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Versions: (draft-ietf-pwe3-mpls-tp-pw-over-bidir-lsp) 00 01 02 03 04 05 06 07 08 09 RFC 7965

Network Working Group                                            M. Chen
Internet-Draft                                                    W. Cao
Intended status: Standards Track                                  Huawei
Expires: January 22, 2017                                      A. Takacs
                                                                Ericsson
                                                                  P. Pan
                                                           July 21, 2016


          LDP Extensions for Pseudowire Binding to LSP Tunnels
            draft-ietf-pals-mpls-tp-pw-over-bidir-lsp-09.txt

Abstract

   Many transport services require that user traffic, in the form of
   Pseudowires (PW), be delivered via either a single co-routed
   bidirectional tunnel or two unidirectional tunnels that share the
   same routes.  This document defines an optional extension to Label
   Distribution Protocol (LDP) that enables the binding between PWs and
   the underlying Traffic Engineering (TE) tunnels.  The extension
   applies to both single-segment and multi-segment PWs.

Requirements 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 RFC 2119 [RFC2119].

Status of This Memo

   This Internet-Draft is submitted in full conformance with the
   provisions of BCP 78 and BCP 79.

   Internet-Drafts are working documents of the Internet Engineering
   Task Force (IETF).  Note that other groups may also distribute
   working documents as Internet-Drafts.  The list of current Internet-
   Drafts is at http://datatracker.ietf.org/drafts/current/.

   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."

   This Internet-Draft will expire on January 22, 2017.







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Copyright Notice

   Copyright (c) 2016 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
   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.  LDP Extensions  . . . . . . . . . . . . . . . . . . . . . . .   4
     2.1.  PSN Tunnel Binding TLV  . . . . . . . . . . . . . . . . .   5
       2.1.1.  PSN Tunnel Sub-TLV  . . . . . . . . . . . . . . . . .   6
   3.  Theory of Operation . . . . . . . . . . . . . . . . . . . . .   8
   4.  PSN Binding Operation for SS-PW . . . . . . . . . . . . . . .   9
   5.  PSN Binding Operation for MS-PW . . . . . . . . . . . . . . .  11
   6.  PSN Tunnel Select Considerations  . . . . . . . . . . . . . .  13
   7.  Security Considerations . . . . . . . . . . . . . . . . . . .  13
   8.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .  13
     8.1.  LDP TLV Types . . . . . . . . . . . . . . . . . . . . . .  13
       8.1.1.  PSN Tunnel Sub-TLVs . . . . . . . . . . . . . . . . .  13
     8.2.  LDP Status Codes  . . . . . . . . . . . . . . . . . . . .  14
   9.  Acknowledgements  . . . . . . . . . . . . . . . . . . . . . .  14
   10. References  . . . . . . . . . . . . . . . . . . . . . . . . .  14
     10.1.  Normative References . . . . . . . . . . . . . . . . . .  14
     10.2.  Informative References . . . . . . . . . . . . . . . . .  15
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  16

1.  Introduction

   Pseudo Wire Emulation Edge-to-Edge (PWE3) [RFC3985] is a mechanism to
   emulate layer 2 services, such as Ethernet Point-to-Point circuits.
   Such services are emulated between two Attachment Circuits, and the
   Pseudowire (PW)-encapsulated layer 2 service payload is transported
   via Packet Switching Network (PSN) tunnels between Provider Edges
   (PEs).  PWE3 typically uses Label Distribution Protocol (LDP)
   [RFC5036] or Resource ReserVation Protocol-Traffic Engineering (RSVP-
   TE) [RFC3209] LSPs as PSN tunnels.  The PEs select and bind the
   Pseudowires to PSN tunnels independently.  Today, there is no
   standardized protocol-based provisioning mechanism to associate PWs



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   to PSN tunnels, such associations must be managed via provisioning or
   other private methods.

   PW-to-PSN Tunnel binding has become increasingly common and important
   in many deployment scenarios, , as it allows service providers to
   provide service level agreements to their customers for such traffic
   attributes as bandwidth, latency, and availability.

   The requirements for explicit control of PW-to-LSP mapping has been
   described in Section 5.3.2 of [RFC6373].  Figure 1 illustrates how
   PWs can be bound to particular LSPs.

                      +------+                  +------+
            ---AC1 ---|..............PWs...............|---AC1---
            ---...----| PE1  |=======LSPs=======| PE2  |---...---
            ---ACn ---|      |-------Links------|      |---ACn---
                      +------+                  +------+

                 Figure 1: Explicit PW-to-LSP binding scenario


   There are two PEs (PE1 and PE2) connected through multiple parallel
   links that may be on different physical fibers.  Each link is managed
   and controlled as a bi-directional LSP.  At each PE, there are a
   large number of bi-directional user flows from multiple Ethernet
   interfaces (access circuits in the figure).  Each user flow uses a
   pair of uni-directional PWs to carry bi-directional traffic.  The
   operators need to make sure that the user flows (that is, the PW-
   pairs) are carried on the same fiber or bidirectional LSP.

   There are a number of reasons behind this requirement.  First, due to
   delay and latency constraints, traffic going over different fibers
   may require a large amount of expensive buffer memory to compensate
   for the differential delay at the headend nodes.  Further, the
   operators may apply different protection mechanisms on different
   parts of the network (e.g., to deloy 1:1 protection in one part and
   1+1 protection in other parts).  As such, operators may prefer to
   have a user's traffic traverse the same fiber.  That implies that
   both forwarding and reserve direction PWs that belong to the same
   user flow need to be mapped to the same co-routed bi-directional LSP
   or two LSPs with the same route.

   Figure 2 illustrates a scenario where PW-LSP binding is not applied.








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                    +----+   +--+ LSP1 +--+   +----+
         +-----+    | PE1|===|P1|======|P2|===| PE2|    +-----+
         |     |----|    |   +--+      +--+   |    |----|     |
         | CE1 |    |............PW................|    | CE2 |
         |     |----|    |      +--+          |    |----|     |
         +-----+    |    |======|P3|==========|    |    +-----+
                    +----+      +--+ LSP2     +----+

          Figure 2: Inconsistent SS-PW to LSP binding scenario

   LSP1 and LSP2 are two bidirectional connections on diverse paths.
   The operator needs to deliver a bi-directional flow between PE1 and
   PE2.  Using existing mechanisms, it's possible that PE1 may select
   LSP1 (PE1-P1-P2-PE2) as the PSN tunnel for traffic from PE1 to PE2,
   while selecting LSP2 (PE2-P3-PE1) as the PSN tunnel for traffic from
   PE2 to PE1.

   Consequently, the user traffic is delivered over two disjoint LSPs
   that may have very different service attributes in terms of latency
   and protection.  This may not be acceptable as a reliable and
   effective transport service to the customer.

   A similar problem may also exist in multi-segment PWs (MS-PWs), where
   user traffic on a particular PW may hop over different networks on
   forward and reverse directions.

   One way to solve this problem is by introducing manual provisioning
   at each PE to bind the PWs to the underlying PSN tunnels.  However,
   this is prone to configuration errors and does not scale.

   This document introduces an automatic solution by extending
   Forwarding Equivalence Class (FEC) 128/129 PW based on [RFC4447].

2.  LDP Extensions

   This document defines a new optional TLV, PSN Tunnel Binding TLV, to
   communicate tunnel/LSPs selection and binding requests between PEs.
   The TLV carries a PW's binding profile and provides explicit or
   implicit information for the underlying PSN tunnel binding operation.

   The binding operation applies in both single-segment (SS) and multi-
   segment (MS) scenarios.

   The extension supports two types of binding requests:

   1.  Strict binding: the requesting PE will choose and explicitly
       indicate the LSP information in the requests; the receiving PE




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       MUST obey the requests, otherwise, the PW will not be
       established.

   2.  Co-routed binding: the requesting PE will suggest an underlying
       LSP to a remote PE.  On receive, the remote PE has the option to
       use the suggested LSP, or reply the information for an
       alternative.

   In this document, the terminology of "tunnel" is identical to the "TE
   Tunnel" defined in Section 2.1 of [RFC3209], which is uniquely
   identified by a SESSION object that includes Tunnel end point
   address, Tunnel ID and Extended Tunnel ID.  The terminology "LSP" is
   identical to the "LSP tunnel" defined in Section 2.1 of [RFC3209],
   which is uniquely identified by the SESSION object together with
   SENDER_TEMPLATE (or FILTER_SPEC) object that consists of LSP ID and
   Tunnel endpoint address.

2.1.  PSN Tunnel Binding TLV

   PSN Tunnel Binding TLV is an optional TLV and MUST be carried in the
   LDP Label Mapping message [RFC5036] if PW to LSP binding is required.
   The format is 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
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |U|F| PSN Tunnel Binding (TBD1) |             Length            |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |C|S|T|    Unallocated flags    |            Reserved           |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    ~                       PSN Tunnel Sub-TLV                      ~
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

                   Figure 3: PSN Tunnel Binding TLV

   The U-bit and F-bit are defined in Section 3.3 [RFC5036].  Since the
   PSN Tunnel Binding TLV is an optional TLV, the U-bit MUST be set to 1
   so that a receiver MUST silently ignore this TLV if unknown to it,
   and continue processing the rest of the message.

   A receiver of this TLV is not allowed to forward the TLV further when
   it does not know the TLV.  So, the F-bit MUST be set to 0.

   The PSN Tunnel Binding TLV type is TBD1.

   The Length field is 2 octets in length.  It defines the length in
   octets of the value field (including Flags, Reserved, sub-TLV
   fields).



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   The Flag field is 2 octets in length, three flags are defined in this
   document.  The rest unallocated flags MUST be set to zero when
   sending, and MUST be ignored when received.

   C (Co-routed path) bit: This informs the remote T-PE/S-PEs about the
   properties of the underlying LSPs.  When set, the remote T-PE/S-PEs
   SHOULD select co-routed LSP (as the forwarding tunnel) as the reverse
   PSN tunnel.  If there is no such tunnel available, it may trigger the
   remote T-PE/S-PEs to establish a new LSP.

   S (Strict) bit: This instructs the PEs with respect to the handling
   of the underlying LSPs.  When set, the remote PE MUST use the tunnel/
   LSP specified in the PSN Tunnel Sub-TLV as the PSN tunnel on the
   reverse direction of the PW, or the PW will fail to be established.

   Either the C-bit or the S-bit MUST be set.  The C-bit and S-bit are
   mutually exclusive from each other, and cannot be set in the same
   message.  If "both C-bit and S-bit are set" or "both C-bit and S-bit
   are clear" are received, a Label Release message with status code set
   to "The C-bit or S-bit unknown" (TBD5) MUST be replied, and the PW
   will not be established.

   T (Tunnel Representation) bit: This indicates the format of the LSP
   tunnels.  When the bit is set, the tunnel uses the tunnel information
   to identify itself, and the LSP Number fields in the PSN Tunnel sub-
   TLV (Section 2.1.1) MUST be set to zero.  Otherwise, both tunnel and
   LSP information of the PSN tunnel are required.  The default is set.
   The motivation for the T-bit is to support the MPLS protection
   operation where the LSP Number fields may be ignored.

   The Reserved field is 2 octets in length and is left for future use.

2.1.1.  PSN Tunnel Sub-TLV

   PSN Tunnel Sub-TLVs are designed for inclusion in the PSN Tunnel
   Binding TLV to specify the tunnel/LSPs to which a PW is required to
   bind.

   Two sub-TLVs are defined: the IPv4 and IPv6 Tunnel sub-TLVs.












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       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(TBD2)  |    Length     |           Reserved            |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |                      Source Global ID                         |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |                       Source Node ID                          |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |      Source Tunnel Number     |     Source LSP Number         |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |                    Destination Global ID                      |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |                     Destination Node ID                       |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |   Destination Tunnel Number   |    Destination LSP Number     |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       0                   1                   2                   3

                   Figure 4: IPv4 PSN Tunnel sub-TLV format

       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(TBD3)  |    Length     |           Reserved            |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |                      Source Global ID                         |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      ~                       Source Node ID                          ~
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |      Source Tunnel Number     |       Source LSP Number       |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |                    Destination Global ID                      |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      ~                     Destination Node ID                       ~
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |   Destination Tunnel Number   |    Destination LSP Number     |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

                   Figure 5: IPv6 PSN Tunnel sub-TLV format


   The definition of Source and Destination Global/Node IDs and Tunnel/
   LSP Numbers are derived from [RFC6370].  This is to describe the
   underlying LSPs.  Note that the LSPs in this notation are globally
   unique.  The ITU-T style identifiers [RFC6923] are not used in this
   document.




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   As defined in Section 4.6.1.2 and Section 4.6.2.2 of [RFC3209], the
   "Tunnel endpoint address" is mapped to Destination Node ID, and
   "Extended Tunnel ID" is mapped to Source Node ID.  Both IDs can be
   IPv4 or IPv6 addresses.  The Node IDs are routable addresses of the
   ingress LSR and egress LSR of the Tunnel/LSP.

   A PSN Tunnel sub-TLV could be used to either identify a tunnel or a
   specific LSP.  The T-bit in the Flag field defines the distinction as
   such that, when the T-bit is set, the Source/Destination LSP Number
   fields MUST be zero and ignored during processing.  Otherwise, both
   Source/Destination LSP Number fields MUST have the actual LSP IDs of
   specific LSPs.

   Each PSN Tunnel Binding TLV MUST only have one such sub-TLV.  When
   sending, only one sub-TLV MUST be carried.  When received, if there
   are more than one sub-TLVs carried, only the first sub-TLV MUST be
   used, the rest sub-TLVs MUST be ignored.

3.  Theory of Operation

   During PW setup, the PEs may choose to select desired forwarding
   tunnels/LSPs, and inform the remote T-PE/S-PEs about the desired
   reverse tunnels/LSPs.

   Specifically, to set up a PW (or PW Segment), a PE may select a
   candidate tunnel/LSP to act as the PSN tunnel.  If none is available
   or satisfies the constraints, the PE will trigger and establish a new
   tunnel/LSP.  The selected tunnel/LSP information is carried in the
   PSN Tunnel Binding TLV and sent with the Label Mapping message to the
   target PE.

   Upon the reception of the Label Mapping message, the receiving PE
   will process the PSN Tunnel Binding TLV, determine whether it can
   accept the suggested tunnel/LSP or to find the reverse tunnel/LSP
   that meets the request, and respond with a Label Mapping message,
   which contains the corresponding PSN Tunnel Binding TLV.

   It is possible that two PEs may request PSN binding to the same PW or
   PW segment over different tunnels/LSPs at the same time.  There may
   cause collisions of tunnel/LSPs selection as both PEs assume the
   active role.

   As defined in (Section 7.2.1, [RFC6073]), each PE may be categorized
   into active and passive roles:

   1.  Active PE: the PE which initiates the selection of the tunnel/
       LSPs and informs the remote PE;




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   2.  Passive PE: the PE which obeys the active PE's suggestion.

   In the remaining of this document, we will elaborate the operation
   for SS-PW and MS-PW:

   1.  SS-PW: In this scenario, both PEs for a particular PW may assume
       the active roles.

   2.  MS-PW: One PE is active, while the other is passive.  The PWs are
       setup using FEC 129.

4.  PSN Binding Operation for SS-PW

   As illustrated in Figure-5, both PEs (say, PE1 and PE2) of a PW may
   independently initiate the setup.  To perform PSN binding, the Label
   Mapping messages MUST carry a PSN Tunnel Binding TLV, and the PSN
   Tunnel sub-TLV MUST contains the desired tunnel/LSPs of the sender.


                    +----+        LSP1        +----+
         +-----+    | PE1|====================| PE2|    +-----+
         |     |----|    |                    |    |----|     |
         | CE1 |    |............PW................|    | CE2 |
         |     |----|    |                    |    |----|     |
         +-----+    |    |====================|    |    +-----+
                    +----+       LSP2         +----+
          Figure 6: PSN binding operation in SS-PW environment

   As outlined previously, there are two types of binding request: co-
   routed and strict.

   In strict binding, a PE (e.g., PE1) will mandate the other PE (e.g.,
   PE2) to use a specified tunnel/LSP (e.g.  LSP1) as the PSN tunnel on
   the reverse direction.  In the PSN Tunnel Binding TLV, the S-bit MUST
   be set, the C-bit MUST be cleared, and the Source and Destination
   IDs/Numbers MUST be filled.

   On receive, if the S-bit is set, as well as following the processing
   procedure defined in Section 5.3.3 of [RFC4447], the receiving PE
   (i.e.  PE2) needs to determine whether to accept the indicated
   tunnel/LSP in PSN Tunnel Sub-TLV.

   If the receiving PE (PE2) is also an active PE, and may have
   initiated the PSN binding requests to the other PE (PE1), if the
   received PSN tunnel/LSP is the same as it has been sent in the Label
   Mapping message by PE2, then the signaling has converged on a
   mutually agreed Tunnel/LSP.  The binding operation is completed.




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   Otherwise, the receiving PE (PE2) MUST compare its own Node ID
   against the received Source Node ID as unsigned integers.  If the
   received Source Node ID is larger, the PE (PE2) will reply with a
   Label Mapping message to complete the PW setup and confirm the
   binding request.  The PSN Tunnel Binding TLV in the message MUST
   contain the same Source and Destination IDs/Numbers as in the
   received binding request, in the appropriate order (where the source
   is PE2 and PE1 becomes the destination).  On the other hand, if the
   receiving PE (PE2) has a Node ID that is larger than the Source Node
   ID carried in the PSN Tunnel Binding TLV, it MUST reply with a Label
   Release message with status code set to "Reject - unable to use the
   suggested tunnel/LSPs" and the received PSN Tunnel Binding TLV, and
   the PW will not be established.

   To support co-routed binding, the receiving PE can select the
   appropriated PSN tunnel/LSP for the reverse direction of the PW, so
   long as the forwarding and reverse PSNs share the same route (links
   and nodes).

   Initially, a PE (PE1) sends a Label Mapping message to the remote PE
   (PE2) with the PSN Tunnel Binding TLV, with C-bit set, S-bit cleared,
   and the appropriate Source and Destination IDs/Numbers.  In case of
   unidirectional LSPs, the PSN Tunnel Binding TLV may only contain the
   Source IDs/Numbers, the Destination IDs/Numbers are set to zero and
   left for PE2 to complete when responding the Label Mapping message.

   On receive, since PE2 is also an active PE, and may have initiated
   the PSN binding requests to the other PE (PE1), if the received PSN
   tunnel/LSP has the same route as the one that has been sent in the
   Label Mapping message to PE1, then the signaling has converged.  The
   binding operation is completed.

   Otherwise, PE2 needs to compare its own Node ID against the received
   Source Node ID as unsigned integers.  If the received Source Node ID
   is larger, PE2 needs to find/establish a tunnel/LSP that meets the
   co-routed constraint, and reply with a Label Mapping message with a
   PSN Binding TLV that contains the Source and Destination IDs/Numbers
   of the tunnel/LSP.  On the other hand, if the receiving PE (PE2) has
   a Node ID that is larger than the Source Node ID carried in the PSN
   Tunnel Binding TLV, it MUST reply with a Label Release message with
   status code set to "Reject - unable to use the suggested tunnel/LSPs"
   (TBD4) and the received PSN Tunnel Binding TLV.

   In addition, if the received PSN tunnel/LSP end points do not match
   the PW end points, PE2 MUST reply with a Label Release message with
   status code set to "Reject - unable to use the suggested tunnel/LSPs"
   (TBD4) and the received PSN Tunnel Binding TLV MUST also be carried.




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   In both strict and co-routed bindings, if T-bit is set, the LSP
   Number field MUST be set to zero.  Otherwise, the field MUST contain
   the actual LSP number for the related PSN LSP.

   After a PW is established, the operators may choose to move the PWs
   from the current tunnel/LSPs to other tunnel/LSPs.  Also the
   underlying PSN tunnel may break due to a network failure.  When
   either of these scenarios occur, a new Label Mapping message MUST be
   sent to notify the remote PE of the changes.  Note that when the
   T-bit is set, the working LSP broken will not provide this update if
   there are protection LSPs in place.

   The message may carry a new PSN Tunnel Binding TLV, which contains
   the new Source and Destination Numbers/IDs.  The handling of the new
   message should be identical to what has been described in this
   section.

   However, if the new Label Mapping message does not contain the PSN
   Tunnel Binding TLV, it declares the removal of any co-routed/strict
   constraints.  The current independent PW to PSN binding will be used.

   Further, as an implementation option, the PEs may choose not to
   remove the traffic from an operational PW, until the completion of
   the underlying PSN tunnel/LSP changes.

5.  PSN Binding Operation for MS-PW

   MS-PW uses FEC 129 for PW setup.  We refer the operation to Figure-6.


             +-----+ LSP1 +-----+ LSP2 +-----+ LSP3 +-----+
     +---+   |T-PE1|======|S-PE1|======|S-PE2|======|T-PE2|   +---+
     |   |---|     |      |     |      |     |      |     |---|   |
     |CE1|   |......................PW....................|   |CE2|
     |   |---|     |      |     |      |     |      |     |---|   |
     +---+   |     |======|     |======|     |======|     |   +---+
             +-----+ LSP4 +-----+ LSP5 +-----+ LSP6 +-----+

         Figure 7: PSN binding operation in MS-PW environment


   When an active PE (that is, T-PE1) starts to signal a MS-PW, a PSN
   Tunnel Binding TLV MUST be carried in the Label Mapping message and
   sent to the adjacent S-PE (that is, S-PE1).  The PSN Tunnel Binding
   TLV includes the PSN Tunnel sub-TLV that carries the desired tunnel/
   LSP of T-PE1's.





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   For strict binding, the initiating PE MUST set the S-bit, clear the
   C-bit and indicate the binding tunnel/LSP to the next-hop S-PE.

   When S-PE1 receives the Label Mapping message, S-PE1 needs to
   determine if the signaling is for forward or reverse direction, as
   defined in Section 6.2.3 of [RFC7267].

   If the Label Mapping message is for forward direction, and S-PE1
   accepts the requested tunnel/LSPs from T-PE1, S-PE1 MUST save the
   tunnel/LSP information for reverse-direction processing later on.  If
   the PSN binding request is not acceptable, S-PE1 MUST reply with a
   Label Release Message to the upstream PE (T-PE1) with Status Code set
   to "Reject - unable to use the suggested tunnel/LSPs" (TBD4).

   Otherwise, S-PE1 relays the Label Mapping message to the next S-PE
   (that is, S-PE2), with the PSN Tunnel sub-TLV carrying the
   information of the new PSN tunnel/LSPs selected by S-PE1.  S-PE2 and
   subsequent S-PEs will repeat the same operation until the Label
   Mapping message reaches to the remote T-PE (that is, T-PE2).

   If T-PE2 agrees with the requested tunnel/LSPs, it will reply with a
   Label Mapping message to initiate to the binding process on the
   reverse direction.  The Label Mapping message contains the received
   PSN Tunnel Binding TLV for confirmation purposes.

   When its upstream S-PE (S-PE2) receives the Label Mapping message,
   the S-PE relays the Label Mapping message to its upstream adjacent
   S-PE (S-PE1), with the previously saved PSN tunnel/LSP information in
   the PSN Tunnel sub-TLV.  The same procedure will be applied on
   subsequent S-PEs, until the message reaches to T-PE1 to complete the
   PSN binding setup.

   During the binding process, if any PE does not agree to the requested
   tunnel/LSPs, it can send a Label Release Message to its upstream
   adjacent PE with Status Code set to "Reject - unable to use the
   suggested tunnel/LSPs" (TBD4).  In addition, if the received PSN
   tunnel/LSP end points do not match the PW Segment end points, the
   receiving PE MUST reply with a Label Release message with status code
   set to "Reject - unable to use the suggested tunnel/LSPs" (TBD4) and
   the received PSN Tunnel Binding TLV MUST also be carried.

   For co-routed binding, the initiating PE (T-PE1) MUST set the C-bit,
   reset the S-bit and indicates the suggested tunnel/LSP in PSN Tunnel
   sub-TLV to the next-hop S-PE (S-PE1).

   During the MS-PW setup, the PEs have the option of ignoring the
   suggested tunnel/LSP, and to select another tunnel/LSP for the
   segment PW between itself and its upstream PE in reverse direction



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   only if the tunnel/LSP is co-routed with the forward one.  Otherwise,
   the procedure is the same as the strict binding.

   The tunnel/LSPs may change after a MS-PW being established.  When a
   tunnel/LSP has changed, the PE that detects the change SHOULD select
   an alternative tunnel/LSP for temporary use while negotiating with
   other PEs following the procedure described in this section.

6.  PSN Tunnel Select Considerations

   As stated in Section 1 of this document, the PSN tunnel that is used
   for binding can be either a co-routed bi-directional LSP or two LSPs
   with the same route.  The co-routed bi-directional LSP has the
   characteristics that both directions not only cross the same nodes
   and links but have the same life span.  But for the two LSPs case,
   even if they have the same route at the beginning, it cannot be
   guaranteed that they will always have the same route all the time.
   For example, when Fast ReRoute (FRR) [RFC4090] is deployed for the
   LSPs, link or node failure may make the two LSPs use different
   routes.  So, if the network supports co-routed bi-directional LSPs,
   it is RECOMMENDED that a co-routed bi-directional LSP should be used;
   otherwise, two LSPs with same route may be used.

7.  Security Considerations

   The ability to control which LSP is used to carry traffic from a PW
   can be a potential security risk both for denial of service and
   traffic interception.  It is RECOMMENDED that PEs do not accept the
   use of LSPs identified in the PSN Tunnel Binding TLV unless the LSP
   end points match the PW or PW segment end points.  Furthermore, it is
   RECOMMENDED that PEs implement the LDP security mechanisms described
   in [RFC5036] and [RFC5920].

8.  IANA Considerations

8.1.  LDP TLV Types

   This document defines a new TLV [Section 2.1 of this document] for
   inclusion in LDP Label Mapping message.  IANA is requested to assign
   TLV type value (TBD1) to the new defined TLVs from LDP "TLV Type Name
   Space" registry.

8.1.1.  PSN Tunnel Sub-TLVs

   This document defines two sub-TLVs [Section 2.1.1 of this document]
   for PSN Tunnel Binding TLV.  IANA is required to create a new PWE3
   registry ("PSN Tunnel Sub-TLV Name Space") for PSN Tunnel sub-TLVs
   and to assign Sub-TLV type values to the following sub-TLVs:



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   IPv4 PSN Tunnel sub-TLV - TBD2

   IPv6 PSN Tunnel sub-TLV - TBD3

   In addition, the values 0 and 255 in this new registry should be
   reserved, and values 1-254 will be allocated by IETF Review.

8.2.  LDP Status Codes

   This document defines two new LDP status codes, IANA is requested to
   assigned status codes to these new defined codes from the LDP "STATUS
   CODE NAME SPACE" registry.

   "Reject - unable to use the suggested tunnel/LSPs" - TBD4

   "The C-bit or S-bit unknown" -TBD5

   The E bit is set to one for both new codes.

9.  Acknowledgements

   The authors would like to thank Adrian Farrel, Kamran Raza, Xinchun
   Guo, Mingming Zhu and Li Xue for their comments and help in preparing
   this document.  Also this draft benefits from the discussions with
   Nabil Bitar, Paul Doolan, Frederic Journay, Andy Malis, Curtis
   Villamizar, Luca Martini, Alexander Vainshtein, Huub van Helvoort,
   Daniele Ceccarelli and Stewart Byant.

   We would especially like to acknowledge Ping Pan, a co-author on the
   early versions of this document.  It was a privilege to have known
   him.

   The coauthors of this document, the working group chairs, the
   responsible AD, and the PALS Working Group wish to dedicate this RFC
   to the memory of our friend and colleague Ping Pan, in recognition
   for his devotion and hard work at the IETF.

10.  References

10.1.  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,
              <http://www.rfc-editor.org/info/rfc2119>.






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   [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,
              DOI 10.17487/RFC4447, April 2006,
              <http://www.rfc-editor.org/info/rfc4447>.

   [RFC6370]  Bocci, M., Swallow, G., and E. Gray, "MPLS Transport
              Profile (MPLS-TP) Identifiers", RFC 6370,
              DOI 10.17487/RFC6370, September 2011,
              <http://www.rfc-editor.org/info/rfc6370>.

10.2.  Informative References

   [RFC3209]  Awduche, D., Berger, L., Gan, D., Li, T., Srinivasan, V.,
              and G. Swallow, "RSVP-TE: Extensions to RSVP for LSP
              Tunnels", RFC 3209, DOI 10.17487/RFC3209, December 2001,
              <http://www.rfc-editor.org/info/rfc3209>.

   [RFC3985]  Bryant, S., Ed. and P. Pate, Ed., "Pseudo Wire Emulation
              Edge-to-Edge (PWE3) Architecture", RFC 3985,
              DOI 10.17487/RFC3985, March 2005,
              <http://www.rfc-editor.org/info/rfc3985>.

   [RFC4090]  Pan, P., Ed., Swallow, G., Ed., and A. Atlas, Ed., "Fast
              Reroute Extensions to RSVP-TE for LSP Tunnels", RFC 4090,
              DOI 10.17487/RFC4090, May 2005,
              <http://www.rfc-editor.org/info/rfc4090>.

   [RFC5036]  Andersson, L., Ed., Minei, I., Ed., and B. Thomas, Ed.,
              "LDP Specification", RFC 5036, DOI 10.17487/RFC5036,
              October 2007, <http://www.rfc-editor.org/info/rfc5036>.

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

   [RFC6073]  Martini, L., Metz, C., Nadeau, T., Bocci, M., and M.
              Aissaoui, "Segmented Pseudowire", RFC 6073,
              DOI 10.17487/RFC6073, January 2011,
              <http://www.rfc-editor.org/info/rfc6073>.

   [RFC6373]  Andersson, L., Ed., Berger, L., Ed., Fang, L., Ed., Bitar,
              N., Ed., and E. Gray, Ed., "MPLS Transport Profile (MPLS-
              TP) Control Plane Framework", RFC 6373,
              DOI 10.17487/RFC6373, September 2011,
              <http://www.rfc-editor.org/info/rfc6373>.





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   [RFC6923]  Winter, R., Gray, E., van Helvoort, H., and M. Betts,
              "MPLS Transport Profile (MPLS-TP) Identifiers Following
              ITU-T Conventions", RFC 6923, DOI 10.17487/RFC6923, May
              2013, <http://www.rfc-editor.org/info/rfc6923>.

   [RFC7267]  Martini, L., Ed., Bocci, M., Ed., and F. Balus, Ed.,
              "Dynamic Placement of Multi-Segment Pseudowires",
              RFC 7267, DOI 10.17487/RFC7267, June 2014,
              <http://www.rfc-editor.org/info/rfc7267>.

Authors' Addresses

   Mach(Guoyi) Chen
   Huawei

   Email: mach.chen@huawei.com


   Wei Cao
   Huawei

   Email: wayne.caowei@huawei.com


   Attila Takacs
   Ericsson
   Laborc u. 1.
   Budapest  1037
   Hungary

   Email: attila.takacs@ericsson.com


   Ping Pan

















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