[Docs] [txt|pdf] [Tracker] [WG] [Email] [Diff1] [Diff2] [Nits] [IPR]

Versions: 00 01 02 03 04 05 06

Network Working Group                                        K. Kompella
Internet-Draft                                          Juniper Networks
Updates: 3209, 3473, 5420                                     M. Hellers
(if approved)                                                       LINX
Intended status: Standards Track                                R. Singh
Expires: September 10, 2015                             Juniper Networks
                                                           March 9, 2015


         Multi-path Label Switched Paths Signaled Using RSVP-TE
                  draft-kompella-mpls-rsvp-ecmp-06.txt

Abstract

   This document describes extensions to Resource ReSerVation Protocol -
   Traffic Engineering for the set up of multi-path Traffic Engineered
   Label Switched Paths (LSPs) in Multi Protocol Label Switching (MPLS)
   and Generalized MPLS networks, i.e., LSPs that conform to traffic
   engineering constraints, but follow multiple independent paths from
   source to destination.

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 September 10, 2015.

Copyright Notice

   Copyright (c) 2015 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



Kompella, et al.       Expires September 10, 2015               [Page 1]


Internet-Draft           Multi-path RSVP-TE LSPs              March 2015


   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 . . . . . . . . . . . . . . . . . . . . . . . . .  3
     1.1.  Terminology  . . . . . . . . . . . . . . . . . . . . . . .  3
     1.2.  Conventions used in this document  . . . . . . . . . . . .  4
   2.  Theory of Operation  . . . . . . . . . . . . . . . . . . . . .  5
     2.1.  Multi-path Label Switched Paths  . . . . . . . . . . . . .  5
     2.2.  ECMP . . . . . . . . . . . . . . . . . . . . . . . . . . .  6
     2.3.  Discussion . . . . . . . . . . . . . . . . . . . . . . . .  8
     2.4.  The Capabilities of TE-based Load Balancing  . . . . . . .  9
   3.  Operation of MLSPs . . . . . . . . . . . . . . . . . . . . . . 10
     3.1.  Signaling MLSPs  . . . . . . . . . . . . . . . . . . . . . 10
       3.1.1.  Indicating Equi-bandwidth (EB) nature  . . . . . . . . 10
     3.2.  Label Allocation . . . . . . . . . . . . . . . . . . . . . 10
     3.3.  Bandwidth Accounting . . . . . . . . . . . . . . . . . . . 10
     3.4.  MLSP Data Plane Actions  . . . . . . . . . . . . . . . . . 11
   4.  Manageability  . . . . . . . . . . . . . . . . . . . . . . . . 13
   5.  Security Considerations  . . . . . . . . . . . . . . . . . . . 14
   6.  Acknowledgments  . . . . . . . . . . . . . . . . . . . . . . . 15
   7.  IANA Considerations  . . . . . . . . . . . . . . . . . . . . . 16
   8.  References . . . . . . . . . . . . . . . . . . . . . . . . . . 17
     8.1.  Normative References . . . . . . . . . . . . . . . . . . . 17
     8.2.  Informative References . . . . . . . . . . . . . . . . . . 17
   Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 19





















Kompella, et al.       Expires September 10, 2015               [Page 2]


Internet-Draft           Multi-path RSVP-TE LSPs              March 2015


1.  Introduction

   In selecting a protocol for setting up and signaling "tunnel" Labeled
   Switched Paths (LSPs) in Multi Protocol Label Switching (MPLS) and
   Generalized MPLS (GMPLS) networks, one first chooses whether one
   wants Equal Cost Multi-Path (ECMP) load balancing or Traffic
   Engineering (TE).  For the former, one uses the Label Distribution
   Protocol (LDP) ([RFC5036]); for the latter, the Resource ReSerVation
   Protocol - Traffic Engineering (RSVP-TE) ([RFC3209]).  [Two other
   criteria, the need for fast protection and the desire for less
   configuration, are no longer the deciding factors they used to be,
   thanks to "IP fast reroute" ([RFC5286]) and "RSVP-TE automesh"
   ([RFC4972])].

   This document describes how one can set up a tunnel LSP that has both
   ECMP and TE characteristics using RSVP-TE.  The techniques described
   in this document can be used to create a "Multipath LSP" (MLSP) to a
   destination, that consists of several "sub-LSPs", each potentially
   taking a different path through the network to the destination.  The
   techniques can also be used to create a single MLSP to multiple
   equivalent destinations (such as equidistant BGP nexthops announcing
   a common set of reachable addresses), such that each destination is
   served by one or more sub-LSPs.

   There are several alternatives to choose from when considering MLSPs.
   One is whether the ingress Label Switching Router (LSR) computes (or
   otherwise obtains) the full path for each sub-LSP, or whether LSRs
   along the various paths can compute paths further downstream (using
   techniques such as "loose hop expansion", as in [RFC5152]).  Another
   is whether the various paths that make up the MLSP have equal cost
   (or distance) from ingress to egress (i.e., ECMP), whether they may
   have differing costs.  Finally, one can choose whether to terminate a
   multi-path LSP on a single egress or on several equivalent egresses.
   For now, the first of each of these alternatives is assumed; future
   work can explore other choices.

1.1.  Terminology

   The term Multipath LSP, or MLSP, will be used to denote the (logical)
   container LSP from an ingress LSR to one or more egress LSR(s).  An
   MLSP is the unit of configuration and management.

   An MLSP consists of one or more "sub-LSPs".  A sub-LSP consists of a
   single path from the ingress of the MLSPs to one of its egresses.  A
   sub-LSP is the unit of signaling of an MLSP.  An Explicit Route
   Object (ERO) will be used to define the path of a sub-LSP.

   The "downstream links" of an MLSP Z at LSR X is the union of the



Kompella, et al.       Expires September 10, 2015               [Page 3]


Internet-Draft           Multi-path RSVP-TE LSPs              March 2015


   downstream links of all sub-LSPs of Z traversing X. Similarly, the
   "upstream links" of an MLSP Z at LSR X is the union of upstream links
   of all sub-LSPs of Z traversing X.

   The agent that takes the configuration parameters of a tunnel and
   computes the corresponding paths is called the Path Computation Agent
   (PCA).  The PCA is responsible for acquiring the tunnel
   configuration, computing the paths of the sub-LSPs, and, if the PCA
   is not co-located with the ingress, informing the ingress about the
   tunnel and the EROs for the sub-LSPs.

1.2.  Conventions used in this document

   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].



































Kompella, et al.       Expires September 10, 2015               [Page 4]


Internet-Draft           Multi-path RSVP-TE LSPs              March 2015


2.  Theory of Operation

2.1.  Multi-path Label Switched Paths

   An MLSP is configured with various constraints associated with TE
   LSPs, such as destination LSR(s), bandwidth (on a per-class basis, if
   desired), link colors, Shared Risk Link Groups, etc.  [Auto-mesh
   techniques ([RFC4972]) can be used to reduce configuration; this is
   not described further here.]  In addition, parameters specifically
   related to MLSPs, such as how many (or the maximum number of) sub-
   LSPs to create, whether traffic should be split equally across sub-
   LSPs or not, etc. may also be specified.  This configuration lives on
   the PCA, which is responsible for computing the paths (i.e., the
   EROs) for the various sub-LSPs.  The PCA informs the ingress LSR
   about the MLSP and the constituent sub-LSPs, including EROs and
   bandwidths.

   The PCA uses the configuration parameters to decide how many sub-LSPs
   to compute for this MLSP, what paths they should take, and how much
   bandwidth each sub-LSP is responsible for.  Each sub-LSP MUST meet
   all the constraints of the MLSP (except bandwidth).  The bandwidths
   (per-class, if applicable) of all the sub-LSPs MUST add up to the
   bandwidth of the MLSP.  A Path Computation Element ([RFC4655]) that
   is multi-path LSP-aware may be used as the PCA.

   Having computed (or otherwise obtained) the paths of all the sub-
   LSPs, the ingress A then signals the MLSP by signaling all the
   individual sub-LSPs across the MPLS/GMPLS network.  To do this, the
   ingress first picks an MLSP ID, a 16-bit number that is unique in the
   context of the ingress.  This ID is used in an ASSOCIATION object
   that is placed in each sub-LSP to let all transit LSRs know that the
   sub-LSPs belong to the same MLSP.

   If multiple sub-LSPs of the same MLSP pass through LSR Y, and Y has
   downstream links YP, YQ and YR for the various sub-LSPs, then Y has
   to load balance incoming traffic for the MLSP across the three
   downstream links in proportion to the sum of the bandwidths of the
   sub-LSPs going to each downstream (see Figure 1).

   One must distinguish carefully between the signaled bandwidth of a
   sub-LSP, a static value capturing the expected or maximum traffic on
   the sub-LSP, and the instantaneous traffic received on a sub-LSP, a
   constantly varying quantity.  Suppose there are three sub-LSPs
   traversing Y, with bandwidths 10Gbps, 20Gbps and 30Gbps, going to P,
   Q and R respectively.  Suppose further Y receives some traffic over
   each of these sub-LSPs.  Y must balance this received traffic over
   the three downstream links YP, YQ and YR in the ratio 1:2:3.




Kompella, et al.       Expires September 10, 2015               [Page 5]


Internet-Draft           Multi-path RSVP-TE LSPs              March 2015


2.2.  ECMP

                          ------------- M -----
                         /                      \
                        /           --- P --     \
                       /           /         \    \
                      A --- X --- Y --- Q --- T --- B
                             \     \              / |
                              \     --- R -------   |
                               \                    |
                                ------- S ----------

   An example network illustrating ECMP.  Assume that paths AMB, AXYPTB,
   AXYQTB, AXYRB and AXSB all have the same path length (cost).

                    Figure 1: Example Network Topology

   In an IP or LDP network, incoming traffic arriving at A headed for B
   will be split equally between M and X at A. Similarly, traffic for B
   arriving at Y will be split equally among P, Q and R. If the traffic
   arriving at A for B is 120Gbps, then the AMB path will carry 60Gbps,
   the paths AXYPTB, AXYQTB and AXYRB will each carry 10Gbps, and the
   AXSB path will carry 30Gbps.  We'll call this "IP-style" load
   balancing.

   Note: all load balancing is subject to the overriding requirement of
   mapping the same "flow" to the same downstream.  (What constitutes a
   "flow" is beyond the scope of this document.)  This requirement takes
   precedence over all attempts to balance traffic among downstreams.
   Thus, the statements above (e.g., "the AMB path will carry 60Gbps")
   are to be interpreted as ideal targets, not hard requirements, of
   load balancing.

   One can simulate the IP or LDP ECMP behavior with TE-based ECMP by
   creating an MLSP with five sub-LSPs S1 through S5 taking paths AMB,
   AXYPTB, AXYQTB, AXYRB and AXSB, with bandwidths 60Gbps, 10Gbps,
   10Gbps, 10Gbps and 30Gbps, respectively.

   With such an arrangement, the MB link carries 60Gbps while the RB
   link carries just 10Gbps.  If one wishes instead to carry equal
   amounts of traffic on the links incoming to B, then one could arrange
   the sub-LSPs S1 to S5 to have bandwidths 30Gbps, 15Gbps, 15Gbps,
   30Gbps and 30Gbps, respectively.  In this case, the bandwidth on each
   of the four links going to B is 30Gbps, illustrating some of the
   capabilities of TE-based ECMP.

   Staying with this example, A has one sub-LSP of bandwidth 30Gbps to M
   and four sub-LSPs of total bandwidth 90Gbps through X. Thus, A should



Kompella, et al.       Expires September 10, 2015               [Page 6]


Internet-Draft           Multi-path RSVP-TE LSPs              March 2015


   load balance traffic in the ratio 1:3 between the AM and the AX
   links.  Similarly, X has three sub-LSPs of total bandwidth 60Gbps to
   Y and one sub-LSP of bandwidth 30Gbps to S, so X should load balance
   traffic 2:1 between Y and S. Y has a sub-LSP of bandwidth 15Gbps to
   each of P and Q and one sub-LSP of bandwidth 30Gbps to R, so Y should
   load balance traffic 1:1:2 among P, Q and R, respectively.  Thus, in
   general, TE-based ECMP does not assume equal distribution of traffic
   among downstream LSRs, unlike IP- or LDP-style ECMP.

                                          ---U---
                                         |       |
                           --L--   --P-- | --V-- |
                          /     \ /     \|/     \|
                         A       S---Q---T---W---B
                          \     / \     /|\     /|
                           --M--   --R-- | --X-- |
                                         |       |
                                          ---Y---

   Another example network illustrating 30 ECMP paths between A and B.

                    Figure 2: Another Network Topology

   In Figure 2, there are potentially 2x3x5=30 ECMP paths between A and
   B. With IP or LDP, exploiting all these paths is straightforward, and
   doesn't need a lot of state.  With an MLSP as seen so far, this would
   require 30 sub-LSPs to achieve equivalent load balancing.  This
   suggests that a different approach is needed to efficiently achieve
   IP-style load balancing with TE LSPs.  To this end, we introduce the
   notion of "equi-bandwidth" (EB) sub-LSPs and EB MLSPs.  A sub-LSP is
   equi-bandwidth if its "E" bit is set (see Section 3.1.1).  An MLSP is
   equi-bandwidth if all of its sub-LSPs are equi-bandwidth.

   If a set of EB sub-LSPs of the same MLSP traverse an LSR S, say to
   downstream links SP, SQ and SR, then S MUST attempt to load balance
   traffic received on these EB sub-LSPs equally among the links SP, SQ
   and SR, independent of how many sub-LSPs go over each of these links.
   Furthermore, S MUST redistribute traffic received from each of its
   upstream LSRs, and SHOULD redistribute all traffic received from
   upstream as a whole.  One can do the former by signaling the same
   label to each of its upstream LSRs; one can do the latter by
   signaling the same label to all upstream LSRs (see Section 3.2).  For
   example, in Figure 2, if L sends 12Gbps of traffic to S and M sends
   18Gbps to S, S can redistribute L's traffic by sending 4Gbps to each
   of P, Q and R; and can similarly send 6Gbps of M's traffic to each of
   P, Q and R. Alternatively, S can load balance the aggregate 30Gbps of
   traffic received from L and M to each of P, Q and R, thus sending
   10Gbps to each.  EB sub-LSPs have an added benefit of not requiring



Kompella, et al.       Expires September 10, 2015               [Page 7]


Internet-Draft           Multi-path RSVP-TE LSPs              March 2015


   unequal load balancing across links, which may pose problems for some
   hardware.

   Given the notion of EB sub-LSPs and EB MLSPs, A can signal an EB MLSP
   Z comprised of five EB sub-LSPs E1 through E5 with the following
   paths: ALSPTUB, AMSQTVB, ALSRTWB, AMSPTXB and ALSQTYB (respectively).
   Then, A has two downstream links for the five sub-LSPs, AL and AM,
   between which A will load balance equally.  Similarly, S has three
   downstream links, SP, SQ and SR; and T has five downstreams, TU, TV,
   TW, TX and TY.  Thus the load balancing behavior of the MLSP will
   replicate IP load balancing.  The state required for an EB MLSP to
   achieve IP-style load balancing is somewhat greater than for LDP
   LSPs, but significantly less than that for multiple "regular" TE
   LSPs, or for a non-EB MLSP.

2.3.  Discussion

   Some of the power of TE-based ECMP was illustrated in the above
   examples.  Another is ability to request that all sub-LSPs avoid
   links colored red.  If in the example network in Figure 1, the QT
   link is colored red but all other links are not, then there are four
   ECMP paths that satisfy these constraints, and the traffic
   distribution among them will naturally be different than it would
   without the link color constraint.

   One can also ask whether an MLSP with sub-LSPs is any better than N
   "regular" LSPs from the same ingress to the same egress.  Here are
   some benefits of an MLSP:

   1.  With an MLSP, there is a single entity to provision, manage and
       monitor, versus N separate entities in the case of LSPs.  A
       consequence of this is that with an MLSP, changes in topology can
       be dealt with easily and autonomously by the ingress LSR, by
       adding, changing or removing sub-LSPs to rebalance traffic, while
       maintaining the same TE constraints.  With individual LSPs, such
       changes would require changes in configuration, and thus are
       harder to automate.

   2.  An ingress LSR, knowing that an MLSP is for load balancing, can
       decide on an optimum number of sub-LSPs, and place them
       appropriately across the network to optimize load balancing.  On
       the other hand, an ingress LSR asked to create N independent LSPs
       will do so without regard to whether N is a good number of equal
       cost paths, and, more importantly, may place several of the N
       LSPs on the same path, defeating the purpose of load balancing.

   3.  The EB sub-LSP mechanism will, in many cases, result in far fewer
       sub-LSPs than independent LSPs and thus less control plane state.



Kompella, et al.       Expires September 10, 2015               [Page 8]


Internet-Draft           Multi-path RSVP-TE LSPs              March 2015


   4.  Finally, an MLSP will usually have less data plane state than N
       independent LSPs: whenever multiple sub-LSPs traverse a link, a
       single label will be used for all of them, whereas if multiple
       LSPs traverse a link, each will need a separate label.

2.4.  The Capabilities of TE-based Load Balancing

   Definition: Let G=(V, E) be a directed graph (or network), and let A
   and B in V be two nodes in G. Let T be the traffic arriving at A
   destined for B. T is said to be "IP-style" load balanced if for every
   node X on a shortest path from A to B, the portion of T arriving at X
   is split equally among all nodes Yi that are adjacent to X and are on
   a shortest path from X to B.

   Theorem: An MLSP can accurately mimic IP-style load balancing between
   any two nodes in any network.

   Proof: left to the reader.

   Corollary: MLSPs provide a strictly more powerful load balancing
   mechanism than IP-style load balancing.






























Kompella, et al.       Expires September 10, 2015               [Page 9]


Internet-Draft           Multi-path RSVP-TE LSPs              March 2015


3.  Operation of MLSPs

3.1.  Signaling MLSPs

   Sub-LSPs of an MLSP are tied together using ASSOCIATION objects.
   ASSOCIATION objects have a new Association Type for MLSPs (TBD).  The
   Association ID is chosen by the ingress of the MLSP; the Association
   Source is the loopback address of the ingress of the MLSP.  All sub-
   LSPs containing an ASSOCIATION object with a given Association Source
   and Type belong to the same MLSP.

3.1.1.  Indicating Equi-bandwidth (EB) nature

   A sub-LSP is considered equi-bandwidth if its Path message carries
   the optional LSP_ATTRIBUTES object ([RFC5420]) with an EBC (equi-
   bandwidth capability) flag in the Attribute Flags TLV.  The bit
   number for the EBC flag is yet to be assigned by IANA.

3.2.  Label Allocation

   A LSR S that receives Path messages for several sub-LSPs of the same
   MLSP from the same upstream LSR SHOULD allocate the same label for
   all the sub-LSPs.  This simplifies load balancing for the aggregate
   traffic on those sub-LSPs.  If the sub-LSPs are EB sub-LSPs, then S
   SHOULD allocate the same label for all EB sub-LSPs of the same MLSP
   that pass through S, regardless of which upstream LSR they come from.
   This allows S to load balance the aggregate traffic received on the
   MLSP, as all the MLSP traffic arrives at S with the same label.
   However, an LSR that can achieve the load balancing requirements
   independent of label allocation strategies is free to do so.

3.3.  Bandwidth Accounting

   Since MLSPs are traffic engineered, there needs to be strict
   bandwidth accounting, or admission control, on every link that an
   MLSP traverses.  For non-EB sub-LSPs, this is straightforward, and
   analogous to regular TE LSPs.  However, for EB sub-LSPs, two new
   procedures are needed, one for signaling bandwidth, and the other for
   admission control.  First, for a given MLSP Z, an LSR X MUST ensure
   (via signaling) that the total incoming bandwidth of EB sub-LSPs of
   MLSP Z is divided equally among all the downstream links of X which
   at least one of the EB sub-LSPs traverses.  Second, LSR X MUST ensure
   that, for each upstream link of X, there is sufficient bandwidth to
   accommodate all EB sub-LSPs of MLSP Z that traverse that link.

   Let's take the example of Figure 2, with MLSP Z having five EB sub-
   LSPs E1 to E5, and say that MLSP Z is configured with a bandwidth of
   30Gbps.  Here are some of the steps involved.



Kompella, et al.       Expires September 10, 2015              [Page 10]


Internet-Draft           Multi-path RSVP-TE LSPs              March 2015


   1.  LSR A, being the ingress, has no upstream links.  A has two
       downstream links, AL and AM.  Three EB sub-LSPs of MLSP Z
       traverse AL, and two traverse AM.  A MUST signal a total of
       15Gbps for the sub-LSPs to L, and a total of 15Gbps for the sub-
       LSPs to M. The required bandwidth may be divided up among the
       sub-LSPs to L (similarly, to M) in any manner so long as the
       total is 15Gbps.  For example, A can signal sub-LSP E1 with
       15Gbps, and sub-LSPs E3 and E5 with 0 bandwidth.

   2.  LSR L has one upstream link AL with three EB sub-LSPs with a
       total bandwidth of 15Gbps.  L MUST ensure that 15Gbps is
       available for the AL link.  If this bandwidth is not available, L
       MUST send a PathErr on ALL of the EB sub-LSPs on the AL link.
       Let's assume that the AL link has sufficient bandwidth.

   3.  Next, it is up to L to decide how to divide the incoming 15Gbps
       among the three downstream EB sub-LSPs to S. Say L signals sub-
       LSP E1 with 15Gbps, and the others with 0 bandwidth.

   4.  LSR S has two upstream links: LS with three EB sub-LSPs with a
       total bandwidth of 15Gbps, and MS with two EB sub-LSPs with a
       total bandwidth of 15Gbps.  S MUST ensure that 15Gbps is
       available for each of the LS and MS links.  S has thus a total
       incoming bandwidth of 30Gbps on MLSP Z. S has to divide this
       equally among its downstream links SP, SQ and SR, yielding 10Gbps
       each.  S MUST ensure that the total bandwidth requested on the SP
       link for sub-LSPs E1 and E4 is 10Gbps.  S may choose to signal
       these sub-LSPs with 5Gbps each.  Similarly for the SQ and SR
       links.

   There are two important points to note here.  One is that the
   bandwidth reservation (TSpec) for a given EB sub-LSP can (and usually
   will) change hop-by-hop.  The second is that as new EB sub-LSPs are
   signaled for an MLSP, the bandwidth reservations for existing EB sub-
   LSPs belonging to the same MLSP may have to be updated.  To minimize
   these updates, it is RECOMMENDED that the first EB sub-LSP on a link
   be signaled with the total required bandwidth (as far as is known),
   and later sub-LSPs on the same link be signaled with 0 bandwidth.

3.4.  MLSP Data Plane Actions

   Traffic intended to be sent over an MLSP is determined at the ingress
   LSR by means outside the scope of this document, and at transit LSRs
   by the label(s) assigned by the transit LSR to its upstream LSRs.  In
   the case of non-EB sub-LSPs, this traffic is load balanced across
   downstream links in the ratio of the bandwidths of the sub-LSPs that
   comprise the MLSP.  In the case of EB sub-LSPs, the traffic belonging
   to an MLSP from an upstream LSR (or better still, the aggregate



Kompella, et al.       Expires September 10, 2015              [Page 11]


Internet-Draft           Multi-path RSVP-TE LSPs              March 2015


   traffic for the MLSP from all upstream LSRs) is load balanced equally
   among all downstream links.

   As noted above, the overriding concern is that flows are mapped to
   the same downstream link (except when the MLSP or some constituent
   sub-LSPs are changing); this is typically done by hashing fields that
   define a flow, and mapping hash results to different downstream LSRs.
   Hash-based load balancing typically assumes that the numbers of flows
   is sufficiently large and the bandwidth per flow is reasonably well-
   balanced so that the results of hashing yields reasonable traffic
   distribution.

   Entropy labels ([RFC6790] and [RFC6391]) can be used to improve load
   balancing at intermediate nodes.





































Kompella, et al.       Expires September 10, 2015              [Page 12]


Internet-Draft           Multi-path RSVP-TE LSPs              March 2015


4.  Manageability

   TBD
















































Kompella, et al.       Expires September 10, 2015              [Page 13]


Internet-Draft           Multi-path RSVP-TE LSPs              March 2015


5.  Security Considerations

   This document introduces no new security concerns in the setup and
   signaling of LSPs using RSVP-TE, or in the use of the RSVP protocol.
   [RFC2205] specifies the message integrity mechanisms for RSVP
   signaling.  These mechanisms apply to RSVP-TE signaling of MLSPs
   described in this document, and are highly recommended pending newer
   integrity mechanisms for RSVP.











































Kompella, et al.       Expires September 10, 2015              [Page 14]


Internet-Draft           Multi-path RSVP-TE LSPs              March 2015


6.  Acknowledgments

   The author would like to thank the Routing Protocol group at Juniper
   Networks for their questions, comments and encouragement for this
   proposal.  While many participated, special thanks go to Yakov
   Rekhter, John Drake and Rahul Aggarwal.  Many thanks too to John for
   suggesting the use of ASSOCIATION objects.












































Kompella, et al.       Expires September 10, 2015              [Page 15]


Internet-Draft           Multi-path RSVP-TE LSPs              March 2015


7.  IANA Considerations

   IANA is requested to assign the following:

   A new Association Type for MLSP.  This Association Type is to be used
   for ASSOCIATION objects with C-Type 1 (IPv4 Source) and 2 (IPv6
   Source).

   A new flag in the Attribute Flags TLV in the LSP_ATTRIBUTES object
   ([RFC5420]: a bit number for the EBC (equi-bandwidth capability) to
   indicate that a specific sub-LSP is an equi-bandwidth sub-LSP.








































Kompella, et al.       Expires September 10, 2015              [Page 16]


Internet-Draft           Multi-path RSVP-TE LSPs              March 2015


8.  References

8.1.  Normative References

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

   [RFC2205]  Braden, B., Zhang, L., Berson, S., Herzog, S., and S.
              Jamin, "Resource ReSerVation Protocol (RSVP) -- Version 1
              Functional Specification", RFC 2205, September 1997.

   [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.

   [RFC4875]  Aggarwal, R., Papadimitriou, D., and S. Yasukawa,
              "Extensions to Resource Reservation Protocol - Traffic
              Engineering (RSVP-TE) for Point-to-Multipoint TE Label
              Switched Paths (LSPs)", RFC 4875, May 2007.

   [RFC5420]  Farrel, A., Papadimitriou, D., Vasseur, JP., and A.
              Ayyangarps, "Encoding of Attributes for MPLS LSP
              Establishment Using Resource Reservation Protocol Traffic
              Engineering (RSVP-TE)", RFC 5420, February 2009.

8.2.  Informative References

   [RFC4655]  Farrel, A., Vasseur, J., and J. Ash, "A Path Computation
              Element (PCE)-Based Architecture", RFC 4655, August 2006.

   [RFC4972]  Vasseur, JP., Leroux, JL., Yasukawa, S., Previdi, S.,
              Psenak, P., and P. Mabbey, "Routing Extensions for
              Discovery of Multiprotocol (MPLS) Label Switch Router
              (LSR) Traffic Engineering (TE) Mesh Membership", RFC 4972,
              July 2007.

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

   [RFC5152]  Vasseur, JP., Ayyangar, A., and R. Zhang, "A Per-Domain
              Path Computation Method for Establishing Inter-Domain
              Traffic Engineering (TE) Label Switched Paths (LSPs)",
              RFC 5152, February 2008.

   [RFC5226]  Narten, T. and H. Alvestrand, "Guidelines for Writing an
              IANA Considerations Section in RFCs", BCP 26, RFC 5226,
              May 2008.




Kompella, et al.       Expires September 10, 2015              [Page 17]


Internet-Draft           Multi-path RSVP-TE LSPs              March 2015


   [RFC5286]  Atlas, A. and A. Zinin, "Basic Specification for IP Fast
              Reroute: Loop-Free Alternates", RFC 5286, September 2008.

   [RFC6391]  Bryant, S., Filsfils, C., Drafz, U., Kompella, V., Regan,
              J., and S. Amante, "Flow-Aware Transport of Pseudowires
              over an MPLS Packet Switched Network", RFC 6391,
              November 2011.

   [RFC6790]  Kompella, K., Drake, J., Amante, S., Henderickx, W., and
              L. Yong, "The Use of Entropy Labels in MPLS Forwarding",
              RFC 6790, November 2012.








































Kompella, et al.       Expires September 10, 2015              [Page 18]


Internet-Draft           Multi-path RSVP-TE LSPs              March 2015


Authors' Addresses

   Kireeti Kompella
   Juniper Networks
   1194 N. Mathilda Ave.
   Sunnyvale, CA  94089
   US

   Email: kireeti.kompella@gmail.com


   Mike Hellers
   LINX

   Email: mikeh@linx.net


   Ravi Singh
   Juniper Networks

   Email: ravis@juniper.net






























Kompella, et al.       Expires September 10, 2015              [Page 19]


Html markup produced by rfcmarkup 1.123, available from https://tools.ietf.org/tools/rfcmarkup/