Internet Engineering Task Force (IETF) H. Jeng
Request for Comments: 7024 J. Uttaro
Category: Standards Track AT&T
ISSN: 2070-1721 L. Jalil
Verizon
B. Decraene
Orange
Y. Rekhter
Juniper Networks
R. Aggarwal
Arktan
October 2013
Virtual Hub-and-Spoke in BGP/MPLS VPNs
Abstract
With BGP/MPLS Virtual Private Networks (VPNs), providing any-to-any
connectivity among sites of a given VPN would require each Provider
Edge (PE) router connected to one or more of these sites to hold all
the routes of that VPN. The approach described in this document
allows the VPN service provider to reduce the number of PE routers
that have to maintain all these routes by requiring only a subset of
these routers to maintain all these routes.
Furthermore, when PE routers use ingress replication to carry the
multicast traffic of VPN customers, the approach described in this
document may, under certain circumstances, reduce bandwidth
inefficiency associated with ingress replication and redistribute the
replication load among PE routers.
Status of This Memo
This is an Internet Standards Track document.
This document is a product of the Internet Engineering Task Force
(IETF). It represents the consensus of the IETF community. It has
received public review and has been approved for publication by the
Internet Engineering Steering Group (IESG). Further information on
Internet Standards is available in Section 2 of RFC 5741.
Information about the current status of this document, any errata,
and how to provide feedback on it may be obtained at
http://www.rfc-editor.org/info/rfc7024.
Jeng, et al. Standards Track [Page 1]
RFC 7024 Virtual Hub-and-Spoke in BGP/MPLS VPNs October 2013 Copyright Notice Copyright (c) 2013 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. Table of Contents 1. Overview ........................................................3 2. Specification of Requirements ...................................4 3. Routing Information Exchange ....................................5 4. Forwarding Considerations .......................................7 5. Internet Connectivity ...........................................9 6. Deployment Considerations ......................................12 7. Multicast Considerations .......................................13 7.1. Terminology ...............................................14 7.2. Eligible Upstream Multicast Hop (UMH) Routes ..............14 7.3. Originating VPN-IP Default Route by a V-Hub ...............14 7.4. Handling C-Multicast Routes ...............................15 7.5. Originating I-PMSI/S-PMSI/SA A-D Routes by V-Spoke ........15 7.6. Originating I-PMSI/S-PMSI/SA A-D Routes by V-Hub ..........16 7.7. Receiving I-PMSI/S-PMSI/SA A-D Routes by V-Spoke ..........17 7.8. Receiving I-PMSI/S-PMSI/SA A-D Routes by V-Hub ............17 7.8.1. Case 1 .............................................17 7.8.2. Case 2 .............................................18 7.9. Use of Ingress Replication with I-PMSI A-D Routes .........20 8. An Example of RT Provisioning ..................................21 8.1. Unicast Routing ...........................................21 8.2. Multicast Routing .........................................22 9. Further Refinements ............................................23 10. Security Considerations .......................................23 11. Acknowledgements ..............................................23 12. References ....................................................24 12.1. Normative References .....................................24 12.2. Informative References ...................................24 Jeng, et al. Standards Track [Page 2]
RFC 7024 Virtual Hub-and-Spoke in BGP/MPLS VPNs October 2013 1. Overview With BGP/MPLS VPNs [RFC4364], providing any-to-any connectivity among sites of a given VPN is usually accomplished by requiring each Provider Edge (PE) router connected to one or more of these sites to hold all that VPN's routes. The approach described in this document allows the VPN service provider (SP) to reduce the number of PEs that have to maintain all these routes by requiring only a subset of these routers to maintain all these routes. Consider a set of PEs that maintain VPN Routing and Forwarding tables (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). The rest of the PEs in the set will be "vanilla" PEs (PEs that implement the procedures described in [RFC4364] but that do not implement the 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, VPNs present on that PE. Likewise, a given PE may act as a V-spoke only for some, but not all, 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 3. Consider a set of V-spokes that are associated with a given V-hub, V-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.). Jeng, et al. Standards Track [Page 3]
RFC 7024 Virtual Hub-and-Spoke in BGP/MPLS VPNs October 2013 This document defines a VPN-IP default route as a VPN-IP route whose VPN-IP prefix contains only a Route Distinguisher (RD) (for the definition of "VPN-IP route", see [RFC4364]). A PE that acts as a V-hub of a given VPN maintains all 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 routes originated by the V-hub(s) associated with that V-spoke (such a PE needs to import only VPN-IP default routes 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 -- has to maintain all 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 its associated V-spoke(s) are in the same Autonomous System (AS). However, if PEs that maintain a given VPN's VRFs span multiple ASes, this document does not restrict all V-hubs of that VPN to be in the same AS -- the V-hubs may be spread among these ASes. One could model the approach defined in this document as a two-level hierarchy, where the top level consists of V-hubs and the bottom level consists of V-spokes. Generalization of this approach to more than two levels of hierarchy is outside the scope of this document. When PEs use ingress replication to carry the multicast traffic of VPN customers, the approach described in this document may, under certain circumstances, reduce bandwidth inefficiency associated with ingress replication and 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 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 the V-spokes associated with that V-hub, rather than replicating the traffic to all 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. 2. 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]. Jeng, et al. Standards Track [Page 4]
RFC 7024 Virtual Hub-and-Spoke in BGP/MPLS VPNs October 2013 3. Routing Information Exchange Routing information exchange among all 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, 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, 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 given VPN's V-spoke to share its outbound traffic load among the V-hubs associated with that V-spoke, each of the VPN's V-hubs MUST use a distinct RD (per V-hub, per VPN) when originating a VPN-IP default route. The 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 or not these V-spokes are associated with the V-hub). A V-hub of a given VPN MUST NOT import a VPN-IP default route unless the imported route is the Internet VPN-IP default route (for the definition of "Internet VPN-IP default route" and information on how to distinguish between a VPN-IP default route and the Internet VPN-IP default route, see Section 5). 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. Jeng, et al. Standards Track [Page 5]
RFC 7024 Virtual Hub-and-Spoke in BGP/MPLS VPNs October 2013 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 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 by using Route Target (RT) extended communities [RFC4360] and VRF export/import policies based on these RTs. This document defines the following procedures for implementing 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 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 PEs (or to be more precise, all 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 VPN-IP routes originated by these PEs. Also, all the V-hubs keep the same import RT-VPN. In addition, each of a given VPN's V-hubs 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. The 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 of 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 5). Thus, this route is imported by all V-spokes associated with the V-hub. Jeng, et al. Standards Track [Page 6]
RFC 7024 Virtual Hub-and-Spoke in BGP/MPLS VPNs October 2013 A V-spoke MAY be provisioned to export VPN-IP routes not just to the 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 a Next Hop Label Forwarding Entry (NHLFE) that identifies the VRF of the V-hub. As a result, when the V-hub receives a packet that carries such a 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 the advertisement of 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 that route has been originated as a result of a) the V-hub receiving an IP default route from one of the VPN Customer Edge (CE) routers connected to it, or b) the V-hub receiving (and importing) the Internet VPN-IP default route (Section 5) from some other PE, or c) the VRF being provisioned with a default route pointing to the routing table that maintains the Internet routes. When a multihomed site is connected to a V-hub and a V-spoke, then the V-hub uses the following OPTIONAL procedures to support Internal BGP (IBGP) / External BGP (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 circuits (for the definition of "VRF attachment circuits", see [RFC4364]) or via some Jeng, et al. Standards Track [Page 7]
RFC 7024 Virtual Hub-and-Spoke in BGP/MPLS VPNs October 2013 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. To illustrate this, consider the following example: <- RD:0/0 RD:0/0-> <- RD:192.0.2 <-192.0.2/24 CE1----PE-S-------------PE-H----------------PE-S1-------------CE2 / | | | | 192.0.2/24 | | CE4 CE3 A multihomed site (not shown in the above figure) is connected via CE2 and CE3. Thus, both CE2 and CE3 advertise a route to 192.0.2/24. CE2 advertises this route (route to 192.0.2/24) to PE-S1, which in turn originates a VPN-IP route RD:192.0.2. 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:192.0.2 and from CE3 a plain IP route to 192.0.2. Thus, the VRF entry on PE-H has two possible next hops for 192.0.2: 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 192.0.2.1. 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 192.0.2.1, 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 CE5 sends a packet to 192.0.2.1, then (due to the IP longest match rule) PE-S1 will always forward this packet to CE2. Jeng, et al. Standards Track [Page 8]
RFC 7024 Virtual Hub-and-Spoke in BGP/MPLS VPNs October 2013 Thus, for a multihomed 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 traffic has been originated within some other site that is connected to the same V-spoke. Moreover, if CE3 advertises 192.0.2.0/25 and 192.0.2/24, while CE2 advertises 192.0.2.128/25 and 192.0.2/24 (which is yet another form of load balancing for a multihomed site), when CE5 sends a packet to 192.0.2.1, 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 a given VPN to provision PEs that have multihomed sites of that VPN connected to them as V-spokes (such PEs could be provisioned as either V-hubs or plain "vanilla" PEs). The second option is for the V-spoke, when it receives an IP route from a CE, to not 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 just forwards the data to the CE without performing an IP lookup on the data. 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 multihomed site connected to it cannot be provisioned as a V-spoke) or (b) result in IBGP/EBGP load balancing not being available for certain scenarios (the scenarios that the second option is intended to cover). 5. Internet Connectivity This document specifies two possible alternatives for 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 a default route in the VPN's VRF on that PE pointing to the routing table on Jeng, et al. Standards Track [Page 9]
RFC 7024 Virtual Hub-and-Spoke in BGP/MPLS VPNs October 2013 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 a "vanilla" PE). If this PE is provisioned as a 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 3 for the definitions 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 and "vanilla" PEs. 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 subcases: (a) the PE is provisioned as a V-hub, and (b) the PE is provisioned as a V-spoke. An implementation MUST support subcase (a). An implementation MAY support subcase (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 installs 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 3 for the definitions 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 and "vanilla" PEs. 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 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, it just forwards the data to the CE without performing an IP lookup on the data. Note that in this case, the VRF on the V-spoke will 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 an IP default route to the V-spoke. Jeng, et al. Standards Track [Page 10]
RFC 7024 Virtual Hub-and-Spoke in BGP/MPLS VPNs October 2013 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. 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 specified in Section 9. In all the scenarios described above 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 (a) receiving an IP default route from a CE or (b) the PE maintaining Internet routes and also provisioning in the VRF of its VPN a default route pointing to its (the PE's) routing table that contains 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, while 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 Jeng, et al. Standards Track [Page 11]
RFC 7024 Virtual Hub-and-Spoke in BGP/MPLS VPNs October 2013 to the V-hub that does not originate the Internet VPN-IP default route, then from that V-hub to the V-hub that does originate the Internet VPN-IP default route). 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 or all of its V-spokes could be grouped into geographically based clusters (e.g., V-spokes within a given cluster could be in close geographical proximity to each other) with any-to-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 a VPN for a large retail chain in which data traffic is hub/spoke between each store and centralized datacenters, but there is a need for direct Voice over IP (VoIP) traffic between stores within the same geographical area. The use of constrained route distribution for BGP/MPLS IP VPNs ("RT constrains") [RFC4684] may further facilitate/optimize routing exchange in support of V-hubs and V-spokes. Introducing a V-spoke PE in a VPN may introduce the following changes 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, et al. Standards Track [Page 12]
RFC 7024 Virtual Hub-and-Spoke in BGP/MPLS VPNs October 2013 7. Multicast Considerations This section describes procedures for supporting Multicast VPN (MVPN) in the presence of Virtual Hub-and-Spoke. The procedures rely on MVPN specifications as defined in [RFC6513], [RFC6514], and [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 Selective Provider Multicast Service Interface (S-PMSI) auto-discovery (A-D) routes [RFC6513] [RFC6514] [RFC6625] are sufficient to discard packets coming from a "wrong" PE for all types of provider tunnels (P-tunnels) specified in [RFC6514] (including Ingress Replication). The existing procedures for Inclusive Provider Multicast Service Interface (I-PMSI) A-D routes [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. Section 7.9 of this document specifies changes to the procedures in [RFC6514], to enable the discarding of packets from a "wrong" PE when Ingress Replication is used for I-PMSI P-tunnels. 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). The use of Virtual Hub-and-Spoke in conjunction with seamless MPLS multicast [MPLS-MCAST] is outside the scope of this document. Jeng, et al. Standards Track [Page 13]
RFC 7024 Virtual Hub-and-Spoke in BGP/MPLS VPNs October 2013 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 (procedures differ from [RFC6514] for the case of I-PMSI and are specified in Section 7.9 of this document). The PE originating the I-PMSI/S-PMSI A-D route uses these unicast tunnels to carry traffic to the PEs that import the route. The PEs that import the route advertise labels for the unicast tunnels in Leaf A-D routes originated in response to the I-PMSI/S-PMSI A-D route. When we say that traffic has been received by a PE on a P-tunnel "bound" to a particular I-PMSI/S-PMSI A-D route imported by that PE, we refer to the unicast tunnel for which the label was advertised in a Leaf A-D route by the PE that imported the I-PMSI/S-PMSI route; the PE that originated that route uses this tunnel to send traffic to the PE that imported the I-PMSI/S-PMSI 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 Address Family Identifier (AFI) and Subsequent Address Family Identifier (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 following the procedures specified in Section 3, also follows the procedures specified in 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, et al. Standards Track [Page 14]
RFC 7024 Virtual Hub-and-Spoke in BGP/MPLS VPNs October 2013 7.4. Handling C-Multicast Routes In the following, the term "C-multicast routes" refers to BGP routes that carry customer multicast routing information [RFC6514]. Origination of C-multicast routes follows the procedures specified in [RFC6514] (irrespective of whether these routes are originated by a V-hub or a V-spoke). When a V-spoke receives a C-multicast route, the V-spoke follows the procedures described in [RFC6514]. When a V-hub receives a C-multicast route, the V-hub determines whether the customer Rendezvous Point (C-RP) or the customer source (C-S) of the route is reachable via one of its VRF interfaces; if yes, then the V-hub follows the procedures described in [RFC6514]. 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 C-multicast 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 Section 11.1.3 of [RFC6514]. The hub also creates the appropriate (C-*, C-G) or (C-S, C-G) state in its MVPN Tree Information Base (MVPN-TIB). 7.5. Originating I-PMSI/S-PMSI/SA A-D Routes by V-Spoke When a V-spoke originates an I-PMSI, an S-PMSI, or Source Active (SA) A-D route, the V-spoke follows the procedures specified in [RFC6514] (or in the case of a wildcard S-PMSI A-D route, the procedures specified in [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 3), then (as a result of following the procedures specified in [RFC6514] or, in the case of a wildcard S-PMSI A-D route, the procedures specified in [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 the other V-spokes. This is because in this scenario, the route will Jeng, et al. Standards Track [Page 15]
RFC 7024 Virtual Hub-and-Spoke in BGP/MPLS VPNs October 2013 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 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 specified in [RFC6514] (or in the case of a wildcard S-PMSI A-D route, the procedures specified in [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 specified in [RFC6514], the V-hub MUST originate another I-PMSI A-D route -- we'll refer to this route as an "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, (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 7.8. 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. Jeng, et al. Standards Track [Page 16]
RFC 7024 Virtual Hub-and-Spoke in BGP/MPLS VPNs October 2013 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. 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 specified in [RFC6514] (or in the case of a wildcard S-PMSI A-D route, the procedures specified in [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 3), 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 describes 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 Jeng, et al. Standards Track [Page 17]
RFC 7024 Virtual Hub-and-Spoke in BGP/MPLS VPNs October 2013 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 an I-PMSI/S-PMSI/SA A-D route, the V-hub simply follows the procedures specified in [RFC6514] (or in the case of a wildcard S-PMSI A-D route, the procedures specified in [RFC6625]). Specifically, the V-hub MUST NOT reoriginate this route as done in Case 2 below. The following specifies the rules that the V-hub MUST follow when handling traffic that the V-hub receives on a P-tunnel bound 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 specified in [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 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 follow the procedures specified in [RFC6514] (or in the case of a wildcard S-PMSI A-D route, the procedures specified in [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 the procedures specified in [RFC6513] and [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 Jeng, et al. Standards Track [Page 18]
RFC 7024 Virtual Hub-and-Spoke in BGP/MPLS VPNs October 2013 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 of 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-only I-PMSI A-D route originated by the V-hub. Whenever a V-hub imports an S-PMSI A-D route (respectively, SA A-D route) in a VRF, the V-hub, in contrast to Case 1 above, MUST originate an S-PMSI A-D route (respectively, SA A-D route) targeted 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 the IP address that the V-hub places in the Global Administrator field of the VRF Route Import Extended Community of the VPN-IP routes advertised by the V-hub. For S-PMSI A-D routes, the V-hub also changes the Originating Router's IP address in the MCAST-VPN NLRI (Network Layer Reachability Information) of the route to the same address as the one in the Next Hop. Moreover, before advertising the new S-PMSI A-D route, the V-hub modifies its PMSI Tunnel attribute as appropriate (e.g., by replacing the P-tunnel rooted at the originator of this route 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 the procedures specified in [RFC6513] and [RFC6514] (or in the case of a wildcard S-PMSI A-D route, the procedures specified in [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 reaggregate (in a different way) this data using the state present in its MVPN-TIB that has been created as a Jeng, et al. Standards Track [Page 19]
RFC 7024 Virtual Hub-and-Spoke in BGP/MPLS VPNs October 2013 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. 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 the discarding of 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] and [RFC6514] are sufficient). The modifications to the procedures are required to be implemented (by all the PEs of a given MVPN) only under the following conditions: + At least one of those PEs is a V-hub or V-spoke PE for the given MVPN. + The given MVPN is configured to use the optional procedure of using Ingress Replication to instantiate an I-PMSI. If Ingress Replication is used with I-PMSI A-D routes, 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 attribute MUST carry no MPLS labels. A PE that receives such an 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: o The Tunnel Type is set to Ingress Replication. o The Tunnel Identifier MUST carry a routable address of the PE that originates the Leaf A-D route. o 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. o The receiving PE MUST assign the label in such a way as to enable the receiving PE to identify (a) the VRF on that PE that should be used to process the traffic received with this label and (b) the PE that sends the traffic with this label. Jeng, et al. Standards Track [Page 20]
RFC 7024 Virtual Hub-and-Spoke in BGP/MPLS VPNs October 2013 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. 8.1. Unicast Routing All the PEs (both V-hubs and V-spokes) are provisioned to export routes using RT-A (just as 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 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 example 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. Jeng, et al. Standards Track [Page 21]
RFC 7024 Virtual Hub-and-Spoke in BGP/MPLS VPNs October 2013 If PE-7 and PE-8, in addition to importing a VPN-IP default route from PE-9, also want to import each other's 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 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 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 a VPN-IP default route from PE-9, also want to import each other's 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 imports an S-PMSI A-D route or SA A-D route originated by either some other V-hub (PE-3 or PE-6) or 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 originates an S-PMSI A-D route (respectively, SA A-D route). The V-hub constructs this route from the imported route Jeng, et al. Standards Track [Page 22]
RFC 7024 Virtual Hub-and-Spoke in BGP/MPLS VPNs October 2013 following the procedures specified in Section 7.8.2. Specifically, the V-hub replaces the RT(s) carried in the imported route with just one RT -- RT-A-VH-3. Thus, the originated 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 to 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 change control-plane resource consumption but would reduce forwarding state on the data plane. 10. Security Considerations This document introduces no new security considerations above and beyond those already specified in [RFC4364]. 11. 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), Jeffrey (Zhaohui) Zhang (Juniper), and Thomas Morin (Orange) for their review and comments. Jeng, et al. Standards Track [Page 23]
RFC 7024 Virtual Hub-and-Spoke in BGP/MPLS VPNs October 2013 12. References 12.1. Normative References [IANA-SAFI] IANA Subsequent Address Family Identifiers (SAFI) Parameters, <http://www.iana.org/assignments/safi-namespace/>. [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, March 1997. [RFC3031] Rosen, E., Viswanathan, A., and R. Callon, "Multiprotocol Label Switching Architecture", RFC 3031, 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] 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, November 2006. [RFC6513] Rosen, E., Ed., and R. Aggarwal, Ed., "Multicast in MPLS/BGP IP VPNs", RFC 6513, February 2012. [RFC6514] Aggarwal, R., Rosen, E., Morin, T., and Y. Rekhter, "BGP Encodings and Procedures for Multicast in MPLS/BGP IP VPNs", RFC 6514, February 2012. [RFC6625] Rosen, E., Ed., Rekhter, Y., Ed., Hendrickx, W., and R. Qiu, "Wildcards in Multicast VPN Auto-Discovery Routes", RFC 6625, May 2012. 12.2. Informative References [MPLS-MCAST] Rekhter, Y., Aggarwal, R., Morin, T., Grosclaude, I., Leymann, N., and S. Saad, "Inter-Area P2MP Segmented LSPs", Work in Progress, May 2013. Jeng, et al. Standards Track [Page 24]
RFC 7024 Virtual Hub-and-Spoke in BGP/MPLS VPNs October 2013
Authors' Addresses
Huajin Jeng
AT&T
EMail: hj2387@att.com
James Uttaro
AT&T
EMail: ju1738@att.com
Luay Jalil
Verizon
EMail: luay.jalil@verizon.com
Bruno Decraene
Orange
EMail: bruno.decraene@orange.com
Yakov Rekhter
Juniper Networks, Inc.
EMail: yakov@juniper.net
Rahul Aggarwal
Arktan
EMail: raggarwa_1@yahoo.com
Jeng, et al. Standards Track [Page 25]
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