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Versions: (draft-marques-l3vpn-end-system) 00 01 02 03 04 05 06

Network Working Group                                          S. Mackie
Internet-Draft                                          Juniper Networks
Intended status: Standards Track                                 L. Fang
Expires: June 18, 2017                                              eBay
                                                                N. Sheth
                                                        Juniper Networks
                                                            M. Napierala
                                                               AT&T Labs
                                                                N. Bitar
                                                                   Nokia
                                                       December 15, 2016


                    BGP-Signaled End-System IP/VPNs
                     draft-ietf-l3vpn-end-system-06

Abstract

   This document describes a solution in which the control plane
   protocol specified in BGP/MPLS IP VPNs is used and extended via the
   XMPP protocol to provide a Virtual Network service to end-systems
   (hosts).  These end-systems may be used to provide network services
   or may host end-user applications.

Status of This Memo

   This Internet-Draft is submitted in full conformance with the
   provisions of BCP 78 and BCP 79.

   Internet-Drafts are working documents of the Internet Engineering
   Task Force (IETF).  Note that other groups may also distribute
   working documents as Internet-Drafts.  The list of current Internet-
   Drafts is at http://datatracker.ietf.org/drafts/current/.

   Internet-Drafts are draft documents valid for a maximum of six months
   and may be updated, replaced, or obsoleted by other documents at any
   time.  It is inappropriate to use Internet-Drafts as reference
   material or to cite them other than as "work in progress."

   This Internet-Draft will expire on June 18, 2017.

Copyright Notice

   Copyright (c) 2016 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



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   (http://trustee.ietf.org/license-info) in effect on the date of
   publication of this document.  Please review these documents
   carefully, as they describe your rights and restrictions with respect
   to this document.  Code Components extracted from this document must
   include Simplified BSD License text as described in Section 4.e of
   the Trust Legal Provisions and are provided without warranty as
   described in the Simplified BSD License.

Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   2
     1.1.  Terminology . . . . . . . . . . . . . . . . . . . . . . .   3
   2.  Requirements  . . . . . . . . . . . . . . . . . . . . . . . .   3
   3.  Applicability of BGP IP VPNs  . . . . . . . . . . . . . . . .   4
   4.  Virtual Network End-Points  . . . . . . . . . . . . . . . . .   7
   5.  VPN Forwarder . . . . . . . . . . . . . . . . . . . . . . . .   9
   6.  XMPP signaling protocol . . . . . . . . . . . . . . . . . . .  11
   7.  End-System Route Server behavior  . . . . . . . . . . . . . .  21
   8.  Operational Model . . . . . . . . . . . . . . . . . . . . . .  21
   9.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .  25
   10. Security Considerations . . . . . . . . . . . . . . . . . . .  25
   11. XML schema  . . . . . . . . . . . . . . . . . . . . . . . . .  26
   12. Acknowledgements  . . . . . . . . . . . . . . . . . . . . . .  28
   13. References  . . . . . . . . . . . . . . . . . . . . . . . . .  28
     13.1.  Normative References . . . . . . . . . . . . . . . . . .  29
     13.2.  Informational References . . . . . . . . . . . . . . . .  30
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  31

1.  Introduction

   This document describes the requirements for a network virtualization
   solution that provides an IP service to end-system virtual
   interfaces.  It then discusses how the control plane for BGP IP VPNs
   [RFC4364] can be used and extended via the XMPP protocol to provide a
   solution that meets these requirements.  Subsequent sections provide
   a detailed discussion of the control and forwarding plane components.

   In BGP IP VPNs, Customer Edge (CE) interfaces connect to a Provider
   Edge (PE) device which provides both the control plane and VPN
   encapsulation functions required to implement a Virtual Network
   service.  This document describes how the control plane and
   forwarding functionality of a PE device can be decoupled in order to
   enable the forwarding functionality to be implemented in multiple
   devices.  For instance, the forwarding function can be implemented
   directly on the operating system of application servers or network
   appliances.





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1.1.  Terminology

   This document makes use of the following terms:

   End-System:  A compute node whose primary function is to run
      applications.  It is assumed that end-systems support multiple
      application instances (e.g., virtual machines), each with its
      independent network configuration.

   End-System Route Server:  A software application that implements the
      control plane functionality of a BGP IP VPN PE device and an XMPP
      server that interacts with VPN Forwarders.

   Virtual Interface:  An interface in an end-system that is used by a
      virtual machine or by applications.  It performs the role of a CE
      interface in a BGP IP VPN network.  This is similar to the concept
      of Virtual Access Point (VAP) in RFC 7365 [RFC7365].

   VPN Forwarder:  The forwarding component of a BGP IP VPN PE device.
      This functionality may be co-located with the virtual interface or
      implemented by an external device.

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
   document are to be interpreted as described in RFC 2119 [RFC2119].

2.  Requirements

   Network virtualization is used in both service provider as well as
   enterprise networks to support multi-tenancy and network-based access
   control.  It may also be used to facilitate application instance
   mobility.

   Multi-tenancy allows a physical network to provide services to
   multiple "customers" or "tenants", whether these are external
   entities in the case of a Service Provider providing managed VPN
   services, or internal departments of an enterprise sharing an IT
   facility.  Multi-tenancy requires isolation of traffic and routing
   information between tenants.

   Within a tenant, it is often required to create multiple distinct
   virtual networks, in order to be able to provide network-based access
   control.  In this service model, each virtual network behaves as a
   "Closed User Group" (CUG) of virtual interfaces that are allowed to
   exchange traffic freely, while traffic between virtual networks is
   subject to access controls.  This scenario can be found in enterprise
   campus networks, branch offices and data centers.




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   It is often the case when network access control is used, that the
   traffic patterns are such that there is significantly more traffic
   crossing a CUG boundary than staying within such boundary.  As an
   example, in campus networks it is common to segregate users into CUGs
   based on some classification such as the user's department.  Campus
   networks often see traffic patterns in which almost all the traffic
   flows northbound to the data center or internet boundaries.  Similar
   traffic patterns can be found in multi-tier applications in IT data
   centers.

   Virtual interfaces are often configured to expect the concept of IP
   subnet to match its closed user group.  A network virtualization
   solution should be able to provide this concept of IP subnet
   regardless of whether the underlying implementation uses a multi-
   access network or not.

   Virtual interfaces should be able to directly access multiple closed
   user groups without needing to traverse a gateway.  Network access
   policy should allow this access whether the source and destination
   CUGs for a particular traffic flow belong to the same tenant or
   different tenants.  It is often the case that infrastructure services
   are provided to multiple tenants.  One such example is voice-over-IP
   gateway services for branch offices.

   Independently, but often associated with the previous two functions,
   IP mobility is another network function that can be implemented using
   network virtualization.  By abstracting the externally visible
   network address from the underlying infrastructure address, mobility
   can be implemented without having to rely upon home agents or large
   L2 broadcast domains.

   IP Mobility requires the ability to "move" a virtual interface
   without disrupting its TCP (or UDP) transport sessions.  This
   requires a mechanism that can efficiently communicate the mappings
   between logical and physical addressing.

   IP Mobility can be a result of devices physically moving (e.g., a
   WiFi enabled laptop) or workload being diverted between physical
   systems such as network appliances or application servers.

3.  Applicability of BGP IP VPNs

   BGP IP VPNs [RFC4364] is the industry de-facto standard for providing
   "closed user group" functionality in WAN environments.  It is used by
   service providers in environments where several millions of routes
   are present.  It supports both isolated VPNs as well as overlapping
   VPNs (often referred to as "extranets").




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   The BGP IP VPN control plane has been designed to be able to
   distribute the mapping between virtual address and location (next-
   hop) to the subset of network nodes for which this information is
   relevant, whenever that mapping changes.  This provides an efficient
   mechanism to address IP mobility requirements as compared to methods
   that depend on a (cached) mapping request from the end-systems.

   In its traditional usage in Service Provider networks, BGP IP VPN
   functionality is implemented in a Provider Edge (PE) device that
   combines both BGP signaling as well as VRF-based forwarding
   functions.  In practice, most PE devices in current use are multi-
   component systems with the signaling and forwarding functionality
   actually implemented in different processors attached to an internal
   network.

   This document assumes a similar separation of functionality in which
   software appliances, the End-System Route Servers, implement the
   control plane functionality of a PE device and a VPN Forwarder
   implements the forwarding function usually found in a PE device
   "line-card".  The VPN Forwarder functionality may be co-located with
   the end-system (e.g., implemented in the hypervisor switch or host OS
   network drivers) or it may be external.  For instance, residing in a
   data center switch or specialized appliance.

   Operationally, BGP IP VPN technology has several important
   characteristics:

   o  It has a high-level of aggregation between customer interfaces and
      managed entities (Provider Edge devices).

   o  It defines VPNs as policies, allowing an interface to directly
      exchange traffic with multiple VPNs and allowing for the topology
      of the virtual network to be modified by modifying the policy
      configuration.

   o  It scales horizontally in terms of event propagation.  By
      increasing the number of signaling devices implementing the PE
      control plane, it is possible to decrease the load on each
      signaling device for events that originate in a specific location
      and which must be propagated across the network.

   The last point is particularly relevant to the convergence
   characteristics required for large scale deployments.  BGP's
   hierarchical route distribution capabilities allow a deployment to
   divide the workload by increasing the number of End-System Route
   Servers.





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   As an example consider a topology in which 100 End-System Route
   Servers are deployed in a network each serving a subset of the VPN
   forwarding elements.  The Route Servers inter-connect to two top-
   level BGP Route Reflectors [RFC4456].

   If an event (i.e., a VPN route change) needs to be propagated from a
   specific end-system to 10,000 clients randomly distributed across the
   network, each of the End-System Route Servers must generate 100
   updates to its respective downstream clients.

   By modifying this topology such that another 100 End-System Route
   Servers are added, each Route Server is now responsible for
   generating 50 client updates.  This example illustrates the linear
   scaling properties of BGP: doubling the number of Route Servers
   (i.e., the processing capacity) reduces by half the number of updates
   generated by each one (i.e. the load at each processing node is
   halved).

   The same horizontal scaling techniques can be applied to the Route
   Reflector layer in the example above by dividing the VPN Route space
   according to some pre-defined criteria (for instance VPN route
   target) and using a pair of Route Reflectors per subset.

   In the previous example we assumed a dense membership in which all
   Route Servers have local clients that are interested in a particular
   event.  BGP also optimizes the route distribution for sparse events.
   The Route Target Constraint [RFC4684] extension, builds an optimal
   distribution tree for XMPP stanza and message propagation based on
   VPN membership.  It ensures that only the PEs with local receivers
   for a particular event do receive it also decreasing the total load
   on the upstream BGP speaker.

   In the WAN environment, BGP IP VPN control plane scaling is not
   primarily focused on route convergence times, but on the memory
   footprint of embedded devices.  While memory footprint does not have
   a similar linear scaling behavior as load, memory technology
   available to software appliances is often at 10x the scale of what is
   commonly found in WAN environments, and so is not so much of a
   concern.

   The functionality present in the BGP IP VPN control plane addresses
   the requirements specified in the previous section.  Specifically, it
   supports multiple potentially overlapping "groups", regular or "hub
   and spoke" topologies and the scaling characteristics necessary.

   The BGP IP VPN control plane supports not only the definition of
   "closed user-groups" (VPNs in its terminology) but also the
   propagation of inter-VPN traffic policies [RFC5575].



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   Note that the signaling protocol itself is rather agnostic of the
   encapsulation used on the wire as long as this encapsulation has the
   ability to carry a label of sufficient length to enumerate all the
   VPNs in an administrative domain (e.g. an MPLS label, which has 20
   bits).

   Several network environments use a network infrastructure that is
   only capable of providing an IP unicast service.  In order to support
   them, implementations of this document should support the MPLS in GRE
   [RFC4023] encapsulation.  Other encapsulations are possible,
   including UDP-based encapsulations RFC 7510 [RFC7510] and VXLAN
   [RFC7348].

4.  Virtual Network End-Points

   This document assumes that end-systems support one or more virtual
   network interfaces in addition to a physical interface that is
   associated with the underlying network infrastructure.  A virtual
   network interfaces can be associated with a specific application via
   a OS-dependent mechanisms like a Virtual Machine (VM), or they can be
   used to provide network connectivity to all user applications in the
   same way that a "VPN tunnel" interface is used to provide access
   between an end-system (e.g., a laptop) and a remote corporate
   network.

   Each virtual network interface is assigned an IP addresses from a
   subnet associated with a "closed user group" or VPN, while the
   physical interface of the machine is addressed in the network
   infrastructure topology.

   A virtual network interface is connected to a VPN Forwarder.  This
   VPN Forwarder MAY be co-located in the end-system or external.  In
   cases where the VPN Forwarder is external to the end-system, they can
   either be directly connected or interconnected with a dedicated
   802.1Q VLAN on a per virtual interface basis.

   Both static and dynamic IP address allocation can be supported.  The
   latter assumes that the VPN Forwarder implements DHCP relay or DHCP
   proxy functionality.












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   Traffic that ingresses or egresses through a virtual network
   interface is routed at the VPN Forwarder, which acts as the first-hop
   router (in the virtual topology).  The IP configuration on the client
   side of this virtual network interface (e.g., in the guest OS) can
   follow one of two models:

   o  Point-to-point interface model

   o  Multipoint interface model

   In a point-to-point interface model, the VPN client routing table
   (e.g., on the guest OS) contains the following routing entries: a
   host route to the local IP address, a host route to the first-hop
   router via the virtual interface and a default route to the first-hop
   router.  This is the model typically used in "VPN tunnel"
   configurations or other access technologies such as cable deployments
   or DSL.  When this model is used, the first-hop router IP address is
   either an address from the tenant's IP address space or a link-local
   address.  This address SHOULD be the same on all first-hop routers
   across a specific deployment so that it does not change when a
   virtual interface moves between end systems.

   In a multi-point interface model, the VPN client routing table (e.g.,
   on the guest OS) contains the following routing entries: a host route
   to the local IP address, a subnet route to the local interface and
   optionally a default route to a specific router address within that
   subnet.  In this model, the VPN client IP stack will issue address
   resolution requests for any IP addresses it considers to be directly
   attached to the subnet.  The VPN Forwarder SHALL answer all address
   resolution requests via Proxy ARP [RFC1027].The same technique is
   applicable when Neighbor Discovery is used to resolve IPv6 addresses.
   Address resolution request SHOULD be answered using a virtual MAC
   address which SHOULD be the same across all VPN Forwarders in a
   specific deployment.  This virtual MAC address SHALL default to the
   VRRP [RFC5798] virtual router MAC address for Virtual Router
   Identifier (VRID) 1.

   When the virtual topology first-hop router resides on the same
   physical machine, the host OS is responsible for mapping the virtual
   interface with a VPN-specific routing table (without taking L2
   addresses into consideration).  In this case the MAC addresses known
   to the guest OS are not used on the wire.

   When the virtual topology first-hop router resides in an external
   system (e.g., the first hop-switch) the virtual interface shall be
   identified by the physical interface of the end-system and a 802.1Q
   VLAN tag.  The first-hop switch should use a virtual router MAC
   address to answer any address resolution queries.



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   Whenever external VPN forwarding is used, and resiliency is desired,
   multiple external VPN Forwarder may be employed in a redundant
   configuration.  It is desirable to use VRRP as a mechanism to control
   the flow of traffic between the end-system and the external VPN
   Forwarder.  VRRP already defines the necessary procedures to elect a
   single forwarder for a LAN.

   This specification uses the VRRP virtual router MAC address as the
   default L2 address for the VPN Forwarder, in order to support a
   client virtual interface moving between locations.

   While the VRRP Virtual Router MAC will be used to answer any address
   resolution request made by the virtual interface client (e.g., the
   guest VM) this does not imply that a single default router is elected
   per virtual IP subnet.  The ingress VPN Forwarder will perform an IP
   forwarding decision based on the destination IP address of the
   (payload) traffic.

   VRRP router election is only relevant in selecting the VPN Forwarder
   associated with a specific machine, when external forwarders are in
   use.

5.  VPN Forwarder

   In this solution, the Host OS/Hypervisor in the end-system must
   participate in the virtual network service.  Given an end-system with
   multiple virtual interfaces, these virtual interfaces must be mapped
   onto the network by the end system OS such that applications on one
   virtual interface cannot send traffic to networks they are not
   authorized to communicate with or using source addresses not assigned
   to the virtual interface.

   When VPN forwarder functionality is implemented by the Host OS/
   Hypervisor, intermediate systems in the network do not require any
   knowledge of the virtual network topology.  This can simplify the
   design and operation of the physical network.

   When it is not possible or desirable to add the VPN forwarding
   functionality to the end-system, it may be implemented by an external
   system, typically located as close as possible to the end-system
   itself.

   Both models, co-located and external VPN Forwarder can co-exist in a
   deployment.







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   In order to implement the BGP IP VPN Forwarder functionality a device
   MUST implement the following functionality:

   o  Support for multiple "Virtual Routing and Forwarding" (VRF)
      tables;

         VRF route entries map prefixes in the virtual network topology
         to a next-hop containing a infrastructure IP address and a
         label allocated by the destination Forwarder.  The VRF table
         lookup follows the standard IP lookup (best-match) algorithm.

   o  Associate an end-system virtual interface with a specific VRF
      table;

         When the Forwarder is co-located with the end-system, this
         association is implemented by an internal mechanism.  When the
         Forwarder is external the association is performed using the
         MAC address of the end-system and an IEEE 802.1Q tag that
         identifies the virtual interface within the end-system.

   o  Encapsulate outgoing traffic (end-system to network) according to
      the result of the VRF lookup;

   o  Associate incoming packets (network to end-system) to a virtual
      interface for direct forwarding, or to a VRF for lookup, according
      to the label contained in the packet;

   The VPN Forwarder MAY support the ability to associate multiple
   virtual interfaces with the same VRF.  When that is the case, locally
   originated routes, that is IP routes to the local virtual interfaces
   SHALL NOT be used to forward outbound traffic (from the virtual
   interfaces to the outside) unless a route advertisement has been
   received that matches that specific IP prefix and next-hop
   information.  This is intended to ensure that the forwarding behavior
   is the same whether the VRF is shared or between multiple interfaces
   of the same virtual-network or not.

   As an example, if a given VRF contains two virtual interfaces,
   "veth0" and "veth1", with the addresses 203.0.113.1/32 and
   203.0.113.2/32 respectively, the initial forwarding state must be
   initialized such that traffic from either of these interfaces does
   not match the other's routing table entry.  It may, for instance,
   match a default route advertised by a remote system.  Traffic
   received from other VPN Forwarders, however, must be delivered to the
   correct local interface.  If at a subsequent stage a route is
   received from the Route Server such that 203.0.113.2/32 has a next-
   hop with the IP address of the local host and the correct label, the
   system may subsequently install a local routing table entry that



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   delivers traffic directly to the "veth1" interface.  This means that
   forwarding table entries apply to downstream traffic only, by
   default.  This capability can be used to implement a hub-and-spoke
   topology, if required.

   The label which is associated with a virtual interface is of local
   significance only and SHOULD be allocated by the VPN Forwarder.

   When an external VPN Forwarder is used the end-system MUST associate
   each virtual interface with a VLAN [IEEE.802-1Q] that is unique on
   the end-system.  The switching infrastructure SHOULD be configured
   such that multi-destination frames sourced from an end-system are
   only delivered to VPN Forwarders used by this end-system and not to
   other end-systems.

6.  XMPP signaling protocol

   End-System Route Servers must be aware of VPN membership on each
   Forwarder as well as what IP addresses are currently associated with
   each virtual interface.

   VPN Forwarders receive VPN route information from which to populate
   their forwarding tables.  External VPN Forwarders also need to
   receive the virtual interface and IP address allocation events for
   the end-system for which they are VPN forwarders.  In this case, the
   end-system assigns an 802.1Q VLAN tag to each virtual interface and
   communicates that information to the Forwarder directly, or via the
   Route Server.

   In order to exchange this information this specification uses the
   XMPP [RFC6120] protocol along with the Publish-Subscribe [pubsub]
   extension.

   VPN forwarders (both co-located and external) establish XMPP sessions
   with End-System Route Servers, acting as XMPP clients.  When an
   external VPN Forwarder is used, end-systems MAY establish XMPP
   sessions with VPN Forwarders.  In such cases, external VPN Forwarders
   act as XMPP servers for end-systems which are associated with them.

   A VPN Forwarder MAY connect to multiple End-System Route Servers for
   reliability.  In this case it SHOULD publish its information to each
   of the Route Servers.  It MAY choose to subscribe to VPN routing
   information from only one of the available Route Servers.  In this
   case, the Forwarder is responsible for switching subscriptions over
   to an alternate Route Server in the case of Route Server failure.
   Alternatively, it MAY choose to subscribe to VPN routing information
   from more than one End-System Route Server.  In this case, the
   Forwarder is responsible for selecting which Route Server is



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   authoritative for each forwarding entry.  The Route Servers SHOULD
   produce the same forwarding information for each destination.  The
   VPN Forwarder is expected to select the entry that it deems as more
   recent for positive updates.  It SHOULD NOT consider a forwarding
   entry to be withdrawn unless it is withdrawn by both Route Servers.

   Each End-System Route Server MUST monitor the XMPP connection status
   of each VPN Forwarder that is connected to it.  The information
   advertised by an XMPP client SHOULD be deleted after a configurable
   timeout, after XMPP session closes.  This timeout SHOULD default to
   60 seconds.

   An End-System Route Server MAY monitor the status of each VPN
   Forwarder that is connected to it, using, for example, the BFD
   [RFC5880] protocol and to delete advertised information after a
   timeout when a failure is detected.  The Route Server MAY choose to
   immediately reduce the preference of routing information received
   from an XMPP client for which a failure has been detected, either
   through an XMPP session close event, or a failure detection mechanism
   such as BFD.

                           +---------+        +--------+
                           |    RS   |--------|  BGP   |
                           +---------+        +--------+
                           /         \        /
                         XMPP         \      /
                         /             \    /
      +--------------------+            \  /
      |  End   |   VPN     |             \/
      | System | Forwarder |             /\
      +--------------------+            /  \
                         \             /    \
                         XMPP         /      \
                           \         /        \
                           +---------+        +--------+
                           |    RS   |--------|  BGP   |
                           +---------+        +--------+

                 VPN Forwarder Connected to Two Routing Systems

                                 Figure 1

   The figure above represents a typical configuration in which an end-
   system with a co-located VPN Forwarder is directly connected to two
   End-System Route Servers, which are in turn connected to multiple BGP
   speakers which may be other L3VPN PEs or BGP route reflectors.





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   In deployment, the number of End-System Route Servers used will
   depend on the desired Route Server to VPN Forwarder ratio which
   affects the convergence time of event propagation.

   The XMPP JID used by the client SHALL be a RFC 7622 [RFC7622]
   compliant address that uniquely identifies it in its administrative
   domain.  The VPN Forwarder SHOULD use its hostname as JID, when
   available, or a unique IP address within the infrastructure network
   using its string representation.  The same naming convention SHOULD
   be used for an End System which has an XMPP session with an external
   VPN Forwarder.

   The XMPP JID used by an End-System Route Server SHOULD be the
   constant string 'route-server@ietf.org'.

   Each VPN shall be identified by an ASCII character string that SHOULD
   NOT exceed 128 octets and MUST be unique within each administrative
   domain.  The VPN identifier is an attribute of each virtual
   interface.  It is assumed that a configuration management system
   exists such that it provisions the Route Servers with VPN identifier
   values and the VPN Forwarders with the mapping of virtual interface
   to VPN identifier.  Such a configuration management system is outside
   the scope of this document.

   Each VPN identifier corresponds to a Pub-Sub node in the Route Server
   XMPP servers.  This Pub-Sub nodes SHOULD be configured such that Pub-
   Sub items are persistent and that event notifications include the
   item payload.  Implementations MAY choose to perform this operation
   explicitly or implicitly by mapping XMPP subscription requests to an
   event observer mechanism that tracks the VRF table corresponding to
   the VPN in question.

   When an external Forwarder is used, its control software MAY operate
   as an XMPP server which processes requests from end-systems and SHALL
   operate as a client of one or more End-System Route Servers.  The
   control software relays to the End-System Route Server(s) VPN
   membership stanzas it receives from the end-system.  VPN routing
   information received from the Route Server(s) SHOULD NOT be
   propagated to the end-system unless it specifically requests such
   information.  End systems MAY have sessions directly with the End-
   System Route Servers, and in this case no XMPP sessions are required
   with VPN Forwarders.

   When a virtual interface is created on an end-system, the host End
   System XMPP client SHALL generate an XMPP Subscribe stanza to its
   server (a Route Server or the external VPN Forwarder).





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   Each Subscribe stanza SHALL be addressed to the JID of the Route
   Server (e.g. route-server@ietf.org), using the VPN Identifier as the
   NodeID.

   If subsequent Virtual Interfaces are created with the same VPN
   Identifier, and the previous Pub-Sub subscription is still in effect,
   then additional XMPP Pub-Sub Subscribe stanzas SHOULD NOT be sent to
   the End-System Route Server.

   Example subscription request from co-located VPN Forwarder to Route
   Server:

   <iq type='set'
       from='forwarder@domain.org'
       to='route-server@ietf.org'
       id='sub1'>
     <pubsub xmlns='http://jabber.org/protocol/pubsub'>
       <subscribe node='vpn-customer-name' jid='fowarder@domain.org'/>
       <options>
         <instance-id>1</instance-id>
       </options>
     </pubsub>
   </iq>

   The above request instructs the End-System Route Server to start
   populating the client's VRF table with any routing information that
   is available for this VPN.  The XMPP node 'vpn-customer-name' is
   assumed to be implicitly created by the End-System Route Server.
   Creation of a virtual interface may precede any IP address becoming
   active on the interface, as is the case with VM instantiation.

   The optional "instance-id" element allows the VPN Forwarder to
   specify a unique 16 bit index that can be used by the Route Server to
   automatically assign a Route Distinguisher (RD) to any route
   subsequently advertised by the VPN Forwarder.  In a scenario where
   the VPN Forwarder is advertising reachability information to multiple
   Route Servers it is desirable for reachability information to have an
   RD composed of the VPN Forwarder identifier (e.g., IPv4 address) and
   the "instance-id".












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   Example subscription request from end-system to external VPN
   Forwarder:

   <iq type='set'
       from='end-system@domain.org'
       to='forwarder@domain.org'
       id='sub1'>
     <pubsub xmlns='http://jabber.org/protocol/pubsub'>
       <subscribe node='vpn-customer-name' jid='forwarder@domain.org'/>
       <options>
         <x xmlns='jabber:x:data' type='submit'>
           <field var='vpn#vlan_id'><value>100</value></field>
         </x>
       </options>
     </pubsub>
   </iq>

   When an external VPN Forwarder is used, the end-system SHOULD include
   the VLAN identifier it assigned to the virtual interface as a
   subscription option.  This option is represented in the XMPP Pub-Sub
   Subscribe stanza a data form [xep-0004] field with the name
   "vpn#vlan_id".  The example above uses the 802.1Q tag value of 100.

   When a Route Server receives a subscription request for a specific
   VPN identifier it SHALL treat this request as an implicit request for
   item retrieval for all items in the Pub-Sub node that corresponds to
   the VPN.

   If at any point all Virtual Interfaces associated with a given VPN
   Identifier are removed or deactivated from the End-System, then the
   End System XMPP client SHOULD generate an XMPP Pub-Sub Unsubscribe
   stanza to its server for the Pub-Sub node associated with the VPN
   Identifier.


















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   Example unsubscribe request from co-located VPN Forwarder to Route
   Server:


   <iq type='set'
       from='forwarder@domain.org'
       to='route-server@ietf.org'
       id='unsub1'>
     <pubsub xmlns='http://jabber.org/protocol/pubsub'>
       <unsubscribe
         node='vpn-identifier'
         jid='forwarder@domain.org'/>
     </pubsub>
   </iq>


   For a collocated VPN forwarder, and for an external VPN forwarder
   when there is an XMPP session with the End System, when an IP address
   is added to a virtual interface and the interface is activated, the
   end-system SHALL generate an XMPP Pub-Sub Publish request.  This
   request publishes an item containing a single entry element based on
   the XML Schema Definition in Section 11.  The ItemID of this item
   MUST be generated by the VPN Forwarder such that the value is unique
   within a Pub-Sub node.  The ItemID MAY be formed by combining the VPN
   Forwarder's IP address, the instance-id value, and the entry address
   element.  This format corresponds to the string representation of a
   BGP L3VPN NLRI in which the Route Distinguisher is given by the VPN
   Forwarder IP address and instance-id, and is easily identifiable by
   network operators.  However, the format and/or structure of the
   ItemID is not stricly defined in this document, so long as uniqueness
   is guaranteed.




















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   Publish request from VPN Forwarder to End-System Route Server:

   <iq type='set'
       from='forwarder@domain.org'
       to='route-server@ietf.org'
       id='request1'>
     <pubsub xmlns='http://jabber.org/protocol/pubsub'>
       <publish node='vpn-customer-name'>
         <item id='192.0.2.1:1:203.0.113.42/32'>
           <entry xmlns='urn:ietf:params:xml:ns:bgp:l3vpn:unicast'>
             <nlri>
               <af>1</af>
               <address>203.0.113.42</address>
             </nlri>
             <next-hops>
               <next-hop>
                 <af>1</af>
                 <address>192.0.2.1</address>
                 <label>10000</label>
                 <tunnel-encapsulation-list>
                   <tunnel-encapsulation>gre</tunnel-encapsulation>
                   <tunnel-encapsulation>udp</tunnel-encapsulation>
                 </tunnel-encapsulation-list>
               </next-hop>
             </next-hops>
             <sequence-number>1</sequence-number>
           </entry>
         </item>
       </publish>
     </pubsub>
   </iq>

   In this example, the VPN Forwarder JID is "forwarder@domain.org".
   The VPN Identifier "vpn-identifier" is used as the value of the node
   attribute of the subscribe element.  The IP address of the Virtual
   Interface is 203.0.113.42/32.  The IP address of the VPN Forwarder is
   192.0.2.1 and it supports receiving MPLS packets via both GRE and UDP
   tunneling.  Label 10000 has been assigned to this particular Virtual
   Interface.

   The End-System Route Server will convert the information received in
   a 'publish' request into the corresponding BGP route information such
   that:

   o  It associates the specific request with a local VRF which it
      resolves by using the Pub-Sub 'node' attribute.





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   o  It creates a BGP VPN route with a 'Route Distinguisher' (RD) which
      contains a unique 32bit value per end-system plus a 16bit
      instance-id, the specified IP prefix and 'label' received from the
      VPN Forwarder as the Network Layer Reachability Information
      (NLRI).  The instance-id is either the value specified by the XMPP
      client in the subscribe stanza for the specific pubsub node or a
      locally generated value when that parameter is omitted.

   o  The BGP next-hop address is set to the address of the VPN
      Forwarder.

   o  A BGP Tunnel Encapsulation Attribute [RFC5512] is generated for
      each 'tunnel-encapsulation' element specified in the XMPP message.

   o  The route is optionally associated with a MAC Mobility extended
      community [RFC7432] containing a sequence number for the route
      advertisement.

   Conversely, when an interface operational status is determined to be
   down or an IP address is unconfigured the VPN forwarder generates an
   XMPP retract message to withdraw the route advertisement.

   Retract request from VPN Forwarder to End-System Route Server:

   <iq type='set'
       from='forwarder@domain.org'
       to='route-server@ietf.org'
       id='retract1'>
     <pubsub xmlns='http://jabber.org/protocol/pubsub'>
       <retract node='vpn-customer-name'>
         <item id='192.0.2.1:1:203.0.113.42/32'/>
       </retract>
     </pubsub>
   </iq>

   The retract stanza uses the ItemId to identify the item being
   retracted.  The example retract stanza above uses the L3VPN NLRI
   string representation ItemId format used in the publish example.

   Consistent with XMPP Pub-Sub [pubsub], event notifications will be
   generated whenever a VPN route is added, modified or deleted.  This
   is true for VPN routes learned via XMPP clients as well as routes
   learned via BGP.  For VPN routes that are learned via BGP (rather
   than XMPP clients) the Route Server SHOULD create XMPP Pub-Sub
   Publish stanzas or otherwise take steps to publish a persistent item
   under the NodeID associated with the VPN Identifier of the
   appropriate VRF(s).  Thus the Pub-Sub node will contain items for
   every route for the associated VPN.  Upon successfully publishing a



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   Pub-Sub item the XMPP server SHALL generate event notification
   messages and send them to all VPN Forwarders that are actively
   subscribed to that node.  These event notification messages SHOULD be
   sent as soon as possible (without delay) in order to facilitate
   convergence and consistent reachability.

   Example update notification message from Route Server to VPN
   Forwarder:

   <message to='forwarder@domain.org' from='route-server@ietf.org'>
     <event xmlns='http://jabber.org/protocol/pubsub#event'>
       <items node='vpn-customer-name'>
         <item id='192.0.2.1:1:203.0.113.42/32'>
           <entry xmlns='urn:ietf:params:xml:ns:bgp:l3vpn:unicast'>
             <nlri>
               <af>1</af>
               <address>203.0.113.42/32</address>
             </nlri>
             <next-hops>
               <next-hop>
                 <af>1</af>
                 <address>192.0.2.1</address>
                 <label>10000</label>
                 <tunnel-encapsulation-list>
                   <tunnel-encapsulation>gre</tunnel-encapsulation>
                   <tunnel-encapsulation>udp</tunnel-encapsulation>
                 </tunnel-encapsulation-list>
               </next-hop>
             </next-hops>
             <sequence-number>1</sequence-number>
           </entry>
         </item>
         <item >
           ...
         </item>
       </items>
     </event>
   </message>

   Notification messages SHOULD be generated whenever a VPN route is
   added, modified or deleted.  These notification messages SHOULD
   contain only items that have been added, modified or deleted since
   any previous information that was sent to the VPN Forwarder.
   Notification messages can be segmented at the convenience of the
   Route Server.

   Note that the Update from the Route Server to the VPN Forwarder does
   not contain the JID of the destination end-system.  The "from"



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   attribute in the 'message' element contains the Route Server JID.
   The XMPP messages are point-to-point in nature, between a Forwarder
   and Route Server, even in the case when one XMPP publish request from
   a Forwarder may cause the Route Server to generate one or more event
   notifications.

   When multiple possible routes exist for a given VPN IP address within
   a VRF it is the responsibility of the Route Server to select the best
   path to advertise to the VPN Forwarders.  The routing entries
   published by the Route Server to VPN Forwarders MAY include multiple
   next-hops for the same forwarding entry.  While BGP L3VPN NLRI
   encodes a single next-hop, multiple NLRI with different RDs may
   result in a single forwarding entry in a VRF with multiple next-hops.
   This functionality is known as "vrf multipath" in standard BGP L3VPN
   implementations.  This "vrf multipath" behavior can be applied to
   both BGP and XMPP learned routing information.  The criteria used for
   multipath selection is outside the scope of this document but SHOULD
   be consistent between the Route Servers within an administrative
   domain.

   A VPN Forwarder uses locally originated information to generate MPLS
   label forwarding state, and this used to forward downstream traffic
   (i.e., traffic received from the network).  Upstream traffic (i.e.,
   received from a virtual interface) is forwarded according to the
   routing information received from one or more Route Servers that the
   VPN forwarder has an XMPP session with.  In the case where multiple
   Router Servers are providing routing information for a specific NLRI
   the VPN Forwarder SHOULD select the following algorithm:

   o  Prefer the highest local-preference value

   o  Prefer the highest sequence-number

   o  Tie-break on the Route Server IP address

   When routes are withdrawn, the End-System Route Server generates an
   item "retract" request.

   Route advertisements can have an optional sequence-number which help
   the route server determine the most recent route advertisement.  The
   sequence number is determined by a mechanism outside the scope of
   this document.  One option is to use time synchronization between
   compute nodes in order to have a globally coordinated timestamp.
   This timestamp can be used to identify the time of interface creation
   on the compute node.






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   Routes can also be associated with a "local-preference" attribute.
   This attribute maps to the BGP attribute of the same name for the
   purposes of route selection.

7.  End-System Route Server behavior

   End-System Route Servers SHALL support the BGP address families: VPN-
   IPv4 (1, 128), VPN-IPv6 (2, 128) and RT-Constraint (1, 132)
   [RFC4684].

   When an End-System Route Server receives a request to create or
   modify a VPN route it SHALL generate a BGP VPN route advertisement
   with the corresponding information.

   It is assumed that the End-System Route Servers have information
   regarding the mapping between the tuple ('end-system', 'vpn-name')
   and the BGP Route Targets used to import and export information from
   associated VRFs.  This mapping is known via an out-of-band mechanism
   not specified in this document.

   Whenever the End-System Route Server receives an XMPP subscription
   request, it SHALL consult its RT-Constraint Routing Information Base
   (RIB).  If the Route Server does not have a locally originated RT-
   Constraint route that corresponds to the vpn-name present in the
   request, it SHALL create one and generate the corresponding BGP route
   advertisement.  This route advertisement should only be withdrawn
   when there are no more downstream XMPP clients subscribed to the VPN.

   End-System Route Servers SHOULD automatically assign a BGP route
   distinguisher per VPN routing table.

8.  Operational Model

   In the simplest case, a VPN is a collection of systems that are
   allowed to exchange traffic with each other, and only with each
   other.  Since all the forwarding tables in this VPN have the same
   routing entries they are often referred to as symmetrical VPNs.

   In order to better illustrate the operation of the protocol, we
   consider a simple example in which host H1 and host H2 both contain a
   virtual interface that is a member of the same VPN.










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                                .------.
   +----+       +-----+        /        \        +-----+       +----+
   | H1 | <===> | RS1 | <===> ( BGP mesh ) <===> | RS2 | <===> | H2 |
   +----+       +-----+        \        /        +-----+       +----+
                                `------'

          Example Network with Two Hosts and Two Route Servers

                                 Figure 2

   Each of these hosts has a collocated VPN forwarder that has an XMPP
   session with an End-System Route Server, RS1 and RS2 our example, and
   these Route Servers are part of the same BGP mesh.

   When a virtual interface is created on host H1, the local XMPP client
   generates an XMPP subscription stanza to its respective Route Server.
   This stanza contains a VPN identifier that has been assigned by the
   provisioning system.  The Route Server maps that identifier to a BGP
   IP VPN configuration which contains the list of import and export
   route targets to be used for that particular VRF.

   Once the interface is operational, host H1 will publish any IP
   addresses that are configured on the respective virtual interface.
   This will in turn cause the End-System Route Server to advertise
   these (directly or indirectly) to any other BGP speaker on the
   network which is connected to an attachment point of that VPN.

   The following table represents the contents of the VRF routing table
   on RS1 after the IPv4 address 203.0.113.42 has been added to the
   virtual interface on H1.

   +-----------------+---------------+-------+-----------+
   | VPN IP address  | NEXT-HOP      | label | Known via |
   +-----------------+---------------+-------+-----------+
   | 203.0.113.42/32 | 192.0.2.1     | 16    | XMPP      |
   |                 |               |       |           |
   | 203.0.113.48/32 | 198.51.100.10 | 20    | BGP       |
   +-----------------+---------------+-------+-----------+

   It assumes that there is an attachment point for this VPN with the
   IPv4 address of 203.0.113.48 which is advertising a route to the IP
   address of an application running on H2 (203.0.113.48/32).  Host H1
   has an infrastructure IP address of 192.0.2.1 configured on its
   physical interface while host H2 has IP address 198.51.100.10.

   The contents of the VRF routing table in the End-System Route Servers
   are advertised via XMPP Update notifications sent to H1, and a route




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   update for the IP address of H1 will be sent into the BGP mesh on to
   Route Server RS2 and from there, via XMPP to H2.

   This information is used by the host to populate the forwarding table
   associated with that VPN.  The following shows the VRF table on host
   H1

   +-----------------+---------------+-------+
   | VPN IP address  | Host address  | label |
   +-----------------+---------------+-------+
   | 203.0.113.42/32 | localhost     | 16    |
   |                 |               |       |
   | 203.0.113.48/32 | 198.51.100.10 | 20    |
   +-----------------+---------------+-------+

   When an application that uses the virtual interface on host H1
   generates packets with a destination IP address of 203.0.113.48 these
   are routed by the VPN Forwarder implemented in the Host OS.  The
   packets are encapsulated with a header that contains a label assigned
   by host H2, as shown in the figure, below.

                  +--------+                 +--------+
   app -- veth0 --|   H1   |=== [network] ===|   H2   |-- veth0 -- app
                  +--------+                 +--------+

   IP pkt ===> encap (GRE + label) ===> [IP net] ===> decap ===> IP pkt
               [192.51.100.10, 20]                 map 20 to veth0

           Packet Flow from Application in H1 to Application in H2

                                 Figure 3

   In the case that the virtual interface on the host is associated with
   a guest OS, this guest OS has had its address resolution queries
   answered with the Virtual Router MAC address, or the MAC address of
   the destination MAY be supplied if it is in the same IP subnet
   (broadcast domain).  When the Virtual Router MAC address is supplied,
   this is the address the guest OS uses as the destination MAC address
   in packets it originates that are outside its IP subnet.  The VPN
   forwarder will replace the its MAC address with the MAC address of
   the next hop in the tenant virtual network (another End System or
   default gateway, for instance) before encapsulating the packet.
   packet.

   End-System Route Servers are software applications that implement
   both the BGP IP VPN PE control plane as well as XMPP server
   functionality.  These applications are not in the forwarding plane
   and MAY not be co-located with a network device.



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   Network devices MAY have direct BGP sessions to the End-System Route
   Servers.  For instance, a router or security appliance that supports
   BGP/MPLS IP VPNs over GRE may use its existing functionality to
   inter-operate directly with a collection of Virtual Machines or other
   network appliances that support this specification.

   End-System Route Servers implement the VRF import policy and export
   policy functionality that is associated with PE routers in standard
   BGP IP/VPN deployments.  VPN Forwarders receive forwarding
   information after policy and route selection is applied.  These are
   unqualified routes in a specific VRF rather than VPN routing
   information qualified by a Route Distinguisher and with a set of
   Route Targets.

   A symmetrical VPN uses a vrf import and vrf export polices that
   contain a single route target, where the route target used for both
   import and export is the same.

   Different VPN topologies can be created by manipulating the vrf
   import and export configuration including "hub-and-spoke" topologies
   or overlapping VPNs.

   An example of a hub-and-spoke VPN configuration is one where all the
   traffic from the VPN clients must be redirected though a middle-box
   for inspection.  Assume that the virtual interfaces of a particular
   user are configured to be in the VPN "tenant1".  At an initial stage
   this "tenant1" VPN is symmetrical and uses a single Route Target in
   both its import and export policies.  The middle-box functionality
   can be incrementally deployed by defining a new VPN, "tenant1-hub",
   and an associated Route Target.  The End-System Route Server
   configuration is changed such that VPN "tenant1" only imports routes
   with the Route Target associated with the hub.  The "hub" VPN is
   assumed to advertise a prefix that covers all the VPN clients IP
   addresses.  The "hub" VPN imports the VPN routes in order for it to
   be able to generate the XMPP updates to the "hub" end-system.  This
   information is required for the return traffic from the hub to the
   spokes (the VPN clients).  In such a scenario, a single physical
   interface can connect the middle-box to the clients in a given VPN
   which appear logically as downstream from it.  Such a middle-box
   would often require connectivity to multiple VPNs, such as, for
   instance, an "outside" VPN which provides external connectivity to
   one or more "inside" VPNs.

   The functionality defined in this document in which the BGP IP VPN PE
   functionality is split into its control (End-System Route Servers)
   and forwarding (VPN Forwarder) components is fully interoperable with
   existing BGP IP VPN PEs.




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   This makes it possible to reuse existing systems.  For example, at
   the edge of a data center facility it may be desirable to use an
   existing router or appliance that aggregates IP VPN routing
   information and/or provides IP based services such as stateful packet
   inspection.

   Such a system can be configured, based on existing functionality, to
   suppress more specific routes than a specified aggregate while
   advertising the aggregate with a BGP NEXT_HOP containing the PE's IP
   address and a locally assigned label corresponding to a VRF where the
   more specific routes are present.

9.  IANA Considerations

   IANA has allocated the value 13 corresponding to "MPLS in UDP
   Encapsulation" from the "BGP Tunnel Encapsulation Attribute Tunnel
   Types" registry, using this document as reference.  We request that
   this allocation be made permanent.

   This document defines a URN namespace used to encode L3VPN Unicast
   routing information compliant with the registration procedure define
   in [RFC3688].

      URI: urn:ietf:params:xml:ns:bgp:l3vpn:unicast

      Description: This is the XML namespace name for L3VPN Unicast
      routing information.

      Registrant Contact: IETF BESS Working Group <bess@ietf.org>

10.  Security Considerations

   As with BGP/MPLS L3VPN, we assume that the tenant networks have no
   direct reachability to the infrastructure network.  The threat models
   to consider are:

   o  The possibility that an attacker on a tenant network may inject
      traffic to a different network (for instance belonging to a
      different tenant).

   o  Denial of service attacks from within a tenant network.

   o  Attacks from a tenant network to the infrastructure via
      unauthorized or malicious control traffic.

   o  Attacks from within the infrastructure network.





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   Traffic in BGP/MPLS L3VPNs is forwarded based on the contents of VRF
   tables, calculated according to configured routing policy (route-
   target import/export policies).  It is assumed that the configuration
   management system responsible for provisioning these policies only
   accepts requests that are correctly authenticated, and follow a pre-
   defined access policy.  It is also assumed that an attacker doesn't
   have the ability to inject packets in the infrastructure that mimic
   the encapsulated used between PE devices.  This specification
   recommends that operators ensure that MPLS over GRE and MPLS over UDP
   traffic is not allowed to enter the infrastructure network.  VPN
   forwarders MAY also choose to perform a reverse path forwarding
   lookup (i.e., lookup the source IP address of the payload packet) and
   discard traffic that doesn't match the expected next-hop(s) for the
   reverse route.

   As with BGP/MPLS L3VPN, an attacker on a tenant network may inject
   packets that consume a disproportional share of infrastructure
   resources, either in terms of bandwidth or CE packet forwarding
   capacity.  VPN forwarders SHOULD provide the ability to rate limit
   traffic from a specific virtual interface.  When the VPN forwarder
   uses other finite resources on a per traffic basis, such as internal
   tables used to cache the result access control validation, it SHOULD
   provide a mechanism to limit the usage of these resources on a per
   virtual interface basis.

   The control protocol exchanges between application instances (e.g.,
   the virtual machine) behind a virtual interface and the VPN forwarder
   are typically limited to ARP/ND exchanges and the proxying of
   services such as DHCP and DNS.  The ARP/ND information received from
   the application instance SHOULD NOT be used to populate routing or
   forwarding tables directly.  The control of what MACs and IP
   addresses are accepted by a virtual interface SHOULD reside in the
   configuration management system that creates said virtual interface.

   The XMPP session between end-systems and the Route Servers SHOULD use
   TLS with mutual authentication.  One possible strategy is to
   distribute pre-signed certificates to end-systems which are presented
   as proof of authorization to the Route Server.  BGP sessions SHOULD
   be authenticated.  This document recommends that BGP speaking systems
   filter traffic on port 179 such that only IP addresses which are
   known to participate in the BGP signaling protocol are allowed.

11.  XML schema

   The following schema defines the XML elements that are used to
   communicate unicast reachability information between the Route Server
   and VPN Forwarder:




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   <xsd:schema xmlns:xsd="http://www.w3.org/2001/XMLSchema"
       targetNamespace=
           "urn:ietf:params:xml:ns:bgp:l3vpn:unicast">

   <xsd:simpleType name="TunnelEncapsulationType">
       <xsd:restriction base="xsd:string">
           <xsd:enumeration value="gre"/>
               <!-- RFC 4023 -->
           <xsd:enumeration value="udp"/>
               <!-- RFC 7510 -->
           <xsd:enumeration value="vxlan"/>
               <!-- RFC 7348 -->
       </xsd:restriction>
   </xsd:simpleType>

   <xsd:complexType name="TunnelEncapsulationListType">
     <xsd:sequence>
       <xsd:element name="tunnel-encapsulation"
           type="TunnelEncapsulationType"
           maxOccurs="unbounded"/>
     </xsd:sequence>
   </xsd:complexType>

   <xsd:complexType name="NextHopType">
     <xsd:sequence>
       <xsd:element name="af" type="xsd:integer"/>
       <xsd:element name="address" type="xsd:string"/>
       <xsd:element name="label" type="xsd:integer"/>
       <xsd:element name="tunnel-encapsulation-list"
           type="TunnelEncapsulationListType"/>
     </xsd:sequence>
   </xsd:complexType>

   <xsd:complexType name="NextHopListType">
     <xsd:sequence>
       <xsd:element name="next-hop" type="NextHopType"
           maxOccurs="unbounded"/>
     </xsd:sequence>
   </xsd:complexType>

   <xsd:complexType name="IPAddressType">
     <xsd:sequence>
       <xsd:element name="af" type="xsd:integer"/>
       <xsd:element name="safi" type="xsd:integer"/>
       <xsd:element name="address" type="xsd:string"/>
     </xsd:sequence>
   </xsd:complexType>




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   <xsd:complexType name="EntryType">
       <xsd:all>
           <xsd:element name="nlri" type="IPAddressType"/>
           <xsd:element name="next-hops" type="NextHopListType"/>
           <xsd:element name="sequence-number" type="xsd:integer"/>
           <xsd:element name="local-preference" type="xsd:integer"/>
       </xsd:all>
   </xsd:complexType>

   <xsd:complexType name="ItemType">
     <xsd:sequence>
       <xsd:element name="entry" type="EntryType"/>
     </xsd:sequence>
   </xsd:complexType>

   <xsd:complexType name="ItemsType">
       <xsd:sequence>
           <xsd:element name="item" type="ItemType"
               maxOccurs="unbounded"/>
       </xsd:sequence>
   </xsd:complexType>

   <xsd:element name="items" type="ItemsType"/>

   </xsd:schema>

12.  Acknowledgements

   Pedro Marques contributed much of the original content of this
   document.

   Yakov Rekhter has contributed to this document by providing detailed
   feedback and suggestions.

   The authors would also like to thank Thomas Morin for his comments.

   Amit Shukla and Ping Pan contributed to earlier versions of this
   document.

   Benson Schliesser provided a detailed review of the document and
   helped clarify several sections.

13.  References








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13.1.  Normative References

   [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
              Requirement Levels", BCP 14, RFC 2119,
              DOI 10.17487/RFC2119, March 1997,
              <http://www.rfc-editor.org/info/rfc2119>.

   [RFC3688]  Mealling, M., "The IETF XML Registry", BCP 81, RFC 3688,
              DOI 10.17487/RFC3688, January 2004,
              <http://www.rfc-editor.org/info/rfc3688>.

   [RFC4023]  Worster, T., Rekhter, Y., and E. Rosen, Ed.,
              "Encapsulating MPLS in IP or Generic Routing Encapsulation
              (GRE)", RFC 4023, DOI 10.17487/RFC4023, March 2005,
              <http://www.rfc-editor.org/info/rfc4023>.

   [RFC4364]  Rosen, E. and Y. Rekhter, "BGP/MPLS IP Virtual Private
              Networks (VPNs)", RFC 4364, DOI 10.17487/RFC4364, February
              2006, <http://www.rfc-editor.org/info/rfc4364>.

   [RFC4456]  Bates, T., Chen, E., and R. Chandra, "BGP Route
              Reflection: An Alternative to Full Mesh Internal BGP
              (IBGP)", RFC 4456, DOI 10.17487/RFC4456, April 2006,
              <http://www.rfc-editor.org/info/rfc4456>.

   [RFC4684]  Marques, P., Bonica, R., Fang, L., Martini, L., Raszuk,
              R., Patel, K., and J. Guichard, "Constrained Route
              Distribution for Border Gateway Protocol/MultiProtocol
              Label Switching (BGP/MPLS) Internet Protocol (IP) Virtual
              Private Networks (VPNs)", RFC 4684, DOI 10.17487/RFC4684,
              November 2006, <http://www.rfc-editor.org/info/rfc4684>.

   [RFC5512]  Mohapatra, P. and E. Rosen, "The BGP Encapsulation
              Subsequent Address Family Identifier (SAFI) and the BGP
              Tunnel Encapsulation Attribute", RFC 5512,
              DOI 10.17487/RFC5512, April 2009,
              <http://www.rfc-editor.org/info/rfc5512>.

   [RFC5798]  Nadas, S., Ed., "Virtual Router Redundancy Protocol (VRRP)
              Version 3 for IPv4 and IPv6", RFC 5798,
              DOI 10.17487/RFC5798, March 2010,
              <http://www.rfc-editor.org/info/rfc5798>.

   [RFC6120]  Saint-Andre, P., "Extensible Messaging and Presence
              Protocol (XMPP): Core", RFC 6120, DOI 10.17487/RFC6120,
              March 2011, <http://www.rfc-editor.org/info/rfc6120>.





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   [RFC7348]  Mahalingam, M., Dutt, D., Duda, K., Agarwal, P., Kreeger,
              L., Sridhar, T., Bursell, M., and C. Wright, "Virtual
              eXtensible Local Area Network (VXLAN): A Framework for
              Overlaying Virtualized Layer 2 Networks over Layer 3
              Networks", RFC 7348, DOI 10.17487/RFC7348, August 2014,
              <http://www.rfc-editor.org/info/rfc7348>.

   [RFC7432]  Sajassi, A., Ed., Aggarwal, R., Bitar, N., Isaac, A.,
              Uttaro, J., Drake, J., and W. Henderickx, "BGP MPLS-Based
              Ethernet VPN", RFC 7432, DOI 10.17487/RFC7432, February
              2015, <http://www.rfc-editor.org/info/rfc7432>.

   [RFC7510]  Xu, X., Sheth, N., Yong, L., Callon, R., and D. Black,
              "Encapsulating MPLS in UDP", RFC 7510,
              DOI 10.17487/RFC7510, April 2015,
              <http://www.rfc-editor.org/info/rfc7510>.

   [RFC7622]  Saint-Andre, P., "Extensible Messaging and Presence
              Protocol (XMPP): Address Format", RFC 7622,
              DOI 10.17487/RFC7622, September 2015,
              <http://www.rfc-editor.org/info/rfc7622>.

   [xep-0004]
              Eatmon, R., Hildebrand, J., Miller, J., Muldowney, T., and
              P. Saint-Andre, "Data Forms", XEP 0004, August 2007.

   [pubsub]   Millard, P., Saint-Andre, P., and R. Meijer, "Publish-
              Subscribe", XEP 0060, July 2010.

13.2.  Informational References

   [RFC1027]  Carl-Mitchell, S. and J. Quarterman, "Using ARP to
              implement transparent subnet gateways", RFC 1027,
              DOI 10.17487/RFC1027, October 1987,
              <http://www.rfc-editor.org/info/rfc1027>.

   [RFC5575]  Marques, P., Sheth, N., Raszuk, R., Greene, B., Mauch, J.,
              and D. McPherson, "Dissemination of Flow Specification
              Rules", RFC 5575, DOI 10.17487/RFC5575, August 2009,
              <http://www.rfc-editor.org/info/rfc5575>.

   [RFC5880]  Katz, D. and D. Ward, "Bidirectional Forwarding Detection
              (BFD)", RFC 5880, DOI 10.17487/RFC5880, June 2010,
              <http://www.rfc-editor.org/info/rfc5880>.







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   [RFC7365]  Lasserre, M., Balus, F., Morin, T., Bitar, N., and Y.
              Rekhter, "Framework for Data Center (DC) Network
              Virtualization", RFC 7365, DOI 10.17487/RFC7365, October
              2014, <http://www.rfc-editor.org/info/rfc7365>.

   [IEEE.802-1Q]
              Institute of Electrical and Electronics Engineers, "Local
              and Metropolitan Area Networks: Virtual Bridged Local Area
              Networks", IEEE Std 802.1Q-2005, May 2006.

Authors' Addresses

   Stuart Mackie
   Juniper Networks
   1133 Innovation Way
   Sunnyvale, CA  94089

   Email: wsmackie@juniper.net


   Luyuan Fang
   eBay
   2025 Hamilton Avenue
   San Jose, CA  95125

   Email: lufang@ebay.com


   Nischal Sheth
   Juniper Networks
   1133 Innovation Way
   Sunnyvale, CA  94089

   Email: nsheth@juniper.net


   Maria Napierala
   AT&T Labs
   200 Laurel Avenue
   Middletown, NJ  07748

   Email: mnapierala@att.com


   Nabil Bitar
   Nokia

   Email: nabil.bitar@nokia.com



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