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RFC 7625

Architecture of an IP/MPLS Network with Hardened Pipes

Pages: 15

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Independent Submission                                         J. T. Hao
Request for Comments: 7625                  Huawei Technologies Co., Ltd
Category: Informational                                    P. Maheshwari
ISSN: 2070-1721                                      Bharti Airtel, Ltd.
                                                                R. Huang
                                                            L. Andersson
                                                                 M. Chen
                                            Huawei Technologies Co., Ltd
                                                             August 2015

         Architecture of an IP/MPLS Network with Hardened Pipes


This document describes an IP/MPLS network that has an infrastructure that can be separated into two or more strata. For the implementation described in this document, the infrastructure has been separated into two strata: one for the "Hard Pipes", called the "Hard Pipe Stratum", and one for the normal IP/MPLS traffic, called the "Normal IP/MPLS Stratum". This document introduces the concept of a Hard Pipe -- an MPLS Label Switched Path (LSP) or a pseudowire (PW) with a bandwidth that is guaranteed and can neither be exceeded nor infringed upon. The Hard Pipe stratum does not use statistical multiplexing; for the LSPs and PWs set up within this stratum, the bandwidth is guaranteed end to end. The document does not specify any new protocol or procedures. It does explain how the MPLS standards implementation has been deployed and operated to meet the requirements from operators that offer traditional Virtual Leased Line (VLL) services.
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Status of This Memo

   This document is not an Internet Standards Track specification; it is
   published for informational purposes.

   This is a contribution to the RFC Series, independently of any other
   RFC stream.  The RFC Editor has chosen to publish this document at
   its discretion and makes no statement about its value for
   implementation or deployment.  Documents approved for publication by
   the RFC Editor are not a candidate for any level of Internet
   Standard; see Section 2 of RFC 5741.

   Information about the current status of this document, any errata,
   and how to provide feedback on it may be obtained at

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
   ( 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.
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Table of Contents

1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3 1.1. Scope . . . . . . . . . . . . . . . . . . . . . . . . . . 4 1.2. Abbreviations . . . . . . . . . . . . . . . . . . . . . . 4 2. The Stratified Network . . . . . . . . . . . . . . . . . . . 5 2.1. The Physical Network . . . . . . . . . . . . . . . . . . 6 2.2. The Hard Pipe Stratum . . . . . . . . . . . . . . . . . . 6 2.3. The Normal IP/MPLS Stratum . . . . . . . . . . . . . . . 7 2.4. Stratum Networks . . . . . . . . . . . . . . . . . . . . 7 3. Configuring the Leased Lines in the Hard Pipe Stratum . . . . 8 4. Efficient State Management . . . . . . . . . . . . . . . . . 9 4.1. State in the Forwarding Plane . . . . . . . . . . . . . . 9 4.2. State in the NMS/Controller . . . . . . . . . . . . . . . 10 4.3. Annotations for Configuring Leased Lines . . . . . . . . 10 5. Setting Up Leased Lines . . . . . . . . . . . . . . . . . . . 12 6. Leased Line Protection . . . . . . . . . . . . . . . . . . . 13 7. Security Considerations . . . . . . . . . . . . . . . . . . . 13 8. Informative References . . . . . . . . . . . . . . . . . . . 13 Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . . 14 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 15

1. Introduction

IP leased line services, Ethernet Private Line (EPL), and Time- Division Multiplexed (TDM) leased line services are commonly offered by operators worldwide. There are customers, e.g., many enterprises, that insist on TDM leased line services. They do so regardless of the fact that the same operators often offer IP leased line services and EPL services at a lower price and with a guaranteed bandwidth. Today we see a trend that TDM (in particular, Synchronous Digital Hierarchy / Synchronous Optical Network (SDH/SONET)) networks are gradually carrying less and less traffic, and many operators want to shut their TDM networks down to reduce costs. In light of these trends, vendors and operators have built and deployed the Hard Pipe service described in this document. It is a way to introduce leased line service with the same characteristics as TDM leased line services in IP/MPLS networks. Even if leased line has been the initial motivation to define the Hard Pipe technology, the Hard Pipe is by no means limited to support leased line services. When guaranteed bandwidth is the priority,
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   Virtual Private Wire Services (VPWS), Virtual Private LAN Services
   (VPLS), L3 Virtual Private Networks (L3VPN), and IP-only Private LAN
   Services can be mapped to a tunnel in the Hard Pipe stratum.

   EPL and Ethernet Private LAN (EPLAN) are out of scope for this

   Virtual Leased Line service is used in examples throughout this

   The solution soon to be deployed has an Ethernet infrastructure that
   has been split into two parallel logical networks -- two parallel
   strata.  The first stratum -- the Hard Pipe Stratum -- does not use
   statistical multiplexing, and bandwidth is guaranteed end to end.
   The second stratum -- the Normal IP/MPLS Stratum -- works as a normal
   IP/MPLS network.  The two strata share the same physical network,
   i.e., routers and links, but the resource reserved for the Hard Pipe
   stratum will never be preempted by the Normal IP/MPLS stratum.

   The routers will handle the traffic belonging to one stratum
   differently from how traffic from the other stratum is handled.  This
   separation in traffic handling is based on support in hardware.

   The reader of this document is assumed to be familiar with RFC 3031
   [RFC3031] and RFC 5921 [RFC5921].

1.1. Scope

This document has the following purposes: o to introduce a two strata IP/MPLS network: the purpose of one of the strata is to provide capabilities for services that are, from a customer's point of view, functionally identical to TDM-like leased lines; and o to indicate how a router differentiates the traffic of the two strata.

1.2. Abbreviations

CC: Continuity Check CV: Connection Verification L-label: Leased Line label LSP: Label Switched Path
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   LSR: Label Switching Router

   MPLS-TP: MPLS Transport Profile

   NMS: Network Management System

   OAM: Operations, Administration, and Maintenance

   P: Provider Router

   PE: Provider Edge Router

   PW: Pseudowire

   T-label: Tunnel label

   TDM: Time-Division Multiplexing

   tLDP: Targeted LDP

   VLL: Virtual Leased Line

   VPLS: Virtual Private LAN Service

   VPWS: Virtual Private Wire Service

2. The Stratified Network

The concept of stratified or strata networks has been around for some time. It appears to have different meaning in different contexts. The way we use the concept is that we logically assign certain characteristics to part of the network. The part of the network that has the special characteristics form one stratum, and the "remainder" forms a second stratum. The network described in this document uses a single link-layer technology, Ethernet. In many cases, a whole physical interface is assigned to a single hard stratum, especially in the scenario where there are many physical links between two nodes. This document does not address the network configuration possibilities for Hard Pipe and IP/MPLS strata in detail. There are configuration options, the basic configuration is that one Hard Pipe stratum and one IP/MPLS stratum are provisioned.
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   However, it is also possible to provision more than one Hard Pipe
   stratum, e.g., if customers want enhanced separation for their leased
   line.  Even though the main driver for the Hard Pipe technology is
   the leased lines, any service for which an operator does not want to
   use statistical multiplexing will benefit from using the Hard Pipes.

2.1. The Physical Network

Consider a network with 10 routers and all the links between are 10G Ethernet, such as shown in Figure 1. This is the network topology we've used for this model and also (with topology variations) in our first deployment. +---+ 10G +---+ 10G +---+ 10G +---+ +---| B |-----------| C |-----------| D |----------| E |---+ 10G | +---+ +---+ +---+ +---+ | 10G | | | | | | +---+ | 10G 10G | 10G | 10G | +---+ --| F | | | | | | G |-- +---+ | | | | +---+ | | | | | | 10G | +---+ +---+ +---+ +---+ | 10G +---| H |-----------| J |-----------| K |----------| L |---+ +---+ 10G +---+ 10G +---+ 10G +---+ Figure 1 In this document, we use the terms "traffic matrix" or "estimated traffic matrix" to indicate an estimate of how much traffic will flow between the ingress and egress (PE) nodes. This may be translated into how much bandwidth is needed per link in the Hard Pipe stratum.

2.2. The Hard Pipe Stratum

When the intention is to define a Hard Pipe stratum, it is, for example, possible to start from an estimated traffic matrix to estimate how much bandwidth to reserve on the links of the Ethernet link-layer network for the Hard Pipes. Note that the implication is that the normal traffic gets the remainder of the available bandwidth. Thus, the link-layer network will be split into two logical networks, or two strata -- one stratum for the hardened pipe network and the other for the "normal" IP and MPLS traffic. This is shown in Figures 2 and 3.
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           +---+    2G     +---+                          +---+
       +---| B |-----------| C |                          | E |---+
    1G |   +---+           +---+                          +---+   |  2G
       |                     |                              |     |
     +---+              2G   |                          1G  |   +---+
   --| F |                   |                              |   | G |--
     +---+                   |                              |   +---+
       |                     |                              |     |
    1G |   +---+           +---+           +---+          +---+   | 2G
       +---| H |-----------| J |-----------| K |----------| L |---+
           +---+      2G   +---+   4G      +---+    4G    +---+

                      Figure 2: The Hard Pipe Stratum

   It is worth noting that even if the figures in this document are
   drawn to indicate "bandwidth on the link", the only bandwidth
   information that the nodes have available is the bandwidth assigned
   to the Hard Pipe stratum and the Normal IP/MPLS stratum.  All other
   information is kept on the NMS/Controller.  The NMS/Controller keeps
   a global bandwidth resource table for the Hard Pipe stratum.

2.3. The Normal IP/MPLS Stratum

Given that the starting point is the physical network in Figure 1 and the Hard Pipe stratum as defined in Figure 2, the Normal IP/MPLS stratum will look as is shown in Figure 3: +---+ 8G +---+ 10G +---+ 10G +---+ +---| B |-----------| C |-----------| D |----------| E |---+ 9G | +---+ +---+ +---+ +---+ | 8G | | | | | | +---+ | 10G 8G | 10G | 9G | +---+ --| F | | | | | | G |-- +---+ | | | | +---+ | | | | | | 9G | +---+ +---+ +---+ +---+ | 9G +---| H |-----------| J |-----------| K |----------| L |---+ +---+ 8G +---+ 6G +---+ 6G +---+ Figure 3: The Normal IP/MPLS Stratum

2.4. Stratum Networks

In this document, the concept of stratum network is used to indicate basically parallel logical networks with strictly separated resources. Traffic sent over one stratum network can not infringe on traffic in the other stratum network.
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   In the case described here, all the traffic in the Hard Pipe stratum
   is MPLS encapsulated.  A number of the labels have been set aside so
   other applications can't allocate them and so the routers recognize
   them as belonging to the Hard Pipe application.

3. Configuring the Leased Lines in the Hard Pipe Stratum

When the strata are provisioned, the IP/MPLS stratum is set up exactly as any other IP/MPLS network. The one small difference between provisioning the Hard Pipe stratum and the IP/MPLS stratum is that no overbooking is done for the Hard Pipe stratum. Overbooking and/or congestion in the IP/MPLS stratum can not affect the Hard Pipe stratum. All labels used for the Hard Pipe stratum are "Configured Labels", i.e., labels that are provisioned and reclaimed by management actions. These management actions can be by manual actions or by an NMS/Controller or a centralized controller. For the size of network being deployed, manual configuration is not practical; we are both provisioning and reclaiming a label from an NMS/Controller. o If an operator wants to set up a leased line, it is first checked if there is a path available in the Hard Pipe stratum that matches the criteria (e.g., bandwidth) for the requested leased line. * If such a path does exist, it is checked if there is a matching MPLS tunnel available over that path. + If such a tunnel exists, it is used to establish the leased line by adding L-labels forming an LSP that are carried by the tunnel. L-labels are known only by the ingress and egress LSRs. They are local to the endpoints the same way that the label signaled by Targeted LDP (tLDP) is local to the endpoints of a targeted session LSP. (Here, "Targeted LDP" means LDP as defined in RFC 5036 [RFC5036], using Targeted Hello messages.) At the same time, the available bandwidth in the Hard Pipe stratum is decremented by the bandwidth that is needed for the leased line for every hop across this stratum in the global resource table (for the Hard Pipe stratum). + If such a tunnel does not exist, it can be established so that the leased line can be set up as above.
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      *  If the path does not exist (not enough bandwidth in the Hard
         Pipe stratum for the leased line), available bandwidth on the
         links is checked to see if the stratum can be expanded to
         accommodate such a path.

         +  If the Hard Pipe stratum can be expanded, this is done and
            the tunnel for the leased line is established as described

            It is likely that other modifications of the Hard Pipe
            stratum, e.g., consolidating already set up Hard IP tunnels
            on to existing links so that room for new leased lines are
            created, may have implications that go well outside the
            leased line service, and it is currently not viewed as a
            fully automated operation.

         +  If it is not possible to expand the Hard Pipe stratum to
            accommodate the new path, set up of the leased line will
            need to be declined.

   Thus, given the existence of a viable Hard Pipe stratum, leased lines
   are configured in two very simple steps.  First, establish a hop-by-
   hop tunnel (T-labels), and second, configure the leased lines
   (L-labels).  The T-labels need to be configured on both the PE and P
   routers while L-labels only need to be configured on the PE routers.

   Note that L-labels may be used for normal IP service [RFC3031],
   BGP/MPLS VPNs [RFC4364], or PWs [RFC3985].

4. Efficient State Management

The system as described here generates a very small amount of state, and most of it is kept in the NMS/Controller.

4.1. State in the Forwarding Plane

The only configured information that is actually kept on the LSRs is o the information needed for the label swapping procedures, i.e., incoming label to outgoing label and port, and whether the label belongs to the set of labels that are set aside for the Hard Pipe stratum tunnels; and o the bandwidth available for the Hard Pipe stratum and the Normal IP/MPLS stratum.
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4.2. State in the NMS/Controller

The following state needs to be kept in the NMS/Controller: o the topology and bandwidth resources available in the Hard Pipe network; see Figure 2. o the total and available bandwidth per link in the Hard Pipe network; see Figure 4. o the T-label mappings; see Figure 5. o the L-label mappings; see Figure 6. o the reserved bandwidth, as well as other constraints and the path per L-label.

4.3. Annotations for Configuring Leased Lines

The annotations given below are neither a programming guideline nor an indication how this architecture could be implemented. It is rather an indication of how much data needs to be saved for each stratum and leased line, as well as where this data could be stored. Considering the Hard Pipe stratum as it has been outlined in Figure 2, there is actually some additional information related to the Hard Pipe stratum that not is shown in the figure. Looking explicitly on the link between LSR J and K we find: +---+ +---+ +---+ +---+ ---| H |-----------| J |-----------| K |----------| L |--- +---+ +---+ +---+ +---+ [4,0]G Figure 4 The annotation [4,0]G means that 4G is allocated to the stratum on the link between J and K, and of these, 0G has been allocated to a service.
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   If we were to allocate two tunnels labels from the labels that have
   been configured to work within the Hard Pipe stratum, the resource
   view would look like this:

           +---+           +---+           +---+          +---+
        ---| H |-----------| J |-----------| K |----------| L |---
           +---+           +---+           +---+          +---+
                               [4,0]G T1 ,T2

                                 Figure 5

   Note that allocating the tunnel labels does not reserve bandwidth for
   the tunnel from the Hard Pipe stratum.

   When the L-labels are assigned, this will consume bandwidth; so we
   need to keep track of the bandwidth per leased line and the total of
   bandwidth allocated from the Hard Pipe stratum.

   The annotation for the link between J and K could look like this:

           +---+           +---+           +---+          +---+
        ---| H |-----------| J |-----------| K |----------| L |---
           +---+           +---+           +---+          +---+
                [4,1.5]G, T1, L1 [.5], L2 [.5], T2, L1 [.5]

                                 Figure 6

   The line [4,1.5]G, T1, L1 [.5], L2 [.5], T2, L1 [.5] would be
   interpreted as follows:

      The Hard Pipe stratum link between nodes J and K has 4G bandwidth
      allocated; of the total bandwidth, 1.5G is allocated for leased

      Tunnel label T1 carries two leased lines, each of 0.5G, and tunnel
      label T2 carries a third leased line of 0.5G.

   Note that it is not necessary to keep this information in the nodes;
   it is held within the NMS/Controller.  Also, it is not necessary to
   keep the bandwidth per leased line, but some operations are
   simplified (e.g., removing a leased line) if this is done.
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5. Setting Up Leased Lines

Consider the case where an operator wants to set up a leased line of 0.4G from F to G in the Hard Pipe stratum in Figure 2. Since there are no constraints other than bandwidth and ingress and egress PEs, the shortest path will be chosen. A tunnel will be configured from F to G over the nodes F, H, J, K, L, and G, and a Leased Line label (a) will be configured on F and G, and the available resources will be recalculated. A second leased line of 0.3G between the same PEs is easily configured by adding a new Leased Line label (b) at the ingress and egress PEs. After these operations, a view of the Hard Pipe stratum resources (available bandwidth) would look like this: +---+ 2G +---+ +---+ +---| B |-----------| C | | E |---+ 1G | +---+ +---+ +---+ | 2G | | | | +---+ 2G | 1G | +---+ --| F | | | | G |-- +---+ | | +---+ | | | | .3G | +---+ +---+ +---+ +---+ | 1.3G +---| H |-----------| J |-----------| K |----------| L |---+ +---+ 1.3G +---+ 3.3G +---+ 3.3G +---+ Figure 7: The Hard Pipe Stratum after Operations If the operator now wishes to establish a new leased line with the criteria being that it should originate from F and terminate at G, have 0.4G bandwidth, and pass through node E, then analysis of the Hard Pipe stratum (after establishing the first two listed lines) and the criteria for the new leased line would give the following: o The existing tunnel cannot be used since it does not pass through E; a new tunnel need to be established. o The hop from F to H cannot be used since the available bandwidth is insufficient. o Since no existing tunnels meet the criteria requested, a new tunnel will be set up from F, to B, C, J, K, L, E (the criteria to pass through E), and to G.
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   A new L-label (c) to be carried over T2 will be configured on F and
   G, and the available resources of the Hard Pipe stratum will be

6. Leased Line Protection

This leased line service uses the MPLS Transport Profile (MPLS-TP) line protection as it is defined in RFC 6378 [RFC6378] and is updated as specified in RFC 7271 [RFC7271] and RFC 7324 [RFC7324] The CV and CC are run over the tunnels between the Maintenance Entity Group End Points (MEP) at each end, i.e., the entire tunnel is protected end to end. In general, all of the MPLS-TP Operations, Administration, and Maintenance (OAM) as defined in RFC 6371 [RFC6371] is v applicable.

7. Security Considerations

The security considerations as defined in "Security Framework for MPLS and GMPLS Networks" (RFC 5920 [RFC5920]) and "MPLS Transport Profile (MPLS-TP) Security Framework" (RFC 6941 [RFC6941]) apply to this document.

8. Informative References

[RFC3031] Rosen, E., Viswanathan, A., and R. Callon, "Multiprotocol Label Switching Architecture", RFC 3031, DOI 10.17487/RFC3031, January 2001, <>. [RFC3985] Bryant, S., Ed. and P. Pate, Ed., "Pseudo Wire Emulation Edge-to-Edge (PWE3) Architecture", RFC 3985, DOI 10.17487/RFC3985, March 2005, <>. [RFC4364] Rosen, E. and Y. Rekhter, "BGP/MPLS IP Virtual Private Networks (VPNs)", RFC 4364, DOI 10.17487/RFC4364, February 2006, <>. [RFC5036] Andersson, L., Ed., Minei, I., Ed., and B. Thomas, Ed., "LDP Specification", RFC 5036, DOI 10.17487/RFC5036, October 2007, <>. [RFC5920] Fang, L., Ed., "Security Framework for MPLS and GMPLS Networks", RFC 5920, DOI 10.17487/RFC5920, July 2010, <>.
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   [RFC5921]  Bocci, M., Ed., Bryant, S., Ed., Frost, D., Ed., Levrau,
              L., and L. Berger, "A Framework for MPLS in Transport
              Networks", RFC 5921, DOI 10.17487/RFC5921, July 2010,

   [RFC6371]  Busi, I., Ed. and D. Allan, Ed., "Operations,
              Administration, and Maintenance Framework for MPLS-Based
              Transport Networks", RFC 6371, DOI 10.17487/RFC6371,
              September 2011, <>.

   [RFC6378]  Weingarten, Y., Ed., Bryant, S., Osborne, E., Sprecher,
              N., and A. Fulignoli, Ed., "MPLS Transport Profile
              (MPLS-TP) Linear Protection", RFC 6378,
              DOI 10.17487/RFC6378, October 2011,

   [RFC6941]  Fang, L., Ed., Niven-Jenkins, B., Ed., Mansfield, S., Ed.,
              and R. Graveman, Ed., "MPLS Transport Profile (MPLS-TP)
              Security Framework", RFC 6941, DOI 10.17487/RFC6941, April
              2013, <>.

   [RFC7271]  Ryoo, J., Ed., Gray, E., Ed., van Helvoort, H.,
              D'Alessandro, A., Cheung, T., and E. Osborne, "MPLS
              Transport Profile (MPLS-TP) Linear Protection to Match the
              Operational Expectations of Synchronous Digital Hierarchy,
              Optical Transport Network, and Ethernet Transport Network
              Operators", RFC 7271, DOI 10.17487/RFC7271, June 2014,

   [RFC7324]  Osborne, E., "Updates to MPLS Transport Profile Linear
              Protection", RFC 7324, DOI 10.17487/RFC7324, July 2014,


The authors want to thank Andy Malis for detailed technical and language review and for valuable comments.
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Authors' Addresses

JiangTao Hao Huawei Technologies Co., Ltd Q13 Huawei Campus No. 156 Beiqing Road Hai-dian District Beijing 100095 China Email: Praveen Maheshwari Bharti Airtel, Ltd. Plot No. 16, Udyog Bihar, Phase IV, Gurgaon - 122015 Haryana India Email: River Huang Huawei Technologies Co., Ltd Q13 Huawei Campus No. 156 Beiqing Road Hai-dian District Beijing 100095 China Email: Loa Andersson Huawei Technologies Co., Ltd Stockholm Sweden Email: Mach(Guoyi) Chen Huawei Technologies Co., Ltd Q14 Huawei Campus No. 156 Beiqing Road Hai-dian District Beijing 100095 China Email: