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rfc:rfc2547

Network Working Group E. Rosen Request for Comments: 2547 Y. Rekhter Category: Informational Cisco Systems, Inc.

                                                            March 1999
                           BGP/MPLS VPNs

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 (1999).  All Rights Reserved.

Abstract

 This document describes a method by which a Service Provider with an
 IP backbone may provide VPNs (Virtual Private Networks) for its
 customers.  MPLS (Multiprotocol Label Switching) is used for
 forwarding packets over the backbone, and BGP (Border Gateway
 Protocol) is used for distributing routes over the backbone.  The
 primary goal of this method is to support the outsourcing of IP
 backbone services for enterprise networks. It does so in a manner
 which is simple for the enterprise, while still scalable and flexible
 for the Service Provider, and while allowing the Service Provider to
 add value. These techniques can also be used to provide a VPN which
 itself provides IP service to customers.

Table of Contents

 1          Introduction  .......................................   2
 1.1        Virtual Private Networks  ...........................   2
 1.2        Edge Devices  .......................................   3
 1.3        VPNs with Overlapping Address Spaces  ...............   4
 1.4        VPNs with Different Routes to the Same System  ......   4
 1.5        Multiple Forwarding Tables in PEs  ..................   5
 1.6        SP Backbone Routers  ................................   5
 1.7        Security  ...........................................   5
 2          Sites and CEs  ......................................   6
 3          Per-Site Forwarding Tables in the PEs  ..............   6
 3.1        Virtual Sites  ......................................   8
 4          VPN Route Distribution via BGP  .....................   8
 4.1        The VPN-IPv4 Address Family  ........................   9
 4.2        Controlling Route Distribution  .....................  10

Rosen & Rekhter Informational [Page 1] RFC 2547 BGP/MPLS VPNs March 1999

 4.2.1      The Target VPN Attribute  ...........................  10
 4.2.2      Route Distribution Among PEs by BGP  ................  12
 4.2.3      The VPN of Origin Attribute  ........................  13
 4.2.4      Building VPNs using Target and Origin Attributes  ...  14
 5          Forwarding Across the Backbone  .....................  15
 6          How PEs Learn Routes from CEs  ......................  16
 7          How CEs learn Routes from PEs  ......................  19
 8          What if the CE Supports MPLS?  ......................  19
 8.1        Virtual Sites  ......................................  19
 8.2        Representing an ISP VPN as a Stub VPN  ..............  20
 9          Security  ...........................................  20
 9.1        Point-to-Point Security Tunnels between CE Routers  .  21
 9.2        Multi-Party Security Associations  ..................  21
 10         Quality of Service  .................................  22
 11         Scalability  ........................................  22
 12         Intellectual Property Considerations  ...............  23
 13         Security Considerations  ............................  23
 14         Acknowledgments  ....................................  23
 15         Authors' Addresses  .................................  24
 16         References  .........................................  24
 17         Full Copyright Statement.............................  25

1. Introduction

1.1. Virtual Private Networks

 Consider a set of "sites" which are attached to a common network
 which we may call the "backbone". Let's apply some policy to create a
 number of subsets of that set, and let's impose the following rule:
 two sites may have IP interconnectivity over that backbone only if at
 least one of these subsets contains them both.
 The subsets we have created are "Virtual Private Networks" (VPNs).
 Two sites have IP connectivity over the common backbone only if there
 is some VPN which contains them both.  Two sites which have no VPN in
 common have no connectivity over that backbone.
 If all the sites in a VPN are owned by the same enterprise, the VPN
 is a corporate "intranet".  If the various sites in a VPN are owned
 by different enterprises, the VPN is an "extranet".  A site can be in
 more than one VPN; e.g., in an intranet and several extranets.  We
 regard both intranets and extranets as VPNs. In general, when we use
 the term VPN we will not be distinguishing between intranets and
 extranets.
 We wish to consider the case in which the backbone is owned and
 operated by one or more Service Providers (SPs).  The owners of the
 sites are the "customers" of the SPs.  The policies that determine

Rosen & Rekhter Informational [Page 2] RFC 2547 BGP/MPLS VPNs March 1999

 whether a particular collection of sites is a VPN are the policies of
 the customers.  Some customers will want the implementation of these
 policies to be entirely the responsibility of the SP.  Other
 customers may want to implement these policies themselves, or to
 share with the SP the responsibility for implementing these policies.
 In this document, we are primarily discussing mechanisms that may be
 used to implement these policies.  The mechanisms we describe are
 general enough to allow these policies to be implemented either by
 the SP alone, or by a VPN customer together with the SP.  Most of the
 discussion is focused on the former case, however.
 The mechanisms discussed in this document allow the implementation of
 a wide range of policies. For example, within a given VPN, we can
 allow every site to have a direct route to every other site ("full
 mesh"), or we can restrict certain pairs of sites from having direct
 routes to each other ("partial mesh").
 In this document, we are particularly interested in the case where
 the common backbone offers an IP service.  We are primarily concerned
 with the case in which an enterprise is outsourcing its backbone to a
 service provider, or perhaps to a set of service providers, with
 which it maintains contractual relationships.  We are not focused on
 providing VPNs over the public Internet.
 In the rest of this introduction, we specify some properties which
 VPNs should have.  The remainder of this document outlines a VPN
 model which has all these properties.  The VPN Model of this document
 appears to be an instance of the framework described in [4].

1.2. Edge Devices

 We suppose that at each site, there are one or more Customer Edge
 (CE) devices, each of which is attached via some sort of data link
 (e.g., PPP, ATM, ethernet, Frame Relay, GRE tunnel, etc.)  to one or
 more Provider Edge (PE) routers.
 If a particular site has a single host, that host may be the CE
 device.  If a particular site has a single subnet, that the CE device
 may be a switch.  In general, the CE device can be expected to be a
 router, which we call the CE router.
 We will say that a PE router is attached to a particular VPN if it is
 attached to a CE device which is in that VPN.  Similarly, we will say
 that a PE router is attached to a particular site if it is attached
 to a CE device which is in that site.
 When the CE device is a router, it is a routing peer of the PE(s) to
 which it is attached, but is not a routing peer of CE routers at

Rosen & Rekhter Informational [Page 3] RFC 2547 BGP/MPLS VPNs March 1999

 other sites.  Routers at different sites do not directly exchange
 routing information with each other; in fact, they do not even need
 to know of each other at all (except in the case where this is
 necessary for security purposes, see section 9).  As a consequence,
 very large VPNs (i.e., VPNs with a very large number of sites) are
 easily supported, while the routing strategy for each individual site
 is greatly simplified.
 It is important to maintain clear administrative boundaries between
 the SP and its customers (cf. [4]).  The PE and P routers should be
 administered solely by the SP, and the SP's customers should not have
 any management access to it.  The CE devices should be administered
 solely by the customer (unless the customer has contracted the
 management services out to the SP).

1.3. VPNs with Overlapping Address Spaces

 We assume that any two non-intersecting VPNs (i.e., VPNs with no
 sites in common) may have overlapping address spaces; the same
 address may be reused, for different systems, in different VPNs.  As
 long as a given endsystem has an address which is unique within the
 scope of the VPNs that it belongs to, the endsystem itself does not
 need to know anything about VPNs.
 In this model, the VPN owners do not have a backbone to administer,
 not even a "virtual backbone". Nor do the SPs have to administer a
 separate backbone or "virtual backbone" for each VPN.  Site-to-site
 routing in the backbone is optimal (within the constraints of the
 policies used to form the VPNs), and is not constrained in any way by
 an artificial "virtual topology" of tunnels.

1.4. VPNs with Different Routes to the Same System

 Although a site may be in multiple VPNs, it is not necessarily the
 case that the route to a given system at that site should be the same
 in all the VPNs.  Suppose, for example, we have an intranet
 consisting of sites A, B, and C, and an extranet consisting of A, B,
 C, and the "foreign" site D.  Suppose that at site A there is a
 server, and we want clients from B, C, or D to be able to use that
 server.  Suppose also that at site B there is a firewall.  We want
 all the traffic from site D to the server to pass through the
 firewall, so that traffic from the extranet can be access controlled.
 However, we don't want traffic from C to pass through the firewall on
 the way to the server, since this is intranet traffic.
 This means that it needs to be possible to set up two routes to the
 server.  One route, used by sites B and C, takes the traffic directly
 to site A.  The second route, used by site D, takes the traffic

Rosen & Rekhter Informational [Page 4] RFC 2547 BGP/MPLS VPNs March 1999

 instead to the firewall at site B.  If the firewall allows the
 traffic to pass, it then appears to be traffic coming from site B,
 and follows the route to site A.

1.5. Multiple Forwarding Tables in PEs

 Each PE router needs to maintain a number of separate forwarding
 tables.  Every site to which the PE is attached must be mapped to one
 of those forwarding tables.  When a packet is received from a
 particular site, the forwarding table associated with that site is
 consulted in order to determine how to route the packet.  The
 forwarding table associated with a particular site S is populated
 only with routes that lead to other sites which have at least one VPN
 in common with S. This prevents communication between sites which
 have no VPN in common, and it allows two VPNs with no site in common
 to use address spaces that overlap with each other.

1.6. SP Backbone Routers

 The SP's backbone consists of the PE routers, as well as other
 routers (P routers) which do not attach to CE devices.
 If every router in an SP's backbone had to maintain routing
 information for all the VPNs supported by the SP, this model would
 have severe scalability problems; the number of sites that could be
 supported would be limited by the amount of routing information that
 could be held in a single router.  It is important to require
 therefore that the routing information about a particular VPN be
 present ONLY in those PE routers which attach to that VPN.  In
 particular, the P routers should not need to have ANY per-VPN routing
 information whatsoever.
 VPNs may span multiple service providers. We assume though that when
 the path between PE routers crosses a boundary between SP networks,
 it does so via a private peering arrangement, at which there exists
 mutual trust between the two providers. In particular, each provider
 must trust the other to pass it only correct routing information, and
 to pass it labeled (in the sense of MPLS [9]) packets only if those
 packets have been labeled by trusted sources. We also assume that it
 is possible for label switched paths to cross the boundary between
 service providers.

1.7. Security

 A VPN model should, even without the use of cryptographic security
 measures, provide a level of security equivalent to that obtainable
 when a level 2 backbone (e.g., Frame Relay) is used.  That is, in the
 absence of misconfiguration or deliberate interconnection of

Rosen & Rekhter Informational [Page 5] RFC 2547 BGP/MPLS VPNs March 1999

 different VPNs, it should not be possible for systems in one VPN to
 gain access to systems in another VPN.
 It should also be possible to deploy standard security procedures.

2. Sites and CEs

 From the perspective of a particular backbone network, a set of IP
 systems constitutes a site if those systems have mutual IP
 interconnectivity, and communication between them occurs without use
 of the backbone. In general, a site will consist of a set of systems
 which are in geographic proximity.  However, this is not universally
 true; two geographic locations connected via a leased line, over
 which OSPF is running, will constitute a single site, because
 communication between the two locations does not involve the use of
 the backbone.
 A CE device is always regarded as being in a single site (though as
 we shall see, a site may consist of multiple "virtual sites"). A
 site, however, may belong to multiple VPNs.
 A PE router may attach to CE devices in any number of different
 sites, whether those CE devices are in the same or in different VPNs.
 A CE device may, for robustness, attach to multiple PE routers, of
 the same or of different service providers.  If the CE device is a
 router, the PE router and the CE router will appear as router
 adjacencies to each other.
 While the basic unit of interconnection is the site, the architecture
 described herein allows a finer degree of granularity in the control
 of interconnectivity. For example, certain systems at a site may be
 members of an intranet as well as members of one or more extranets,
 while other systems at the same site may be restricted to being
 members of the intranet only.

3. Per-Site Forwarding Tables in the PEs

 Each PE router maintains one or more "per-site forwarding tables".
 Every site to which the PE router is attached is associated with one
 of these tables.  A particular packet's IP destination address is
 looked up in a particular per-site forwarding table only if that
 packet has arrived directly from a site which is associated with that
 table.
 How are the per-site forwarding tables populated?

Rosen & Rekhter Informational [Page 6] RFC 2547 BGP/MPLS VPNs March 1999

 As an example, let PE1, PE2, and PE3 be three PE routers, and let
 CE1, CE2, and CE3 be three CE routers. Suppose that PE1 learns, from
 CE1, the routes which are reachable at CE1's site.  If PE2 and PE3
 are attached respectively to CE2 and CE3, and there is some VPN V
 containing CE1, CE2, and CE3, then PE1 uses BGP to distribute to PE2
 and PE3 the routes which it has learned from CE1.  PE2 and PE3 use
 these routes to populate the forwarding tables which they associate
 respectively with the sites of CE2 and CE3.  Routes from sites which
 are not in VPN V do not appear in these forwarding tables, which
 means that packets from CE2 or CE3 cannot be sent to sites which are
 not in VPN V.
 If a site is in multiple VPNs, the forwarding table associated with
 that site can contain routes from the full set of VPNs of which the
 site is a member.
 A PE generally maintains only one forwarding table per site, even if
 it is multiply connected to that site.  Also, different sites can
 share the same forwarding table if they are meant to use exactly the
 same set of routes.
 Suppose a packet is received by a PE router from a particular
 directly attached site, but the packet's destination address does not
 match any entry in the forwarding table associated with that site.
 If the SP is not providing Internet access for that site, then the
 packet is discarded as undeliverable.  If the SP is providing
 Internet access for that site, then the PE's Internet forwarding
 table will be consulted.  This means that in general, only one
 forwarding table per PE need ever contain routes from the Internet,
 even if Internet access is provided.
 To maintain proper isolation of one VPN from another, it is important
 that no router in the backbone accept a labeled packet from any
 adjacent non-backbone device unless (a) the label at the top of the
 label stack was actually distributed by the backbone router to the
 non-backbone device, and (b) the backbone router can determine that
 use of that label will cause the packet to leave the backbone before
 any labels lower in the stack will be inspected, and before the IP
 header will be inspected.  These restrictions are necessary in order
 to prevent packets from entering a VPN where they do not belong.
 The per-site forwarding tables in a PE are ONLY used for packets
 which arrive from a site which is directly attached to the PE.  They
 are not used for routing packets which arrive from other routers that
 belong to the SP backbone.  As a result, there may be multiple
 different routes to the same system, where the route followed by a
 given packet is determined by the site from which the packet enters
 the backbone.  E.g., one may have one route to a given system for

Rosen & Rekhter Informational [Page 7] RFC 2547 BGP/MPLS VPNs March 1999

 packets from the extranet (where the route leads to a firewall), and
 a different route to the same system for packets from the intranet
 (including packets that have already passed through the firewall).

3.1. Virtual Sites

 In some cases, a particular site may be divided by the customer into
 several virtual sites, perhaps by the use of VLANs.  Each virtual
 site may be a member of a different set of VPNs. The PE then needs to
 contain a separate forwarding table for each virtual site.  For
 example, if a CE supports VLANs, and wants each VLAN mapped to a
 separate VPN, the packets sent between CE and PE could be contained
 in the site's VLAN encapsulation, and this could be used by the PE,
 along with the interface over which the packet is received, to assign
 the packet to a particular virtual site.
 Alternatively, one could divide the interface into multiple "sub-
 interfaces" (particularly if the interface is Frame Relay or ATM),
 and assign the packet to a VPN based on the sub-interface over which
 it arrives.  Or one could simply use a different interface for each
 virtual site.  In any case, only one CE router is ever needed per
 site, even if there are multiple virtual sites.  Of course, a
 different CE router could be used for each virtual site, if that is
 desired.
 Note that in all these cases, the mechanisms, as well as the policy,
 for controlling which traffic is in which VPN are in the hand of the
 customer.
 If it is desired to have a particular host be in multiple virtual
 sites, then that host must determine, for each packet, which virtual
 site the packet is associated with.  It can do this, e.g., by sending
 packets from different virtual sites on different VLANs, our out
 different network interfaces.
 These schemes do NOT require the CE to support MPLS.  Section 8
 contains a brief discussion of how the CE might support multiple
 virtual sites if it does support MPLS.

4. VPN Route Distribution via BGP

 PE routers use BGP to distribute VPN routes to each other (more
 accurately, to cause VPN routes to be distributed to each other).
 A BGP speaker can only install and distribute one route to a given
 address prefix.  Yet we allow each VPN to have its own address space,
 which means that the same address can be used in any number of VPNs,
 where in each VPN the address denotes a different system.  It follows

Rosen & Rekhter Informational [Page 8] RFC 2547 BGP/MPLS VPNs March 1999

 that we need to allow BGP to install and distribute multiple routes
 to a single IP address prefix.  Further, we must ensure that POLICY
 is used to determine which sites can be use which routes; given that
 several such routes are installed by BGP, only one such must appear
 in any particular per-site forwarding table.
 We meet these goals by the use of a new address family, as specified
 below.

4.1. The VPN-IPv4 Address Family

 The BGP Multiprotocol Extensions [3] allow BGP to carry routes from
 multiple "address families".  We introduce the notion of the "VPN-
 IPv4 address family".  A VPN-IPv4 address is a 12-byte quantity,
 beginning with an 8-byte "Route Distinguisher (RD)" and ending with a
 4-byte IPv4 address.  If two VPNs use the same IPv4 address prefix,
 the PEs translate these into unique VPN-IPv4 address prefixes.  This
 ensures that if the same address is used in two different VPNs, it is
 possible to install two completely different routes to that address,
 one for each VPN.
 The RD does not by itself impose any semantics; it contains no
 information about the origin of the route or about the set of VPNs to
 which the route is to be distributed.  The purpose of the RD is
 solely to allow one to create distinct routes to a common IPv4
 address prefix.  Other means are used to determine where to
 redistribute the route (see section 4.2).
 The RD can also be used to create multiple different routes to the
 very same system.  In section 3, we gave an example where the route
 to a particular server had to be different for intranet traffic than
 for extranet traffic.  This can be achieved by creating two different
 VPN-IPv4 routes that have the same IPv4 part, but different RDs.
 This allows BGP to install multiple different routes to the same
 system, and allows policy to be used (see section 4.2.3) to decide
 which packets use which route.
 The RDs are structured so that every service provider can administer
 its own "numbering space" (i.e., can make its own assignments of
 RDs), without conflicting with the RD assignments made by any other
 service provider.  An RD consists of a two-byte type field, an
 administrator field, and an assigned number field.  The value of the
 type field determines the lengths of the other two fields, as well as
 the semantics of the administrator field.  The administrator field
 identifies an assigned number authority, and the assigned number
 field contains a number which has been assigned, by the identified
 authority, for a particular purpose.  For example, one could have an
 RD whose administrator field contains an Autonomous System number

Rosen & Rekhter Informational [Page 9] RFC 2547 BGP/MPLS VPNs March 1999

 (ASN), and whose (4-byte) number field contains a number assigned by
 the SP to whom IANA has assigned that ASN.  RDs are given this
 structure in order to ensure that an SP which provides VPN backbone
 service can always create a unique RD when it needs to do so.
 However, the structuring provides no semantics. When BGP compares two
 such address prefixes, it ignores the structure entirely.
 If the Administrator subfield and the Assigned Number subfield of a
 VPN-IPv4 address are both set to all zeroes, the VPN-IPv4 address is
 considered to have exactly the same meaning as the corresponding
 globally unique IPv4 address. In particular, this VPN-IPv4 address
 and the corresponding globally unique IPv4 address will be considered
 comparable by BGP. In all other cases, a VPN-IPv4 address and its
 corresponding globally unique IPv4 address will be considered
 noncomparable by BGP.
 A given per-site forwarding table will only have one VPN-IPv4 route
 for any given IPv4 address prefix.  When a packet's destination
 address is matched against a VPN-IPv4 route, only the IPv4 part is
 actually matched.
 A PE needs to be configured to associate routes which lead to
 particular CE with a particular RD.  The PE may be configured to
 associate all routes leading to the same CE with the same RD, or it
 may be configured to associate different routes with different RDs,
 even if they lead to the same CE.

4.2. Controlling Route Distribution

 In this section, we discuss the way in which the distribution of the
 VPN-IPv4 routes is controlled.

4.2.1. The Target VPN Attribute

 Every per-site forwarding table is associated with one or more
 "Target VPN" attributes.
 When a VPN-IPv4 route is created by a PE router, it is associated
 with one or more "Target VPN" attributes.  These are carried in BGP
 as attributes of the route.
 Any route associated with Target VPN T must be distributed to every
 PE router that has a forwarding table associated with Target VPN T.
 When such a route is received by a PE router, it is eligible to be
 installed in each of the PE's per-site forwarding tables that is
 associated with Target VPN T. (Whether it actually gets installed
 depends on the outcome of the BGP decision process.)

Rosen & Rekhter Informational [Page 10] RFC 2547 BGP/MPLS VPNs March 1999

 In essence, a Target VPN attribute identifies a set of sites.
 Associating a particular Target VPN attribute with a route allows
 that route to be placed in the per-site forwarding tables that are
 used for routing traffic which is received from the corresponding
 sites.
 There is a set of Target VPNs that a PE router attaches to a route
 received from site S. And there is a set of Target VPNs that a PE
 router uses to determine whether a route received from another PE
 router could be placed in the forwarding table associated with site
 S. The two sets are distinct, and need not be the same.
 The function performed by the Target VPN attribute is similar to that
 performed by the BGP Communities Attribute.  However, the format of
 the latter is inadequate, since it allows only a two-byte numbering
 space.  It would be fairly straightforward to extend the BGP
 Communities Attribute to provide a larger numbering space.  It should
 also be possible to structure the format, similar to what we have
 described for RDs (see section 4.1), so that a type field defines the
 length of an administrator field, and the remainder of the attribute
 is a number from the specified administrator's numbering space.
 When a BGP speaker has received two routes to the same VPN-IPv4
 prefix, it chooses one, according to the BGP rules for route
 preference.
 Note that a route can only have one RD, but it can have multiple
 Target VPNs.  In BGP, scalability is improved if one has a single
 route with multiple attributes, as opposed to multiple routes.  One
 could eliminate the Target VPN attribute by creating more routes
 (i.e., using more RDs), but the scaling properties would be less
 favorable.
 How does a PE determine which Target VPN attributes to associate with
 a given route?  There are a number of different possible ways.  The
 PE might be configured to associate all routes that lead to a
 particular site with a particular Target VPN.  Or the PE might be
 configured to associate certain routes leading to a particular site
 with one Target VPN, and certain with another.  Or the CE router,
 when it distributes these routes to the PE (see section 6), might
 specify one or more Target VPNs for each route.  The latter method
 shifts the control of the mechanisms used to implement the VPN
 policies from the SP to the customer.  If this method is used, it may
 still be desirable to have the PE eliminate any Target VPNs that,
 according to its own configuration, are not allowed, and/or to add in
 some Target VPNs that according to its own configuration are
 mandatory.

Rosen & Rekhter Informational [Page 11] RFC 2547 BGP/MPLS VPNs March 1999

 It might be more accurate, if less suggestive, to call this attribute
 the "Route Target" attribute instead of the "VPN Target" attribute.
 It really identifies only a set of sites which will be able to use
 the route, without prejudice to whether those sites constitute what
 might intuitively be called a VPN.

4.2.2. Route Distribution Among PEs by BGP

 If two sites of a VPN attach to PEs which are in the same Autonomous
 System, the PEs can distribute VPN-IPv4 routes to each other by means
 of an IBGP connection between them.  Alternatively, each can have an
 IBGP connection to a route reflector.
 If two sites of VPN are in different Autonomous Systems (e.g.,
 because they are connected to different SPs), then a PE router will
 need to use IBGP to redistribute VPN-IPv4 routes either to an
 Autonomous System Border Router (ASBR), or to a route reflector of
 which an ASBR is a client.  The ASBR will then need to use EBGP to
 redistribute those routes to an ASBR in another AS.  This allows one
 to connect different VPN sites to different Service Providers.
 However, VPN-IPv4 routes should only be accepted on EBGP connections
 at private peering points, as part of a trusted arrangement between
 SPs.  VPN-IPv4 routes should neither be distributed to nor accepted
 from the public Internet.
 If there are many VPNs having sites attached to different Autonomous
 Systems, there does not need to be a single ASBR between those two
 ASes which holds all the routes for all the VPNs; there can be
 multiple ASBRs, each of which holds only the routes for a particular
 subset of the VPNs.
 When a PE router distributes a VPN-IPv4 route via BGP, it uses its
 own address as the "BGP next hop".  It also assigns and distributes
 an MPLS label.  (Essentially, PE routers distribute not VPN-IPv4
 routes, but Labeled VPN-IPv4 routes. Cf. [8]) When the PE processes a
 received packet that has this label at the top of the stack, the PE
 will pop the stack, and send the packet directly to the site from to
 which the route leads.  This will usually mean that it just sends the
 packet to the CE router from which it learned the route.  The label
 may also determine the data link encapsulation.
 In most cases, the label assigned by a PE will cause the packet to be
 sent directly to a CE, and the PE which receives the labeled packet
 will not look up the packet's destination address in any forwarding
 table.  However, it is also possible for the PE to assign a label
 which implicitly identifies a particular forwarding table.  In this
 case, the PE receiving a packet that label would look up the packet's
 destination address in one of its forwarding tables.  While this can

Rosen & Rekhter Informational [Page 12] RFC 2547 BGP/MPLS VPNs March 1999

 be very useful in certain circumstances, we do not consider it
 further in this paper.
 Note that the MPLS label that is distributed in this way is only
 usable if there is a label switched path between the router that
 installs a route and the BGP next hop of that route.  We do not make
 any assumption about the procedure used to set up that label switched
 path.  It may be set up on a pre-established basis, or it may be set
 up when a route which would need it is installed.  It may be a "best
 effort" route, or it may be a traffic engineered route.  Between a
 particular PE router and its BGP next hop for a particular route
 there may be one LSP, or there may be several, perhaps with different
 QoS characteristics.  All that matters for the VPN architecture is
 that some label switched path between the router and its BGP next hop
 exists.
 All the usual techniques for using route reflectors [2] to improve
 scalability, e.g., route reflector hierarchies, are available.  If
 route reflectors are used, there is no need to have any one route
 reflector know all the VPN-IPv4 routes for all the VPNs supported by
 the backbone.  One can have separate route reflectors, which do not
 communicate with each other, each of which supports a subset of the
 total set of VPNs.
 If a given PE router is not attached to any of the Target VPNs of a
 particular route, it should not receive that route; the other PE or
 route reflector which is distributing routes to it should apply
 outbound filtering to avoid sending it unnecessary routes.  Of
 course, if a PE router receives a route via BGP, and that PE is not
 attached to any of the route's target VPNs, the PE should apply
 inbound filtering to the route, neither installing nor redistributing
 it.
 A router which is not attached to any VPN, i.e., a P router, never
 installs any VPN-IPv4 routes at all.
 These distribution rules ensure that there is no one box which needs
 to know all the VPN-IPv4 routes that are supported over the backbone.
 As a result, the total number of such routes that can be supported
 over the backbone is not bound by the capacity of any single device,
 and therefore can increase virtually without bound.

4.2.3. The VPN of Origin Attribute

 A VPN-IPv4 route may be optionally associated with a VPN of Origin
 attribute.  This attribute uniquely identifies a set of sites, and
 identifies the corresponding route as having come from one of the
 sites in that set.  Typical uses of this attribute might be to

Rosen & Rekhter Informational [Page 13] RFC 2547 BGP/MPLS VPNs March 1999

 identify the enterprise which owns the site where the route leads, or
 to identify the site's intranet.  However, other uses are also
 possible.  This attribute could be encoded as an extended BGP
 communities attribute.
 In situations in which it is necessary to identify the source of a
 route, it is this attribute, not the RD, which must be used.  This
 attribute may be used when "constructing" VPNs, as described below.
 It might be more accurate, if less suggestive, to call this attribute
 the "Route Origin" attribute instead of the "VPN of Origin"
 attribute.  It really identifies the route only has having come from
 one of a particular set of sites, without prejudice as to whether
 that particular set of sites really constitutes a VPN.

4.2.4. Building VPNs using Target and Origin Attributes

 By setting up the Target VPN and VPN of Origin attributes properly,
 one can construct different kinds of VPNs.
 Suppose it is desired to create a Closed User Group (CUG) which
 contains a particular set of sites. This can be done by creating a
 particular Target VPN attribute value to represent the CUG. This
 value then needs to be associated with the per-site forwarding tables
 for each site in the CUG, and it needs to be associated with every
 route learned from a site in the CUG.  Any route which has this
 Target VPN attribute will need to be redistributed so that it reaches
 every PE router attached to one of the sites in the CUG.
 Alternatively, suppose one desired, for whatever reason, to create a
 "hub and spoke" kind of VPN.  This could be done by the use of two
 Target Attribute values, one meaning "Hub" and one meaning "Spoke".
 Then routes from the spokes could be distributed to the hub, without
 causing routes from the hub to be distributed to the spokes.
 Suppose one has a number of sites which are in an intranet and an
 extranet, as well as a number of sites which are in the intranet
 only.  Then there may be both intranet and extranet routes which have
 a Target VPN identifying the entire set of sites.  The sites which
 are to have intranet routes only can filter out all routes with the
 "wrong" VPN of Origin.
 These two attributes allow great flexibility in allowing one to
 control the distribution of routing information among various sets of
 sites, which in turn provides great flexibility in constructing VPNs.

Rosen & Rekhter Informational [Page 14] RFC 2547 BGP/MPLS VPNs March 1999

5. Forwarding Across the Backbone

 If the intermediate routes in the backbone do not have any
 information about the routes to the VPNs, how are packets forwarded
 from one VPN site to another?
 This is done by means of MPLS with a two-level label stack.
 PE routers (and ASBRs which redistribute VPN-IPv4 addresses) need to
 insert /32 address prefixes for themselves into the IGP routing
 tables of the backbone.  This enables MPLS, at each node in the
 backbone network, to assign a label corresponding to the route to
 each PE router.  (Certain procedures for setting up label switched
 paths in the backbone may not require the presence of the /32 address
 prefixes.)
 When a PE receives a packet from a CE device, it chooses a particular
 per-site forwarding table in which to look up the packet's
 destination address.  Assume that a match is found.
 If the packet is destined for a CE device attached to this same PE,
 the packet is sent directly to that CE device.
 If the packet is not destined for a CE device attached to this same
 PE, the packet's "BGP Next Hop" is found, as well as the label which
 that BGP next hop assigned for the packet's destination address. This
 label is pushed onto the packet's label stack, and becomes the bottom
 label.  Then the PE looks up the IGP route to the BGP Next Hop, and
 thus determines the IGP next hop, as well as the label assigned to
 the address of the BGP next hop by the IGP next hop.  This label gets
 pushed on as the packet's top label, and the packet is then forwarded
 to the IGP next hop.  (If the BGP next hop is the same as the IGP
 next hop, the second label may not need to be pushed on, however.)
 At this point, MPLS will carry the packet across the backbone and
 into the appropriate CE device.  That is, all forwarding decisions by
 P routers and PE routers are now made by means of MPLS, and the
 packet's IP header is not looked at again until the packet reaches
 the CE device.  The final PE router will pop the last label from the
 MPLS label stack before sending the packet to the CE device, thus the
 CE device will just see an ordinary IP packet.  (Though see section 8
 for some discussion of the case where the CE desires to received
 labeled packets.)
 When a packet enters the backbone from a particular site via a
 particular PE router, the packet's route is determined by the
 contents of the forwarding table which that PE router associated with
 that site.  The forwarding tables of the PE router where the packet

Rosen & Rekhter Informational [Page 15] RFC 2547 BGP/MPLS VPNs March 1999

 leaves the backbone are not relevant.  As a result, one may have
 multiple routes to the same system, where the particular route chosen
 for a particular packet is based on the site from which the packet
 enters the backbone.
 Note that it is the two-level labeling that makes it possible to keep
 all the VPN routes out of the P routers, and this in turn is crucial
 to ensuring the scalability of the model.  The backbone does not even
 need to have routes to the CEs, only to the PEs.

6. How PEs Learn Routes from CEs

 The PE routers which attach to a particular VPN need to know, for
 each of that VPN's sites, which addresses in that VPN are at each
 site.
 In the case where the CE device is a host or a switch, this set of
 addresses will generally be configured into the PE router attaching
 to that device.  In the case where the CE device is a router, there
 are a number of possible ways that a PE router can obtain this set of
 addresses.
 The PE translates these addresses into VPN-IPv4 addresses, using a
 configured RD.  The PE then treats these VPN-IPv4 routes as input to
 BGP.  In no case will routes from a site ever be leaked into the
 backbone's IGP.
 Exactly which PE/CE route distribution techniques are possible
 depends on whether a particular CE is in a "transit VPN" or not.  A
 "transit VPN" is one which contains a router that receives routes
 from a "third party" (i.e., from a router which is not in the VPN,
 but is not a PE router), and that redistributes those routes to a PE
 router.  A VPN which is not a transit VPN is a "stub VPN".  The vast
 majority of VPNs, including just about all corporate enterprise
 networks, would be expected to be "stubs" in this sense.
 The possible PE/CE distribution techniques are:
    1. Static routing (i.e., configuration) may be used. (This is
       likely to be useful only in stub VPNs.)
    2. PE and CE routers may be RIP peers, and the CE may use RIP to
       tell the PE router the set of address prefixes which are
       reachable at the CE router's site.  When RIP is configured in
       the CE, care must be taken to ensure that address prefixes from
       other sites (i.e., address prefixes learned by the CE router
       from the PE router) are never advertised to the PE.  More
       precisely: if a PE router, say PE1, receives a VPN-IPv4 route

Rosen & Rekhter Informational [Page 16] RFC 2547 BGP/MPLS VPNs March 1999

       R1, and as a result distributes an IPv4 route R2 to a CE, then
       R2 must not be distributed back from that CE's site to a PE
       router, say PE2, (where PE1 and PE2 may be the same router or
       different routers), unless PE2 maps R2 to a VPN-IPv4 route
       which is different than (i.e., contains a different RD than)
       R1.
    3. The PE and CE routers may be OSPF peers.  In this case, the
       site should be a single OSPF area, the CE should be an ABR in
       that area, and the PE should be an ABR which is not in that
       area.  Also, the PE should report no router links other than
       those to the CEs which are at the same site. (This technique
       should be used only in stub VPNs.)
    4. The PE and CE routers may be BGP peers, and the CE router may
       use BGP (in particular, EBGP to tell the PE router the set of
       address prefixes which are at the CE router's site. (This
       technique can be used in stub VPNs or transit VPNs.)
       From a purely technical perspective, this is by far the best
       technique:
            a) Unlike the IGP alternatives, this does not require the
               PE to run multiple routing algorithm instances in order
               to talk to multiple CEs
            b) BGP is explicitly designed for just this function:
               passing routing information between systems run by
               different administrations
            c) If the site contains "BGP backdoors", i.e., routers
               with BGP connections to routers other than PE routers,
               this procedure will work correctly in all
               circumstances.  The other procedures may or may not
               work, depending on the precise circumstances.
            d) Use of BGP makes it easy for the CE to pass attributes
               of the routes to the PE.  For example, the CE may
               suggest a particular Target for each route, from among
               the Target attributes that the PE is authorized to
               attach to the route.
        On the other hand, using BGP is likely to be something new for
        the CE administrators, except in the case where the customer
        itself is already an Internet Service Provider (ISP).

Rosen & Rekhter Informational [Page 17] RFC 2547 BGP/MPLS VPNs March 1999

        If a site is not in a transit VPN, note that it need not have
        a unique Autonomous System Number (ASN).  Every CE whose site
        which is not in a transit VPN can use the same ASN.  This can
        be chosen from the private ASN space, and it will be stripped
        out by the PE.  Routing loops are prevented by use of the Site
        of Origin Attribute (see below).
        If a set of sites constitute a transit VPN, it is convenient
        to represent them as a BGP Confederation, so that the internal
        structure of the VPN is hidden from any router which is not
        within the VPN.  In this case, each site in the VPN would need
        two BGP connections to the backbone, one which is internal to
        the confederation and one which is external to it.  The usual
        intra-confederation procedures would have to be slightly
        modified in order to take account for the fact that the
        backbone and the sites may have different policies.  The
        backbone is a member of the confederation on one of the
        connections, but is not a member on the other.  These
        techniques may be useful if the customer for the VPN service
        is an ISP.  This technique allows a customer that is an ISP to
        obtain VPN backbone service from one of its ISP peers.
        (However, if a VPN customer is itself an ISP, and its CE
        routers support MPLS, a much simpler technique can be used,
        wherein the ISP is regarded as a stub VPN.  See section 8.)
 When we do not need to distinguish among the different ways in which
 a PE can be informed of the address prefixes which exist at a given
 site, we will simply say that the PE has "learned" the routes from
 that site.
 Before a PE can redistribute a VPN-IPv4 route learned from a site, it
 must assign certain attributes to the route. There are three such
 attributes:
  1. Site of Origin
      This attribute uniquely identifies the site from which the PE
      router learned the route.  All routes learned from a particular
      site must be assigned the same Site of Origin attribute, even if
      a site is multiply connected to a single PE, or is connected to
      multiple PEs.  Distinct Site of Origin attributes must be used
      for distinct sites.  This attribute could be encoded as an
      extended BGP communities attribute (section 4.2.1).
  1. VPN of Origin
      See section 4.2.1.

Rosen & Rekhter Informational [Page 18] RFC 2547 BGP/MPLS VPNs March 1999

  1. Target VPN
      See section 4.2.1.

7. How CEs learn Routes from PEs

 In this section, we assume that the CE device is a router.
 In general, a PE may distribute to a CE any route which the PE has
 placed in the forwarding table which it uses to route packets from
 that CE.  There is one exception: if a route's Site of Origin
 attribute identifies a particular site, that route must never be
 redistributed to any CE at that site.
 In most cases, however, it will be sufficient for the PE to simply
 distribute the default route to the CE.  (In some cases, it may even
 be sufficient for the CE to be configured with a default route
 pointing to the PE.)  This will generally work at any site which does
 not itself need to distribute the default route to other sites.
 (E.g., if one site in a corporate VPN has the corporation's access to
 the Internet, that site might need to have default distributed to the
 other site, but one could not distribute default to that site
 itself.)
 Whatever procedure is used to distribute routes from CE to PE will
 also be used to distribute routes from PE to CE.

8. What if the CE Supports MPLS?

 In the case where the CE supports MPLS, AND is willing to import the
 complete set of routes from its VPNs, the PE can distribute to it a
 label for each such route.  When the PE receives a packet from the CE
 with such a label, it (a) replaces that label with the corresponding
 label that it learned via BGP, and (b) pushes on a label
 corresponding to the BGP next hop for the corresponding route.

8.1. Virtual Sites

 If the CE/PE route distribution is done via BGP, the CE can use MPLS
 to support multiple virtual sites.  The CE may itself contain a
 separate forwarding table for each virtual site, which it populates
 as indicated by the VPN of Origin and Target VPN attributes of the
 routes it receives from the PE.  If the CE receives the full set of
 routes from the PE, the PE will not need to do any address lookup at
 all on packets received from the CE.  Alternatively, the PE may in
 some cases be able to distribute to the CE a single (labeled) default
 route for each VPN.  Then when the PE receives a labeled packet from

Rosen & Rekhter Informational [Page 19] RFC 2547 BGP/MPLS VPNs March 1999

 the CE, it would know which forwarding table to look in; the label
 placed on the packet by the CE would identify only the virtual site
 from which the packet is coming.

8.2. Representing an ISP VPN as a Stub VPN

 If a particular VPN is actually an ISP, but its CE routers support
 MPLS, then the VPN can actually be treated as a stub VPN.  The CE and
 PE routers need only exchange routes which are internal to the VPN.
 The PE router would distribute to the CE router a label for each of
 these routes.  Routers at different sites in the VPN can then become
 BGP peers.  When the CE router looks up a packet's destination
 address, the routing lookup always resolves to an internal address,
 usually the address of the packet's BGP next hop.  The CE labels the
 packet appropriately and sends the packet to the PE.

9. Security

 Under the following conditions:
    a) labeled packets are not accepted by backbone routers from
       untrusted or unreliable sources, unless it is known that such
       packets will leave the backbone before the IP header or any
       labels lower in the stack will be inspected, and
    b) labeled VPN-IPv4 routes are not accepted from untrusted or
       unreliable sources,
 the security provided by this architecture is virtually identical to
 that provided to VPNs by Frame Relay or ATM backbones.
 It is worth noting that the use of MPLS makes it much simpler to
 provide this level of security than would be possible if one
 attempted to use some form of IP-within-IP tunneling in place of
 MPLS.  It is a simple matter to refuse to accept a labeled packet
 unless the first of the above conditions applies to it.  It is rather
 more difficult to configure the a router to refuse to accept an IP
 packet if that packet is an IP-within-IP tunnelled packet which is
 going to a "wrong" place.
 The use of MPLS also allows a VPN to span multiple SPs without
 depending in any way on the inter-domain distribution of IPv4 routing
 information.
 It is also possible for a VPN user to provide himself with enhanced
 security by making use of Tunnel Mode IPSEC [5].  This is discussed
 in the remainder of this section.

Rosen & Rekhter Informational [Page 20] RFC 2547 BGP/MPLS VPNs March 1999

9.1. Point-to-Point Security Tunnels between CE Routers

 A security-conscious VPN user might want to ensure that some or all
 of the packets which traverse the backbone are authenticated and/or
 encrypted. The standard way to obtain this functionality today would
 be to create a "security tunnel" between every pair of CE routers in
 a VPN, using IPSEC Tunnel Mode.
 However, the procedures described so far do not enable the CE router
 transmitting a packet to determine the identify of the next CE router
 that the packet will traverse.  Yet that information is required in
 order to use Tunnel Mode IPSEC.  So we must extend those procedures
 to make this information available.
 A way to do this is suggested in [6].  Every VPN-IPv4 route can have
 an attribute which identifies the next CE router that will be
 traversed if that route is followed.  If this information is provided
 to all the CE routers in the VPN, standard IPSEC Tunnel Mode can be
 used.
 If the CE and PE are BGP peers, it is natural to present this
 information as a BGP attribute.
 Each CE that is to use IPSEC should also be configured with a set of
 address prefixes, such that it is prohibited from sending insecure
 traffic to any of those addresses.  This prevents the CE from sending
 insecure traffic if, for some reason, it fails to obtain the
 necessary information.
 When MPLS is used to carry packets between the two endpoints of an
 IPSEC tunnel, the IPSEC outer header does not really perform any
 function.  It might be beneficial to develop a form of IPSEC tunnel
 mode which allows the outer header to be omitted when MPLS is used.

9.2. Multi-Party Security Associations

 Instead of setting up a security tunnel between each pair of CE
 routers, it may be advantageous to set up a single, multiparty
 security association. In such a security association, all the CE
 routers which are in a particular VPN would share the same security
 parameters (.e.g., same secret, same algorithm, etc.). Then the
 ingress CE wouldn't have to know which CE is the next one to receive
 the data, it would only have to know which VPN the data is going to.
 A CE which is in multiple VPNs could use different security
 parameters for each one, thus protecting, e.g., intranet packets from
 being exposed to the extranet.

Rosen & Rekhter Informational [Page 21] RFC 2547 BGP/MPLS VPNs March 1999

 With such a scheme, standard Tunnel Mode IPSEC could not be used,
 because there is no way to fill in the IP destination address field
 of the "outer header".  However, when MPLS is used for forwarding,
 there is no real need for this outer header anyway; the PE router can
 use MPLS to get a packet to a tunnel endpoint without even knowing
 the IP address of that endpoint; it only needs to see the IP
 destination address of the "inner header".
 A significant advantage of a scheme like this is that it makes
 routing changes (in particular, a change of egress CE for a
 particular address prefix) transparent to the security mechanism.
 This could be particularly important in the case of multi-provider
 VPNs, where the need to distribute information about such routing
 changes simply to support the security mechanisms could result in
 scalability issues.
 Another advantage is that it eliminates the need for the outer IP
 header, since the MPLS encapsulation performs its role.

10. Quality of Service

 Although not the focus of this paper, Quality of Service is a key
 component of any VPN service.  In MPLS/BGP VPNs, existing L3 QoS
 capabilities can be applied to labeled packets through the use of the
 "experimental" bits in the shim header [10], or, where ATM is used as
 the backbone, through the use of ATM QoS capabilities.  The traffic
 engineering work discussed in [1] is also directly applicable to
 MPLS/BGP VPNs.  Traffic engineering could even be used to establish
 LSPs with particular QoS characteristics between particular pairs of
 sites, if that is desirable.  Where an MPLS/BGP VPN spans multiple
 SPs, the architecture described in [7] may be useful.  An SP may
 apply either intserv or diffserv capabilities to a particular VPN, as
 appropriate.

11. Scalability

 We have discussed scalability issues throughout this paper.  In this
 section, we briefly summarize the main characteristics of our model
 with respect to scalability.
 The Service Provider backbone network consists of (a) PE routers, (b)
 BGP Route Reflectors, (c) P routers (which are neither PE routers nor
 Route Reflectors), and, in the case of multi-provider VPNs, (d)
 ASBRs.

Rosen & Rekhter Informational [Page 22] RFC 2547 BGP/MPLS VPNs March 1999

 P routers do not maintain any VPN routes.  In order to properly
 forward VPN traffic, the P routers need only maintain routes to the
 PE routers and the ASBRs. The use of two levels of labeling is what
 makes it possible to keep the VPN routes out of the P routers.
 A PE router to maintains VPN routes, but only for those VPNs to which
 it is directly attached.
 Route reflectors and ASBRs can be partitioned among VPNs so that each
 partition carries routes for only a subset of the VPNs provided by
 the Service Provider. Thus no single Route Reflector or ASBR is
 required to maintain routes for all the VPNs.
 As a result, no single component within the Service Provider network
 has to maintain all the routes for all the VPNs.  So the total
 capacity of the network to support increasing numbers of VPNs is not
 limited by the capacity of any individual component.

12. Intellectual Property Considerations

 Cisco Systems may seek patent or other intellectual property
 protection for some of all of the technologies disclosed in this
 document. If any standards arising from this document are or become
 protected by one or more patents assigned to Cisco Systems, Cisco
 intends to disclose those patents and license them on reasonable and
 non-discriminatory terms.

13. Security Considerations

 Security issues are discussed throughout this memo.

14. Acknowledgments

 Significant contributions to this work have been made by Ravi
 Chandra, Dan Tappan and Bob Thomas.

Rosen & Rekhter Informational [Page 23] RFC 2547 BGP/MPLS VPNs March 1999

15. Authors' Addresses

 Eric C. Rosen
 Cisco Systems, Inc.
 250 Apollo Drive
 Chelmsford, MA, 01824
 EMail: erosen@cisco.com
 Yakov Rekhter
 Cisco Systems, Inc.
 170 Tasman Drive
 San Jose, CA, 95134
 EMail: yakov@cisco.com

16. References

 [1] Awduche, Berger,  Gan, Li, Swallow, and Srinavasan,  "Extensions
     to RSVP for LSP Tunnels", Work in Progress.
 [2] Bates, T. and R. Chandrasekaran, "BGP Route Reflection: An
     alternative to full mesh IBGP", RFC 1966, June 1996.
 [3] Bates, T., Chandra, R., Katz, D. and Y. Rekhter, "Multiprotocol
     Extensions for BGP4", RFC 2283, February 1998.
 [4] Gleeson, Heinanen, and Armitage, "A Framework for IP Based
     Virtual Private Networks", Work in Progress.
 [5] Kent and Atkinson, "Security Architecture for the Internet
     Protocol", RFC 2401, November 1998.
 [6] Li, "CPE based VPNs using MPLS", October 1998, Work in Progress.
 [7] Li, T. and Y. Rekhter, "A Provider Architecture for
     Differentiated Services and Traffic Engineering (PASTE)", RFC
     2430, October 1998.
 [8] Rekhter and Rosen, "Carrying Label Information in BGP4", Work in
     Progress.
 [9] Rosen, Viswanathan, and Callon, "Multiprotocol Label Switching
     Architecture", Work in Progress.
[10] Rosen, Rekhter, Tappan, Farinacci, Fedorkow, Li, and Conta, "MPLS
     Label Stack Encoding", Work in Progress.

Rosen & Rekhter Informational [Page 24] RFC 2547 BGP/MPLS VPNs March 1999

17. Full Copyright Statement

 Copyright (C) The Internet Society (1999).  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.
 This document and the information contained herein is provided on an
 "AS IS" basis and THE INTERNET SOCIETY AND THE INTERNET ENGINEERING
 TASK FORCE DISCLAIMS ALL WARRANTIES, EXPRESS OR IMPLIED, INCLUDING
 BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF THE INFORMATION
 HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED WARRANTIES OF
 MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE.

Rosen & Rekhter Informational [Page 25]

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