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rfc:rfc2917

Network Working Group K. Muthukrishnan Request for Comments: 2917 Lucent Technologies Category: Informational A. Malis

                                                  Vivace Networks, Inc.
                                                         September 2000
                  A Core MPLS IP VPN Architecture

Status of this Memo

 This memo provides information for the Internet community.  It does
 not specify an Internet standard of any kind.  Distribution of this
 memo is unlimited.

Copyright Notice

 Copyright (C) The Internet Society (2000).  All Rights Reserved.

Abstract

 This memo presents an approach for building core Virtual Private
 Network (VPN) services in a service provider's MPLS backbone.  This
 approach uses Multiprotocol Label Switching (MPLS) running in the
 backbone to provide premium services in addition to best effort
 services. The central vision is for the service provider to provide a
 virtual router service to their customers. The keystones of this
 architecture are ease of configuration, user security, network
 security, dynamic neighbor discovery, scaling and the use of existing
 routing protocols as they exist today without any modifications.

1. Acronyms

      ARP     Address Resolution Protocol
      CE      Customer Edge router
      LSP     Label Switched Path
      PNA     Private Network Administrator
      SLA     Service Level Agreement
      SP      Service Provider
      SPED    Service Provider Edge Device
      SPNA    SP Network Administrator
      VMA     VPN Multicast Address
      VPNID   VPN Identifier
      VR      Virtual Router
      VRC     Virtual Router Console

Muthukrishnan & Malis Informational [Page 1] RFC 2917 Core VPNs September 2000

2. Introduction

 This memo describes an approach for building IP VPN services out of
 the backbone of the SP's network. Broadly speaking, two possible
 approaches present themselves: the overlay model and the virtual
 router approach. The overlay model is based on overloading some
 semantic(s) of existing routing protocols to carry reachability
 information.  In this document, we focus on the virtual router
 service.
 The approach presented here does not depend on any modifications of
 any existing routing protocols. Neighbor discovery is aided by the
 use of  an emulated LAN and is achieved by the use of ARP. This memo
 makes a concerted effort to draw the line between the SP and the PNA:
 the SP owns and manages layer 1 and layer 2 services while layer 3
 services belong to and are manageable by the PNA. By the provisioning
 of fully logically independent routing domains, the PNA has been
 given the flexibility to use private and unregistered addresses. Due
 to the use of private LSPs and the use of VPNID encapsulation using
 label stacks over shared LSPs, data security is not an issue.
 The approach espoused in this memo differs from that described in RFC
 2547 [Rosen1] in that no specific routing protocol has been
 overloaded to carry VPN routes.  RFC 2547 specifies a way to modify
 BGP to carry VPN unicast routes across the SP's backbone. To carry
 multicast routes, further architectural work will be necessary.

3. Virtual Routers

 A virtual router is a collection of threads, either static or
 dynamic, in a routing device, that provides routing and forwarding
 services much like physical routers. A virtual router need not be a
 separate operating system process (although it could be); it simply
 has to provide the illusion that a dedicated router is available to
 satisfy the needs of the network(s) to which it is connected. A
 virtual router, like its physical counterpart, is an element in a
 routing domain. The other routers in this domain could be physical or
 virtual routers themselves. Given that the virtual router connects to
 a specific (logically discrete) routing domain and that a physical
 router can support multiple virtual routers, it follows that a
 physical router supports multiple (logically discreet) routing
 domains.
 From the user (VPN customer) standpoint, it is imperative that the
 virtual router be as equivalent to a physical router as possible. In
 other words, with very minor and very few exceptions, the virtual
 router should appear for all purposes (configuration, management,
 monitoring and troubleshooting) like a dedicated physical router. The

Muthukrishnan & Malis Informational [Page 2] RFC 2917 Core VPNs September 2000

 main motivation behind this requirement is to avoid upgrading or re-
 configuring the large installed base of routers and to avoid
 retraining of network administrators.
 The aspects of a router that a virtual router needs to emulate are:
 1. Configuration of any combination of routing protocols
 2. Monitoring of the network
 3. Troubleshooting.
 Every VPN has a logically independent routing domain. This enhances
 the SP's ability to offer a fully flexible virtual router service
 that can fully serve the SP's customer without requiring physical
 per-VPN routers. This means that the SP's "hardware" investments,
 namely routers and links between them, can be re-used by multiple
 customers.

4. Objectives

 1. Easy, scalable configuration of VPN endpoints in the service
    provider network. At most, one piece of configuration should be
    necessary when a CE is added.
 2. No use of SP resources that are globally unique and hard to get
    such as IP addresses and subnets.
 3. Dynamic discovery of VRs (Virtual Routers) in the SP's cloud. This
    is an optional, but extremely valuable "keep it simple" goal.
 4. Virtual Routers should be fully configurable and monitorable by
    the VPN network administrator. This provides the PNA with the
    flexibility to either configure the VPN themselves or outsource
    configuration tasks to the SP.
 5. Quality of data forwarding should be configurable on a VPN-by-VPN
    basis.  This should translate to continuous (but perhaps discrete)
    grades of service.  Some examples include best effort, dedicated
    bandwidth, QOS, and policy based forwarding services.
 6. Differentiated services should be configurable on a VPN-by-VPN
    basis, perhaps based on LSPs set up for exclusive use for
    forwarding data traffic in the VPN.

Muthukrishnan & Malis Informational [Page 3] RFC 2917 Core VPNs September 2000

 7. Security of internet routers extended to virtual routers. This
    means that the virtual router's data forwarding and routing
    functions should be as secure as a dedicated, private physical
    router.  There should be no unintended leak of information (user
    data and reachability information) from one routing domain to
    another.
 8. Specific routing protocols should not be mandated between virtual
    routers. This is critical to ensuring the VPN customer can setup
    the network and policies as the customer sees fit. For example,
    some protocols are strong in filtering, while others are strong in
    traffic engineering. The VPN customer might want to exploit both
    to achieve "best of breed" network quality.
 9. No special extensions to existing routing protocols such as BGP,
    RIP, OSPF, ISIS etc. This is critical to allowing the future
    addition of other services such as NHRP and multicast. In
    addition, as advances and addenda are made to existing protocols
    (such as traffic engineering extensions to ISIS and OSPF), they
    can be easily incorporated into the VPN implementation.

5. Architectural Requirements

 The service provider network must run some form of multicast routing
 to all nodes that will have VPN connections and to nodes that must
 forward multicast datagrams for virtual router discovery. A specific
 multicast routing protocol is not mandated. An SP may run MOSPF or
 DVMRP or any other protocol.

6. Architectural Outline

 1.  Every VPN is assigned a VPNID which is unique within the SP's
     network.  This identifier unambiguously identifies the VPN with
     which a packet or connection is associated. The VPNID of zero is
     reserved; it is associated with and represents the public
     internet.  It is recommended, but not required that these VPN
     identifiers will be compliant with RFC 2685 [Fox].
 2.  The VPN service is offered in the form of a Virtual Router
     service.  These VRs reside in the SPED and are as such confined
     to the edge of the SP's cloud. The VRs will use the SP's network
     for data and control packet forwarding but are otherwise
     invisible outside the SPEDs.
 3.  The "size" of the VR contracted to the VPN in a given SPED is
     expressed by the quantity of IP resources such as routing
     interfaces, route filters, routing entries etc. This is entirely
     under the control of the SP and provides the fine granularity

Muthukrishnan & Malis Informational [Page 4] RFC 2917 Core VPNs September 2000

     that the SP requires to offer virtually infinite grades of VR
     service on a per-SPED level. [Example: one SPED may be the
     aggregating point (say headquarters of the corporation) for a
     given VPN and a number of other SPEDs may be access points
     (branch offices). In this case, the SPED connected to the
     headquarters may be contracted to provide a large VR while the
     SPEDs connected to the branch offices may house small, perhaps
     stub VRs]. This provision also allows the SP to design the
     network with an end goal of distributing the load among the
     routers in the network.
 4.  One indicator of the VPN size is the number of SPEDs in the SP's
     network that have connections to CPE routers in that VPN.  In
     this respect, a VPN with many sites that need to be connected is
     a "large" VPN whereas one with a few sites is a "small" VPN.
     Also, it is conceivable that a VPN grows or shrinks in size over
     time. VPNs may even merge due to corporate mergers, acquisitions
     and partnering agreements. These changes are easy to accommodate
     in this architecture, as globally unique IP resources do not have
     to be dedicated or assigned to VPNs. The number of SPEDs is not
     limited by any artificial configuration limits.
 5.  The SP owns and manages Layer 1 and Layer 2 entities. To be
     specific, the SP controls physical switches or routers, physical
     links, logical layer 2 connections (such as DLCI in Frame Relay
     and VPI/VCI in ATM) and LSPs (and their assignment to specific
     VPNs).  In the context of VPNs, it is the SP's responsibility to
     contract and assign layer 2 entities to specific VPNs.
 6.  Layer 3 entities belong to and are manageable by the PNA.
     Examples of these entities include IP interfaces, choice of
     dynamic routing protocols or static routes, and routing
     interfaces. Note that although Layer 3 configuration logically
     falls under the PNA's area of responsibility, it is not necessary
     for the PNA to execute it.  It is quite viable for the PNA to
     outsource the IP administration of the virtual routers to the
     Service Provider.  Regardless of who assumes responsibility for
     configuration and monitoring, this approach provides a full
     routing domain view to the PNA and empowers the PNA to design the
     network to achieve intranet, extranet and traffic engineering
     goals.
 7.  The VPNs can be managed as if physical routers rather than VRs
     were deployed.  Therefore, management may be performed using SNMP
     or other similar methods or directly at the VR console (VRC).

Muthukrishnan & Malis Informational [Page 5] RFC 2917 Core VPNs September 2000

 8.  Industry-standard troubleshooting tools such as 'ping,'
     'traceroute,' in a routing domain domain comprised exclusively of
     dedicated physical routers.  Therefore, monitoring and .bp
     troubleshooting may be performed using SNMP or similar methods,
     but may also include the use of these standard tools. Again, the
     VRC may be used for these purposes just like any physical router.
 9.  Since the VRC is visible to the user, router specific security
     checks need to be put in place to make sure the VPN user is
     allowed access to Layer 3 resources in that VPN only and is
     disallowed from accessing physical resources in the router.  Most
     routers achieve this through the use of database views.
 10. The VRC is available to the SP as well. If configuration and
     monitoring has been outsourced to the SP, the SP may use the VRC
     to accomplish these tasks as if it were the PNA.
 11. The VRs in the SPEDs form the VPN in the SP's network. Together,
     they represent a virtual routing domain. They dynamically
     discover each other by utilizing an emulated LAN resident in the
     SP's network.
 Each VPN in the SP's network is assigned one and only one multicast
 address. This address is chosen from the administratively scoped
 range (239.192/14) [Meyer] and the only requirement is that the
 multicast address can be uniquely mapped to a specific VPN. This is
 easily automated by routers by the use of a simple function to
 unambiguously map a VPNid to the multicast address.  Subscription to
 this multicast address allows a VR to discover and be discovered by
 other VRs. It is important to note that the multicast address does
 not have to be configured.
 12. Data forwarding may be done in one of several ways:
    1. An LSP with best-effort characteristics that all VPNS can use.
    2. An LSP dedicated to a VPN and traffic engineered by the VPN
       customer.
    3. A private LSP with differentiated characteristics.
    4. Policy based forwarding on a dedicated L2 Virtual Circuit
 The choice of the preferred method is negotiable between the SP and
 the VPN customer, perhaps constituting part of the SLA between them.
 This allows the SP to offer different grades of service to different
 VPN customers.

Muthukrishnan & Malis Informational [Page 6] RFC 2917 Core VPNs September 2000

 Of course, hop-by-hop forwarding is also available to forward routing
 packets and to forward user data packets during periods of LSP
 establishment and failure.
 13. This approach does not mandate that separate operating system
     tasks for each of the routing protocols be run for each VR that
     the SPED houses. Specific implementations may be tailored to the
     particular SPED in use. Maintaining separate routing databases
     and forwarding tables, one per VR, is one way to get the highest
     performance for a given SPED.

7. Scalable Configuration

 A typical VPN is expected to have 100s to 1000s of endpoints within
 the SP cloud.  Therefore, configuration should scale (at most)
 linearly with the number of end points. To be specific, the
 administrator should have to add a couple of configuration items when
 a new customer site joins the set of VRs constituting a specific VPN.
 Anything worse will make this task too daunting for the service
 provider.  In this architecture, all that the service provider needs
 to allocate and configure is the ingress/egress physical link (e.g.
 Frame Relay DLCI or ATM VPI/VCI) and the virtual connection between
 the VR and the emulated LAN.

8. Dynamic Neighbor Discovery

 The VRs in a given VPN reside in a number of SPEDs in the network.
 These VRs need to learn about each other and be connected.
 One way to do this is to require the manual configuration of
 neighbors.  As an example, when a new site is added to a VPN, this
 would require the configuration of all the other VRs as neighbors.
 This is obviously not scalable from a configuration and network
 resource standpoint.
 The need then arises to allow these VRs to dynamically discover each
 other.  Neighbor discovery is facilitated by providing each VPN with
 a limited emulated LAN. This emulated LAN is used in several ways:
 1. Address resolution uses this LAN to resolve next-hop (private) IP
    addresses associated with the other VRs.
 2. Routing protocols such as RIP and OSPF use this limited emulated
    LAN for neighbor discovery and to send routing updates.
 The per-VPN LAN is emulated using an IP multicast address.  In the
 interest of conserving public address space and because this
 multicast address needs to be visible only in the SP network space,

Muthukrishnan & Malis Informational [Page 7] RFC 2917 Core VPNs September 2000

 we would use an address from the Organizationally scoped multicast
 addresses (239.192/14) as described in [Meyer]. Each VPN is allocated
 an address from this range.  To completely eliminate configuration in
 this regard, this address is computed from the VPNID.

9. VPN IP Domain Configuration

                              151.0.0.1
                              ################
                             #              #
                            #  ROUTER 'A'  #
                           #              #
                          ################
                               #       #
                              #         #
                             #           #
                            #             #
                       #############    ###############
                      #           #    #             #
                     # ROUTER 'B'#    # ROUTER 'C'  #
                    #           #    #             #
                   #           #    #             #
                  #############    ###############
                  152.0.0.2         153.0.0.3
                 Figure 1 'Physical Routing Domain'
 The physical domain in the SP's network is shown in the above figure.
 In this network, physical routers A, B and C are connected together.
 Each of the routers has a 'public' IP address assigned to it. These
 addresses uniquely identify each of the routers in the SP's network.

Muthukrishnan & Malis Informational [Page 8] RFC 2917 Core VPNs September 2000

       172.150.0/18                                172.150.128/18

———————– —————————|

           |                                       |          |
           |                                       |     172.150.128.1
           |               ROUTER 'A' (151.0.0.1)  |       |---------|
           |               #############           |       |Parts DB |
           |           ---#-----------#            |       /---------/
           |    OSPF   | #           #     ISIS    |      /----------/
           ------------|#  VR - A   #|--------------
                       #-------|---#-|
                      #############10.0.1/24
           |----|------------#-#---------------|-----|
                |10.0.0.2/24#   #              |10.0.0.3/24
         |------|-------|  #     #    ---------|-------|
         |  ###############       #   |############### |
         | #  VR - B    |#         #  #    VR - C   #  |
         |#-------------# ROUTER 'B'##|------------#----

(152.0.0.2)############### ############### (153.0.0.3)

  1. ———————— ROUTER 'C' | Extranet

172.150.64/18 V

                                            Vendors
              Figure 2 'Virtual Routing Domain'
 Each Virtual Router is configurable by the PNA as though it were a
 private physical router. Of course, the SP limits the resources that
 this Virtual Router may consume on a SPED-by-SPED basis. Each VPN has
 a number of physical connections (to CPE routers) and a number of
 logical connections (to the emulated LAN). Each connection is IP-
 capable and can be configured to utilize any combination of the
 standard routing protocols and routing policies to achieve specific
 corporate network goals.
 To illustrate, in Figure 1, 3 VRs reside on 3 SPEDs in VPN 1. Router
 'A' houses VR-A, router 'B' houses VR-B and router 'C' houses VR-C.
 VR-C and VR-B have a physical connection to CPE equipment, while VR-A
 has 2 physical connections. Each of the VRs has a fully IP-capable
 logical connection to the emulated LAN.  VR-A has the (physical)
 connections to the headquarters of the company and runs OSPF over
 those connections. Therefore, it can route packets to 172.150.0/18
 and 172.150.128/18. VR-B runs RIP in the branch office (over the
 physical connection) and uses RIP (over the logical connection) to
 export 172.150.64/18 to VR-A. VR-A advertises a default route to VR-B
 over the logical connection.  Vendors use VR-C as the extranet
 connection to connect to the parts database at 172.150.128.1. Hence,
 VR-C advertises a default route to VR-A over the logical connection.
 VR-A exports only 175.150.128.1 to VR-C. This keeps the rest of the
 corporate network from a security problem.

Muthukrishnan & Malis Informational [Page 9] RFC 2917 Core VPNs September 2000

 The network administrator will configure the following:
 1. OSPF connections to the 172.150.0/18 and 172.150.128/18 network
    in VR-A.
 2. RIP connections to VR-B and VR-C on VR-A.
 3. Route policies on VR-A to advertise only the default route to
    VR-B.
 4. Route policies on VR-A to advertise only 172.159.128.1 to VR-C.
 5. RIP on VR-B to VR-A.
 6. RIP on VR-C to advertise a default route to VR-A.

10. Neighbor Discovery Example

 In Figure #1, the SPED that houses VR-A (SPED-A) uses a public
 address of 150.0.0.1/24, SPED-B uses 150.0.0.2/24 and SPED-C uses
 150.0.0.3/24.  As noted, the connection between the VRs is via an
 emulated LAN.  For interface addresses on the emulated LAN
 connection, VR-A uses 10.0.0.1/24, VR-B uses 10.0.0.2/24 and VR-C
 uses 10.0.0.3/24.
 Let's take the case of VR-A sending a packet to VR-B. To get VR-B's
 address (SPED-B's address), VR-A sends an ARP request packet with the
 address of VR-B (10.0.0.2) as the logical address. The source logical
 address is 10.0.0.1 and the hardware address is 151.0.0.1. This ARP
 request is encapsulated in this VPN's multicast address and sent out.
 SPED B and SPED-C receive a copy of the packet.  SPED-B recognizes
 10.0.0.2 in the context of VPN 1 and responds with 152.0.0.2 as the
 "hardware" address. This response is sent to the VPN multicast
 address to promote the use of promiscuous ARP and the resulting
 decrease in network traffic.
 Manual configuration would be necessary if neighbor discovery were
 not used. In this example, VR-A would be configured with a static ARP
 entry for VR-B's logical address (10.0.0.1) with the "hardware"
 address set to 152.0.0.2.

11. Forwarding

 As mentioned in the architectural outline, data forwarding may be
 done in one of several ways. In all techniques except the Hop-by-Hop
 technique for forwarding routing/control packets, the actual method

Muthukrishnan & Malis Informational [Page 10] RFC 2917 Core VPNs September 2000

 is configurable. At the high end, policy based forwarding for quick
 service and at the other end best effort forwarding using public LSP
 is used. The order of forwarding preference is as follows:
 1. Policy based forwarding.
 2. Optionally configured private LSP.
 3. Best-effort public LSP.

11.1 Private LSP

 This LSP is optionally configured on a per-VPN basis. This LSP is
 usually associated with non-zero bandwidth reservation and/or a
 specific differentiated service or QOS class. If this LSP is
 available, it is used for user data and for VPN private control data
 forwarding.

11.2 Best Effort Public LSP

 VPN data packets are forwarded using this LSP if a private LSP with
 specified bandwidth and/or QOS characteristics is either not
 configured or not presently available. The LSP used is the one
 destined for the egress router in VPN 0. The VPNID in the shim header
 is used to de-multiplex data packets from various VPNs at the egress
 router.

12. Differentiated Services

 Configuring private LSPs for VPNs allows the SP to offer
 differentiated services to paying customers. These private LSPs could
 be associated with any available L2 QOS class or Diff-Serv
 codepoints. In a VPN, multiple private LSPs with different service
 classes could be configured with flow profiles for sorting the
 packets among the LSPs. This feature, together with the ability to
 size the virtual routers, allows the SP to offer truly differentiated
 services to the VPN customer.

13. Security Considerations

13.1 Routing Security

 The use of standard routing protocols such as OSPF and BGP in their
 unmodified form means that all the encryption and security methods
 (such as MD5 authentication of neighbors) are fully available in VRs.
 Making sure that routes are not accidentally leaked from one VPN to
 another is an implementation issue. One way to achieve this is to
 maintain separate routing and forwarding databases.

Muthukrishnan & Malis Informational [Page 11] RFC 2917 Core VPNs September 2000

13.2 Data Security

 This allows the SP to assure the VPN customer that data packets in
 one VPN never have the opportunity to wander into another. From a
 routing standpoint, this could be achieved by maintaining separate
 routing databases for each virtual router. From a data forwarding
 standpoint, the use of label stacks in the case of shared LSPs
 [Rosen2] [Callon] or the use of private LSPs guarantees data privacy.
 Packet filters may also be configured to help ease the problem.

13.3 Configuration Security

 Virtual routers appear as physical routers to the PNA. This means
 that they may be configured by the PNA to achieve connectivity
 between offices of a corporation. Obviously, the SP has to guarantee
 that the PNA and the PNA's designees are the only ones who have
 access to the VRs on the SPEDs the private network has connections
 to. Since the virtual router console is functionally equivalent to a
 physical router, all of the authentication methods available on a
 physical console such as password, RADIUS, etc. are available to the
 PNA.

13.4 Physical Network Security

 When a PNA logs in to a SPED to configure or monitor the VPN, the PNA
 is logged into the VR for the VPN. The PNA has only layer 3
 configuration and monitoring privileges for the VR. Specifically, the
 PNA has no configuration privileges for the physical network. This
 provides the guarantee to the SP that a VPN administrator will not be
 able to inadvertently or otherwise adversely affect the SP's network.

14. Virtual Router Monitoring

 All of the router monitoring features available on a physical router
 are available on the virtual router. This includes utilities such as
 "ping" and "traceroute". In addition, the ability to display private
 routing tables, link state databases, etc. are available.

15. Performance Considerations

 For the purposes of discussing performance and scaling issues,
 today's routers can be split into two planes: the routing (control)
 plane and the forwarding plane.
 In looking at the routing plane, most modern-day routing protocols
 use some form of optimized calculation methodologies to calculate the
 shortest path(s) to end stations. For instance, OSPF and ISIS use the
 Djikstra algorithm while BGP uses the "Decision Process". These

Muthukrishnan & Malis Informational [Page 12] RFC 2917 Core VPNs September 2000

 algorithms are based on parsing the routing database and computing
 the best paths to end stations. The performance characteristics of
 any of these algorithms is based on either topological
 characteristics (ISIS and OSPF) or the number of ASs in the path to
 the destinations (BGP). But it is important to note that the overhead
 in setting up and beginning these calculations is very little for
 most any modern day router. This is because, although we refer to
 routing calculation input as "databases", these are memory resident
 data structures.
 Therefore, the following conclusions can be drawn:
 1. Beginning a routing calculation for a routing domain is nothing
    more than setting up some registers to point to the right database
    objects.
 2. Based on 1, the performance of a given algorithm is not
    significantly worsened by the overhead required to set it up.
 3. Based on 2, it follows that, when a number of routing calculations
    for a number of virtual routers has to be performed by a physical
    router, the complexity of the resulting routing calculation is
    nothing more than the sum of the complexities of the routing
    calculations of the individual virtual routers.
 4. Based on 3, it follows that whether an overlay model is used or a
    virtual routing model is employed, the performance characteristics
    of a router are dependent purely on its hardware capabilities and
    the choice of data structures and algorithms.
 To illustrate, let's say a physical router houses N VPNs, all running
 some routing protocol say RP. Let's also suppose that the average
 performance of RP's routing calculation algorithm is  f(X,Y) where x
 and y are parameters that determine performance of the algorithm for
 that routing protocol. As an example, for Djikstra algorithm users
 such as OSPF, X could be the number of nodes in the area while Y
 could be the number of links. The performance of an arbitrary VPN n
 is f (Xn, Yn). The performance of the (physical) router is the sum of
 f(Xi, Yi) for all values of i in 0 <= i <= N. This conclusion is
 independent of the chosen VPN approach (virtual router or overlay
 model).
 In the usual case, the forwarding plane has two inputs: the
 forwarding table and the packet header. The main performance
 parameter is the lookup algorithm. The very best performance one can
 get for a IP routing table lookup is by organizing the table as some
 form of a tree and use binary search methods to do the actual lookup.
 The performance of this algorithm is O(log n).

Muthukrishnan & Malis Informational [Page 13] RFC 2917 Core VPNs September 2000

 Hence, as long as the virtual routers' routing tables are distinct
 from each other, the lookup cost is constant for finding the routing
 table and O(log n) to find the entry. This is no worse or different
 from any router and no different from a router that employs overlay
 techniques to deliver VPN services. However, when the overlay router
 utilizes integration of multiple VPNs' routing tables, the
 performance is O(log m*n) where 'm' is the number of VPNs that the
 routing table holds routes for.

16. Acknowledgements

 The authors wish to thank Dave Ryan, Lucent Technologies for his
 invaluable in-depth review of this version of this memo.

17. References

 [Callon] Callon R., et al., "A Framework for Multiprotocol Label
          Switching", Work in Progress.
 [Fox]    Fox, B. and B. Gleeson,"Virtual Private Networks
          Identifier", RFC 2685, September 1999.
 [Meyer]  Meyer, D., "Administratively Scoped IP Multicast", RFC 2365,
          July 1998.
 [Rosen1] Rosen, E. and Y. Rekhter, "BGP/MPLS VPNs", RFC 2547, March
          1999.
 [Rosen2] Rosen E., Viswanathan, A. and R. Callon, "Multiprotocol
          Label Switching Architecture", Work in Progress.

Muthukrishnan & Malis Informational [Page 14] RFC 2917 Core VPNs September 2000

18. Authors' Addresses

 Karthik Muthukrishnan
 Lucent Technologies
 1 Robbins Road
 Westford, MA 01886
 Phone: (978) 952-1368
 EMail: mkarthik@lucent.com
 Andrew Malis
 Vivace Networks, Inc.
 2730 Orchard Parkway
 San Jose, CA 95134
 Phone: (408) 383-7223
 EMail: Andy.Malis@vivacenetworks.com

Muthukrishnan & Malis Informational [Page 15] RFC 2917 Core VPNs September 2000

19. Full Copyright Statement

 Copyright (C) The Internet Society (2000).  All Rights Reserved.
 This document and translations of it may be copied and furnished to
 others, and derivative works that comment on or otherwise explain it
 or assist in its implementation may be prepared, copied, published
 and distributed, in whole or in part, without restriction of any
 kind, provided that the above copyright notice and this paragraph are
 included on all such copies and derivative works.  However, this
 document itself may not be modified in any way, such as by removing
 the copyright notice or references to the Internet Society or other
 Internet organizations, except as needed for the purpose of
 developing Internet standards in which case the procedures for
 copyrights defined in the Internet Standards process must be
 followed, or as required to translate it into languages other than
 English.
 The limited permissions granted above are perpetual and will not be
 revoked by the Internet Society or its successors or assigns.
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Acknowledgement

 Funding for the RFC Editor function is currently provided by the
 Internet Society.

Muthukrishnan & Malis Informational [Page 16]

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