Internet DRAFT - draft-zzhang-teas-rmr-rsvp-p2mp

draft-zzhang-teas-rmr-rsvp-p2mp







TEAS WG                                                         Z. Zhang
Internet-Draft                                               A. Deshmukh
Updates: 4875 (if approved)                                     R. Singh
Intended status: Standards Track                        Juniper Networks
Expires: August 2, 2019                                 January 29, 2019


                      RSVP-TE P2MP Tunnels on RMR
                   draft-zzhang-teas-rmr-rsvp-p2mp-02

Abstract

   This document specifies the optimization in RSVP-TE P2MP tunnel
   signaling over Resilient MPLS Rings (RMR).

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 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 https://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 August 2, 2019.

Copyright Notice

   Copyright (c) 2019 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



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   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.  Specification . . . . . . . . . . . . . . . . . . . . . . . .   4
     2.1.  RMR Object  . . . . . . . . . . . . . . . . . . . . . . .   4
     2.2.  Procedures  . . . . . . . . . . . . . . . . . . . . . . .   4
       2.2.1.  PATH Message/State  . . . . . . . . . . . . . . . . .   4
       2.2.2.  RESV Message/State  . . . . . . . . . . . . . . . . .   5
   3.  Security Considerations . . . . . . . . . . . . . . . . . . .   5
   4.  Acknowledgements  . . . . . . . . . . . . . . . . . . . . . .   6
   5.  Normative References  . . . . . . . . . . . . . . . . . . . .   6
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .   6

1.  Introduction

   Traditional RSVP-TE P2MP tunnel signaling could be quite involving.
   With RMR, this could be significantly simplified:

   There is no need for ERO/RRO/SERO/SRRO or hop by hop routing.  The
   tunnel ingress simply sends PATH messages in one or both directions
   of the ring, depending on how leaves are best reached.  The <S2L Sub-
   LSP Descriptor List> only needs to list the tunnel leaves, and a
   transit router does not need to "branch" a PATH message into multiple
   ones.  Therefore, unless there are many tunnel leaves on a huge ring,
   a single PATH message is enough.  In the rare situation of a large
   tunnel with many leaves to list, a small number of PATH messages
   should suffice.  Additionally, there is no need to signal and
   maintain individual sub-LSPs (one for each leaf) any more.  As a
   result, corresponding PATH/RESV state is also reduced.  Each node
   only needs to maintain a single PATH state and a single RESV state
   for each P2MP tunnel, and the RESV state does not need to track
   individual leaves - it just need to track if a RESV is received from
   downstream and/or if this node itself is a leaf.

   A RESV message is triggered to the PHOP when the RESV state is first
   created (either because the node is a leaf or because a RESV message
   is received from downstream) and it is refreshed periodically.  A
   RESV Tear is sent when the RESV state is deleted (when the node is no
   longer a Leaf and the RESV from downstream has timed out or a RESV
   Tear is received).

   Optionally, the tunnel ingress may not need to list any/all leaves.
   It could simply send the PATH message around the ring, with the <S2L



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   Sub-LSP Descriptor List> listing the root itself.  Through methods
   outside the scope of this document, a node determines if it is a leaf
   of the tunnel, and if yes, it will send back a RESV message.  With
   this, a single PATH message is surely enough.

   In this document, leaves in <S2L Sub-LSP Descriptor List> are
   referred to as explicit leaves, and leaves not listed there but self-
   determined by ring nodes are referred to as implicit leaves.  There
   could be both explicit and implicit leaves for a tunnel.  The ingress
   allows implicit leaves by including itself as the last one in the
   <S2L Sub-LSP Descriptor List>.

   Optionally, the RESV message could also include a <S2L Sub-LSP
   Descriptor List> to list all the leaves on the established tunnel so
   that the each node knows its downstream leaves.  In that case, when
   the set of downstream leaves changes, a RESV message with the new
   <S2L Sub-LSP Descriptor List> is triggered.

   Adding/removing explicit leaves is straightforward.  The ingress
   simply sends a triggered PATH message with new <S2L Sub-LSP
   Descriptor List>.  As it passes around the ring, each node determines
   if it is an explicit leaf and updates its state accordingly.  The
   triggered PATH message does not have to go all the way to the last
   leaf - if on a node the <S2L Sub-LSP Descriptor List> in the would-
   be-sent PATH message is the same as what was sent before, the
   triggered PATH message will not be sent further.

   To indicate that the tunnel signaling is with above mentioned RMR
   optimizations, a new object is included in the PATH message to
   specify the Ring ID and direction.

   Link/Node protection is achieved by tunneling packets to the next
   node using the Ring LSP to that node in the other direction.  This
   does not need any additional signaling but is based on a reasonable
   premise that unicast Ring LSPs are always in place.  Once the ingress
   learns the failure (through IGP discovery or through other error
   detection/notification mechanisms), global repair kicks in to reach
   some leaves via PATH message sent in the other direction.  Before
   global repair is finished, traffic continues to flow in the original
   path except that at the failure point it is tunneled to the next
   node.

   If an RMR is just part of a general RSVP network the optimization can
   also be applied on the ring nodes.  If the tunnel ingress knows the
   leaves that are on the ring, it could put all those leaves in the
   single PATH message and construct the ERO/SERO only towards the entry
   point on the ring.  The entry point then includes the RMR object in
   the PATH messages that it sends.  For leaves beyond the ring, the



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   ingress may include the exit points on the ring as loose hops in the
   ERO/SERO, and when a ring node needs to send the PATH message off the
   ring, it removes the RMR object.  Details will be provided in future
   revisions of this document.

2.  Specification

2.1.  RMR Object

   The RMR object is a new object of the following:

   o  Class Name: RMR

   o  Class-Num: TBA1 (to be assigned by IANA)

   o  C-Type: TBA2 (to be assigned by IANA)

   The format of the object content following the common object header
   is the following:

        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
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |                       Ring ID (4 octets)                      |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |D| Flags       |      Reserved                                 |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   Following the 4-octect Ring ID, there is an 8-bit Flags field.  The
   first bit of the Flags field indicates the direction.  If it is set,
   it is clockwise direction.  Otherwise, it is anti-clockwise.

2.2.  Procedures

   This section describes the differences in the procedures for ring
   nodes to set up RSVP-TE P2MP tunnels across the ring, compared to the
   conventional non-RMR-aware case.  For now it is assumed that all
   nodes (ingress, transit, and leaves) on the tunnel are on the ring.

   More details will be provided in future revisions.

2.2.1.  PATH Message/State

   The tunnel ingress includes the RMR object with the Ring ID and the
   direction flag bit set accordingly.  The explicit tunnel leaves are
   encoded in the <S2L Sub-LSP Descriptor List>, and no ERO/SERO is
   included.  If the tunnel allows implicit leaves, the descriptor list
   encodes the ingress itself as the last element.  The message is sent



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   to the next node on the ring in the direction specified in the RMR
   object, w/o using ERO/SERO or hop-by-hop routing.

   When a node receives a PATH message with the RMR object, it checks if
   itself is listed in the <S2L Sub-LSP Descriptor List>, or if the <S2L
   Sub-LSP Descriptor List> encodes the tunnel ingress as the last
   element and this node itself is an implicit leaf.  If yes, it creates
   corresponding RESV state and sends a RESV message to the PHOP.

   The receiving node removes itself from the <S2L Sub-LSP Descriptor
   List> in the PATH message, and saves the list locally.  The PATH
   message is sent to the next node on the ring in the specified
   direction with the saved <S2L Sub-LSP Descriptor List>, if one of the
   following conditions is met:

   o  The <S2L Sub-LSP Descriptor List> encodes the tunnel ingress
      itself as the last element.

   o  The <S2L Sub-LSP Descriptor List> is not empty and either the PATH
      state is newly created or the <S2L Sub-LSP Descriptor List> is
      different from the previously saved one.

   If <S2L Sub-LSP Descriptor List> is empty and different from the
   previously saved one, a PATH Teardown is sent instead.

2.2.2.  RESV Message/State

   A ring node may know that it is a leaf when the PATH message is first
   processed as described in the previous section.  In case of implicit
   leaves, it may become a leaf after the PATH messages has been
   processed.  A non-leaf node may also receive a RESV message from its
   NHOP.  In all these cases, the node creates RESV state and sends a
   RESV message to the PHOP, w/o encoding RRO/SRRO.

   If a ring node was a leaf but stops being a leaf, either because it
   is no longer listed in the <S2L Sub-LSP Descriptor List> or it is no
   longer an implicit leaf, it removes/updates corresponding local
   state.  A RESV Teardown is sent to the PHOP if there is no RESV
   received from its downstream either.

3.  Security Considerations

   This document does not introduce new security risks.








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4.  Acknowledgements

5.  Normative References

   [I-D.ietf-mpls-rmr]
              Kompella, K. and L. Contreras, "Resilient MPLS Rings",
              draft-ietf-mpls-rmr-09 (work in progress), January 2019.

   [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>.

   [RFC4875]  Aggarwal, R., Ed., Papadimitriou, D., Ed., and S.
              Yasukawa, Ed., "Extensions to Resource Reservation
              Protocol - Traffic Engineering (RSVP-TE) for Point-to-
              Multipoint TE Label Switched Paths (LSPs)", RFC 4875,
              DOI 10.17487/RFC4875, May 2007,
              <https://www.rfc-editor.org/info/rfc4875>.

Authors' Addresses

   Zhaohui Zhang
   Juniper Networks

   EMail: zzhang@juniper.net


   Abhishek Deshmukh
   Juniper Networks

   EMail: adeshmukh@juniper.net


   Ravi Singh
   Juniper Networks

   EMail: ravis@juniper.net













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