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Versions: 00 01 02 draft-ietf-mpls-rmr

MPLS WG                                                      K. Kompella
Internet-Draft                                    Juniper Networks, Inc.
Intended status: Standards Track                        October 26, 2014
Expires: April 29, 2015


                          Resilient MPLS Rings
                       draft-kompella-mpls-rmr-00

Abstract

   This document describes the use of the MPLS control and data planes
   on ring topologies.  It describes the special nature of rings, and
   proceeds to show how MPLS can be effectively used in such topologies.
   It describes how MPLS rings are configured, auto-discovered and
   signaled, as well as how the data plane works.  Companion documents
   describe the details of discovery and signaling for specific
   protocols.

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 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 April 29, 2015.

Copyright Notice

   Copyright (c) 2014 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



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   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
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   described in the Simplified BSD License.


Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . . . 3
     1.1.  Definitions . . . . . . . . . . . . . . . . . . . . . . . . 3
   2.  Motivation  . . . . . . . . . . . . . . . . . . . . . . . . . . 4
   3.  Theory of Operation . . . . . . . . . . . . . . . . . . . . . . 4
     3.1.  Configuration . . . . . . . . . . . . . . . . . . . . . . . 4
     3.2.  Auto-discovery  . . . . . . . . . . . . . . . . . . . . . . 5
     3.3.  Signaling . . . . . . . . . . . . . . . . . . . . . . . . . 5
     3.4.  Installing Primary LFIB Entries . . . . . . . . . . . . . . 5
     3.5.  Installing FRR LFIB Entries . . . . . . . . . . . . . . . . 5
     3.6.  Protection  . . . . . . . . . . . . . . . . . . . . . . . . 5
   4.  Security Considerations . . . . . . . . . . . . . . . . . . . . 6
   5.  IANA Considerations . . . . . . . . . . . . . . . . . . . . . . 6
   6.  References  . . . . . . . . . . . . . . . . . . . . . . . . . . 6
     6.1.  Normative References  . . . . . . . . . . . . . . . . . . . 6
     6.2.  Informative References  . . . . . . . . . . . . . . . . . . 6
   Author's Address  . . . . . . . . . . . . . . . . . . . . . . . . . 6























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1.  Introduction

   Rings are a very common topology in transport networks.  A ring is
   the simplest topology offering link and node resilience.  Rings are
   nearly ubiquitous in access and aggregation networks.  As MPLS
   increases its presence in such networks, and takes on a greater role
   in transport, it is imperative that MPLS handles rings well; this is
   not the case today.

   This document describes the special nature of rings, and the special
   needs of MPLS on rings.  It then shows how these needs can be met in
   several ways, some of which involve extensions to protocols such as
   IS-IS [RFC1195], OSPF[RFC2328], RSVP-TE [RFC3209] and LDP [RFC5036].

1.1.  Definitions

   A (directed) graph G = (V, E) consists of a set of vertices (or
   nodes) V and a set of edges (or links) E. An edge is an ordered pair
   of nodes (a, b), where a and b are in V. (In this document, the terms
   node and link will be used instead of vertex and edge.)

   A ring is a subgraph of G. A ring consists of a subset of nodes {R_i,
   1 <= i <= n} of V. For convenience, we define R_0 = R_n.  The edges
   {(R_i, R_i+1) and (R_i+1, R_i), 0 <= i < n} must be a subset of E. We
   define the direction from node R_i to R_i+1 (0 <= i < n) (and hence
   from R_n = R_0 to R_1) as "downstream" (DS) and the reverse direction
   as "upstream" (US).  As there may be several rings in a graph, we
   number each ring with a distinct "Ring ID" RID.


                               R1 . . . R2
                             .             .
                          R8                 R3
                       |  .        Ring       .  |
              Upstream |  .                   .  | Downstream
                       v  .      RID = 17     .  v
                          R7                 R4
                             .             .
                               R6 . . . R5

                        Figure 1: Ring with 8 nodes

   The following terminology is used for ring LSPs:

   RL_k:  A Ring LSP anchored on node R_k is denoted RL_k.






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   DL_jk (UL_jk):  A label allocated by R_j for RL_k in the DS (US)
      direction.

   P_jk (Q_jk):  A Path (Resv) message sent by R_j for RL_k.


2.  Motivation

   A ring is the simplest topology that offers resilience.  This is
   perhaps the main reason to lay out fiber in a ring.  Thus, effective
   mechanisms for fast failover on rings are needed.  Furthermore, there
   are large numbers of rings.  Thus, configuration of rings needs to be
   as simple as possible.  Finally, bandwidth management on access rings
   is very important, as bandwidth is generally quite constrained here.

   The goals of this document are to present mechanisms for improved
   MPLS-based resilience in ring networks (using ideas that are
   reminiscent of Bidirectional Line Switched Rings), automatic bring-up
   of LSPs, better bandwidth management and auto-hierarchy.  These goals
   can be achieved using extensions to existing IGP and MPLS signaling
   protocols, using central provisioning, or in other ways.


3.  Theory of Operation

   Say a ring has n nodes R_i, 0 <= i <= n, where R_0 = R_n.  Each node
   is the anchor of one or more Ring LSPs.  A Ring LSP RL_i anchored on
   node R_i consists of two counter-rotating LSPs that start and end at
   R_i.  A ring LSP is "multipoint"; any node R_j can use RL_i to send
   traffic to R_i in either direction.  Bidirectional connectivity
   between nodes R_i and R_j is achieved by using ring LSPs RL_j (to
   reach R_j) and RL_i (to reach R_i); each can be used in either
   direction.

3.1.  Configuration

   An MPLS ring is configured by assigning RIDs to all the nodes in the
   ring.  The links between adjacent ring nodes are ring links (unless
   told otherwise); this may also be configured, or it may be
   discovered, say by means of IGP hellos.  Once ring nodes and ring
   links are identified, the ring has been defined.

   Ring LSPs are not provisioned; they are created automatically when an
   MPLS ring is defined.  Each node R_j allocates DS and US labels for
   each ring LSP RL_k and sends these to its ring neighbors.  The
   signaling protocol used to send labels can be RSVP-TE or LDP; these
   extensions will be described later.  When R_j receives DS and US
   labels for RL_k, it can install LFIB entries for RL_k.



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3.2.  Auto-discovery

   A link-state IGP such as IS-IS or OSPF can be used to simplify the
   configuration of MPLS rings.  Details will be given in a companion
   document.

3.3.  Signaling

   Both RSVP-TE and LDP, with appropriate extensions, can be used to
   signal ring LSPs.  Details will be given in companion documents.

3.4.  Installing Primary LFIB Entries

   In setting up RL_k, a node R_j sends out two labels: DL_jk to R_j-1
   and UL_jk to R_j+1.  R_j also receives two labels: DL_j+1,k from
   R_j+1, and UL_j-1,k from R_j-1.  R_j can now set up the forwarding
   entries for RL_k.  In the DS direction, R_j swaps incoming label
   DL_jk with DL_j+1,k with next hop R_j+1.  In the US direction, R_j
   swaps incoming label UL_jk with UL_j-1,k with next hop R_j-1.  R_k
   does not install LFIB entries in this manner.

3.5.  Installing FRR LFIB Entries

   At the same time that R_j sets up its DS and US LFIB entries, it can
   also set up the protection forwarding entries for RL_k.  In the DS
   direction, R_j sets up an FRR LFIB entry to swap incoming label DL_jk
   with UL_j-1,k with next hop R_j-1.  In the US direction, R_j sets up
   an FRR LFIB entry to swap incoming label UL_jk with DL_j+1,k with
   next hop R_j+1.  Again, R_k does not install FRR LFIB entries in this
   manner.

3.6.  Protection

   Note that in this scheme, there are no protection LSPs as such -- no
   node or link bypasses, nor detours, nor LFA-type protection.
   Protection is via the "other" direction around the ring, which is why
   ring LSPs are in counter-rotating pairs.

   If a node R_j detects a failure DS from R_j+1, it switches traffic on
   all DS ring LSPs to the US direction using the FRR LFIB entries.
   This switchover can be very fast, as the FRR LFIB entries can be
   preprogrammed.  If the detection is fast too, then traffic loss is
   minimal.

   R_j then sends an indication to R_j-1 that the DS direction is not
   working, so that R_j-1 can similarly switch traffic to the US
   direction.  These indications propagate US until each traffic source
   on the ring uses the US direction.  Thus, within a short period,



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   traffic will be flowing in the optimal path, given that there is a
   failure on the ring.  This contrasts with (say) bypass protection,
   where until the ingress recomputes a new path, traffic will be
   suboptimal.


4.  Security Considerations

   It is not anticipated that either the notion of MPLS rings or the
   extensions to various protocols to support them will cause new
   security loopholes.  As this document is updated, this section will
   also be updated.


5.  IANA Considerations

   There are no requests to IANA for this document.


6.  References

6.1.  Normative References

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

6.2.  Informative References

   [RFC1195]  Callon, R., "Use of OSI IS-IS for routing in TCP/IP and
              dual environments", RFC 1195, December 1990.

   [RFC2328]  Moy, J., "OSPF Version 2", STD 54, RFC 2328, April 1998.

   [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.

   [RFC5036]  Andersson, L., Minei, I., and B. Thomas, "LDP
              Specification", RFC 5036, October 2007.












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Author's Address

   Kireeti Kompella
   Juniper Networks, Inc.
   1194 N.  Mathilda Avenue
   Sunnyvale, CA  94089
   USA

   Email: kireeti.kompella@gmail.com










































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