Network Working Group Huajin Jeng
Internet Draft AT&T
Intended status: Standards Track
Expires: January 2014 James Uttaro
AT&T
Luay Jalil
Verizon
Bruno Decraene
France Telecom
Yakov Rekhter
Juniper Networks
Rahul Aggarwal
Arktan
July 1 2013
Virtual Hub-and-Spoke in BGP/MPLS VPNs
draft-ietf-l3vpn-virtual-hub-08.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-08.txt July 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.
Abstract
With BGP/MPLS VPNs, providing 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 the VPN service provider 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 under certain circumstances 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-08.txt July 2013
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 ......................... 22
8.1 Unicast routing ....................................... 22
8.2 Multicast routing ..................................... 23
9 Further Refinements ................................... 24
10 IANA Considerations ................................... 24
11 Security Considerations ............................... 24
12 Acknowledgements ...................................... 24
13 Normative References .................................. 25
14 Informative References ................................ 25
15 Authors' Addresses .................................... 26
Jeng [Page 3]
Internet Draft draft-ietf-l3vpn-virtual-hub-08.txt July 2013
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 the VPN service
provider 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".
Jeng [Page 4]
Internet Draft draft-ietf-l3vpn-virtual-hub-08.txt July 2013
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...)
This document defines a VPN-IP default route as a VPN-IP route whose
VPN-IP prefix contains just an RD (for the definition of VPN-IP route
see [rfc4364]).
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 its associated V-
spoke(s) are in the same Autonomous System. 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.
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 multicast traffic of VPN
customers, the approach described in this document may under certain
circumstances 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
Jeng [Page 5]
Internet Draft draft-ietf-l3vpn-virtual-hub-08.txt July 2013
capabilities and/or have links with limited bandwidth.
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.
Jeng [Page 6]
Internet Draft draft-ietf-l3vpn-virtual-hub-08.txt July 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 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.
Jeng [Page 7]
Internet Draft draft-ietf-l3vpn-virtual-hub-08.txt July 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 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 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
Jeng [Page 8]
Internet Draft draft-ietf-l3vpn-virtual-hub-08.txt July 2013
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 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 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 that 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.
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
Jeng [Page 9]
Internet Draft draft-ietf-l3vpn-virtual-hub-08.txt July 2013
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 multi-homed site), then 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 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 Next Hop Label
Forwarding Entry (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
Jeng [Page 10]
Internet Draft draft-ietf-l3vpn-virtual-hub-08.txt July 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 as 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 "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 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 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 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 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
Jeng [Page 11]
Internet Draft draft-ietf-l3vpn-virtual-hub-08.txt July 2013
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 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
Jeng [Page 12]
Internet Draft draft-ietf-l3vpn-virtual-hub-08.txt July 2013
route, and 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/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-08.txt July 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], [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. When Ingress Replication is used for
I-PMSI P-tunnels, section "Use of Ingress Replication with I-PMSI A-D
route" of the this document 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-08.txt July 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
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 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-08.txt July 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 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 customer RP (C-RP) or the customer source (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 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 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, or S-PMSI, or Source Active (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,
Jeng [Page 16]
Internet Draft draft-ietf-l3vpn-virtual-hub-08.txt July 2013
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
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
Jeng [Page 17]
Internet Draft draft-ietf-l3vpn-virtual-hub-08.txt July 2013
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 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
Jeng [Page 18]
Internet Draft draft-ietf-l3vpn-virtual-hub-08.txt July 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 I-PMSI/S-PMSI/SA A-D route the V-hub simply follows
the procedures of [rfc6514] (or in the case of a wildcard S-PMSI A-D
route the procedures of [rfc6625]). Specifically, the V-hub MUST NOT
re-originate 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 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
Jeng [Page 19]
Internet Draft draft-ietf-l3vpn-virtual-hub-08.txt July 2013
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-
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 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 advertising the new S-
PMSI A-D route, the V-hub modifies their PMSI Tunnel attribute 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-08.txt July 2013
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).
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, 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.
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.
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.
Jeng [Page 21]
Internet Draft draft-ietf-l3vpn-virtual-hub-08.txt July 2013
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 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.
Jeng [Page 22]
Internet Draft draft-ietf-l3vpn-virtual-hub-08.txt July 2013
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
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 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 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 originates an S-PMSI A-D route (respectively SA A-D
route). The V-hub constructs this route from the imported route
following the procedures specified in section "Case 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
Jeng [Page 23]
Internet Draft draft-ietf-l3vpn-virtual-hub-08.txt July 2013
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
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),
Jeffrey (Zhaohui) Zhang (Juniper), and Thomas Morin (France Telecom)
for their review and comments.
Jeng [Page 24]
Internet Draft draft-ietf-l3vpn-virtual-hub-08.txt July 2013
13. Normative References
[rfc1918] Rekhter, Y., et.al., "Address Allocation for Private
Internets", RFC 1918, February 1996.
[rfc2119] "Key words for use in RFCs to Indicate Requirement
Levels.", Bradner, March 1997
[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
[rfc6625] Eric Rosen, et. al., "Wildcards in Multicast VPN Auto-
Discovery Routes", RFC6625, May 2012
[IANA-SAFI] http://www.iana.org/assignments/safi-namespace/safi-
namespace.xhtml
14. Informative References
[seamless-MPLS-multicast] Yakov Rekhter, et. al., "Inter-Area P2MP
Segmented LSPs", draft-ietf-mpls-seamless-mcast, work in progress.
Jeng [Page 25]
Internet Draft draft-ietf-l3vpn-virtual-hub-08.txt July 2013
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 26]
