router and is directly connected
   to the add-drop port on a WDM node.

   The optical signal originating on "Router A" is tuned to a particular
   wavelength.  On "WDM-Node F", it gets multiplexed with optical
   signals at other wavelengths.  Depending on the implementation of
   this multiplexing function, it may not be acceptable to have the
   router send the signal into the optical network unless it is at the
   appropriate wavelength.  In other words, having the router send
   signals with a wrong wavelength may adversely impact existing optical
   trails.  If the clients do not have full visibility into the optical
   network, they are not in a position to pick the correct wavelength in
   advance.



Zhang, et al.                Standards Track                    [Page 5]

RFC 8359             Network Assigned Upstream-Label          March 2018


   The rest of this section examines how the protocol mechanism proposed
   in this document allows the optical network to select and communicate
   the correct wavelength to its clients.

4.1.  Initial Setup

         +---+                 /-\             /-\                 +---+
         | A |----------------( F ) ~~~~~~~~~ ( I )----------------| B |
         +---+                 \-/             \-/                 +---+

            Path
              Upstream Label (Unassigned/0xFFFFFFFF)
            --------------------->
                                  -- ~~ -- ~~ -->
                                                  Path
                                                  -------------------->
                                                  Resv
                                                  <--------------------
                                  <-- ~~ -- ~~ --
            Resv
              Label (Assigned)
            <---------------------

                     Figure 3: Initial Setup Sequence

   Steps:

   o  "Router A" does not have enough information to pick an appropriate
      client wavelength.  It sends a Path message downstream requesting
      the network to assign an appropriate symmetric label for its use.
      Since the client wavelength is unknown, the laser is off at the
      ingress client.

   o  The downstream node (Node F) receives the Path message, chooses
      the appropriate wavelength values, and forwards them in
      appropriate label fields to the egress client ("Router B").

   o  "Router B" receives the Path message, turns the laser ON and tunes
      it to the appropriate wavelength (received in the UPSTREAM_LABEL/
      LABEL_SET of the Path) and sends a Resv message upstream.

   o  The Resv message received by the ingress client carries a valid
      symmetric label in the LABEL object.  "Router A" turns on the
      laser and tunes it to the wavelength specified in the network
      assigned symmetric LABEL.






Zhang, et al.                Standards Track                    [Page 6]

RFC 8359             Network Assigned Upstream-Label          March 2018


   For cases where the egress-node relies on RSVP signaling to determine
   exactly when to start using the LSP, implementations may choose to
   integrate the above sequence with any of the existing graceful setup
   procedures:

   o  "ResvConf" setup procedure ([RFC2205])

   o  Two-step "ADMIN STATUS" based setup procedure ("A" bit set in the
      first step; "A" bit cleared when the LSP is ready for use)
      ([RFC3473])

4.2.  Wavelength Change

   After the LSP is set up, the network may decide to change the
   wavelength for the given LSP.  This could be for a variety of reasons
   including policy reasons, restoration within the core, preemption,
   etc.

   In such a scenario, if the ingress client receives a changed label
   via the LABEL object in a modified Resv message, it retunes the laser
   at the ingress to the new wavelength.  Similarly, if the egress
   client receives a changed label via UPSTREAM_LABEL/LABEL_SET in a
   modified Path message, it retunes the laser at the egress to the new
   wavelength.

5.  IANA Considerations

   IANA maintains the "Generalized Multi-Protocol Label Switching
   (GMPLS) Signaling Parameters" registry.  IANA has added a new
   subregistry titled "Special Purpose Generalized Label Values".  New
   values are assigned according to Standards Action [RFC8126].

   Special Purpose Generalized Label Values

   Pattern/    Label Name            Applicable        Reference
   Value                             Objects
   --------    ----------------      --------------    ----------
   all-ones    Unassigned            UPSTREAM_LABEL    [RFC8359]
               Upstream Label

6.  Security Considerations

   This document defines a special label value to be carried in the
   UPSTREAM_LABEL object of a Path message.  This special label value is
   used to enable the function of requesting network assignment of an
   upstream label.  The changes proposed in this document pertain to the
   semantics of a specific field in an existing RSVP object and the




Zhang, et al.                Standards Track                    [Page 7]

RFC 8359             Network Assigned Upstream-Label          March 2018


   corresponding procedures.  Thus, there are no new security
   implications raised by this document and the security considerations
   discussed by [RFC3473] still apply.

   For a general discussion on MPLS and GMPLS related security issues,
   see the MPLS/GMPLS security framework [RFC5920].

7.  References

7.1.  Normative References

   [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
              Requirement Levels", BCP 14, RFC 2119,
              DOI 10.17487/RFC2119, March 1997,
              <https://www.rfc-editor.org/info/rfc2119>.

   [RFC2205]  Braden, R., Ed., Zhang, L., Berson, S., Herzog, S., and S.
              Jamin, "Resource ReSerVation Protocol (RSVP) -- Version 1
              Functional Specification", RFC 2205, DOI 10.17487/RFC2205,
              September 1997, <https://www.rfc-editor.org/info/rfc2205>.

   [RFC3471]  Berger, L., Ed., "Generalized Multi-Protocol Label
              Switching (GMPLS) Signaling Functional Description",
              RFC 3471, DOI 10.17487/RFC3471, January 2003,
              <https://www.rfc-editor.org/info/rfc3471>.

   [RFC3473]  Berger, L., Ed., "Generalized Multi-Protocol Label
              Switching (GMPLS) Signaling Resource ReserVation Protocol-
              Traffic Engineering (RSVP-TE) Extensions", RFC 3473,
              DOI 10.17487/RFC3473, January 2003,
              <https://www.rfc-editor.org/info/rfc3473>.

   [RFC6205]  Otani, T., Ed. and D. Li, Ed., "Generalized Labels for
              Lambda-Switch-Capable (LSC) Label Switching Routers",
              RFC 6205, DOI 10.17487/RFC6205, March 2011,
              <https://www.rfc-editor.org/info/rfc6205>.

   [RFC8174]  Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC
              2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174,
              May 2017, <https://www.rfc-editor.org/info/rfc8174>.











Zhang, et al.                Standards Track                    [Page 8]

RFC 8359             Network Assigned Upstream-Label          March 2018


7.2.  Informative References

   [RFC5920]  Fang, L., Ed., "Security Framework for MPLS and GMPLS
              Networks", RFC 5920, DOI 10.17487/RFC5920, July 2010,
              <https://www.rfc-editor.org/info/rfc5920>.

   [RFC8126]  Cotton, M., Leiba, B., and T. Narten, "Guidelines for
              Writing an IANA Considerations Section in RFCs", BCP 26,
              RFC 8126, DOI 10.17487/RFC8126, June 2017,
              <https://www.rfc-editor.org/info/rfc8126>.

Acknowledgements

   The authors would like to thank Adrian Farrel and Chris Bowers for
   their inputs.

Contributors

   John Drake
   Juniper Networks
   Email: jdrake@juniper.net

   Gert Grammel
   Juniper Networks
   Email: ggrammel@juniper.net

   Pawel Brzozowski
   ADVA Optical Networking
   Email: pbrzozowski@advaoptical.com

   Zafar Ali
   Cisco Systems, Inc.
   Email: zali@cisco.com


















Zhang, et al.                Standards Track                    [Page 9]

RFC 8359             Network Assigned Upstream-Label          March 2018


Authors' Addresses

   Xian Zhang (editor)
   Huawei Technologies

   Email: zhang.xian@huawei.com


   Vishnu Pavan Beeram (editor)
   Juniper Networks

   Email: vbeeram@juniper.net


   Igor Bryskin
   Huawei Technologies

   Email: igor.bryskin@huawei.com


   Daniele Ceccarelli
   Ericsson

   Email: daniele.ceccarelli@ericsson.com


   Oscar Gonzalez de Dios
   Telefonica

   Email: ogondio@tid.es





















Zhang, et al.                Standards Track                   [Page 10]

