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Internet Engineering Task Force (IETF)                     C. VillamizarRequest for Comments: 7190             Outer Cape Cod Network ConsultingCategory: Informational                                       March 2014ISSN: 2070-1721Use of Multipath with MPLS and MPLS Transport Profile (MPLS-TP)Abstract   Many MPLS implementations have supported multipath techniques, and   many MPLS deployments have used multipath techniques, particularly in   very high-bandwidth applications, such as provider IP/MPLS core   networks.  MPLS Transport Profile (MPLS-TP) has strongly discouraged   the use of multipath techniques.  Some degradation of MPLS-TP   Operations, Administration, and Maintenance (OAM) performance cannot   be avoided when operating over many types of multipath   implementations.   Using MPLS Entropy Labels (RFC 6790), MPLS Label Switched Paths   (LSPs) can be carried over multipath links while also providing a   fully MPLS-TP-compliant server layer for MPLS-TP LSPs.  This document   describes the means of supporting MPLS as a server layer for MPLS-TP.   The use of MPLS-TP LSPs as a server layer for MPLS LSPs is also   discussed.Status of This Memo   This document is not an Internet Standards Track specification; it is   published for informational purposes.   This document is a product of the Internet Engineering Task Force   (IETF).  It represents the consensus of the IETF community.  It has   received public review and has been approved for publication by the   Internet Engineering Steering Group (IESG).  Not all documents   approved by the IESG are a candidate for any level of Internet   Standard; seeSection 2 of RFC 5741.   Information about the current status of this document, any errata,   and how to provide feedback on it may be obtained athttp://www.rfc-editor.org/info/rfc7190.Villamizar                    Informational                     [Page 1]

RFC 7190               MPLS and MPLS-TP Multipath             March 2014Copyright Notice   Copyright (c) 2014 IETF Trust and the persons identified as the   document authors.  All rights reserved.   This document is subject toBCP 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 Contents1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .22.  Definitions . . . . . . . . . . . . . . . . . . . . . . . . .43.  MPLS as a Server Layer for MPLS-TP  . . . . . . . . . . . . .53.1.  MPLS-TP Forwarding and Server-Layer Requirements  . . . .53.2.  Methods of Supporting MPLS-TP Client LSPs over MPLS . . .74.  MPLS-TP as a Server Layer for MPLS  . . . . . . . . . . . . .115.  Summary . . . . . . . . . . . . . . . . . . . . . . . . . . .116.  Acknowledgements  . . . . . . . . . . . . . . . . . . . . . .127.  Security Considerations . . . . . . . . . . . . . . . . . . .138.  References  . . . . . . . . . . . . . . . . . . . . . . . . .138.1.  Normative References  . . . . . . . . . . . . . . . . . .138.2.  Informative References  . . . . . . . . . . . . . . . . .131.  Introduction   Today the requirement to handle large aggregations of traffic can be   met by a number of techniques that we will collectively call   "multipath".  Multipath applied to parallel links between the same   set of nodes includes Ethernet Link Aggregation [IEEE-802.1AX], link   bundling [RFC4201], or other aggregation techniques, some of which   could be vendor specific.  Multipath applied to diverse paths rather   than parallel links includes Equal-Cost Multipath (ECMP) as applied   to OSPF, IS-IS, or BGP, and equal-cost Label Switched Paths (LSPs).   Some vendors support load splitting across equal-cost MPLS LSPs where   the load is split proportionally to the reserved bandwidth of the set   of LSPs.RFC 5654 requirement 33 requires the capability to carry a client   MPLS Transport Profile (MPLS-TP) or MPLS layer over a server MPLS-TP   or MPLS layer [RFC5654].  This is possible in all cases with one   exception.  When an MPLS LSP exceeds the capacity of any singleVillamizar                    Informational                     [Page 2]

RFC 7190               MPLS and MPLS-TP Multipath             March 2014   component link, it MAY be carried by a network using multipath   techniques, but it SHOULD NOT be carried by a single MPLS-TP LSP due   to the inherent MPLS-TP capacity limitation imposed by MPLS-TP   Operations, Administration, and Maintenance (OAM) fate-sharing   constraints and MPLS-TP Loss Measurement OAM packet-ordering   constraints (seeSection 3.1).  Instead, multiple MPLS-TP LSPs SHOULD   be used to carry a large MPLS LSP (seeSection 4).   The term "composite link" is more general than terms such as "link   aggregation" (which is specific to Ethernet) or "ECMP" (which implies   equal-cost paths within a routing protocol).  The use of the term   "composite link" here is consistent with the broad definition in   [ITU-T.G.800].  Multipath is very similar to composite link as   defined by ITU-T but specifically excludes inverse multiplexing.   MPLS LSPs today are able to function as a server layer and carry   client MPLS LSPs.  When control-plane signaling is used, forwarding   adjacency (FA) advertisements are used to inform the set of Label   Switching Routers (LSRs) of Packet Switching Capable (PSC) LSPs   within the MPLS topology [RFC4206].  Client MPLS LSP at a higher   layer (lower PSC number) may signal their intention to use PSC LSPs   as hops in the RSVP-TE Explicit Route Object (ERO).  LSRs with no   explicit support forRFC 4206 see the PSC LSPs as ordinary links and   therefore use them.   An MPLS LSP that has been set up using RSVP-TE appears to its ingress   LSR as a viable IP next hop to a distant LSR.  If LDP is used and   bidirectional RSVP-TE LSP connectivity is available, then LDP   signaling can be set up among the RSVP-TE LSP endpoints, and LDP can   make use of the RSVP-TE LSP as an LDP hop.  This is another form of   existing MPLS-in-MPLS use.  MPLS LSPs may also make use of hierarchy   that is configured through the management plane rather than signaled   using RSVP-TE.   These existing forms of MPLS-in-MPLS may traverse multipath hops such   as Ethernet Link Aggregation Group (LAG) [IEEE-802.1AX] or MPLS Link   Bundling [RFC4201].  MPLS-TP brings with it a new set of requirements   not considered in past deployments of the various forms of MPLS-in-   MPLS where multipath was in use.  This document merely discusses use   of existing forwarding and protocol mechanisms that can support the   case where either the client-layer LSPs or the server-layer LSPs are   MPLS-TP and where multipath is used.Villamizar                    Informational                     [Page 3]

RFC 7190               MPLS and MPLS-TP Multipath             March 20142.  Definitions   Please refer to the terminology related to multipath introduced in   [ADV-MULTIPATH-REQ].  The following additional terms are used in this   document; related terms are grouped together.   Link Bundle       Link bundling is a multipath technique specific to MPLS       [RFC4201].  Link bundling supports two modes of operations.       Either an LSP can be placed on one component link of a link       bundle, or an LSP can be load-split across all members of the       bundle.  There is no signaling defined that allows a per-LSP       preference regarding load split, therefore whether to load split       is generally configured per bundle and applied to all LSPs across       the bundle.   All-Ones Component       Within the context of link bundling, [RFC4201] defines a special       case where the same label is to be valid across all component       links.  This case is indicated in signaling by a bit value of       "all ones" when identifying a component link.  Following the       publication ofRFC 4201, for brevity this special case has been       referred to as the "all-ones component".   Equal-Cost Multipath (ECMP)       Equal-Cost Multipath (ECMP) is a specific form of multipath in       which the costs of the links or paths must be equal in a given       routing protocol.  The load may be split equally across all       available links (or available paths), or the load may be split       proportionally to the capacity of each link (or path).   Loop-Free Alternate Paths (LFA)       "Loop-free alternate paths" (LFA) are defined inSection 5.2 of       RFC 5714 [RFC5714] as follows: "Such a path exists when a direct       neighbor of the router adjacent to the failure has a path to the       destination that can be guaranteed not to traverse the failure."       Further detail can be found in [RFC5286].  LFA as defined for IP       Fast Reroute (IPFRR) can be used to load balance by relaxing the       equal-cost criteria of ECMP, though IPFRR defined LFA for use in       selecting protection paths.  When used with IP, proportional       split is generally not used.  LFA use in load balancing is       implemented by some vendors, though it may be rare or non-       existent in deployments.Villamizar                    Informational                     [Page 4]

RFC 7190               MPLS and MPLS-TP Multipath             March 2014   Link Aggregation       The term "link aggregation" generally refers to Ethernet Link       Aggregation as defined by [IEEE-802.1AX].  Ethernet Link       Aggregation defines a Link Aggregation Control Protocol (LACP)       which coordinates inclusion of Link Aggregation Group (LAG)       members in the LAG.   Link Aggregation Group (LAG)       A group of physical Ethernet interfaces that are treated as a       logical link when using Ethernet Link Aggregation is referred to       as a Link Aggregation Group (LAG).   LAG Member       Ethernet Link Aggregation as defined in [IEEE-802.1AX] refers to       an individual link in a LAG as a LAG member.  A LAG member is a       component link.  An Ethernet LAG is a composite link.  IEEE does       not use the terms "composite link" or "component link".   A small set of requirements are discussed.  These requirements make   use of keywords such as MUST and SHOULD as described in [RFC2119].3.  MPLS as a Server Layer for MPLS-TP   An MPLS LSP may be used as a server layer for MPLS-TP LSPs as long as   all MPLS-TP requirements are met.Section 3.1 reviews the basis for   requirements of a server layer that supports MPLS-TP as a client   layer.  Key requirements include OAM "fate-sharing" and that packets   within an MPLS-TP LSP (including both payload and OAM packets) not be   reordered.Section 3.2 discusses implied requirements where MPLS is   the server layer for MPLS-TP client LSPs and describes a set of   solutions that use existing MPLS mechanisms.3.1.  MPLS-TP Forwarding and Server-Layer Requirements   [RFC5960] defines the data-plane requirements for MPLS-TP.  Two very   relevant paragraphs inSection 3.1.1 ("LSP Packet Encapsulation and   Forwarding") are the following:RFC 5960, Section 3.1.1, Paragraph 3       Except for transient packet reordering that may occur, for       example, during fault conditions, packets are delivered in order       on L-LSPs, and on E-LSPs within a specific ordered aggregate.Villamizar                    Informational                     [Page 5]

RFC 7190               MPLS and MPLS-TP Multipath             March 2014RFC 5960, Section 3.1.1, Paragraph 6       Equal-Cost Multi-Path (ECMP) load-balancing MUST NOT be performed       on an MPLS-TP LSP.  MPLS-TP LSPs as defined in this document MAY       operate over a server layer that supports load-balancing, but       this load-balancing MUST operate in such a manner that it is       transparent to MPLS-TP.  This does not preclude the future       definition of new MPLS-TP LSP types that have different       requirements regarding the use of ECMP in the server layer.[RFC5960], Section 3.1.1, Paragraph 3 requires that packets within a   specific ordered aggregate be delivered in order.  This same   requirement is already specified by Differentiated Services   [RFC2475].[RFC5960], Section 3.1.1, Paragraph 6 explicitly allows a   server layer to use ECMP, provided that it is transparent to the   MPLS-TP client layer.   [RFC6371] adds a requirement for data traffic and OAM traffic "fate-   sharing".  The following paragraph inSection 1 ("Introduction")   summarizes this requirement.RFC 6371, Section 1, Paragraph 7       OAM packets that instrument a particular direction of a transport       path are subject to the same forwarding treatment (i.e., fate-       share) as the user data packets and in some cases, where       Explicitly TC-encoded-PSC LSPs (E-LSPs) are employed, may be       required to have common per-hop behavior (PHB) Scheduling Class       (PSC) End-to-End (E2E) with the class of traffic monitored.  In       case of Label-Only-Inferred-PSC LSP (L-LSP), only one class of       traffic needs to be monitored, and therefore the OAM packets have       common PSC with the monitored traffic class.   [RFC6371] does not prohibit multilink techniques inSection 4.6   ("Fate-Sharing Considerations for Multilink"), where multilink is   defined as Ethernet Link Aggregation and the use of Link Bundling for   MPLS, but it does declare that such a network would be only partially   MPLS-TP compliant.  The characteristic that is to be avoided is   contained in the following sentence in that section.RFC 6371, Section 4.6, Paragraph 1, last sentence       These techniques frequently share the characteristic that an LSP       may be spread over a set of component links and therefore be       reordered, but no flow within the LSP is reordered (except when       very infrequent and minimally disruptive load rebalancing       occurs).   A declaration that implies that Link Bundling for MPLS yields a   partially MPLS-TP-compliant network is perhaps overstated since only   the Link Bundling all-ones component link has this characteristic.Villamizar                    Informational                     [Page 6]

RFC 7190               MPLS and MPLS-TP Multipath             March 2014   [RFC6374] defines a direct Loss Measurement (LM) where LM OAM packets   cannot be reordered with respect to payload packets.  This will   require that payload packets themselves not be reordered.  The   following paragraph inSection 2.9.4 ("Equal Cost Multipath") gives   the reason for this restriction.RFC 6374, Section 2.9.4, Paragraph 2       The effects of ECMP on loss measurement will depend on the LM       mode.  In the case of direct LM, the measurement will account for       any packets lost between the sender and the receiver, regardless       of how many paths exist between them.  However, the presence of       ECMP increases the likelihood of misordering both of LM messages       relative to data packets and of the LM messages themselves.  Such       misorderings tend to create unmeasurable intervals and thus       degrade the accuracy of loss measurement.  The effects of ECMP       are similar for inferred LM, with the additional caveat that,       unless the test packets are specially constructed so as to probe       all available paths, the loss characteristics of one or more of       the alternate paths cannot be accounted for.3.2.  Methods of Supporting MPLS-TP Client LSPs over MPLS   Supporting MPLS-TP LSPs over a fully MPLS-TP conformant MPLS LSP   server layer where the MPLS LSPs are making use of multipath requires   special treatment of the MPLS-TP LSPs such that those LSPs meet MPLS-   TP forwarding requirements (seeSection 3.1).  This implies the   following brief set of requirements.   MP#1  It MUST be possible for a midpoint MPLS-TP Label Switching         Router (LSR) that is serving as ingress to a server-layer MPLS         LSP to identify MPLS-TP LSPs, so that MPLS-TP forwarding         requirements can be applied, or to otherwise accommodate the         MPLS-TP forwarding requirements.   MP#2  The ability to completely exclude MPLS-TP LSPs from the         multipath hash and load split SHOULD be supported.  If the         selected component link no longer meets requirements, an LSP is         considered down, which may trigger protection and/or may         require that the ingress LSR select a new path and signal a new         LSP.   MP#3  It SHOULD be possible to ensure that MPLS-TP LSPs will not be         moved to another component link as a result of a load-         rebalancing operation for multipath.  If the selected component         link no longer meets requirements, another component link may         be selected; however, a change in path SHOULD NOT occur solely         for load balancing.Villamizar                    Informational                     [Page 7]

RFC 7190               MPLS and MPLS-TP Multipath             March 2014   MP#4  Where a Resource Reservation Protocol - Traffic Engineering         (RSVP-TE) control plane is used, it MUST be possible for an         ingress LSR that is setting up an MPLS-TP or an MPLS LSP to         determine at path selection time whether a link or Forwarding         Adjacency (FA; see [RFC4206]) within the topology can support         the MPLS-TP requirements of the LSP.   The reason for requirement MP#1 may not be obvious.  An MPLS-TP LSP   may be aggregated along with other client LSPs by a midpoint LSR into   a very large MPLS server-layer LSP, as would be the case in a core-   node-to-core-node MPLS LSP between major cities.  In this case, the   ingress of the MPLS LSP, being a midpoint LSR for a set of client   LSPs, has no signaling mechanism that can be used to determine   whether one of its specific client LSPs is using MPLS or MPLS-TP.   Multipath load splitting can be avoided for MPLS-TP LSPs if at the   MPLS server-layer LSP ingress LSR an Entropy Label Indicator (ELI)   and Entropy Label (EL) are added to the label stack by the midpoint   LSR for the client MPLS-TP LSP, at the ingress of the MPLS LSP   [RFC6790].  For those client LSPs that are MPLS-TP LSPs, a single   per-LSP EL value must be chosen.  For those client LSPs that are MPLS   LSPs, per-packet entropy below the top label must, for practical   reasons, be used to determine the entropy label value.  The resulting   label stack contains the server MPLS LSP label, ELI, EL and the   client LSP label.  Requirement MP#1 simply states that there must be   a means to make this decision.   There is currently no signaling mechanism defined to support   requirement MP#1, though that does not preclude a new extension being   defined later.  In the absence of a signaling extension, MPLS-TP can   be identified through some form of configuration, such as   configuration that provides an MPLS-TP-compatible server layer to all   LSPs arriving on a specific interface or originating from a specific   set of ingress LSRs.   Alternatively, the need for requirement MP#1 can be eliminated if   every MPLS-TP LSP created by an MPLS-TP ingress makes use of an   Entropy Label Indicator (ELI) and Entropy Label (EL) below the MPLS-   TP label [RFC6790].  This would require that all MPLS-TP LSRs in a   deployment support Entropy Label, which may render it impractical in   many deployments.   Some hardware that exists today can support requirement MP#2.   Signaling in the absence of MPLS Entropy Labels can make use of link   bundling with the path pinned to a specific component for MPLS-TP   LSPs and link bundling using the all-ones component for MPLS LSPs.   This prevents MPLS-TP LSPs from being carried within MPLS LSPs but   does allow the coexistence of MPLS-TP and very large MPLS LSPs.Villamizar                    Informational                     [Page 8]

RFC 7190               MPLS and MPLS-TP Multipath             March 2014   When Entropy Label Indicators (ELIs) and Entropy Labels (ELs) are not   applied by MPLS-TP ingresses, MPLS-TP LSPs can be carried as client   LSPs within an MPLS server LSP if the ingress of the MPLS server-   layer LSP pushes an Entropy Label Indicator (ELI) and Entropy Label   (EL) below the server-layer LSP label(s) in the label stack, just   above the MPLS-TP LSP label entry [RFC6790].  The value of EL can be   randomly selected at the client MPLS-TP LSP setup time, and the same   EL value can be used for all packets of that MPLS-TP LSP.  This   allows MPLS-TP LSPs to be carried as client LSPs within MPLS LSPs and   satisfies MPLS-TP forwarding requirements but requires that MPLS LSRs   be able to identify MPLS-TP LSPs (requirement MP#1).   MPLS-TP traffic can be protected from degraded performance due to an   imperfect load split if the MPLS-TP traffic is given queuing   priority.  For example, using (1) strict priority and policing,   shaping at ingress, or per-LSP shaping locally, or (2) per-LSP   weighted queuing locally.  This can be accomplished using the Traffic   Class (TC) field and Diffserv treatment of traffic [RFC5462]   [RFC2475].  In the event of congestion due to load imbalance, only   non-prioritized traffic will suffer as long as there is a low   percentage of prioritized traffic.   If MPLS-TP LSPs are carried within MPLS LSPs and ELI and EL are used,   requirement MP#3 is satisfied (1) for uncongested links where load   balancing is not required, or (2) for MPLS-TP LSPs using Traffic   Class (TC) and Diffserv, where the load rebalancing implementation   rebalances only the less preferred traffic.  Load rebalance is   generally needed only when congestion occurs; therefore, restricting   MPLS-TP to be carried over MPLS LSPs that are known to traverse only   links that are expected to be uncongested can satisfy requirement   MP#3.   An MPLS-TP LSP can be pinned to a Link Bundle component link if the   behavior of requirement MP#2 is preferred.  An MPLS-TP LSP can be   assigned to a Link Bundle but not pinned if the behavior of   requirement MP#3 is preferred.  In both of these cases, the MPLS-TP   LSP must be the top-level LSP, except as noted above.   If MPLS-TP LSPs can be moved among component links, then the Link   Bundle all-ones component link can be used or server-layer MPLS LSPs   can be used with no restrictions on the server-layer MPLS use of   multipath, except that Entropy Labels must be supported along the   entire path.  An Entropy Label must be used to ensure that all of the   MPLS-TP payload and OAM traffic are carried on the same component,   except during very infrequent transitions due to load balancing.   Since the Entropy Label Indicator and Entropy Label are always placed   above the Generic Associated Channel Label (GAL) in the stack, theVillamizar                    Informational                     [Page 9]

RFC 7190               MPLS and MPLS-TP Multipath             March 2014   presence of a GAL will not affect the selection of a component link   as long as the LSR does not hash on the label stack entries below the   Entropy Label.   An MPLS-TP LSP may not traverse multipath links on the path where   MPLS-TP forwarding requirements cannot be met.  Such links include   any using pre-[RFC6790] Ethernet Link Aggregation, pre-[RFC6790] Link   Bundling using the all-ones component link, or any other form of   multipath that does not support termination of the entropy search at   the EL as called for in [RFC6790].  An MPLS-TP LSP MUST NOT traverse   a server-layer MPLS LSP that traverses any form of multipath that   does not support termination of the entropy search at the EL.  For   this to occur, the MPLS-TP ingress LSR MUST be aware of these links.   This is the reason for requirement MP#4.   Requirement MP#4 can be supported using administrative attributes.   Administrative attributes are defined in [RFC3209].  Some   configuration is required to support this.   In MPLS Link Bundling the requirement for bidirectional co-routing   can be interpreted as meaning that the same set of LSRs must be   traversed or can be interpreted to mean that the same set of   component links must be traversed [RFC4201] [RFC3473].  Following the   procedures ofSection 3 of RFC 3473 where Link Bundling is used only   ensures that the same set of LSRs are traversed and that acceptable   labels are created in each direction.   When an MPLS-TP LSP is set up over a MPLS LSP, if the MPLS-TP LSP is   a bidirectional LSP, then providers who want to only set these MPLS-   TP LSPs over bidirectional co-routed MPLS LSPs can make use of   administrative attributes [RFC3209] to ensure that this occurs.  If   MPLS-TP LSPs are carried by unidirectional MPLS LSPs, the MPLS-TP OAM   will be unaffected, as only the MPLS LSP endpoints will appear as   MPLS-TP OAM Maintenance Entity Group Intermediate Points (MIPs).   Two methods of adding an Entropy Label are described above.  The   MPLS-TP ingress must have a means to determine which links can   support MPLS-TP in selecting a path (MP#4).  Administrative   attributes can satisfy that requirement.  If the MPLS-TP LSR is   capable of adding ELI/EL to the label stack, this method is   preferred.  However, equipment furthest from a provider's network   core is the least likely to supportRFC 6790 in the near term.  For   portions of the topology where an MPLS-TP is carried within a server-   layer MPLS LSP, the ingress of the server-layer MPLS LSP can add ELI/   EL using a fixed EL value per client LSP, except those known not to   require MPLS-TP treatment.  There are numerous ways to determine   which client LSPs are MPLS-TP LSPs and which are not.  While thisVillamizar                    Informational                    [Page 10]

RFC 7190               MPLS and MPLS-TP Multipath             March 2014   determination is out of scope and will vary among deployments,   configuration or the presence of specific attribute affinities in   RSVP-TE signaling are among the likely means to do so.4.  MPLS-TP as a Server Layer for MPLS   Carrying MPLS LSPs that are larger than a component link over an   MPLS-TP server layer requires that the large MPLS client-layer LSP be   accommodated by multiple MPLS-TP server-layer LSPs.  MPLS multipath   can be used in the client-layer MPLS.   Creating multiple MPLS-TP server-layer LSPs places a greater Incoming   Label Map (ILM) scaling burden on the LSR.  High-bandwidth MPLS cores   with a smaller amount of nodes have the greatest tendency to require   LSPs in excess of component links; therefore, the reduction in the   number of nodes offsets the impact of increasing the number of   server-layer LSPs in parallel.  Today, only in cases where deployed   LSR ILMs are small would this be an issue.   The most significant disadvantage of MPLS-TP as a server layer for   MPLS is that the use of MPLS-TP server-layer LSPs reduces the   efficiency of carrying the MPLS client layer.  The service that   provides by far the largest offered load in provider networks is the   Internet, for which the LSP capacity reservations are predictions of   expected load.  Many of these MPLS LSPs may be smaller than component   link capacity.  Using MPLS-TP as a server layer results in bin-   packing problems for these smaller LSPs.  For those LSPs that are   larger than component link capacity, the LSP capacities need not be   (and often are not) integer multiples of convenient capacity   increments such as 10 Gbit/s.  Using MPLS-TP as an underlying server   layer greatly reduces the ability of the client-layer MPLS LSPs to   share capacity.  For example, when one MPLS LSP is underutilizing its   predicted capacity, the fixed allocation of MPLS-TP to component   links may not allow another LSP to exceed its predicted capacity.   Using MPLS-TP as a server layer may result in less efficient use of   resources and may result in a less cost-effective network.   No additional requirements beyond MPLS-TP as it is now currently   defined are required to support MPLS-TP as a server layer for MPLS.   It is therefore viable but has some undesirable characteristics   discussed above.5.  Summary   MPLS equipment deployed in the core currently supports multipath.   For large service providers, core LSR must support some form of   multipath to be deployable.  Deployed MPLS access and edge equipment   is often oblivious to the use of multipath in the core.  It isVillamizar                    Informational                    [Page 11]

RFC 7190               MPLS and MPLS-TP Multipath             March 2014   expected that at least first-generation MPLS-TP equipment will be   oblivious to the use of multipath in the core.  This first-generation   MPLS-TP equipment is deployable in a core using multipath, with no   adverse impact to RSVP-TE signaling, if:   1.  the edge equipment can support administrative attributes (RFC3209),   2.  the core equipment can support ELI/EL, and   3.  the core equipment can put a per-LSP fixed EL value on any LSP       that indicates a particular attribute affinity or can identify a       client MPLS-TP LSP through some other means.   There are no issues carrying MPLS over MPLS-TP, except when the MPLS   LSP is too big to be carried by a single MPLS-TP LSP.  Most MPLS core   equipment and some edge equipment can configure an MPLS Link Bundle   [RFC4201] over multiple component links where the component links are   themselves MPLS LSP.  This existing capability can be used to carry   large MPLS LSPs and overcome the limited capacity of any single   server-layer MPLS-TP LSP.   MPLS OAM and MPLS-TP OAM are unaffected in the following cases   proposed in this document:   1.  Where MPLS is carried over a single MPLS-TP, all traffic flows on       one link, MPLS OAM is unaffected and need not use multipath       support in LSP Ping [RFC4379].   2.  Where MPLS-TP is carried over MPLS, all traffic for that MPLS-TP       LSP is carried over one link thanks to the fixed EL value.  In       this case, MPLS-TP OAM is unaffected.   3.  Where MPLS LSPs are carried over MPLS LSPs (an existing case) or       over multiple MPLS-TP LSPs, the multipath support in LSP Ping is       used and LSP Ping operation is unaffected [RFC4379] [RFC6425].6.  Acknowledgements   Carlos Pignataro, Dave Allan, and Mach Chen provided valuable   comments and suggestions.  Carlos suggested that MPLS-TP requirements   inRFC 5960 be explicitly referenced or quoted.  An email   conversation with Dave led to the inclusion of references and quotes   from RFCs 6371 and 6374.  Mach made suggestions to improve the   clarity of the document.Villamizar                    Informational                    [Page 12]

RFC 7190               MPLS and MPLS-TP Multipath             March 20147.  Security Considerations   This document specifies use of existing MPLS and MPLS-TP mechanisms   to support MPLS and MPLS-TP as client and server layers for each   other.  This use of existing mechanisms supports coexistence of MPLS/   GMPLS (without MPLS-TP) when used over a packet network, MPLS-TP, and   multipath.  The combination of MPLS, MPLS-TP, and multipath does not   introduce any new security threats.  The security considerations for   MPLS/GMPLS and for MPLS-TP are documented in [RFC5920] and [RFC6941].8.  References8.1.  Normative References   [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate              Requirement Levels",BCP 14,RFC 2119, March 1997.   [RFC5654]  Niven-Jenkins, B., Brungard, D., Betts, M., Sprecher, N.,              and S. Ueno, "Requirements of an MPLS Transport Profile",RFC 5654, September 2009.   [RFC5960]  Frost, D., Bryant, S., and M. Bocci, "MPLS Transport              Profile Data Plane Architecture",RFC 5960, August 2010.   [RFC6371]  Busi, I. and D. Allan, "Operations, Administration, and              Maintenance Framework for MPLS-Based Transport Networks",RFC 6371, September 2011.   [RFC6374]  Frost, D. and S. Bryant, "Packet Loss and Delay              Measurement for MPLS Networks",RFC 6374, September 2011.   [RFC6790]  Kompella, K., Drake, J., Amante, S., Henderickx, W., and              L. Yong, "The Use of Entropy Labels in MPLS Forwarding",RFC 6790, November 2012.8.2.  Informative References   [ADV-MULTIPATH-REQ]              Villamizar, C., McDysan, D., Ning, S., Malis, A., and L.              Yong, "Requirements for Advanced Multipath in MPLS              Networks", Work in Progress, February 2014.   [IEEE-802.1AX]              IEEE, "IEEE Standard for Local and Metropolitan Area              Networks - Link Aggregation", IEEE Std 802.1AX-2008, 2006,              <http://standards.ieee.org/getieee802/download/802.1AX-2008.pdf>.Villamizar                    Informational                    [Page 13]

RFC 7190               MPLS and MPLS-TP Multipath             March 2014   [ITU-T.G.800]              ITU-T, "Unified functional architecture of transport              networks", ITU-T G.800, 2007, <http://www.itu.int/rec/T-REC-G/recommendation.asp?parent=T-REC-G.800>.   [RFC2475]  Blake, S., Black, D., Carlson, M., Davies, E., Wang, Z.,              and W. Weiss, "An Architecture for Differentiated              Services",RFC 2475, December 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.   [RFC3473]  Berger, L., "Generalized Multi-Protocol Label Switching              (GMPLS) Signaling Resource ReserVation Protocol-Traffic              Engineering (RSVP-TE) Extensions",RFC 3473, January 2003.   [RFC4201]  Kompella, K., Rekhter, Y., and L. Berger, "Link Bundling              in MPLS Traffic Engineering (TE)",RFC 4201, October 2005.   [RFC4206]  Kompella, K. and Y. Rekhter, "Label Switched Paths (LSP)              Hierarchy with Generalized Multi-Protocol Label Switching              (GMPLS) Traffic Engineering (TE)",RFC 4206, October 2005.   [RFC4379]  Kompella, K. and G. Swallow, "Detecting Multi-Protocol              Label Switched (MPLS) Data Plane Failures",RFC 4379,              February 2006.   [RFC5286]  Atlas, A. and A. Zinin, "Basic Specification for IP Fast              Reroute: Loop-Free Alternates",RFC 5286, September 2008.   [RFC5462]  Andersson, L. and R. Asati, "Multiprotocol Label Switching              (MPLS) Label Stack Entry: "EXP" Field Renamed to "Traffic              Class" Field",RFC 5462, February 2009.   [RFC5714]  Shand, M. and S. Bryant, "IP Fast Reroute Framework",RFC5714, January 2010.   [RFC5920]  Fang, L., "Security Framework for MPLS and GMPLS              Networks",RFC 5920, July 2010.   [RFC6425]  Saxena, S., Swallow, G., Ali, Z., Farrel, A., Yasukawa,              S., and T. Nadeau, "Detecting Data-Plane Failures in              Point-to-Multipoint MPLS - Extensions to LSP Ping",RFC6425, November 2011.Villamizar                    Informational                    [Page 14]

RFC 7190               MPLS and MPLS-TP Multipath             March 2014   [RFC6941]  Fang, L., Niven-Jenkins, B., Mansfield, S., and R.              Graveman, "MPLS Transport Profile (MPLS-TP) Security              Framework",RFC 6941, April 2013.Author's Address   Curtis Villamizar   Outer Cape Cod Network Consulting   EMail: curtis@occnc.comVillamizar                    Informational                    [Page 15]