TEAS Working Group                                         X. Zhang, Ed.
Internet-Draft                                       Huawei Technologies
Updates: 3473 (if approved)                               V. Beeram, Ed.
Intended status: Standards Track                        Juniper Networks
Expires: February 12, 2018                                    I. Bryskin
                                                     Huawei Technologies
                                                           D. Ceccarelli
                                                     O. Gonzalez de Dios
                                                         August 11, 2017

                    Network Assigned Upstream-Label


   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

Status of This Memo

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   This Internet-Draft will expire on February 12, 2018.

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Copyright Notice

   Copyright (c) 2017 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
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   include Simplified BSD License text as described in Section 4.e of
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   described in the Simplified BSD License.

Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   2
     1.1.  Requirements Language . . . . . . . . . . . . . . . . . .   3
   2.  Unassigned Upstream Label . . . . . . . . . . . . . . . . . .   3
     2.1.  Processing Rules  . . . . . . . . . . . . . . . . . . . .   3
     2.2.  Backwards Compatibility . . . . . . . . . . . . . . . . .   4
   3.  Use-Case: Wavelength Setup for IP over Optical Networks . . .   4
     3.1.  Initial Setup . . . . . . . . . . . . . . . . . . . . . .   5
     3.2.  Wavelength Change . . . . . . . . . . . . . . . . . . . .   6
   4.  Acknowledgements  . . . . . . . . . . . . . . . . . . . . . .   6
   5.  Contributors  . . . . . . . . . . . . . . . . . . . . . . . .   6
   6.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .   7
   7.  Security Considerations . . . . . . . . . . . . . . . . . . .   7
   8.  References  . . . . . . . . . . . . . . . . . . . . . . . . .   7
     8.1.  Normative References  . . . . . . . . . . . . . . . . . .   7
     8.2.  Informative References  . . . . . . . . . . . . . . . . .   8
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .   8

1.  Introduction

   The Generalized Multi-Protocol Label Switching (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 where it is not desirable or possible for a given
   node to pick the upstream label on its own.  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

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   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.  This
   document updates [RFC3473] as it defines processing for a special
   label value.

1.1.  Requirements Language

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

2.  Unassigned Upstream Label

   This document proposes the use of 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.  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.  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

2.1.  Processing Rules

   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 PATH-ERR 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

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   when it needs to change the label at a later time.  If the upstream
   node receives an unacceptable changed label, then the error procedure
   defined in [RFC3473] MUST be followed.

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

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

                               Label (Assigned - L2)

                         Unassigned UPSTREAM_LABEL

                                 Figure 1

2.2.  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

   If the behavior that is exhibited is (a), then there are obviously no
   backwards compatibility concerns.  If there is some existing
   implementation that exhibits the behavior in (b), then there could be
   some potential issues.  However, at the time of publication, there is
   no documented evidence of any existing implementation that uses the
   "all-ones" bit pattern as a valid label.  Thus, it is safe to assume
   that the behavior in (b) will never be exhibited.

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

   Consider the network topology depicted in Figure 2.  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

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   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

   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.

3.1.  Initial Setup

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

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

                          Initial Setup Sequence

                                 Figure 2


   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.

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   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.

   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

   o  "RESV-CONF" setup procedure ([RFC2205])

   o  2-step "ADMIN STATUS" based setup procedure ("A" bit set in the
      first step; "A" bit cleared when the LSP is ready for use).

3.2.  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

   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

4.  Acknowledgements

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

5.  Contributors

   John Drake
   Juniper Networks
   Email: jdrake@juniper.net

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   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

6.  IANA Considerations

   This document makes no requests for IANA action.

7.  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
   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].

8.  References

8.1.  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,

   [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, <http://www.rfc-editor.org/info/rfc2205>.

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   [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,

8.2.  Informative References

   [RFC5920]  Fang, L., Ed., "Security Framework for MPLS and GMPLS
              Networks", RFC 5920, DOI 10.17487/RFC5920, July 2010,

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

   Email: daniele.ceccarelli@ericsson.com

   Oscar Gonzalez de Dios

   Email: ogondio@tid.es

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