[Docs] [txt|pdf] [Tracker] [WG] [Email] [Diff1] [Diff2] [Nits]

Versions: (draft-rekhter-l3vpn-virtual-hub) 00 01 02 03 04 05 06 08 RFC 7024

Network Working Group                                        Huajin Jeng
Internet Draft                                                      AT&T
Intended status: Standards Track
Expires: May 2013                                           James Uttaro
                                                                    AT&T

                                                              Luay Jalil
                                                                 Verizon

                                                          Bruno Decraene
                                                          France Telecom

                                                           Yakov Rekhter
                                                        Juniper Networks

                                                          Rahul Aggarwal
                                                                  Arktan

                                                        November 19 2012


                 Virtual Hub-and-Spoke in BGP/MPLS VPNs


                  draft-ietf-l3vpn-virtual-hub-03.txt

Status of this Memo

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

   Internet-Drafts are working documents of the Internet Engineering
   Task Force (IETF), its areas, and its working groups. Note that other
   groups may also distribute working documents as Internet-Drafts.

   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."

   The list of current Internet-Drafts can be accessed at
   http://www.ietf.org/ietf/1id-abstracts.txt.

   The list of Internet-Draft Shadow Directories can be accessed at
   http://www.ietf.org/shadow.html.






Jeng                                                            [Page 1]

Internet Draft     draft-ietf-l3vpn-virtual-hub-03.txt     November 2012


Copyright Notice

   Copyright (c) 2011 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
   (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.


Abstract

   With BGP/MPLS VPNs any-to-any connectivity among sites of a given
   Virtual Private Network would require each Provider Edge router that
   has one or more of these sites connected to it to hold all the routes
   of that Virtual Private Network. The approach described in this
   document allows to reduce the number of Provider Edge routers that
   have to maintain all these routes by requiring only a subset of these
   routers to maintain all these routes.

   Furthermore, when Provider Edge routers use ingress replication to
   carry multicast traffic of VPN customers, the approach described in
   this document may allow to reduce bandwidth inefficiency associated
   with ingress replication, and to redistribute the replication load
   among Provider Edge routers.




















Jeng                                                            [Page 2]

Internet Draft     draft-ietf-l3vpn-virtual-hub-03.txt     November 2012


Table of Contents

 1          Specification of requirements  .........................   4
 2          Overview  ..............................................   4
 3          Routing Information Exchange  ..........................   6
 4          Forwarding Considerations  .............................   8
 5          Internet Connectivity  .................................  10
 6          Deployment Considerations  .............................  13
 7          Multicast Considerations  ..............................  14
 7.1        Terminology  ...........................................  15
 7.2        Eligible Upstream Multicast Hop (UMH) routes  ..........  15
 7.3        Originating VPN-IP default route by a V-hub  ...........  15
 7.4        Handling C-multicast routes  ...........................  16
 7.5        Originating I-PMSI/S-PMSI/SA A-D routes by V-spoke  ....  16
 7.6        Originating I-PMSI/S-PMSI/SA A-D routes by V-hub  ......  17
 7.7        Receiving I-PMSI/S-PMSI/SA A-D routes by V-spoke  ......  18
 7.8        Receiving I-PMSI/S-PMSI/SA A-D routes by V-hub  ........  18
 7.8.1      Case 1  ................................................  18
 7.8.2      Case 2  ................................................  19
 7.9        Use of Ingress Replication with I-PMSI A-D routes  .....  21
 8          An example of RT provisioning  .........................  21
 8.1        Unicast routing  .......................................  22
 8.2        Multicast routing  .....................................  22
 9          Further Refinements  ...................................  23
10          IANA Considerations  ...................................  24
11          Security Considerations  ...............................  24
12          Acknowledgements  ......................................  24
13          Normative References  ..................................  24
14          Non-normative References  ..............................  25
15          Authors' Addresses  ....................................  25
















Jeng                                                            [Page 3]

Internet Draft     draft-ietf-l3vpn-virtual-hub-03.txt     November 2012


1. Specification of requirements

   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 [RFC2119].


2. Overview

   With BGP/MPLS VPNs [rfc4364] providing any-to-any connectivity among
   sites of a given Virtual Private Network (VPN) is usually
   accomplished by requiring each Provider Edge router (PE) that has one
   or more of these sites connected to it to hold all the routes of that
   VPN.  The approach described in this document allows to reduce the
   number of PEs that have to maintain all these routes by requiring
   only a subset of such PEs to maintain all these routes.

   Consider a set of PEs that maintain VRFs of a given VPN. In the
   context of this VPN we designate a subset of these PEs as "Virtual
   Spoke" PEs (or just Virtual Spokes), while some other (non-
   overlapping) subset of these PEs will be "Virtual Hub" PEs (or just
   Virtual Hubs), with the rest of the PEs in the set will be "vanilla"
   PEs (PEs that implement the [rfc4364] procedures, but do not
   implement procedures specified in this document).

   For the sake of brevity we will use the term "V-hub" to denote a
   Virtual Hub, and "V-spoke" to denote a Virtual Spoke.

   For a given VPN, its set of V-hubs may include not only the PEs that
   have sites of that VPN connected to them, but also PEs that have no
   sites of that VPN connected to them. On such PEs the VRF associated
   with that VPN may import routes from other VRFs of that VPN, even if
   the VRF has no sites of that VPN connected to it.

   Note that while in the context of one VPN a given PE may act as a V-
   hub, in the context of another VPN the same PE may act as a V-spoke,
   and vice versa. Thus a given PE may act as a V-hub only for some, but
   not all the VPNs present on that PE. Likewise, a given PE may act as
   a V-spoke only for some, but not all the VPNs present on that PE.

   For a given VPN each V-spoke of that VPN is "associated" with one or
   more V-hubs of that VPN (one may use two V-hubs for redundancy to
   avoid a single point of failure). Note that a given V-hub may have no
   V-spokes associated with it. For more on how a V-spoke and a V-hub
   become "associated" with each other see section "Routing Information
   Exchange".

   Consider a set of V-spokes that are associated with a given V-hub, V-



Jeng                                                            [Page 4]

Internet Draft     draft-ietf-l3vpn-virtual-hub-03.txt     November 2012


   hub-1. If one of these V-spokes is also associated with some other V-
   hub, V-hub-2, then other V-spokes in the set need not be associated
   with the same V-hub, V-hub-2, but may be associated with some other
   V-hubs (e.g., V-hub-3, V-hub-4, etc...)

   This document defines a VPN-IP default route as a VPN-IP route whose
   VPN-IP prefix contains just an RD.

   A PE that acts as a V-hub of a given VPN maintains all the routes of
   that VPN (such a PE imports routes from all other V-hubs and V-
   spokes, as well as from "vanilla" PEs of that VPN). A PE that acts as
   a V-spoke of a given VPN needs to maintain only the routes of that
   VPN that are originated by the sites of that VPN connected to that
   PE, plus one or more VPN-IP default route originated by the V-hub(s)
   associated with that V-spoke (such a PE need to import only VPN-IP
   default route from certain V-hubs). This way, only a subset of PEs
   that maintain VRFs of a given VPN, namely only the PEs acting as V-
   hubs of that VPN, have to maintain all the routes of that VPN. PEs
   acting as V-spokes of that VPN need to maintain only a (small) subset
   of the routes of that VPN.

   This document assumes that a given V-hub and associated with it V-
   spoke(s) are in the same Autonomous Systems. However, if PEs that
   maintain VRFs of a given VPN span multiple Autonomous Systems, this
   document does not restrict all the V-hubs of that VPN to be in the
   same Autonomous System - the V-hubs may be spread among these
   Autonomous Systems.

   When PEs use ingress replication to carry multicast traffic of VPN
   customers, the approach described in this document may allow to
   reduce bandwidth inefficiency associated with ingress replication,
   and to redistribute the replication load among the PEs. This is
   because a PE that acts as a V-spoke of a given VPN would need to
   replicate multicast traffic only to other V-hubs (while other V-hubs
   would replicate this traffic to the V-spokes associated with these V-
   hubs), rather than to all the PEs of that VPN. Likewise, a PE that
   acts as a V-hub of a given VPN would need to replicate multicast
   traffic to other V-hubs, and the V-spokes, but only to the V-spokes
   associated with that V-hub, rather than replicating the traffic to
   all the PEs of that VPN. Limiting replication could be especially
   beneficial if the V-spoke PEs have limited replication capabilities
   and/or have links with limited bandwidth.









Jeng                                                            [Page 5]

Internet Draft     draft-ietf-l3vpn-virtual-hub-03.txt     November 2012


3. Routing Information Exchange

   Routing information exchange among all the PEs of a given VPN is
   subject to the following rules.

   A PE that has sites of a given VPN connected to it has to retain
   routing information received from these sites. This is irrespective
   of whether this PE acts as a V-hub or a V-spoke of that VPN, and
   follows the rules specified in [rfc4364].

   A PE that has sites of a given VPN connected to it follows the rules
   specified in [rfc4364] when exporting (as VPN-IP routes) the routes
   received from these sites. This is irrespective of whether this PE
   acts as a V-hub or a V-spoke of that VPN.

   In addition, a V-hub of a given VPN MUST export a VPN-IP default
   route for that VPN. This route MUST be exported to only the V-spokes
   of that VPN that are associated with that V-hub.

   To enable a V-spoke of a given VPN to share its outbound traffic load
   among the V-hubs associated with that V-spoke, each V-hub of that
   VPN, when originating a VPN-IP default route MUST use a distinct RD
   (per V-hub, per VPN). Use of Type 1 RDs may be an attractive option
   for such RDs.

   If a V-spoke imports several VPN-IP default routes, each originated
   by its own V-hub, and these routes have the same preference, then
   traffic from the V-spoke to other sites of that VPN would be load
   shared among the V-hubs.

   Following the rules specified in [rfc4364], a V-hub of a given VPN
   imports all the non-default VPN-IP routes originated by all other PEs
   that have sites of that VPN connected to them (irrespective of
   whether these other PEs act as V-hubs or V-spokes or just "vanilla"
   PEs for that VPN, and irrespective of whether these V-spokes are
   associated with the V-hub or not).

   A V-hub of a given VPN MUST NOT import a VPN-IP default route unless
   this is the Internet VPN-IP default route (for the definition of the
   "Internet VPN-IP default route", and how to distinguish between a
   VPN-IP default route and the Internet VPN-IP default route see
   section "Internet Connectivity").

   Within a given VPN, a V-spoke MUST import all VPN-IP default routes
   that have been originated by the V-hubs associated with that V-spoke.

   In addition, a V-spoke of a given VPN MAY import VPN-IP routes for
   that VPN that have been originated by some other V-spokes of that



Jeng                                                            [Page 6]

Internet Draft     draft-ietf-l3vpn-virtual-hub-03.txt     November 2012


   VPN, but only by the V-spokes that are associated with the same V-
   hub(s) as the V-spoke itself.

   The above rules are realized using Route Target (RT) extended
   communities [rfc4360] and VRF export/import policies based on these
   RTs. This document defines the following procedures for realizing the
   above rules.

   Consider a "vanilla" any-to-any VPN. This document assumes that all
   the PEs of that VPN (or to be more precise, all the VRFs of that VPN)
   are provisioned with the same export and import RT - we will refer to
   this RT as RT-VPN (of course, for a given VPN service provider each
   VPN would use its own RT-VPN, distinct from RT-VPNs used by other
   VPNs).

   To evolve this VPN into V-hubs and V-spokes all the PEs (or to be
   more precise all the VRFs) that are designated as either V-hubs or V-
   spokes of that VPN keep the same export RT-VPN. This RT-VPN is
   attached to all the VPN-IP routes originated by these PEs. Also, all
   the V-hubs keep the same import RT-VPN.

   In addition, each V-hub of a given VPN is provisioned with its own
   export RT, called RT-VH. This RT-VH MUST be different from the export
   RT (RT-VPN) provisioned on that V-hub. Furthermore, for a given VPN
   service provider no two VPNs can use the same RT-VH.

   A given V-spoke becomes associated with a given V-hub by virtue of
   provisioning the V-spoke to import only the VPN-IP route(s) that
   carry RT-VH provisioned on the V-hub (thus associating a new V-spoke
   with a given V-hub requires provisioning only on that V-spoke - no
   provisioning changes are required on the V-hub).

   To avoid the situation where within a given VPN all the V-spokes
   would be associated with every V-hub (in other words, to partition V-
   spokes among V-hubs), different V-hubs within that VPN MAY use
   different RT-VHs. At one extreme every V-hub may use a distinct RT-
   VH.  Use of IP-address specific RTs may be an attractive option for
   this scenario. However, it is also possible for several V-hubs to use
   the same RT-VH, in which case all these V-hubs would be associated
   with the same set of V-spokes.

   When a V-hub originates a (non-Internet) VPN-IP default route, the V-
   hub MUST attach RT-VH to that route (the case where a V-hub
   originates the Internet VPN-IP default route is covered in section
   "Internet Connectivity"). Thus this route is imported by all the V-
   spokes associated with the V-hub.

   A V-spoke MAY be provisioned to export VPN-IP routes not just to the



Jeng                                                            [Page 7]

Internet Draft     draft-ietf-l3vpn-virtual-hub-03.txt     November 2012


   V-hubs, but also to the V-spokes that import the same VPN-IP default
   route(s) as the V-spoke itself. The V-spoke accomplishes this by
   adding its import RT-VH(s) to the VPN-IP routes exported by the V-
   spoke.


4. Forwarding Considerations

   This section describes changes/modifications to the forwarding
   procedures specified in [rfc4364].

   For a given VPN, the MPLS label that a V-hub of that VPN advertises
   with a VPN-IP default route MUST be the label that is mapped to an
   NHLFE that identifies the VRF of the V-hub. As a result, when the V-
   hub receives a packet that carries such label, the V-hub pops the
   label and determines further disposition of the packet based on the
   lookup in the VRF.

   Note that this document does not require to advertise labels mapped
   to an NHLFE that identifies a VRF for routes other than the VPN-IP
   default route.

   When a V-hub of a given VPN originates a VPN-IP default route for
   that VPN, the V-hub MUST NOT install in its VRF of that VPN a default
   route, unless this route has been originated either (a) as a result
   of the V-hub receiving an IP default route from one of the CEs of
   that VPN connected to it, or (b) as a result of the V-hub receiving
   (and importing) the Internet VPN-IP default route from some other PE
   (for the definition of the "Internet VPN-IP default route" see
   section "Internet Connectivity"), or (c) the VRF being provisioned
   with a default route pointing to the routing table on the same PE
   that maintains the Internet routes.

   When a multi-homed site is connected to a V-hub and a V-spoke, then
   the V-hub uses the following OPTIONAL procedures to support IBGP/EBGP
   load balancing for the site's inbound traffic that has been
   originated by some other V-spoke associated with the V-hub. When the
   V-hub receives from some other PE a packet that carries an MPLS label
   that the V-hub advertised in the VPN-IP default route, then the V-hub
   uses the label to identify the VRF that should be used for further
   disposition of the packet. If (using the information present in the
   VRF) the V-hub determines that the packet has to be forwarded using a
   non-default route present in the VRF, and this route indicates that
   the packet's destination is reachable either over one of the VRF
   attachment circuit (for the definition of "VRF attachment circuits"
   see [rfc4364]) or via some other (V-spoke) PE, the V-hub forwards the
   packet either over this attachment circuit, or via that other PE. The
   choice between the two is a local matter to the V-hub.



Jeng                                                            [Page 8]

Internet Draft     draft-ietf-l3vpn-virtual-hub-03.txt     November 2012


   To illustrate this consider the following example:

                 <- RD:0/0           RD:0/0->

                                  <- RD:10.2.1        <-10.2.1/24
   CE1----PE-S-------------PE-H----------------PE-S1-------------CE2
                          /
                          |    |
                          |    |  10.2.1/24
                          |    |
                         CE4   CE3

   A multi-homed site (not shown in the above figure) is connect via CE2
   and CE3. Thus both CE2 and and CE3 advertise a route to 10.2.1/24.
   CE2 advertises this route (route to 10.2.1/24) to PE-S1, which in
   turn originates a VPN-IP route RD:10.2.1. CE3 advertises this route
   to PE-H.

   PE-H is a V-hub, while PE-S and PE-S1 are V-spokes associated with
   that V-hub. Thus PE-H originates a VPN-IP default route (RD:0/0), and
   both PE-S and PE-S1 import that route.

   PE-H receives from PE-S1 a VPN-IP route to RD:10.2.1 and from CE3 a
   plain IP route to 10.2.1. Thus the VRF entry on PE-H has two possible
   next hops for 10.2.1: CE3 and PE-S1 (the latter is a next hop that is
   not directly connected to PE-H).

   Now consider what happens when CE1 originates a packet destined to
   10.2.1.1. When PE-S receives this packet, PE-S (following the VPN-IP
   default route) forwards the packet to PE-H. The MPLS label in the
   packet is the label that PE-H advertised to PE-S in the VPN-IP
   default route. Thus, following the rule specified above, PE-H may
   forward the packet either via CE3 or via PE-S1 (with PE-S1
   subsequently forwarding the packet to CE2), resulting in IBGP/EBGP
   load balancing.

   Likewise, if CE4 originates a packet destined to 10.2.1.1, PE-H may
   forward the packet either via CE3 or via PE-S1 (with PE-S1
   subsequently forwarding the traffic to CE2), resulting in IBGP/EBGP
   load balancing.

   Note however, that if there is some other CE, CE5, connected to PE-
   S1, and that CE5 sends a packet to 10.2.1.1, then (due to the IP
   longest match rule) PE-S1 will always forward this packet to CE2.
   Thus for a mult-homed site connected to a V-hub and a V-spoke
   IBGP/EBGP load balancing will be available for some, but not all the
   traffic destined to that site. Specifically, IBGP/EBGP load balancing
   will not be available for the traffic destined to that site if this



Jeng                                                            [Page 9]

Internet Draft     draft-ietf-l3vpn-virtual-hub-03.txt     November 2012


   traffic has been originated within some other site that is connected
   to the same V-spoke.

   Moreover, if CE3 advertises 10.2.1.0/25 and 10.2.1/24, while CE2
   advertises 10.2.1.128/25 and 10.2.1/24 (which is yet another form of
   load balancing for a multi-homed site), then when CE5 sends a packet
   to 10.2.1.1, then (due to the IP longest match rule) PE-S1 will
   always forward this packet to CE2, even though the VPN customer would
   expect this traffic to flow via CE3.

   This document proposes two options to address the issues raised in
   the previous two paragraphs. The first option is to disallow for a
   given VPN to provision PEs that have multi-homed sites of that VPN
   connected to them as V-spokes (such PEs could be provisioned as
   either V-hubs, or as plain "vanilla" PEs). The second option is for
   the V-spoke, when it receives an IP route from a CE, not to install
   this route in its forwarding table, but just re-advertise this route
   as a VPN-IP route, together with an MPLS label. The NHLFE [rfc3031]
   associated with that label MUST specify the CE that advertises the IP
   route as the next hop. As a result, when the PE receives data that
   carries that label, the PE performs no IP lookup on the data, and
   just forwards the data to the CE. Note that doing this would result
   in forcing the traffic between a pair of sites connected to the same
   V-spoke to go through the V-hub of that V-spoke.

   An implementation that supports IBGP/EBGP load balancing, as
   specified above, SHOULD support the second option. If the
   implementation does not support the second option, then deploying
   this implementation to support IBGP/EBGP load balancing, as specified
   above, would either (a) restrict the set of PEs that could be
   provisioned as V-spokes (any PE that has a multi-homed site connected
   to it can not be provisioned as a V-spoke), or (b) IBGP/EBGP load
   balancing may not be available for certain scenarios (the scenarios
   that the second option is intended to cover).


5. Internet Connectivity

   This document specifies two possible alternatives of providing
   Internet connectivity for a given VPN.

   The first alternative is when a PE that maintains Internet routes
   also maintains a VRF of a given VPN. In this case the Internet
   connectivity for that VPN MAY be provided by provisioning in the
   VPN's VRF on that PE a default route pointing to the routing table on
   that PE that maintains the Internet routes. This PE MUST NOT be
   provisioned as a V-spoke for that VPN (this PE may be provisioned as
   either a V-hub, or as a "vanilla" PE). If this PE is provisioned as a



Jeng                                                           [Page 10]

Internet Draft     draft-ietf-l3vpn-virtual-hub-03.txt     November 2012


   V-hub, then this PE MUST originate a VPN-IP default route. The route
   MUST carry both RT-VPN and RT-VH of the V-hub (see section "Routing
   Information Exchange" for the definition of "RT-VPN" and "RT-VH").
   Thus this route will be imported by all the V-spokes associated with
   the V-hub, as well as by other V-hubs. An implementation MUST support
   the first alternative.

   The second alternative is when a site of a given VPN has connection
   to the Internet, and a CE of that site advertises an IP default route
   to the PE connected to that CE. This alternative has two sub-cases:
   (a) PE is provisioned as a V-hub, and (b) PE is provisioned as a V-
   spoke. An implementation MUST support the sub-case (a). An
   implementation MAY support the sub-case (b).

   If a PE is provisioned as a V-hub, then the PE re-advertises this IP
   default route as a VPN-IP default route, and install in its VRF an IP
   default route with the next hop specifying the CE(s) that advertise
   the IP default route to the PE. Note, that when re-advertising the
   VPN-IP default route, the route MUST carry both RT-VPN and RT-VH of
   the V-hub (see section "Routing Information Exchange" for the
   definition of "RT-VPN" and "RT-VH"). Thus this route will be imported
   by all the V-spokes associated with the V-hub, as well as by other V-
   hubs.

   If a PE is provisioned as a V-spoke, then receiving a default route
   from a CE MUST NOT cause the V-spoke to install an IP default route
   in its VRF. The V-spoke MUST originate a VPN-IP default route with a
   (non-null) MPLS label. The route MUST carry only RT-VPN (as a result,
   this route is not imported by any of the V-spokes, but is imported by
   V-hubs). The packet's next hop of the Next Hop Label Forwarding Entry
   (NHLFE) [rfc3031] associated with that label MUST specify the CE that
   advertises the IP default route. As a result, when the V-spoke
   receives data that carries that label, the V-spoke performs no IP
   lookup on the data, and just forwards the data to the CE. Note that
   in this case the VRF on the V-spoke is going to have an IP default
   route, but this route would be created as a result of receiving a
   VPN-IP default route from one of the V-hubs associated with that V-
   spoke (and not as a result of receiving the IP default route from the
   CE). Note also that if this V-spoke has other sites of that VPN
   connected to it, then traffic from these sites to the Internet would
   go to that V-spoke, then to the V-hub selected by the V-spoke, then
   from that V-hub back to the V-spoke, and then to the CE that
   advertises IP default route to the V-spoke.

   If a PE is provisioned as a V-spoke of a given VPN, and if a CE of
   that VPN advertises an IP default route to the PE (as the CE belongs
   to the site that provides the Internet connectivity for the VPN),
   then the PE MUST NOT advertise an IP default route back to that CE.



Jeng                                                           [Page 11]

Internet Draft     draft-ietf-l3vpn-virtual-hub-03.txt     November 2012


   Yet, the CE has to specify that PE as the next hop for all the
   traffic to other sites of that VPN. A way to accomplish this is to
   require the V-spoke to implement procedures of section "Further
   Refinements".

   In all of the above scenarios described in this section we refer to
   the originated VPN-IP default route as the "Internet VPN-IP default
   route". Specifically, the Internet VPN-IP default route is a VPN-IP
   default route originated by a PE (this PE could be either a V-hub or
   a V-spoke) as a result of either (a) receiving an IP default route
   from a CE, or (b) of PE maintaining Internet routes, and by
   provisioning in the VPN's VRF on that PE a default route pointing to
   the routing table on that PE that maintains the Internet routes.

   The difference between the Internet VPN-IP default route and a non-
   Internet VPN-IP default route originated by a V-hub is in the RTs
   carried by the route - for a given VPN and a given V-hub of that VPN
   the Internet VPN-IP default route carries both RT-VPN and RT-VH of
   that V-hub, the non-Internet VPN-IP default route carries just RT-VH
   of that V-hub.

   When a V-hub originates the Internet VPN-IP default route, the V-hub
   MUST withdraw the non-Internet VPN-IP default route that has been
   originated by the V-hub. When a V-hub withdraws the Internet VPN-IP
   default route that has been originated by the V-hub, the V-hub MUST
   originate a non-Internet VPN-IP default route. That is, at any given
   point in time a given V-hub originates either the Internet VPN-IP
   default route, or a non-Internet VPN-IP default route.

   As a result of the rules specified above, if a V-hub originates the
   Internet VPN-IP default route, then all the V-spokes associated with
   that V-hub MUST import that route. In addition (and in contrast with
   a non-Internet VPN-IP default route), other V-hubs MAY import that
   route. A V-hub MAY also import the Internet VPN-IP default routes
   originated by V-spoke(s). A V-spoke MUST NOT import the Internet VPN-
   IP default route originated by any other V-spoke. Such a route MAY be
   imported only by V-hubs.

   If the Internet VPN-IP default route originated by a V-hub has the
   same preference as the (non Internet) VPN-IP default route originated
   by some other V-hub, then a V-spoke that imports VPN-IP default
   routes originated by both of these V-hubs would load share the
   outgoing Internet traffic between these two V-hubs (and thus some of
   the outgoing Internet traffic from that V-spoke will first be routed
   to the V-hub that does not originate the Internet VPN-IP default
   route, and then from that V-hub to the V-hub that does originate the
   Internet VPN-IP default route).




Jeng                                                           [Page 12]

Internet Draft     draft-ietf-l3vpn-virtual-hub-03.txt     November 2012


   If taking an extra-hub hop for the Internet traffic is viewed as
   undesirable, then it is RECOMMENDED that the Internet VPN-IP default
   route be of higher preference than a (non-Internet) VPN-IP default
   route originated by some other V-hub. However, in this case the
   traffic from the V-spokes to other sites of that VPN will not be load
   shared between these two V-hubs.



6. Deployment Considerations

   For a given VPN a V-hub and a set of V-spokes associated with that V-
   hub should be chosen in a way that minimizes the additional network
   distance/latency penalty, given that VPN geographic footprint.

   For a given VPN some/all of its V-spokes could be grouped into
   geographically-based clusters (V-spokes within a given cluster be in
   close geographical proximity to each other) with any-any connectivity
   within each cluster. Note that the V-spokes within a given cluster
   need not be associated with the same V-hub(s). Likewise, not all V-
   spokes associated with a given V-hub need to be in the same cluster.
   A use case for this would be VPN for large retail chain in which data
   traffic is hub/spoke between each store and centralized data-centers
   but there is need for direct VoIP traffic between stores within same
   geographical area.

   Use of RT Constrains [rfc4684] may further facilitate/optimize
   routing exchange in support of V-hubs and V-spokes.

   Introducing V-spoke PE in a VPN may introduce the following change
   for the customer of that VPN:

     + traceroute from a CE connected to a V-spoke may report an
       additional hop: the V-hub PE.

     + latency for traffic sent from a CE connected to a V-spoke may
       increase, depending on the location of the V-hub in the layer 3
       and layer 1 network topology of the SP.













Jeng                                                           [Page 13]

Internet Draft     draft-ietf-l3vpn-virtual-hub-03.txt     November 2012


7. Multicast Considerations

   This section describes procedures for supporting MVPN in the presence
   of Virtual Hub-and-Spoke. The procedures rely on MVPN specifications
   as defined in [rfc6513], [rfc6514], [rfc6625].

   The procedures assume that for the purpose of ensuring non-
   duplication both V-hubs and V-spokes can discard packets from a
   "wrong" PE, as specified in section 9.1.1 of [rfc6513]. The existing
   procedures for S-PMSI A-D routes ([rfc6513], [rfc6514], [rfc6625])
   are sufficient to discard packets coming from a "wrong" PE for all
   types of P-tunnels specified in [rfc6514] (including Ingress
   Replication). The existing procedures for I-PMSI A-D routesa
   (rfc6513], rfc6514]) are sufficient to discard packets coming from a
   "wrong" PE for all types of P-tunnels specified in [rfc6514], except
   for Ingress Replication. When Ingress Replication is used for I-PMSI
   P-tunnels section "Use of Ingress Replication with I-PMSI A-D route"
   specifies changes to the procedures in [rfc6514] to enable discard
   packets from a "wrong" PE.

   The V-hub/V-spoke architecture, as specified in this document,
   affects certain multicast scenarios. In particular, it affects
   multicast scenarios where the source of a multicast flow is at a site
   attached to a V-hub, and a receiver of that flow is at a site
   attached to a V-spoke that is not associated with that same V-hub.
   It also affects multicast scenarios where the source of a multicast
   flow is at a site attached to a V-spoke, a receiver of that flow is
   at a site attached to a different V-spoke, and the set intersection
   between the V-hub(s) associated with the first V-spoke and the V-
   hub(s) associated with the second V-spoke is empty. It may also
   affect multicast scenarios where the source of a multicast flow is at
   a site connected to a V-spoke, a receiver of that flow is at a site
   attached to a different V-spoke, and the set intersection between the
   V-hub(s) associated with the first V-spoke and the V-hub(s)
   associated with the second V-spoke is non-empty (the multicast
   scenarios are affected if the I-PMSI/S-PMSI A-D routes originated by
   the first V-spoke are not imported by the second V-spoke).

   Use of Virtual Hub-and-Spoke in conjunction with seamless MPLS
   multicast [seamless-MPLS-multicast] is outside the scope of this
   document.










Jeng                                                           [Page 14]

Internet Draft     draft-ietf-l3vpn-virtual-hub-03.txt     November 2012


7.1. Terminology

   We will speak of a P-tunnel being "bound" to a particular I-PMSI/S-
   PMSI A-D route if the P-tunnel is specified in that route's PMSI
   Tunnel Attribute.

   When Ingress Replication is used, the P-tunnel bound to a particular
   I-PMSI/S-PMSI A-D route is actually a set of unicast tunnels. The PE
   originating the route uses these unicast tunnels to carry traffic to
   the PEs that import the route. When we say that traffic has been
   received by a PE on a P-tunnel "bound" to particular I-PMSI/S-PMSI A-
   D route received by that PE, we refer to the unicast tunnel that the
   PE originating the route uses to send traffic to the PE that receives
   the route.


7.2. Eligible Upstream Multicast Hop (UMH) routes

   On a V-spoke the set of Eligible UMH routes consists of all the
   unicast VPN-IP routes received by the V-spoke, including the default
   VPN-IP routes received from its V-hub(s). Note that such routes MAY
   include routes received from other V-spokes. The routes received from
   other V-spokes could be either "vanilla" VPN-IP routes (routes using
   the IPv4 or IPv6 AFI, and SAFI set to 128 "MPLS-labeled VPN address"
   [IANA-SAFI]), or routes using the IPv4 or IPv6 AFI (as appropriate),
   but with the SAFI set to SAFI 129 "Multicast for BGP/MPLS IP Virtual
   Private Networks (VPNs)" [IANA-SAFI].

   The default VPN-IP routes received from the V-hub(s) may be either
   Internet default VPN-IP routes, or non-Internet default VPN-IP
   routes.


7.3. Originating VPN-IP default route by a V-hub

   When originating a VPN-IP default route, a V-hub, in addition to the
   procedures specified in section "Routing Information Exchange", also
   follows the procedures of sections 6 and 7 of [rfc6514] (see also
   section 5.1 of [rfc6513]). Specifically the V-hub MUST add the VRF
   Route Import extended community that embeds the V-hub's IP address.
   The route also MUST include the Source AS extended community.










Jeng                                                           [Page 15]

Internet Draft     draft-ietf-l3vpn-virtual-hub-03.txt     November 2012


7.4. Handling C-multicast routes

   Origination of C-multicast routes follow the procedures of [rfc6514]
   (this is irrespective of whether these routes are originated by a V-
   hub or by a V-spoke).

   When a V-spoke receives a C-multicast route, the V-spoke follows the
   [rfc6514] procedures.

   When a V-hub receives a C-multicast route, the V-hub determines
   whether the C-RP/C-S of the route is reachable via one of its VRF
   interfaces, and if yes, then the V-hub follows the [rfc6514]
   procedures.

   Otherwise, the C-RP/C-S of the route is reachable via some other PE
   (this is the case where the received route was originated by a V-
   spoke that sees the V-hub as the "upstream PE" for a given source,
   but the V-hub sees some other PE (either V-hub or V-spoke) as the
   "upstream PE" for that source). In this case the V-hub uses the type
   (Source Tree Join vs Shared Tree Join), the Multicast Source, and
   Multicast Group from the received route to construct a new route of
   the same type, with the same Multicast Source and Multicast Group.
   The hub constructs the rest of the new route following procedures
   specified in 11.1.3 of [rfc6514]. The hub also creates the
   appropriate (C-*, C-G)/(C-S, C-G) state in its MVPN-TIB.


7.5. Originating I-PMSI/S-PMSI/SA A-D routes by V-spoke

   When a V-spoke originates an I-PMSI/S-PMSI/SA A-D route, the V-spoke
   follows the procedures of [rfc6514] (or in the case of a wildcard S-
   PMSI A-D route the procedures of [rfc6625]), including the procedures
   for constructing RT(s) carried by the route. Note that as a result,
   such a route will be imported by the V-hubs. In the case of an I-
   PMSI/S-PMSI A-D route, the P-tunnel bound to this route is used to
   carry to these V-hubs traffic originated by the sites connected to
   the V-spoke.

   If the V-spoke exports its (unicast) VPN-IP routes not just to the V-
   hubs, but also to some other V-spokes (as described in section
   "Routing Information Exchange"), then (as a result of following the
   procedures of [rfc6514], or in the case of a wildcard S-PMSI A-D
   route the procedures of [rfc6625]) the I-PMSI/S-PMSI/SA A-D route
   originated by the V-spoke will be imported not just by the V-hubs,
   but also by these other V-spokes. This is because in this scenario
   the route will carry more than one RT; one of these RTs, RT-VPN, will
   result in importing the route by the V-hubs, while other RT(s) will
   result in importing the route by the V-spokes (the other RT(s) are



Jeng                                                           [Page 16]

Internet Draft     draft-ietf-l3vpn-virtual-hub-03.txt     November 2012


   the RT(s) that the V-spoke uses for importing the VPN-IP default
   route). In this case the P-tunnel bound to this I-PMSI/S-PMSI A-D
   route is also used to carry traffic originated by the sites connected
   to the V-spoke that originates the route to these other V-spokes.


7.6. Originating I-PMSI/S-PMSI/SA A-D routes by V-hub

   When a V-hub originates an I-PMSI/S-PMSI/SA A-D route, the V-hub
   follows the procedures of [rfc6514] (or in the case of a wildcard S-
   PMSI A-D route the procedures of [rfc6625]), except that in addition
   to the RT(s) constructed following these procedures, the route MUST
   also carry the RT of the VPN-IP default route advertised by the V-hub
   (RT-VH).  Note that as a result, such a route will be imported by
   other V-hubs, and also by the V-spokes, but only by the V-spokes that
   are associated with the V-hub (the V-spokes that import the VPN-IP
   default route originated by the V-hub). In the case of an I-PMSI/S-
   PMSI A-D route, the P-tunnel bound to this route is used to carry to
   these other V-hubs and V-spokes the traffic originated by the sites
   connected to the V-hub that originates the route.

   In addition, if a V-hub originates an I-PMSI A-D route following the
   procedures of [rfc6514], the V-hub MUST originate another I-PMSI A-D
   route - we'll refer to this route as a "Associated-V-spoke-only I-
   PMSI A-D route". The RT carried by this route MUST be the RT that is
   carried in the VPN-IP default route advertised by the V-hub (RT-VH).
   Therefore, this route will be imported only by the V-spokes
   associated with the V-hub (the V-spokes that import the VPN-IP
   default route advertised by this V-hub). The P-tunnel bound to this
   route is used to carry to these V-spokes traffic originated by the
   sites connected to either (a) other V-hubs, or (b) other V-spokes,
   including the V-spokes that import the VPN-IP default route from the
   V-hub, or (c) "vanilla" PEs. More details on the use of this P-tunnel
   are described in section "Receiving I-PMSI/S-PMSI/SA A-D routes by V-
   hub".

   As a result, a V-hub originates not one, but two I-PMSI A-D routes -
   one is a "vanilla" I-PMSI A-D route, and another is an Associated-V-
   spoke-only I-PMSI A-D route. Each of these routes MUST have a
   distinct RD.

   When a V-hub receives traffic from one of the sites connected to the
   V-hub, and the V-hub determines (using some local policies) that this
   traffic should be transmitted using an I-PMSI, the V-hub forwards
   this traffic on the P-tunnel bound to the "vanilla" I-PMSI A-D route,
   but MUST NOT forward it on the P-tunnel bound to the Associated-V-
   spoke-only I-PMSI A-D route.




Jeng                                                           [Page 17]

Internet Draft     draft-ietf-l3vpn-virtual-hub-03.txt     November 2012


7.7. Receiving I-PMSI/S-PMSI/SA A-D routes by V-spoke

   When a V-spoke receives an I-PMSI/S-PMSI/SA A-D route, the V-spoke
   follows the procedures of [rfc6514] (or in the case of a wildcard S-
   PMSI A-D route the procedures of [rfc6625]). As a result, a V-spoke
   that is associated with a given V-hub (the V-spoke that imports the
   VPN-IP default route originated by that V-hub) will also import I-
   PMSI/S-PMSI/SA A-D routes originated by that V-hub. Specifically, the
   V-spoke will import both the "vanilla" I-PMSI A-D route and the
   Associated-V-spoke-only I-PMSI A-D route originated by the V-hub.

   In addition, if a V-spoke imports the (unicast) VPN-IP routes
   originated by some other V-spokes (as described in section "Routing
   Information Exchange"), then the V-spoke will also import I-PMSI/S-
   PMSI/SA A-D routes originated by these other V-spokes.


7.8. Receiving I-PMSI/S-PMSI/SA A-D routes by V-hub

   The following describe procedures that a V-hub MUST follow when it
   receives an I-PMSI/S-PMSI/SA A-D route.


7.8.1. Case 1

   This is the case where a V-hub receives an I-PMSI/S-PMSI/SA A-D
   route, and one of the RT(s) carried in the route is the RT that the
   V-hub uses for advertising its VPN-IP default route (RT-VH).

   In this case the receiving route was originated either

     + by a V-spoke associated with the V-hub (the V-spoke that imports
       the VPN-IP default route originated by the V-hub), or

     + by some other V-hub that uses the same RT as the receiving V-hub
       for advertising the VPN-IP default route.


   In this case the received I-PMSI/S-PMSI/SA A-D route carries more
   than one RT. One of these RTs results in importing this route by the
   V-hubs. Another of these RTs is the RT that the V-hub uses when
   advertising its VPN-IP default route (RT-VH). This RT results in
   importing the received I-PMSI/S-PMSI/SA A-D route by all the V-spokes
   associated with the V-hub (the V-spokes that import the VPN-IP
   default route originated by the V-hub).

   In handling such I-PMSI/S-PMSI/SA A-D route the V-hub follows the
   procedures of [rfc6514] (or in the case of a wildcard S-PMSI A-D



Jeng                                                           [Page 18]

Internet Draft     draft-ietf-l3vpn-virtual-hub-03.txt     November 2012


   route the procedures of [rfc6625]). Specifically, in contrast to Case
   2 below, the V-hub MUST NOT re-advertise this route.

   The following specifies the rules that the V-hub MUST follow when
   handling traffic that the V-hub receives on a P-tunnel bounded to
   this I-PMSI/S-PMSI A-D route. The V-hub may forward this traffic to
   only the sites connected to that V-hub (forwarding this traffic to
   these sites follows the procedures specified in [rfc6514], or in the
   case of a wildcard S-PMSI A-D route the procedures of [rfc6625]). The
   V-hub MUST NOT forward the traffic received on this P-tunnel to any
   other V-hubs or V-spokes, including the V-spokes that import the VPN-
   IP default route originated by the V-hub (V-spokes associated with
   the V-hub). Specifically, the V-hub MUST NOT forward the traffic
   received on the P-tunnel advertised in the received I-PMSI A-D route
   over the P-tunnel that the V-hub binds to its Associated-V-spoke-only
   I-PMSI A-D route.


7.8.2. Case 2

   This is the case where a V-hub receives an I-PMSI/S-PMSI/SA A-D
   route, and the route does not carry the RT that the receiving V-hub
   uses when advertising its VPN-IP default route (RT-VH).

   In this case the receiving I-PMSI/S-PMSI/SA A-D route was originated
   by either some other V-hub, or by a V-spoke. The I-PMSI/S-PMSI/SA A-D
   route is imported by the V-hub (as well as by other V-hubs), but not
   by any of the V-spokes associated with the V-hub (V-spokes that
   import the VPN-IP default route originated by the V-hub).

   In this case the V-hubs follows the procedures of [rfc6514] (or in
   the case of a wildcard S-PMSI A-D route the procedures of [rfc6625])
   with the following additions.

   Once a V-hub accepts an I-PMSI A-D route, when the V-hub receives
   data on the P-tunnel bound to that I-PMSI A-D route, the V-hub
   follows procedures in [rfc6513], [rfc6514] to determine whether to
   accept the data. If the data is accepted, then the V-hub further
   forwards the data over the P-tunnel bound to the Associated-V-spoke-
   only I-PMSI A-D route originated by the V-hub. Note that in deciding
   whether to forward the data over the P-tunnel bound to the
   Associated-V-spoke-only I-PMSI A-D route originated by the V-hub, the
   V-hub SHOULD take into account the (multicast) state present in its
   MVPN-TIB that has been created as a result receiving C-multicast
   routes from the V-spokes associated with the V-hub. If (using the
   information present in the MVPN-TIB) the V-hub determines that none
   of these V-spokes have receivers for the data, the V-hub SHOULD NOT
   forward the data over the P-tunnel bound to the Associated-V-spoke-



Jeng                                                           [Page 19]

Internet Draft     draft-ietf-l3vpn-virtual-hub-03.txt     November 2012


   only I-PMSI A-D route originated by the V-hub.

   Whenever a V-hub accepts an S-PMSI/SA A-D route, the V-hub, in
   contrast to Case 1 above, MUST re-advertise this route to its V-
   spokes. To accomplish this, the V-hub replaces the RT(s) carried in
   the route with the RT that the V-hub uses when originating its VPN-IP
   default route (RT-VH), changes the RD of the route to the RD that the
   V-hub uses when originating its Associated-V-spoke-only I-PMSI A-D
   route, and sets Next Hop to self. For S-PMSI A-D routes the V-hub
   also changes the Originating Router's IP address in the MCAST-VPN
   NLRI of the route to its own IP address (the same address as the one
   in the Next Hop). Moreover, before re-advertising S-PMSI A-D routes
   to V-spokes, the V-hub modifies the PMSI Tunnel attribute of these
   routes as appropriate (e.g., by replacing the P-tunnel rooted at the
   originator of these routes with a P-tunnel rooted at the V-hub).

   Note that a V-hub of a given MVPN may receive and accept multiple
   (C-*, C-*) wildcard S-PMSI A-D routes [rfc6625], each originated by
   its own PE. Yet, even if the V-hub receives and accepts such multiple
   (C-*, C-*) S-PMSI A-D routes, the V-hub re-advertises just one (C-*,
   C-*) S-PMSI A-D route, thus aggregating the received (C-*, C-*) S-
   PMSI A-D routes. The same applies for (C-*, C-G) S-PMSI A-D routes.

   Whenever a V-hub receives data on the P-tunnel bound to a received S-
   PMSI A-D route, the V-hub follows procedures of [rfc6513], [rfc6514]
   (or in the case of a wildcard S-PMSI A-D route the procedures of
   [rfc6625]) to determine whether to accept the data.  If the data is
   accepted, then the V-hub further forwards it over the P-tunnel bound
   to the S-PMSI A-D route that has been re-advertised by the V-hub.

   If multiple S-PMSIs received by a V-hub have been aggregated into the
   same P-tunnel, then the V-hub, prior to forwarding to the V-spokes
   associated with that V-hub the data received on this P-tunnel MAY de-
   aggregate and then re-aggregate (in a different way) this data using
   the state present in its MVPN-TIB that has been created as a result
   of receiving C-multicast routes from the V-spokes. Even if S-PMSIs
   received by the V-hub each have their own P-tunnel, the V-hub, prior
   to forwarding to the V-spokes the data received on these P-tunnels
   MAY aggregate these S-PMSIs using the state present in its MVPN-TIB
   that has been created as a result of receiving C-multicast routes
   from the V-spokes.










Jeng                                                           [Page 20]

Internet Draft     draft-ietf-l3vpn-virtual-hub-03.txt     November 2012


7.9. Use of Ingress Replication with I-PMSI A-D routes

   The following modifications to the procedures specified in [rfc6514]
   for originating/receiving I-PMSI A-D routes enable to discard packets
   coming from a "wrong" PE when Ingress Replication is used for I-PMSI
   P-tunnels (for other types of P-tunnels the procedures specified in
   [rfc6513], [rfc6514] are sufficient).

   If Ingress Replication is used with I-PMSI A-D routes, then when a PE
   advertises such routes, the Tunnel Type in the PMSI Tunnel attribute
   MUST be set to Ingress Replication; the Leaf Information Required
   flag MUST be set to 1; the the attribute MUST carry no MPLS labels.

   A PE that receives such I-PMSI A-D route MUST respond with a Leaf A-D
   route. The PMSI Tunnel attribute of that Leaf A-D route is
   constructed as follows. The Tunnel Type is set to Ingress
   Replication.  The Tunnel Identifier MUST carry a routable address of
   the PE that originates the Leaf A-D route. The PMSI Tunnel attribute
   MUST carry a downstream assigned MPLS label that is used to
   demultiplex the traffic received over a unicast tunnel by the PE.

   This document assumes that for a given MVPN all the PEs that have
   sites of that MVPN connected to them implement the procedures
   specified in this section.


8. An example of RT provisioning

   Consider a VPN A that consists of 9 sites - site-1 through site-9.
   Each site is connected to its own PE - PE-1 through PE-9.

   We designate PE-3, PE-6, and PE-9 as V-hubs.

   To simplify the presentation the following example assumes that each
   V-spoke is associated with just one V-hub. However, as mentioned
   earlier, in practice each V-spoke should be associated with two or
   more V-hubs.

   PE-1 and PE-2 are V-spokes associated with PE-3. PE-4 and PE-5 are V-
   spokes associated with PE-6. PE-7 and PE-8 are V-spokes associated
   with PE-9.










Jeng                                                           [Page 21]

Internet Draft     draft-ietf-l3vpn-virtual-hub-03.txt     November 2012


8.1. Unicast routing

   All the PEs (both V-hubs and V-spokes) are provisioned to export
   routes using RT-A (just as it would be with "vanilla" any-to-any
   VPN).

   All the V-hubs (PE-3, PE-6, and PE-9) are provisioned to import
   routes with RT-A (just as it would be with "vanilla" any-to-any VPN).

   In addition, PE-3 is provisioned to originate a VPN-IP default route
   with RT-A-VH-1 (but not with RT-A), while PE-1 and PE-2 are
   provisioned to import routes with RT-A-VH-1.

   Likewise, PE-6 is provisioned to originate a VPN-IP default route
   with RT-A-VH-2 (but not with RT-A), while PE-4 and PE-5 are
   provisioned to import routes with RT-A-VH-2.

   Finally, PE-9 is provisioned to originate a VPN-IP default route with
   RT-A-VH-3 (but not with RT-A), while PE-7 and PE-8 are provisioned to
   import routes with RT-A-VH-3.

   Now let's modify the above a bit by assuming that site-3 has Internet
   connectivity. Thus site-3 advertises an IP default route to PE-3.
   PE-3, in turn originates a VPN-IP default route. In this case, the
   VPN-IP default route carries RT-A and RT-A-VH-1 (rather than just RT-
   A-VH-1, as before), which results in importing this route to PE-6 and
   PE-9, as well as to PE-1 and PE-2.

   If PE-7 and PE-8, in addition to importing VPN-IP default route from
   PE-9, also want to import each other VPN-IP routes, then PE-7 and
   PE-8 export their VPN-IP routes with two RTs: RT-A and RT-A-VH-3.


8.2. Multicast routing

   All the PEs designated as V-spokes (PE-1, PE-2, PE-4, PE-5, PE-7, and
   PE-8) are provisioned to export their I-PMSI/S-PMSI/SA A-D routes
   using RT-A (just as it would be with "vanilla" any-to-any MVPN). Thus
   these routes could be imported by all the V-hubs (PE-3, PE-6, and
   PE-9).

   The V-hub on PE-3 is provisioned to export its I-PMSI/S-PMSI/SA A-D
   routes with two RTs: RT-A and RT-A-VH-1. Thus these routes could be
   imported by all the other V-hubs (PE-6 and PE-9), and also by the V-
   spokes, but only by the V-spokes associated with the V-hub on PE-3
   (PE-1 and PE-2). In addition, the V-hub on PE-3 originates the
   Associated-V-spoke-only I-PMSI A-D route with RT-A-VH-1. This route
   could be imported only by the V-spokes associated with the V-hub on



Jeng                                                           [Page 22]

Internet Draft     draft-ietf-l3vpn-virtual-hub-03.txt     November 2012


   PE-3 (PE-1 and PE-2).

   The V-hub on PE-6 is provisioned to export its I-PMSI/S-PMSI/SA A-D
   routes with two RTs: RT-A and RT-A-VH-2. Thus these routes could be
   imported by all the other V-hubs (PE-3 and PE-9), and also by the V-
   spokes, but only by the V-spokes associated with the V-hub on PE-6
   (PE-4 and PE-5). In addition, the V-hub on PE-6 originates the
   Associated-V-spoke-only I-PMSI A-D route with RT-A-VH-2. This route
   could be imported only by the V-spokes associated with the V-hub on
   PE-6 (PE-4 and PE-5).

   The V-hub on PE-9 is provisioned to export its I-PMSI/S-PMSI/SA A-D
   routes with two RTs: RT-A and RT-A-VH-3. Thus these routes could be
   imported by all the other V-hubs (PE-3 and PE-6), and also by the V-
   spokes, but only by the V-spokes associated with the V-hub on PE-9
   (PE-7 and PE-8). In addition, the V-hub on PE-9 originates the
   Associated-V-spoke-only I-PMSI A-D route with RT-A-VH-3. This route
   could be imported only by the V-spokes associated with the V-hub on
   PE-9 (PE-7 and PE-8).

   If PE-7 and PE-8, in addition to importing VPN-IP default route from
   PE-9, also want to import each other VPN-IP routes, then PE-7 and
   PE-8 export their I-PMSI/S-PMSI/SA A-D routes with two RTs: RT-A and
   RT-A-VH-3.

   If the V-hub on PE-9 receives an S-PMSI/SA A-D route originated by
   either some other V-hub (PE-3 or PE-6), or by a V-spoke that is not
   associated with this V-hub (PE-1, or PE-2, or PE-4, or PE-5), the V-
   hub, before re-advertising this route replaces the RT(s) carried in
   this route with just one RT - RT-A-VH-3. Thus, the re-advertised
   route could be imported only by the V-spokes associated with the V-
   hub on PE-9 (PE-7 and PE-8).


9. Further Refinements

   In some cases a VPN customer may not want to rely solely on an (IP)
   default route being advertised from a V-spoke to a CE, but may want
   CEs to receive all the VPN routes (e.g., for the purpose of faster
   detection of VPN connectivity failures, and activating some backup
   connectivity).

   In this case an OPTIONAL approach would be to install in the V-
   spoke's data plane only the VPN-IP default route advertised by the V-
   hub associated with the V-spoke, even if the V-spoke receives an IP
   default route from the CE, and keep all the VPN-IP routes in the V-
   spoke's control plane (thus being able to advertise these routes as
   IP routes from the V-spoke to the CEs). Granted, this would not



Jeng                                                           [Page 23]

Internet Draft     draft-ietf-l3vpn-virtual-hub-03.txt     November 2012


   change control plane resource consumption, but would reduce
   forwarding state on the data plane.


10. IANA Considerations

   This document introduces no new IANA Considerations.


11. Security Considerations

   This document introduces no new Security Considerations, above and
   beyond what is already specified in [rfc4364].


12. Acknowledgements

   We would like to acknowledge Han Nguyen (AT&T) for his contributions
   to this document. We would like to thank Eric Rosen(Cisco) for his
   review and comments. We would also like to thank Samir Saad (AT&T)
   and Jeffrey (Zhaohui) Zhang (Juniper) for their review and comments.


13. Normative References

   [rfc1918] Rekhter, Y., et.al., "Address Allocation for Private
   Internets", RFC 1918, February 1996.

   [rfc3031] Rosen, E., et. al., "MPLS Architecture", RFC3031, January
   2001.

   [rfc4360] Sangli, S., Tappan, D., and Y. Rekhter, "BGP Extended
   Communities Attribute", RFC 4360, February 2006.

   [rfc4364] Rosen, E. and Y. Rekhter, "BGP/MPLS IP Virtual Private
   Networks (VPNs)", RFC 4364, February 2006.

   [rfc4684] Pedro Marques, et al., "Constrained Route Distribution for
   Border Gateway Protocol/MultiProtocol Label Switching (BGP/MPLS)
   Internet Protocol (IP) Virtual Private Networks (VPNs)", RFC4684,
   November 2006

   [rfc6513] Eric C. Rosen, Rahul Aggarwal, et. al., "Multicast in
   MPLS/BGP IP VPNs", RFC6513, February 2012

   [rfc6514] R. Aggarwal, E. Rosen, T. Morin, Y. Rekhter, "BGP Encodings
   and Procedures for Multicast in MPLS/BGP IP VPNs", RFC6514, February
   2012



Jeng                                                           [Page 24]

Internet Draft     draft-ietf-l3vpn-virtual-hub-03.txt     November 2012


   [rfc6625] Eric Rosen, et. al., "Wildcards in Multicast VPN Auto-
   Discovery Routes", RFC6625, May 2012


14. Non-normative References

   [seamless-MPLS-multicast] Yakov Rekhter, et. al., "Inter-Area P2MP
   Segmented LSPs", draft-ietf-mpls-seamless-mcast, work in progress.


15. Authors' Addresses

   Huajin Jeng
   AT&T
   e-mail: hj2387@att.com

   James Uttaro
   AT&T
   e-mail: ju1738@att.com

   Luay Jalil
   Verizon
   e-mail: luay.jalil@verizon.com

   Bruno Decraene
   France Telecom
   e-mail: bruno.decraene@orange.com

   Rahul Aggarwal
   e-mail: raggarwa_1@yahoo.com

   Yakov Rekhter
   Juniper Networks, Inc.
   e-mail: yakov@juniper.net

















Jeng                                                           [Page 25]


Html markup produced by rfcmarkup 1.108, available from http://tools.ietf.org/tools/rfcmarkup/