One document matched: draft-ietf-ppvpn-vpn-vr-03.txt
Differences from draft-ietf-ppvpn-vpn-vr-02.txt
Provider Provisioned VPN WG Paul Knight (Editor)
Internet Draft Hamid Ould-Brahim
draft-ietf-ppvpn-vpn-vr-03.txt Gregory Wright
Expiration Date: January 2003 Nortel Networks
Bryan Gleeson
Tahoe Networks
Rainer Bach Timon Sloane
T-Data Webstacks
Abraham Young Rick Bubenik
Huawei Technologies SAVVIS Communications
Luyuan Fang Chandru Sargor
AT&T Cosine Communications
Dr. Christian Weber Isaac Negusse
Arcor Sprint
Jieyun Jessica Yu
SingWave Consulting
July 2002
Network based IP VPN Architecture
using Virtual Routers
Status of this Memo
This document is an Internet-Draft and is in full conformance with
all provisions of Section 10 of RFC2026 [RFC-2026].
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.
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Abstract
This draft describes a network-based VPN architecture using virtual
routers. The VPN service is built based on the virtual router (VR)
concept, which has exactly the same mechanisms as a physical router,
and therefore inherits all existing mechanisms and tools for
configuration, operation, accounting, and maintenance. Within a VPN
domain, an instance of routing is used to distribute VPN
reachability information among VR routers. Any routing protocol can
be used, and no VPN-related modifications or extensions are needed
to the routing protocol for achieving VPN reachability. Virtual
routers can be deployed in different VPN configurations, direct VR
to VR connectivity through layer-2 or by aggregating multiple VRs
into a single VR combined with IP or MPLS based tunnels. This
architecture accommodates various backbone deployment scenarios,
both where the VPN service provider owns the backbone, and where the
VPN service provider obtains backbone service from one or more other
service providers.
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in
this document are to be interpreted as described in RFC-2119.
Table of Contents
1 Introduction ........................................ 3
2 Virtual Router Architecture Requirements ............. 4
2.1 Membership .......................................... 4
2.2 Scalability .......................................... 4
2.3 Quality of Service ................................... 5
2.4 Auto-Discovery ....................................... 5
2.5 Routing .............................................. 5
2.5.1 Routing between PE and CE ............................ 5
2.5.2 Routing in the Service Provider Network .............. 5
2.5.3 Routing between PEs................................... 5
2.6 Security ............................................. 5
2.7 Topology ............................................. 5
2.8 Tunneling ............................................ 6
2.9 Management ........................................... 6
2.10 General Requirements ................................. 6
3 Network Reference Model .............................. 6
3.1 The Backbone ........................................ 7
4 Virtual Router Definition ............................ 7
5 How VPNs are built and deployed using VRs ............ 8
5.1 VR to VR Connectivity over layer-2 Connections........ 8
5.2 VR to VR Connectivity through IP or MPLS Tunnels...... 9
5.3 Virtual Router Backbone Aggregation .................. 9
5.3.1 Tunneling ............................................ 10
5.3.1.1 MPLS Tunnels ...................................... 10
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5.3.1.2 IPSec Tunnels ..................................... 11
5.3.2 Routing .............................................. 11
5.3.3 Relationship between the VRs and the Backbone VR ..... 11
5.3.4 Multiple Backbones connected to a single PE .......... 11
6 VPN Auto-Discovery ................................... 12
7 VRs and Extranets .................................... 13
8 VPNs across Domains .................................. 13
9 Internet Access ...................................... 14
10 Carrier's Carrier Case................................ 14
11 Operations and Management ............................ 14
11.1 Backbone Migration ................................... 15
11.2 Troubleshooting ...................................... 15
12 Quality of Service ................................... 15
13 Scalability .......................................... 15
14 Security Considerations .............................. 16
15 Document Change History .............................. 16
16 References ........................................... 16
17 Acknowledgments ..................................... 17
18 Authors' Addresses .................................. 18
1. Introduction
Several solutions have been put forward to achieve various levels of
network privacy and traffic isolation when building VPNs across a
shared IP backbone. Most of these solutions require separate per-VPN
forwarding capabilities and make use of IP- or MPLS-based tunnels
across the backbone [VPN-RFC2764], [RFC-2917], and [VPN-RFC2547bis].
This document describes a network-based VPN architecture using
virtual routers. The architecture complies with the IP VPN framework
described in [VPN-RFC2764]. The objective is to provide per-VPN
routing, forwarding, quality of service, and service management
capabilities. The VPN service is based on the virtual router
concept, which has exactly the same mechanisms as a physical router,
and therefore can inherit all existing mechanisms and tools for
configuration, deployment, operation, troubleshooting, monitoring,
and accounting. Virtual routers can be deployed in various VPN
configurations. Direct VR to VR connectivity may be configured
through layer-2 links or through a variety of tunnel mechanisms,
using IP- or MPLS-based tunnels. Multiple VRs may be aggregated over
a "backbone VR." This architecture accommodates various backbone
deployment scenarios, including where the VPN service provider owns
the backbone, and where the VPN service provider obtains backbone
service from one or more other service providers.
Within a VPN domain, an instance of routing is used to distribute
VPN reachability information among VR routers. Any routing protocol
can be used, and no VPN-related modifications or extensions are
needed to the routing protocol for achieving VPN reachability. VPN
reachability information to and from customer sites can be
dynamically learned from the CE using standard routing protocols, or
it can be statically provisioned on the VR. The routing protocol
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between the virtual routers and CEs is independent of the routing
used in the VPN backbone, between the VRs. That is, the routing
protocol between the VRs may be the same or it might be different
than the routing mechanism used between the CE and VR. Likewise,
since the VR-to-VR connectivity can use tunnels, the inter-VR
routing protocol can be independent of the routing used in the
backbone network(s) over which the VR-based VPN runs.
There are two fundamental architectures for implementing network-
based VPNs: virtual routers (VR) and piggybacking. The main
difference between the two architectures resides in the model used
to achieve VPN reachability and membership functions. In the VR
model, each VR in the VPN domain is running an instance of routing
protocol responsible for disseminating VPN reachability information
between VRs. Therefore, VPN membership and VPN reachability are
treated as separate functions, and separate mechanisms are used to
implement these functions. VPN reachability is carried out by a per-
VPN instance of routing, and a range of mechanisms is possible for
determining membership (see section 6.0). In the piggyback model the
VPN network layer is terminated at the edge of the backbone, and a
backbone routing protocol (i.e., extended BGP-4) is responsible for
disseminating the VPN membership and reachability information
between provider edge routers (PE) for all the VPNs configured on
the PE. [VPN-RFC2547bis] is an example of a piggyback VPN
architecture.
2. Virtual Router Architecture Requirements
2.1 Membership
All virtual routers that are members of a specific VPN MUST share
the same VPN identifier (VPN-ID). This should be the Globally Unique
Identifier (GID) defined in [VPN-GID] or the VPN-ID format defined
in [VPN-RFC2685].
2.2 Scalability
In this architecture, the backbone internal nodes (e.g., P devices)
are not required to be VPN aware or VR aware, and therefore they
don't keep any VPN state within the backbone. Thus the VR
architecture is not a significant contributor to issues of backbone
scalability.
The PE on which the VRs run (and the VRs themselves) should be able
to accommodate rapid growth in the number of routes per VR, since
this number can change suddenly as membership changes. The PE should
be able to accommodate substantial growth in the number of VRs and
CEs supported, to avoid reconfiguration that can disrupt existing
connectivity. The use of the "backbone VR" (Section 5.3) improves
the scalability of the PE, since many VRs on the PE may use the
backbone VR for connectivity to other VPN sites.
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2.3 Quality of Service
Existing quality of service mechanisms developed for physical
routers should all be available to be used on a per-VR basis.
Therefore, quality of service (policing, shaping, classification,
and scheduling) SHOULD be configurable on a per-VPN basis.
2.4 Auto-discovery
It should be possible for the VRs to automatically discover each
other, set up tunnels to each other, and exchange private routing
information across the backbone. It is required that the auto-
discovery mechanism take into consideration the case where the VPNs
are implemented across administrative domains. We assume in this
document that an auto-discovery mechanism which provides services
similar to BGP (as described in [VPN-BGP]) is used as the mechanism
to distribute membership, topology, and tunnel information among VRs
which are members of the same VPN.
2.5 Routing
2.5.1 Routing between PE and CE
Any existing routing protocol can be used between PE and the CE.
Typically, the routing protocol of the specific VPN site will be
used. Static routes may be used. The routing protocol between the PE
and the CE can be independent of the PE-to-PE routing.
2.5.2 Routing in the Service Provider Network (Backbone)
The choice of the backbone routing protocol should not be
constrained by the VPNs.
2.5.3 Routing between PEs
Any existing routing protocol can be used between PEs. The routing
protocol between the PEs can be independent of the CE-to-PE routing.
As with any network design, care must be taken when multiple routing
protocols are used, due to differences in metrics, detail of
information, etc.
2.6 Security
The architecture MUST accommodate different levels of security for
data, routing, and other control information. The architecture must
provide authentication and encryption services for VPNs requiring
strong security capabilities.
2.7 Topology
VPN topologies such as a hub and spoke, and full mesh MUST be
supported. It should be possible to build arbitrary VPN topologies.
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For example, in the case where the internal nodes (P devices) are
also VR aware (NOTE this is not required - see section 2.2) then it
is possible to have either tunnels from the PE or the CE connecting
to these internal VRs. This type of VPN deployment can be useful
when the internal nodes are geographically suitable to be a VPN hub.
2.8 Tunneling
The architecture should not be limited to a single tunneling
mechanism. It should be possible to use IPSec, GRE, IP in IP, and
MPLS tunnels. It should also be possible to allow multiple VPNs to
share a tunnel across a backbone. Therefore within a single VPN,
different types of tunnels can be used.
2.9 Management
It should be easy to configure, deploy, operate and troubleshoot
each VPN independently, using existing mechanisms and tools. Tools
used for operating, managing and debugging IP networks can continue
to be used without any modification.
Most aspects of the management of the multiple VRs on the PE by the
Service Provider are implementation-specific, and beyond the scope
of this document.
2.10 General Requirements
The followings are some general requirements for the VR
architecture:
1) The architecture should accommodate different sizes of VPNs, and
one VPN should not impact other VPNs on the PE.
2) The architecture MUST support overlapping VPN address spaces in
separate VPNs.
3) The architecture should support direct paths between VPN sites
that bypass the service provider backbone (backdoor links).
Traffic can be directed to the backdoor link, or injected to the
backbone with the flexibility of using both the backbone access,
and the backdoor link as internal or external paths.
4) The architecture MUST work over different deployment scenarios,
e.g. where the service provider owns its own backbone, and where
the service provider obtains backbone service from one or more
other service providers.
3. Network Reference Model
A VPN customer site is connected to the provider backbone by means
of a connection between a Customer Edge (CE) device, (which can be a
bridge or a router) and a virtual router (VR). CE devices are
preconfigured to connect to one or more VRs.Multiple VRs
may coexist on the same service provider edge device (PE).
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CE devices can be attached to VRs over any type of access link (e.g.
ATM, frame relay, ethernet, PPP or IP tunneling mechanism such as
IPSec, L2TP or GRE tunnels).
+---+ +---+
| P |....| P |
+---+ +---+
PE / \ PE
+----+ +------+ +------+ +---+
| CEs|--|-{VRs}| |{VRs}-|--|CEs|
+----+ +------+ +------+ +---+
\ /
+---+ +---+
| P |....| P |
+---+ +---+
Figure 1: Network Reference Model
CE sites can be statically connected to the provider network via
dedicated circuits, or can use dial-up links. Routing tables
associated with each virtual router define the site-to-site
reachability for each VPN. The internal backbone provider routers
(P) are not VPN aware and do not keep VPN state.
3.1 Backbone
In general the backbone is a shared network infrastructure, which
represents either:
1) A layer-2 ATM or frame relay network.
2) An IP network.
3) An MPLS network.
Not all VPNs existing on the same PE are necessarily connected to
the same backbone. A single VPN can be built from multiple transport
technologies.
4. Virtual Router Definition
A virtual router (VR) is an emulation of a physical router at the
software and/or hardware levels. Virtual routers have independent IP
routing and forwarding tables and they are isolated from each other.
This means that a VPN's address space can overlap with another VPN's
address space. The addresses need only be unique within a VPN
domain.
A virtual router has two main functions:
1) Constructing routing tables for the paths between VPN sites using
any routing technologies (e.g., static, OSPF, RIP, or BGP).
2) Forwarding packets to the next hops within the VPN domain.
From the VPN user point of view, a virtual router provides the same
functionality as a physical router. Separate routing, and forwarding
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capabilities provide each VR with the appearance of a dedicated
router that guarantees isolation from the traffic of other VPNs,
while running on shared forwarding and transmission resources.
Virtual routers belonging to the same VPN domain must have the same
Virtual Private Network Identifier (VPN-ID). Examples of VPN-ID
formats are described in [VPN-RFC2685] and [VPN-GID]. To the CE
access device, the virtual router appears as a neighbor router in
the CE based network. The CE sends all traffic for non-local VPN
destinations to the VR, unless the specific VPN topology provides
alternate routes. Each CE access device must learn the set of
destinations reachable through its connection to the virtual router;
this may be as simple as a default route. Virtual routers
participating in a single VPN domain are responsible for learning
and disseminating VPN reachability information among themselves. A
given VR holds the routes only for the specific VPN configured for
that VR. Any routing protocol can be used between the VRs and the
CEs.
5. How VPNs are built and deployed using VRs
Three main VR deployment scenarios can be used for building virtual
private networks:
1) VR to VR connectivity over a layer 2 connection.
2) VR to VR connectivity tunneled over an IP or MPLS network.
3) Aggregating multiple virtual routers over a "backbone virtual
router," which will provide connectivity over a layer 2, IP, or
MPLS network.
The above VR deployment scenarios can coexist on a single PE and
they are not mutually exclusive.
5.1 VR to VR Connectivity over Layer 2 Connections
As illustrated in figure 2, virtual routers can be deployed over
direct layer-2 frame relay or ATM connections or other layer-2
transport technology.
PE PE
+---------------+ +---------------+
+-----+ | | | | +-----+
|VPN-A| | +----+ Layer-2 connections +----+ | |VPN-A|
|sites|-|-|VR-A|<---------------------------->|VR-A|-|-|sites|
+-----+ | +----+ | -------- | +----+ | +-----+
| |-( Layer-2)-| |
+-----+ | +----+ | (Backbone) | +----+ | +-----+
|VPN-B|-|-|VR-B| | -------- | |VR-B|-|-|VPN-B|
|sites| | +----+<--------------------|------->+----+ | |sites|
+-----+ | | | | +-----+
+---------------+ +---------------+
Figure 2: VR to VR connectivity over a layer-2 backbone
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This type of VR deployment allows direct quality of service
engineering on a per-VPN connection basis. The connections can be
statically configured or dynamically established.
5.2 VR to VR Connectivity through IP or MPLS tunnels
Virtual routers can connect over an IP or MPLS backbone. In a manner
analogous to layer-2 transport, they can use the backbone to support
tunneled connections among the VRs. The topology can be described
similar to that for layer-2 transport, as in figure 2.
Although it is clearly possible to use a topology similar to the
layer-2 model over an IP or MPLS backbone, the VR capability can
support a different network deployment besides full mesh tunnels
between VRs. This is the creation (on each PE) of another VR facing
into the backbone network, which is used to build a kind of backbone
VPN that may be shared among multiple customer VPNs. This is
described below as the "backbone VR."
5.3 Virtual Router Backbone Aggregation
Another typical VPN configuration consists of connecting multiple
virtual routers to the backbone through the use of a single virtual
router (figure 3). For easy reference in the following sections we
call this single virtual router "the backbone virtual router" or
"the backbone VR".
The backbone virtual router is not functionally different than other
virtual routers. It is only a virtual router that is configured and
deployed in a special configuration.
PE PE
+---------------+ +---------------+
+-----+ | | | | +-----+
|VPN-A| | +----+ MPLS/IP based Tunnels +----+ | |VPN-A|
|sites|-|-|VR-A|\.......|<---------->|........|VR-A|-|-|sites|
+-----+ | +----+ +----+ | --------- | +----+/+----+ | +-----+
| |VR-1|-|-(IP/MPLS )-|-|VR-2| |
+-----+ | +----+/+----+ |(Backbones) | +----+\+----+ | +-----+
|VPN-B|-|-|VR-B| | --------- | |VR-B|-|-|VPN-B|
|sites| | +----+........|<---------->|........+----+ | |sites|
+-----+ | MPLS/IP based Tunnels | +-----+
| | | |
+---------------+ +---------------+
Figure 3: VR-1 and VR-2 used as backbone VRs
The backbone virtual router connects each PE to a shared backbone
infrastructure. Backbone virtual routers can be deployed over ATM,
FR, IP, or MPLS networks. Since the backbone VR allows the
aggregation of VRs from multiple VPNs, backbone configuration can
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remain unaffected as new VPNs or VPN sites are added. The
relationship between the VRs and the backbone VR is an overlay
relationship.
Note that although the concept is described above using a single
backbone VR, there may be multiple backbone VRs per PE.
5.3.1 Tunneling
VPN data and routing information is tunneled through the use of IP
or MPLS based tunnels (e.g., IPSec, GRE, IP in IP, MPLS). Depending
on the tunnel technology used, the tunnels can be statically
configured or dynamically established. The tunnel appears to VRs as
a point-to-point link. Traffic sent through the tunnel, and
forwarded by the backbone VR is opaque to the underlying backbone
technology used.
A tunnel can be established per VPN or shared among many VPNs (VRs).
The tunnel can originate from the backbone virtual router or from
the VRs. This can provide an opportunity for service
differentiation, in which a service provider can offer a higher
level of service (at a higher price point) for individually mapped
VPN connections among a customer's VRs.
The backbone VR makes it appear as if each VR within a VPN is
directly connected (full and partial mesh configurations supported).
Each VR within the VPN exchanges routing information directly with
the other VRs in the VPN.
VPNs may use different type of tunnels for inter-VR connectivity.
Some sites may use MPLS as their tunnel technology of choice. Other
sites (which transit through non-secure domains) may choose to use
IPSec to encrypt their data.
The scalability and security of dynamic tunnel establishment between
VRs will be enhanced by the ability to exchange a VPN-ID. [VPN-BGP]
supports auto-discovery of the VPN-ID within BGP-based networks.
Further work is needed to determine the requirements and usage of
the VPN-ID exchange within IPsec-based tunneling scenarios.
5.3.1.1 MPLS Tunnels
MPLS tunneling can be used in different forwarding scenarios. A
hierarchy of two labels can be used. One simple forwarding scenario
is where the inner label identifies the VR intended to receive the
private packet (to be forwarded to the CE). Another forwarding
scenario is to distribute the inner label on a per-VPN basis across
the tunnel. In this case the label distribution process can be
achieved using BGP or an existing label distribution protocol on a
per-VPN basis. The inner label relates to the private VPN prefix.
The label and reachability distribution is done through the tunnels.
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On the egress side traffic will be directed to the egress interface
by looking up the inner label.
5.3.1.2 IPSec Tunnels
IPSec is needed when there is a requirement for strong encryption or
strong authentication. It also supports multiplexing and a
signalling protocol - IKE. IPSec tunnels can be established between
two VPN sites across the backbone (originating from the backbone
VRs).
5.3.2 Routing
The backbone VR exchanges backbone routing information with other
backbone entities (P routers and possibly other backbone VRs). The
backbone routing is separated from the customer VPN routing.
Virtual routers can run any routing protocol on their local VPN
domain. Both static routes and dynamic routing protocols such as
RIP, OSPF, and BGP-4 can be used. VPN sites exchange routing
information through the tunnels over the backbone.
If a backdoor link is used between VPN sites running any IGP, then
by adjusting the backdoor link costs appropriately, the backbone
link can be favored for forwarding VPN traffic. By lowering the
weight, the backdoor link can be used as a backup link in case the
backbone path fails.
5.3.3 Relationship between the VRs and the Backbone VR
The routing domain of a set of VRs participating in a single VPN has
no relation to the routing domain of the backbone VR. The backbone
VR is not necessarily aware of the routing instances running on each
private virtual router. However, because the backbone VR is also a
virtual router, it can build routing relationships with other VRs if
needed.
5.3.4 Multiple Backbones connected to a single PE
Figure 4 illustrates an example where multiple backbones are
connected to the same PE. This type of configuration can be used
when the PE is connected to multiple service provider backbones, or
when the service provider offers different VPN services for
different types of backbones.
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PE PE
+---------------+ +---------------+
+-----+ | | | | +-----+
|VPN-A|-|-+----+ | | +----+-|-|VPN-A|
|sites| | |VR-A|\ | | |VR-A| | |sites|
+-----+ | +----+ +----+ | --------- | +----+/+----+ | +-----+
| |VR-1|-|-(Backbone )|-|VR-2| |
+-----+ | +----+/+----+ | ( 1 )| +----+\+----+ | +-----+
|VPN-B|-|-|VR-B| | --------- | |VR-B|-|-|VPN-B|
|sites| | +----+ | | +----+ | |sites|
+-----+ | | | | +-----+
| | | |
+-----+ | | | | +-----+
|VPN-C| | +----+ | | +----+ | |VPN-C|
|sites|-|-|VR-C|\ | | |VR-C|-|-|sites|
+-----+ | +----+ +----+ | -------- | +----+/+----+ | +-----+
| |VR-3|-|-(Backbone)-|-|VR-4| |
+-----+ | +----+/+----+ | ( 2 & 3 ) | +----+\+----+ | +-----+
|VPN-D|-|-|VR-D| | -------- | |VR-D|-|-|VPN-D|
|sites| | +----+ | | +----+ | |sites|
+-----+ | | | | +-----+
+---------------+ +---------------+
Figure 4: Multiple Backbones connected to a single PE
6. VPN Auto-Discovery
The virtual router approach explicitly separates the mechanisms used
for distributing reachability information from mechanisms used for
distributing VPN topology and membership information. VPN membership
information refers to the set of PEs that have customers in a
particular VPN. VPN topology represents the set of PEs and their
interconnectivity within the VPN. The topology can be a full-mesh of
PEs, a hub and spoke, or anything in between. Dynamic topology can
also be handled due to on-demand VPN customers.
VPN discovery can be achieved through different mechanisms, for
example:
- Directory server approach, in which VRs query a server to
determine their neighbors.
- Explicit configuration via a management platform.
- Piggybacking VPN membership and topology information using
existing routing protocols (e.g., BGP) [VPN-BGP].
- Other VPN membership and topology auto-discovery approaches.
The above mechanisms can be combined on a single PE. As an example,
for some VPNs topology discovery is done only through a management
platform. For others, dynamic topology discovery is achieved using
existing routing protocols.
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In this document it is assumed that a mechanism that provides
services similar to BGP is used to achieve auto-discovery of VPN
members. As described in [VPN-BGP], VR addresses are exchanged,
along with the information needed to enable the PEs to determine
which VRs are in the same VPN ("membership"), and which of those VRs
are to have VPN connectivity ("topology"). Once the VRs are
reachable through the tunnels, routes ("reachability") are then
exchanged by running existing routing protocols on a per-VPN basis
across the tunnels.
It is important to note that, for the VR architecture, the auto-
discovery mechanism is only used to automatically exchange VPN
control information between VRs. It is not intended for piggybacking
VPN private reachability information onto the backbone routing
instance, as is done in [VPN-RFC2547bis], for example.
7. VRs and Extranets
Extranets are commonly used to refer to a scenario whereby two or
more companies have network access to a limited amount of each
other's corporate data. An important feature of extranets is the
control of who can access what data, and this is essentially a
policy decision. Policy decisions are enforced at the
interconnection points between different domains [VPN-RFC2764]. The
enforcement may be done via a firewall, a router with access list
functionality, or any device capable of applying policy decisions to
transit traffic.
In the VR architecture, policy can be enforced between two VPNs, or
between a VPN and the Internet, in exactly the same manner as is
done today without VPNs. For example, two VRs (VPNs) could be
interconnected, with each VR locally imposing its own policy
controls, via a firewall or other enforcement mechanism, on all
traffic that enters its VPN from the outside (whether from another
VR or from the Internet). Combining firewalls and exchanging private
routes between VRs (members of different VPNs) provide a flexible
mechanism to build different flavors of extranets.
8. VPNs across Domains
It is possible that a VPN may cross multiple domains administered by
different service providers. In the VR model, tunnels are used to
provide intra-VPN connectivity across the backbones. The main
requirement on the service provider in order to achieve end-to-end
cross-domain VPN connectivity is the ability for both domains to
support a common tunnel technology. Once the tunnel is established,
private data (e.g., routing information, and private customer data)
can flow from one domain to the other with the same level of
security as is provided in a single service provider network.
Another possible scenario is to use two virtual routers configured
on each PE at the interconnection point. Each VR will use policy
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decisions and firewalling to control VPN traffic transiting from one
domain to the other.
The ability to use a standard VPN-ID format also allows unambiguous
VPN identification across domains.
9. Internet Access
The same link attaching the CE to the VR can be used to provide
Internet access to the VPN sites. The VR operations are decoupled
from the mechanisms used by the customer sites to access the
Internet.
There are a number of ways to provide Internet access to a VPN using
the VR model. One way of providing VPN Internet access is to
configure the backbone VR to steer private traffic to the VPN VR,
and Internet traffic to the normal backbone/Internet forwarding
table. The backbone VR can hold the Internet routes (so it will not
be necessary for the VPN VRs to handle them). Firewalls should be
used to secure the access (with the ability to use NAT).
Other options are also valid. One may want to have a particular VR
handling Internet access only (rather than going to the backbone
VR), or a default route to an Internet gateway can be used.
10. Carrier's Carrier Case
It is possible that a VPN service is also a network of a service
provider offering VPN services. Different options can be used to
implement the VPN hierarchy.
In one approach, tunnels are built from the VPN edges to the CEs,
and the VRs transparently provide VPN service to the remote CEs.
This can be useful in the case where the CEs are themselves VRs and
the service provider is also outsourcing the management of his
customer VPN services.
Another case is where the remote VPN services are completely
transparent to the VRs (on the PEs). This is the default case. It is
up to the VPN network to distribute VPN reachability across the CEs.
Another option is for the VPN service to implement the VR
architecture. In this option, the VPN Backbone VRs appear as CEs to
the VRs configured on the PEs.
11. Operations and Management
Each VR operates independently, and can be individually reconfigured
without affecting other VRs on the same PE. In some
implementations, it may be possible for a VR to be "rebooted" by a
customer without affecting other VRs. In case of PE failure (e.g.,
migration, upgrades, etc.), the service provider may want to control
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and decide what VPN services gets reestablished first. This
particular point is important when a large number of VPNs is
supported on the PE where each VPN service has different service
availability requirements.
Since each VR operates as an independent router, it is possible for
the management of the VRs to be outsourced. VPN customers may
choose to configure (or perhaps only to monitor) the VRs that make
up their VPN. It is also possible that the backbone VRs could be
managed by a separate entity.
11.1 Backbone Migration
One benefit in using multiple backbone virtual routers is the
ability for the backbone network administrator to migrate its
backbone from one core technology to another with minimal disruption
to VPN services. Conversely, a VPN configuration change or a VPN-
software upgrade is totally transparent to the backbone protocol and
policies (this is due to decoupling the VPN routing protocol from
the provider backbone routing protocol).
11.2 Troubleshooting
The service provider or the VPN customer can use all existing
troubleshooting tools on a per-VPN basis (e.g. ping and traceroute).
As an example, a VPN customer may be able to telnet to its own VR
and perform some troubleshooting operations. In this particular
case, the service provider can configure for each VPN customer
restricted privileges over the virtual router associated with the
customer VPN network. This access may provide only the privilege to
monitor (with no privilege to change) the layer 3 status of the
customer's VPN. The service provider may be able to offer VPN
customers an SNMP-based method for read-only access to information
about their own VPN. However, backbone topology information is
completely hidden to the VPN VR, and therefore to the service
provider's customer.
12. Quality of Service
This architecture can utilize a variety of Quality of Service
mechanisms. QoS mechanisms developed for physical routers can be
used with VRs, on a per-VR basis, including classification,
policing, drop policies, traffic shaping and scheduling/bandwidth
reservation. The architecture allows separate quality of service
engineering of the VPNs and the backbone.
13. Scalability
Only the PEs are handling the VPN type information. The internal
backbone routers (the P routers) are usually not VPN aware.
Furthermore, virtual routers allow multiple private CE-based
networks to connect to a single PE.
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One advantage of the ability to contain the VPN address space and
VPN routing and forwarding capabilities within the virtual router
entity is the possibility to distribute PE system resources on a
per-VPN basis. Indeed, as an example, different scheduling
mechanisms can be used for processing each VPN activity within the
PE. This type of per-VPN resource management contributes to
establishing a wide range of priority schemes among the VPNs within
the PE.
14. Security Considerations
Various levels of data, routing and configuration security can be
implemented. Any existing security-related mechanisms supported by
existing routing protocols (e.g. authentication) can be used
unmodified in the VR architecture. If IPSec tunneling is used as the
tunneling protocol, then both the control and data traffic that
travels over the tunnel can be secured; so that routing specific
security enhancements are not needed. Any private routing,
forwarding and addressing manipulation is done within the virtual
router context. Direct layer-2 connections (ATM, FR), or specific
tunneling mechanisms can also provide various levels of data
security.
15. Document Change History
Version -03:
Document change history section added.
References updated.
Author information updated.
Section 5.3.1 - Paragraph on VPN-ID exchange added.
16. References
[GRE-RFC1701] Hanks, S., Li, T., Farinacci, D. and P. Traina,
"Generic Routing Encapsulation (GRE)", RFC 1701, October 1994.
[RFC-3212] Jamoussi, B., et al, "Constraint-based LSP Setup using
LDP", RFC 3212, January 2002.
[RFC-2003] Perkins, C., "IP Encapsulation within IP", RFC 2003,
October 1996.
[RFC-2026] Bradner, S., "The Internet Standards Process -- Revision
3", RFC 2026, October 1996.
[RFC-2401] Kent, S., Atkinson, R., "Security Architecture for the
Internet Protocol", RFC 2401, November 1998.
Ould-Brahim, et al. July 2002 [Page 16]
Internet-Draft draft-ietf-ppvpn-vpn-vr-03.txt January 2003
[RFC-2411] Thayer, R., et al, "IP Security Document Roadmap", RFC
2411, November 1998.
[RFC-2661] Townsley, W., et al, "Layer Two Tunneling Protocol L2TP",
RFC2661, August 1999.
[RFC-2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", RFC 2119, March 1997.
[RFC-2917] Muthukrishnan, K., Malis, A., "Core MPLS IP VPN
Architecture", RFC 2917, September 2000.
[VPN-BGP] Ould-Brahim, H., et al., "Using BGP as an Auto-Discovery
Mechanism for Network-based VPNs", draft-ietf-ppvpn-bgpvpn-auto-
02.txt, work in progress, January 2002.
[VPN-RFC2547bis] Rosen, E., et al, "BGP/MPLS VPNs", draft-ietf-
ppvpn-rfc2547bis-01.txt, work in progress, January 2002.
[VPN-RFC2685] Fox, B., et al, "Virtual Private Networks Identifier",
RFC 2685, September 1999.
[VPN-RFC2764] Gleeson, B., et al., "A Framework for IP Based Virtual
Private Networks", RFC 2764, February 2000.
[VPN-GID] Ould-Brahim, H., Gleeson, B., and Rekhter, Y., "Global
Unique Identifiers (GID)", draft-ouldbrahim-ppvpn-gid-00.txt,
work in progress, January 2002.
17. Acknowledgments
The authors would like to acknowledge the following individuals for
their helpful comments and suggestions: Bilel Jamoussi, David
Hudson, David Drynan, Ru Wadasinghe, Scott Larrigan, Peter Ashwood-
Smith, Martin Pepin, Ahmad Khalid, Don Fedyk, Keerti Melkote, Ron
Bonica, Jerry Sydir, Mark Duffy, and Benson Schliesser.
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18. Author's Addresses
Document Editor (Please send comments to editor.)
Paul Knight
Nortel Networks
600 Technology Park Drive
Billerica, MA 01821 USA
Email: paknight@nortelnetworks.com
Phone: +1 (978) 288 6414
Hamid Ould-Brahim Bryan Gleeson
Nortel Networks Tahoe Networks
P O Box 3511 Station C 3052 Orchard Drive
Ottawa, ON K1Y 4H7 San Jose CA 95134
Canada USA
Phone: +1 (613) 765 3418 Email: bryan@tahoenetworks.com
Email: hbrahim@nortelnetworks.com
Gregory Wright Timon Sloane
Nortel Networks Webstacks
P O Box 3511 Station C 444 Oakmead Parkway
Ottawa, ON K1Y 4H7 Sunnyvale, CA 94085
Canada USA
Phone: +1 (613) 765 7912 Phone: +1 408-524-8484
Email: gwright@nortelnetworks.com Email:timon@webstacksinc.com
Rainer Bach Rick Bubenik,
T-Data SAVVIS Communications
Hans-Guenther-Sohl-Strasse7 717 Office Parkway
40235, Duesseldorf St. Louis, Mo. 63141
Germany USA
Phone: +49 211 694 2420 Phone: +1 (314) 468-7021
Email: Rainer.Bach@telekom.de rickb@savvis.net
Abraham Young Jieyun Jessica Yu
Huawei Technologies Co., Ltd. SingWave Consulting
Kefa Road Email: jyy_99@yahoo.com
Science-Based Industrial Park
Nanshan District, Shenzhen 518057
China
Phone: +86-755-6540808
Email: abyoung@huawei.com
Chandru Sargor Isaac Negusse
Cosine Communications Sprint
1200 Bridge Parkway 2002 Edmund Halley Drive
Redwood City, CA 94065 Reston, VA 20191
USA USA
Phone: +1 (650) 637-2416 Phone: +1 (703) 295-5706
Chandramouli.Sargor@cosinecom.com isaac.negusse@mail.sprint.com
Ould-Brahim, et al. July 2002 [Page 18]
Internet-Draft draft-ietf-ppvpn-vpn-vr-03.txt January 2003
Luyuan Fang Dr. Christian Weber
AT&T Arcor AG & Co.
200 Laurel Avenue Koelner Strasse 5
Middletown, NJ 07748 65760 Eschborn
USA Germany
Phone: +1 (732) 420-1921 Phone: +49(0)69-2169-3973
Email: Luyuanfang@att.com Christian-Weber@arcor.net
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