Layer 3 VPN Working Group
Internet Draft Ananth Nagarajan
Document: draft-ietf-l3vpn-as-vr-02.txt Juniper Networks
Expires: February 2007
Junichi Sumimoto
Muneyoshi Suzuki
NTT Corporation
Paul Knight
Nortel Networks
Benson Schliesser
SAVVIS Communications
August 2006
Applicability Statement for Virtual Router-based Layer 3 PPVPN
Approaches
Status of this Memo
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Abstract
This document is an applicability statement for Layer 3 Provider
Provisioned VPNs (L3 PPVPNs) that are based on Virtual Router (VR)
approaches. This document describes how VR-based approaches meet the
key requirements that are outlined in the PPVPN Applicability
Statements Guideline document.
Conventions used in this document
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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].
Table of Contents
1. Introduction...................................................2
2. Service Provider Provisioning Model............................3
2.1 Auto-Discovery.............................................4
3. Supported Topology and Traffic Types...........................4
4. Isolated Exchange of Routing and Data Information..............5
4.1 Isolation of Routing Information...........................5
4.2 Isolation of Data..........................................6
5. Access Control and Authentication..............................6
6. Security.......................................................6
6.1 Protection of User Data....................................6
6.2 Service Provider Security Measures.........................7
6.3 PPVPN Security Framework Template..........................8
7. Addressing.....................................................8
8. Interoperability and Interworking..............................8
9. Network Access.................................................9
9.1 Physical and Link Layer Topology...........................9
9.2 Temporary Access...........................................9
9.3 Access Connectivity........................................9
10. Service Access................................................9
10.1 Internet Access...........................................9
10.2 Hosting, ASP, other services..............................9
11. Service Provider Routing.....................................10
11.1 Core Router Awareness of Mechanisms Used.................11
12. Migration Impacts............................................11
13. Scalability..................................................12
14. QoS/SLA......................................................13
15. SLA Monitoring...............................................13
16. Management...................................................14
16.1 Service Provider Management of Customer Site.............14
16.2 Customer Management of VR................................14
16.3 Service Provider Network Management......................14
17. Security considerations......................................15
Appendix A: Responses to Security Evaluation Template..........16
References.......................................................26
Acknowledgments..................................................27
Author's Addresses...............................................27
1.
Introduction
The virtual router concept for L3 PPVPNs is described in [PPVPNVR].
Based on the taxonomy of PPVPNs described in [FRAMEWORK], Virtual
Router based approaches are classified as PE-based Layer 3 PPVPNs.
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VR-based PPVPNs are used in the following situations:
- The customer wishes to outsource the maintenance and management of
inter-site VPN connectivity to the Service Provider (SP).
- The SP desires to provide VPN service without upgrading its core
network to support any specific technology (e.g., MPLS), i.e., the SP
wants to provide a Layer 3 VPN service over a range of core network
technologies, including existing IP routed or Layer 2 switched core
networks, MPLS, or a combination of these technologies.
- The customer is not aware of the topology or mechanisms used in
the SP core network and is responsible for routing between customer
routers, which is independent of the routing used in the SP core. The
customer-facing sides of the PE devices in the SP network are visible
to the customer. The logical links between VRs are also visible to
the customer, and optionally it is possible for the full private
network topology (including the logical links) to be visible to
routers within a site.
- The customer wishes to exercise control of routing functions at
the CE routers at each of its VPN sites, while depending on the SP to
provide transport for data traffic and for the customer's routing
information across the SP core. From the viewpoint of any of the
customer's routers, there will usually appear to be a single router
hop to any other VPN site. The only routes exchanged between the CE
routers and the PE devices are the customer's internal routes (with
the possible addition of routes desired by the customer for Internet
access via the SP, such as a default route).
- The customer sends IP traffic across the VPN, possibly including
non-IP traffic encapsulated in IP by the customer.
- The VPN service provider does not own a backbone network but
wishes to provide PPVPN services over a backbone obtained from some
other provider.
- Several cooperating SPs desire to offer PPVPN service at points
that span multiple administrative domains of the backbone, perhaps
over the public Internet.
This document describes how Virtual Router based VPN approaches
satisfy key requirements listed in the PPVPN Service Requirements
document [REQTS] and the PPVPN Security Framework [SEC-FRMWK].
2.
Service Provider Provisioning Model
Virtual Routers (VRs) can interact with other routers so as to be
indistinguishable from an individual physical router. However,
multiple instances of VRs can be configured within a single physical
device. This provides a significant improvement in manageability and
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provisioning flexibility. In addition, there is potential statistical
multiplexing gain on "uplinks" from the PE router to P router,
compared with use of multiple physical routers. Each VR can maintain
its own separate routing tables, so if two virtual routers are in the
same physical router, an interaction of one VR with one of its peers
does not have any effect on the interaction of another VR with any of
its own peers. In some implementations, VRs may share physical
interface bandwidth.
VPNs are constructed via tunnels connecting VR pairs across the
service provider backbone network. Per-VR routing protocol
instantiations are run to distribute VPN reachability information.
VPN membership information distribution is treated separately, and is
achieved via sharing a VPN-ID, for example [RFC2685], between VRs
that are members of a specific VPN. The detailed VR model is
described in [PPVPNVR].
2.1
Auto-Discovery
In the VR-based PPVPNS, various auto discovery mechanisms are
supported. VPN discovery can be achieved through directory servers
[RADIUS-DIS], explicit configuration via a management platform, using
multicast [COREVPN] or by piggybacking VPN membership and topology
information via routing protocols such as BGP [VPN-BGP]. A
combination of these mechanisms may also be used on a PE. For
example, for some VPNs topology discovery is done only through a
management platform. For others, dynamic topology discovery is
achieved using existing routing protocol. BGP-based auto-discovery
is described in [VPN-BGP], and may be used for membership and
topology discovery.
It is important to note that, for the VR architecture, the auto-
discovery mechanism is only used to automatically exchange control
VPN information between VRs. It is not intended for interchange of
the VPN routing information, which is accomplished by standard
routing protocols running between the VRs, as discussed in [PPVPNVR].
3.
Supported Topology and Traffic Types
VR-based PPVPNs can be constructed using either MPLS or IP tunnels
(GRE, IP-in-IP, L2TP, IPSec) in the core network, or Layer 2
connections such as ATM or Frame Relay. The choice of the tunneling
mechanism may impact other properties of the VPN itself, including
scalability, manageability, QoS, security, etc. For example, the use
of IPSec tunnels for encryption may impact forwarding performance on
some devices, and therefore impact the number of sites or routes per
VPN, the number of VPNs per PE, etc. The performance of IPSec tunnels
may be improved through the use of dedicated hardware, which allows
greater performance and scaling but potentially at increased cost.
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Tunnels are created on a per-VPN basis. For transport across the
network, a number of these tunnels may be aggregated and carried
within a PE-PE tunnel. The SP has a high degree of flexibility in
configuring the topology of a VPN interconnecting customer sites. The
topology can be full-mesh, partial-mesh, or any arbitrary topology
that has been agreed to by the customer and the SP.
4.
Isolated Exchange of Routing and Data Information
By definition of a Virtual Private Network, the details of its
addressing, topology, connectivity, and reachability as well as the
data that it transports are implicitly considered to be private, and
should therefore be isolated from other networks, including others
that may be supported with the PPVPN infrastructure. [FRAMEWORK]
4.1
Isolation of Routing Information
In any PPVPN, the SP is responsible for maintaining isolation between
networks except as explicitly intended by the VPN owner. In the VR
model, a key mechanism for maintaining isolation is through isolating
routing information, thereby constraining the distribution of
reachability information.
The VR model of PPVPNs provides for isolation by instantiating
multiple Virtual Routers (VR) on a single physical platform to
support multiple VPNs. [PPVPNVR] Each VR has its own logical
interfaces, routing tables, forwarding tables, and routing protocol
instances. Note that a VR may share physical interfaces with other
VRs, depending on the implementation and specific topology. This
provides for isolated topology, addressing, and reachability for the
VPN.
Addressing and Reachability includes the assignment, discovery, and
distribution of source and/or destination information for the PPVPN.
The isolation of this information implies that other networks,
including other VPNs and the Internet, will have no visibility into
the PPVPN except as explicitly configured.
Routing information carried between VRs is carried in through the
same tunnels as data itself, and is therefore segregated from the
underlying backbone infrastructure by the same mechanisms that
segregate data between VPNs.
This model supports arbitrary routing architectures, including
support for back-door links among customer VPN sites or other
potentially unique routing architecture requirements. The support
for arbitrary routing architectures, however, is accompanied by
scalability and management issues. These issues are discussed later
in this document.
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In the VR approach, virtual routers are connected to the CEs through
local links, and to each other across the backbone through tunneling
services provided by the service provider across the backbone. All
data traffic within the VR-based VPN is isolated from non-VPN traffic
by these mechanisms.
Some VR implementations may provide the ability for customers to
exercise limited management operations upon the VRs which are
connected to the customer CEs. This may allow the customer to view
routing tables, or traffic statistics, or to exercise some control
over the customers routing. VRs MUST NOT allow any customer to
circumvent the isolation of routing or data among VPNs.
4.2
Isolation of Data
Data for different VPNs in the VR model is segregated through the use
of different link-layer connections or tunnels over a common SP
backbone. [PPVPNVR] Examples of such tunnels include GRE, L2TP,
IPSec, MPLS or Layer 2 connections such as ATM or Frame Relay. It
should be noted that this isolation can be impacted by
misconfiguration.
5.
Access Control and Authentication
CE-PE authentication has not been specified for VR-based VPNs. PE/CE
mutual authentication may be done via any mechanism supported by the
routing protocol in which the CE and PE are peers (e.g., use of the
TCP MD5 authentication when the CE/PE protocol is BGP), or by any
other mechanism that may be desired by the customer.
In order for VR-based PPVPNs to support confidentiality, integrity,
authentication, and replay attack prevention, mechanisms such as
IPsec may be used as tunneling mechanism or used over VPN tunnels.
Even with the use of IPsec, the security level offered is dependent
on the scope of the IPsec security associations: encrypting on a CE-
to-CE basis (as in CE-based VPNs) will offer a wider scope of
protection than only encrypting on a PE-to-PE basis (as in PE-based
VPNs), since the CE-PE link remains unencrypted in the latter case.
However, PE-PE IPsec offers substantial advantages in efficiency,
outsourcing, and integration with the dynamic membership and dynamic
routing nature of the PPVPN. CE-PE IPsec can also be used to protect
traffic on the CE-PE section of the network. In this case the
traffic is only unprotected by IPsec within the PE device. Policy-
based security and access control mechanisms or firewalls may be used
between sites in the same VPN. These can be implemented on the PE
router, or on the CE.
6.
Security
6.1
Protection of User Data
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As described above, end-to-end (CE-to-CE) IPSec may be used to
protect user data. SPs may choose to provide CE-based IPSec as a
value added service. If the SP core network is also part of the
public Internet, the SP may choose to provide PE-to-PE IPSec as the
tunneling mechanism between VRs.
If inter-SP VPNs are to be provided, IPSec tunnels may be used. The
impact on QoS and SLAs in this case will have to be studied.
In general, user data is protected via the inherent isolation
provided by the inter-VR tunnels. Varying levels of security of user
data may be provided based on the type of tunnel that is used.
6.2
Service Provider Security Measures
In general, the SP should ensure that non-VPN traffic does not
accidentally or maliciously enter a VPN. Since VRs can be configured
very specifically for a customer, the SP can offer customers anti-
spoofing or other traffic or route filtering services tailored for
the customer's network. The SP's PE and P devices should be protected
against intrusion or denial of service attacks. This is especially
important because the SP core network may be used to provide general
Internet services apart from VPN services. Therefore any Denial of
Service attack or misconfiguration that impacts other VPN services
and Internet services should be prevented. Since most of the traffic
from CE to PE, apart from control (routing and network management)
traffic, gets encapsulated to be carried across the SP network, the
possibility of users sending traffic to other (non-PE) systems in the
core network is minimized or eliminated. The inherent isolation of VR
mechanisms helps provide this protection against attacks from
customer sites, but additional specific measures are available:
- VR routing sessions can be authenticated between the PE and CE,
and among PEs.
- If BGP is used as an auto-discovery mechanism between VRs, it
should be further authenticated using mechanisms such as TCP MD5.
- Filtering of any management data entering the PE should be
performed in order to prevent the acceptance of unauthorized packets
from customers or other SPs into that PE.
Denial of Service attacks may occur via routing traffic or network
management traffic, either intentionally or accidentally via routing
instabilities or misconfigurations in the VPN. With Virtual router
VPNs, in many cases a dynamic routing protocol will be run between CE
routers and VRs within PE routers. Either the same or a different
dynamic routing protocol may be run between VR instances in each PE
associated with a VPN. If routing is unstable in the private network,
it is possible for this instability to be propagated to the PE
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routers. For example, in some cases a large number of routing updates
could be sent from the CE router to a VR within a PE router, or
between VR instances in different PE routers. This could potentially
place a major or excessive processing load on the PE routers.
This issue can be mitigated via resource partitioning in the PE, in
order to limit the amount of resources (e.g., CPU and memory) which
any one VR is permitted to use in PE routers. Also, rate limits may
be applied to the routing traffic sent from the CE to the PE.
Alternately, when this problem is detected on the CE to PE link, the
CE to PE interface may be shut down.
In order to prevent DoS attacks due to network management traffic,
the functions available to the customer need to be strictly
controlled. It may also be useful to limit the resource use of this
capability. Resource partitioning may be appropriate internal to PE
routers, and network management traffic from the CE to the PE may be
rate limited (for example, to prevent network management traffic from
CE to PE from being used in a DoS attack).
6.3
PPVPN Security Framework Template
As stated in the "PPVPN Security Framework" [SEC-FRMWK], "An
evaluation of a given PPVPN approach using this template should
appear in the applicability statement for each PPVPN approach."
Please refer to Appendix A for this detailed response.
7.
Addressing
Virtual Routers may provide any or all of the services which are
provided by a physical router, including Network Address Translation
(NAT), packet filtering, etc. These VR capabilities can simplify the
process of joining previously independent site networks, which may
have overlapping address spaces. NAT can be used to satisfy intra-
VPN non-unique addressing requirements. This facilitates the
construction of short-term or ad-hoc VPNS. It should be noted,
however, that NAT has accompanying scaling problems, and other
mechanisms are needed to ensure proper routing updates, when two
sites share the same routing domain.
Non-unique and private customer addresses may be supported by using
encapsulation within the tunneling mechanisms employed between VR
pairs (e.g., GRE, IP-in-IP etc.). As such, support for private
addressing as specified in [RFC1918] allows for non-unique addresses
between different VPNs.
8.
Interoperability and Interworking
Interoperability and Interworking of VR-based VPNs with other L3
PPVPN mechanisms such as [RFC2547bis] is for further study. Since
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VRs provide all IP router functionalities, various VR-based solutions
interwork and interoperate to the extent that IP networks
interoperate and interwork.
9.
Network Access
9.1
Physical and Link Layer Topology
VR-based mechanisms do not affect the choice of physical and link
layer technologies or topologies.
9.2
Temporary Access
Temporary access for a dial-up user to a VR can be provided via PPP
and AAA, using a Remote Access Server. Other access mechanisms such
as IPSec can also be used. Thus, it is possible provide login and
password based access to a VR-based VPN from an authorized user
connected to the Internet.
9.3
Access Connectivity
Multi-homing of CEs to multiple VRs (within the same or different
PEs) is supported. The PEs (and consequently the VRs) may belong to
different SPs.
Load sharing based on IGP or other traffic engineering mechanisms
used in the SP core are naturally supported by VR-based VPNs.
10.
Service Access
10.1
Internet Access
Simultaneous VPN and Internet Access can be supported via various
mechanisms. A specific VR may be assigned as a default VR that is
connected to the Internet. If a single VR is to be used to carry a
customer's VPN as well as Internet traffic, Internet traffic can be
distinguished from VPN traffic by associating a default VPN-ID with
Internet traffic and pointing it to a default route to the Internet.
This default route to the Internet need not be direct, but may
instead point to a firewall or other security device which may use
different interfaces for VPN access and Internet access.
10.2
Hosting, ASP, other services
All of the above "external" services can be supported by associating
a separate address for every service that is not being used within
the VPN. If a single server (for example, a web hosting server) is
used to provide a particular service to all VPNs, NAT may be used to
provide a unique address for clients to access that particular
service. NAT can be performed either at the customer site or can be
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integrated into the PE. The scaling impacts of adding NAT to the PE
will have to be considered.
11.
Service Provider Routing
VR-based PPVPNs do not impose any additional requirements on the IGP
used in the service provider core network. However, if the customer
VPN runs an IGP, the VRs (and consequently the PEs) must support that
IGP. This customer IGP need not be the same as the IGP running in the
Service Provider's core network.
From the customers viewpoint of its VPN IGP routing topology (if it
uses one), the SPs network topology appears much simpler than it may
actually be. Depending on the VR implementation, the SPs service
offering, and the SPs physical topology, it may appear as either a
single large router with interfaces for each VPN site, as a full
mesh, with two routers between any two sites, as a hub-and spoke
topology (when the customer wants all inter-site traffic to pass
through one or more specific sites, for application of services such
as security filtering), or other arbitrary topology. In general, the
SP's actual core routing topology is invisible to the customer.
Fault handling is a specific problem when the timers used for the VR-
to-VR routing peering are shorter than the timers used for the
routing peering within the service provider(s) network. In this case
a single failure within a service provider network may look like a
collection of un-correlated failures in the VPN.
Moreover, since a VR doesn't really "know" what causes the failure,
the VR may react to such a failure by re-routing along some other
tunnel, while this other tunnel may be also affected by the same
failure. As a result, this would slow down routing convergence within
the VPN.
To avoid the problems mentioned above one may consider making the
timers used for the VR-to-VR peering longer than the timers used for
the routing peering within the service provider network (so that
failures within the service provider network would be "invisible" to
the VR-VR tunnels). But that has its own set of problems. While
this may be possible to accomplish within a single routing domain
(one needs to appropriately set the IGP timers within the domain),
doing this in a network that includes more than one routing domain
may be difficult (as timers include both IGP and BGP timers, and
moreover, timers include IGP timers in several routing domains).
Another consequence of making the timers used for the VR-to-VR
peering over the tunnels longer than the timers used for the routing
peering within the service provider network is that it would increase
the amount of traffic that will be "black holed" in the case of VR
failures.
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A key aspect of the issue here is that layer 3 problems in the SP
network may appear as layer 2 problems in the VPN. Thus stability of
the SP network, with an emphasis on quick recovery, is a key element
in delivering satisfactory service.
Prevention of Denial of Service attacks caused by routing
instabilities has been discussed in Section 6.2.
11.1
Core Router Awareness of Mechanisms Used
Since tunnels are established between VR pairs, the core router (P
router) does not have any information of the mechanisms used to
construct the VPN. If MPLS is the tunneling mechanism that is used
between the VRs, the core routers may have to be MPLS enabled in
order to leverage the benefits of MPLS tunnels (e.g., traffic
engineering). As such, while the core routers are not aware of VPN-
specific information, they should support requirements to meet
relevant SLAs. (e.g., for guaranteed QoS, the core routers may need
to support appropriate QoS mechanisms).
12.
Migration Impacts
Similar to other Layer 3 PPVPN architectures, any CE using services
provided using the VR approach can access a PE similar to the way it
would access another CE router in a private network using leased
lines. As the VR approach makes use of standard routing protocols
without any extensions, there is no requirement for additional
capabilities on the part of CEs in order to interoperate with a VR-
based PPVPN.
Key design considerations include:
- The PEs will introduce extra router hops
- If the VR-VR backbone routing protocol differs from the sites,
then IGP metric implications should be carefully evaluated. This
would be particularly true for multihomed VPN sites.
In general, a VR-based PPVPN offers the customer a greatly simplified
network topology compared to a customer-managed private network,
since each CE router sees a single link as the next-hop route to all
other VPN sites. There is no need to configure multiple physical or
logical interfaces on the CE routers.
Multi-homed VPN sites or sites with back-door connections will
involve design decisions as to whether each of the multiple links
should operate as a backup link or as a load-sharing link.
Also, since the VR approach does not depend on the backbone
architecture in terms of routing protocols, a VR-based L3 PPVPN can
be offered on a service provider core network without the need for
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specific core technologies. For example, the core network does not
need specific mechanisms like MPLS to be implemented on the P
routers. Similarly, if the core network is a Layer 2 network based
on ATM or Frame Relay, VR-based VPNs can still be constructed.
It should be noted, however, that core network mechanisms would
determine the overall properties and services that may be provided
over the VPN. For example, in order to support customer QoS SLAs,
the core network should be robustly engineered or should support QoS
mechanisms, in addition to SLA marking at the PE.
Thus, while migration impacts in the case of basic VPN functionality
using VR are minimal from the customers' or providers' point of view,
appropriate core mechanisms may be necessary for certain services.
13.
Scalability
VR is a technology for implementing logical routing instances in a PE
device. A PE device may contain more than one VR and a VR supports
one VPN. Therefore, scalability of a VR and conventional physical
router are basically the same, e.g., if different routing protocols
are used for customer and network sides of a VR or physical router,
the load is increased compared with the case when the same protocols
are used.
The major factor contributing to scalability constraint in the VR
approach is the number of VRs which can be supported by a PE. This is
because, the number of VRs in a PE device is equal to the number of
VPNs which are supported by the PE.
Resources used by a VR instance include memory and processor
resources, used to support VPN tunnel mechanisms, routing protocol
instances, route tables, interface management, etc. The extent to
which these resources are utilized impact scalability.
Much of the resource utilization for a given VPN will be affected by
the topology of the VPN. For instance, a VPN with a full-mesh
topology will require that VRs have more peers for the VPN tunneling
mechanism, for routing protocol adjacencies, for security protocols,
etc., while a hub-and-spoke model will constrain the resources
required for 'spoke' PE routers.
From a VR perspective, scalability also depends on whether the same
routing protocols are used between VRs as in the backbone network. If
the inter-VR routing protocols are different from the backbone IGP,
the scaling and management impacts for configuring routing protocols
on a per-VR basis may be significant. For example, it may be
necessary to maintain OSPF databases for the entire customer VPN
topology, as opposed to maintaining information for only directly
connected customer sites. Additionally, the customer IGP may need to
maintain information about the entire VR topology, for the VRs which
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are connected to the customer's CEs. Other concerns include routing
loop avoidance, route redistribution, etc. Thus, while the VR model
allows the routing protocols between customers and VRs to be
different than the backbone IGP, this flexibility can be accompanied
by scalability concerns. Mechanisms such as OSPF areas may be used
to circumvent such scaling issues.
It is normal in many cases for a VR located in a PE router to run a
routing instance with each other VR which is part of the same VPN. In
some cases this could result in a large number of routing
adjacencies. The number of routing adjacencies could aggravate the
impact of instability in routing in the private network, or aggravate
the impact of routing protocol DOS attack described in Section 6.2.
As mentioned in Section 6.2, this can be mitigated by appropriate
resource partitioning in the PE, and by rate limiting of routing
packets, including packets from CE to PE and well as packets from PE
to PE. Also, while this consideration may limit the number of VRs
which may potentially be supported from a single PE device, it does
not have any significant effect on the overall scaling of a network
implementing the VR approach.
14.
QoS/SLA
VR-based PPVPNs support any kind of QoS that the core network and the
tunneling mechanism used support.
VR-based VPNs can utilize different quality of service mechanisms.
QoS mechanisms developed for physical routers can be used with VRs,
on a per-VR basis. e.g. classification, policing, drop policies,
traffic shaping and scheduling/bandwidth reservation. The
architecture allows separate quality of service engineering of the
VPNs and the backbone. However, the tunneling mechanisms themselves
should support relevant QoS mechanisms.
15.
SLA Monitoring
VR-based VPNs can implement a variety of methods to monitor
compliance with Service Level Agreements. Since the links between
VRs make use of tunnels across the underlying backbone network, the
SLA monitoring capabilities of the backbone network can be used to
monitor the performance of the inter-VR links. Because the inter-VR
links are tunnels, and the SLA monitoring capabilities of the
backbone network may not include per-tunnel monitoring capabilities,
some VR implementations support additional SLA monitoring mechanisms.
Performance to SLA requirements within the PEs hosting the VRs is
typically monitored via internal processes to ensure compliance from
end to end. In addition, either the service provider or the VPN
customer can use all existing SLA tracking tools (round trip time
measurement, traceroute mapping, etc.) within the VR-based VPN.
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16.
Management
16.1
Service Provider Management of Customer Site
The SP may choose to manage the customer site (i.e., the CE devices)
for added revenue. If the SP uses a centralized customer management
system, care should be taken to uniquely identify various CEs
belonging to different VPNs, so that CE devices from different VPNs
do not reach each other.
The customer may desire to have access to the PE device for
monitoring purposes (e.g., ping, traceroute). Providing such access
is at the discretion of the SP.
Traffic statistics in order to prove SLAs to customers may be
provided on a periodic basis. Other statistics that can show
enhanced SP capabilities, including protection against Denial of
Service attacks, failure etc., can be provided to the customer.
16.2
Customer Management of VR
Some VR implementations may provide the ability for customers to
exercise limited management operations upon the VRs which are
connected to the customer CEs. This may allow the customer to view
routing tables, or traffic statistics, or to exercise some control
over the customers routing.
Customer network management and troubleshooting systems will
generally have less ability to gather information from the VRs than
from the customers own routers, and will also have little or no
ability to directly change VR configurations. The customers systems
should be planned so as to accommodate the restricted capabilities of
the VRs to respond to customer network management processes.
Prevention of Denial of Service attacks due to network management
traffic originating from customer management of the VR has been
discussed in Section 6.2.
16.3
Service Provider Network Management
When an SP provides VR-based VPN services, it is highly likely that
the PE devices used are complex because of the number of VRs
supported, the number of routing adjacencies between VR pairs,
maintenance of tunnel and VPN-specific information and possibly other
information such as QoS. Thus the management of the PE is extremely
critical for the SP. If the SP core is also used to provide Internet
services, adequate mechanisms should be in place in order to not
allow misconfigurations or instabilities in the PE control plane to
affect the general Internet operations or impact other VPN customers.
In addition to normal SP network management, prevention of Denial of
Service attacks must be in place in the PEs. Resource partitioning
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and rate limiting, as described in Section 6.2 are examples of such
mechanisms.
17.
Security considerations
There are no additional security considerations besides those already
addressed in this document in Section 6, and in Appendix A. VR-based
VPNs are expected to meet the security framework described in [SEC-
FRMWK].
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Appendix A: Responses to Security Evaluation Template
This Appendix presents an evaluation of how the Virtual Router model
measures up against the Security Evaluation Template developed in the
PPVPN Security Framework [SEC-FRMWK]. As stated in that document,
"An evaluation of a given PPVPN approach using this template should
appear in the applicability statement for each PPVPN approach."
NOTE: For ease of reference to the PPVPN Security Framework [SEC-
FRMWK], the assertion numbering scheme from the Security Template of
that document is retained in this Appendix.
1. The approach provides complete IP address space separation for
each L3 VPN.
The VR approach completely addresses the requirement by instantiating
a separate VR for each VPN that is configured on any specific PE.
Each VR maintains separate routing tables, so each L3 VPN has
complete IP address separation from other VPNs. Connections between
VRs in the same VPN are tunneled across the Service Provider's
network, providing separation between the IP address space of the SP
and each VPN.
2. The approach provides complete L2 address space separation for
each L2 VPN.
The requirement is not applicable to the VR approach because VR is a
L3 VPN.
3. The approach provides complete VLAN ID space separation for each
L2 VPN.
The requirement is not applicable to the VR approach because VR is a
L3 VPN.
4. The approach provides complete IP route separation for each L3
VPN.
The VR approach completely addresses the requirement by instantiating
a separate VR for each VPN that is configured on any specific PE.
Each VR maintains separate routing tables, so each L3 VPN has
complete IP route separation from other VPNs. Routes for each VPN
are distributed by tunneling across the Service Provider's network
between VRs of the same VPN, providing separation between the various
VPN routes, and between the routes of the SP and each VPN.
5. The approach provides complete L2 forwarding separation for each
L2 VPN.
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The requirement is not applicable to the VR approach because VR is a
L3 VPN.
6. The approach provides a means to prevent improper cross-connection
of sites in separate VPNs.
The VR approach completely addresses the requirement by using a VPN-
ID to positively identify the VPN membership of each VR. The VPN ID
is used when BGP is used for auto-discovery. It might also be used
when a management system is used for discovery, in which case the
VPN-ID is used by the appropriate MIB, for example [VR-MIB]. VRs of
different VPNs will not form routing adjacencies or exchange VPN
data. Alternatively, CE to CE authentication [L3-VERIF], could also
be used to protect against the threat of improper cross-connection.
7. The approach provides a means to detect improper cross-connection
of sites in separate VPNs.
The VR approach partially addresses the requirement by using a VPN-ID
to positively identify the VPN membership of each VR. VRs connected
to the wrong VPN (for instance, through an ATM or MPLS configuration
error) would not establish routing adjacencies or exchange VPN data.
However, there is not a requirement in [L3VPNVR] to specifically
detect improper cross-connection. The improper cross-connection
would simply result in a non-working VPN link, which would need to be
detected and corrected by normal troubleshooting techniques.
In the case of misconfiguration of a VR with the wrong VPN-ID and
other VPN attributes, the VR approach does not specify a method of
detecting the improper cross-connection. However, a method of
detecting PE misconfiguration is described in [L3-VERIF], based on
tokens exchanged between CEs and PEs. The VR approach is compatible
with either the BGP-based or UDP-based token exchange models that are
described in that document, to address the case of misconfiguration
of VPN membership on the PE.
8. The approach protects against the introduction of unauthorized
packets into each VPN.
a. In the CE-PE link
The VR approach completely addresses the requirement by supporting
the optional use of IPsec protection for the CE-PE link. The VR
approach allows a choice of CE-PE link configurations, thereby
allowing the PPVPN customer and the PPVPN Service Provider to select
the link type which will provide the desired degree of protection
against this threat. However, the VR approach by itself does not
provide specific packet-by-packet protection against this threat.
b. In a single- or multi- provider PPVPN backbone
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The VR approach partially addresses the requirement by specifying the
use of tunnels between VRs across the backbone. Thus it provides
protection against the introduction of unauthorized packets to the
full extent of the underlying tunnel technologies. However, the VR
model by itself does not completely address the requirement, because
it allows the use of tunneling technologies such as GRE or IP-in-IP
which may not provide protection against this threat.
With the optional use of IPsec, the VR approach completely supports
the requirement.
c. In the Internet used as PPVPN backbone
The VR approach partially addresses the requirement by specifying the
use of tunnels between VRs across the backbone, including across the
Internet. IPsec tunnels provide reliable protection against the
introduction of unauthorized packets in this case, and the VR model
completely addresses the requirement when IPsec is used. However,
the VR model by itself does not completely address the requirement,
because it allows the use of tunneling technologies such as GRE or
IP-in-IP which may not provide protection against this threat.
9. The approach provides confidentiality (secrecy) protection for
PPVPN user data.
a. In the CE-PE link
The VR approach completely addresses the requirement by supporting
the optional use of IPsec protection for the CE-PE link. However,
the VR approach by itself does not provide specific confidentiality
protection.
b. In a single- or multi- provider PPVPN backbone
The VR approach completely addresses the requirement by supporting
the optional use of IPsec protection for the backbone links. Other
tunnel types offer varying degrees of confidentiality.
c. In the Internet used as PPVPN backbone
The VR approach completely addresses the requirement by supporting
the optional use of IPsec protection for the backbone links,
including links over the Internet. Other tunnel types offer varying
degrees of confidentiality, and may not be reliably supported over an
arbitrary Internet path.
10. The approach provides sender authentication for PPVPN user data.
a. In the CE-PE link
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The VR approach completely addresses the requirement by supporting
the optional use of IPsec authentication on the CE-PE link. When the
IPsec Security Association is established, the use of authentication
can be specified. Authentication will be applied to each packet.
When IPsec is not used, the VR approach does not inherently provide
sender authentication on the CE-PE link.
b. In a single- or multi- provider PPVPN backbone
The VR approach partially addresses the requirement of sender
authentication across the backbone, through the use of the VPN-ID.
The VPN-ID acts to authenticate the VRs configured on the PEs to each
other as senders across the backbone, although it does not
authenticate the CE senders, since the VPN-ID is only used between
the VRs. This is a cryptographically weak authentication, but since
the PE configurations are managed by the Service Provider(s) and
should not be subject to manipulation by attackers, it is of
significant value against accidental misconfiguration.
In addition, IPsec authentication can be configured between the VRs,
and between the CEs and VRs, so that a chain of authentication can be
established between CE senders across the PPVPN. With the use of
IPsec, the VR approach completely addresses the requirement across
the backbone in either a single- or multi-provider case.
c. In the Internet used as PPVPN backbone
The VR approach partially addresses the requirement of sender
authentication across the Internet through the use of IPsec and the
VPN-ID, as discussed in the previous response (10.b).
11. The approach provides integrity protection for PPVPN user data.
a. In the CE-PE link
b. In a single- or multi- provider PPVPN backbone
c. In the Internet used as PPVPN backbone
In each situation (11.a-c), the VR approach completely addresses the
requirement of integrity protection, through the optional use of
IPsec. Integrity checking is typically performed along with the
authentication protection discussed in item 10 above. The VR
approach does not provide additional integrity checking in its basic
form.
12. The approach provides protection against replay attacks for PPVPN
user data.
a. In the CE-PE link
b. In a single- or multi- provider PPVPN backbone
c. In the Internet used as PPVPN backbone
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In each situation (12.a-c), the VR approach completely addresses the
requirement of protection against replay attacks, through the
optional use of IPsec with replay protection enabled. Replay attack
protection is accomplished by checking the sequence number in the
IPsec AH or ESP packet header, and is typically performed along with
the authentication protection discussed in item 10 above. The VR
approach does not provide additional replay attack protection in its
basic form.
13. The approach provides protection against unauthorized traffic
pattern analysis for PPVPN user data.
a. In the CE-PE link
The VR approach partially addresses the requirement of protection
against traffic pattern analysis through the optional use of IPsec on
the CE-PE link. Since IPsec-protected traffic on the CE-PE link only
reveals the amount of traffic between the CE and PE, and not the
ultimate destination of that traffic within the VPN, only limited
information on traffic patterns could be gained by analyzing any
particular CE-PE link. If an attacker is able to measure the traffic
on all CE-PE links of a VPN, then a fairly detailed traffic pattern
analysis could be performed. Where the CE-PE traffic is not
protected by IPsec in the VR approach, the traffic would be visible
to an attacker with access to the data stream, and the attacker could
derive a significant amount of traffic pattern analysis information.
However, note that it is unusual for an attacker to have access to
the data stream on any CE-PE link, unless the user taps the line or
compromises the CE or PE devices. In this case, traffic pattern
analysis may be a relatively minor concern compared to other concerns
of direct data interception.
b. In a single- or multi- provider PPVPN backbone
The VR approach partially addresses the requirement of protection
against traffic pattern analysis through the optional use of IPsec on
the backbone. This obscures the actual source and destination of
traffic, along with the traffic contents. Only the fact that data is
being transmitted between PEs or VRs can be detected through traffic
interception. If multiple CEs of a single VPN are connected to a
single VR, then an attacker analyzing the backbone traffic would not
be able to distinguish between traffic to or from the various CEs.
In addition, an attacker would need to obtain detailed information on
the internal configurations of the Service Provider's PE devices in
order to correlate captured backbone traffic with any particular VPN.
An optional extension to the VR approach completely addresses the
requirement of protection against traffic pattern analysis by using a
backbone virtual router in addition to using IPsec on the backbone.
Since the backbone VR links act to multiplex data of multiple VPNs,
and the IPsec obscures other information which could identify the VPN
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source or destination, an attacker would face an almost
insurmountable obstacle to reliable traffic pattern analysis based on
capturing backbone traffic.
c. In the Internet used as PPVPN backbone
Similar to (13.c.) above for a provider-managed backbone, the VR
approach provides either partial or complete protection, using IPsec
and the backbone VR, over the Internet. Traffic interception may be
a somewhat more likely problem on the Internet than on a SP backbone,
but the VR approach provides a means of addressing the threat in
either case.
14. The control protocol(s) used for each of the following functions
provide for message integrity and peer authentication:
a. VPN membership discovery
The VR approach can use several types of membership discovery,
including BGP-based auto-discovery and configuration. When BGP-based
auto-discovery is used, the VR approach completely addresses the
requirement of providing control message integrity and peer
authentication using the MD5 option. The protection of configuration
mechanisms for VR approaches is outside the scope of the VR
mechanism. VPN membership discovery using the VR approach provides
integrated peer authentication through the use of the VPN-ID, which
is common to all VRs within a single VPN.
b. Tunnel establishment
The VR approach does not specify a control protocol for tunnel
establishment, but when IPsec tunnels are used, the VR approach
completely addresses the requirement of providing message integrity
and peer authentication. In addition, the use of the VPN-ID provides
an integrated method of peer authentication among VRs within a single
VPN.
c. VPN topology and reachability advertisement
i. PE-PE
In the VR approach, VPN topology and reachability advertisement uses
standard routing protocols between the VRs, carried within tunnels.
These routing protocols can provide message integrity and peer
authentication when the protocol supports it, as in MD5 options. In
addition, when IPsec is used for the tunnels, it provides complete
support for security for any routing protocol running between the VRs
(between the PEs).
ii. PE-CE
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The VR approach uses standard routing protocols between the VR (PE)
and CE to provide VPN topology and reachability advertisement. The
security features of routing protocols, such as MD5 options, can be
applied, with or without IPsec. In addition, the VR-CE link can be
protected with IPsec to provide complete support for securing the
routing protocols. In the VR approach, some aspects of topology and
reachability in the PE-CE relationship will be configured rather than
exchanged dynamically. The security of configuration mechanisms is
beyond the scope of the VR specification.
d. VPN provisioning and management
The VPN provisioning and management requirement is addressed in a way
that is beyond the scope of the VR approach. Most parts of the VPN
provisioning and management will be performed via configuration
within the VR model, and thus there are no specific protocols defined
within the VR VPN scheme for these functions.
e. VPN monitoring and attack detection and reporting
VPN monitoring and attack detection and reporting requirements are
addressed in a way that is beyond the scope of the VR approach. Most
parts of these functions will be performed via a variety of network
management tools within the VR model, and thus there are no specific
protocols defined within the VR VPN scheme for these functions.
Since the VR approach is based on standard router functionality, the
management technologies which have been developed in the industry for
router security will be widely applicable for VR-based VPNs.
f. Other VPN-specific control protocols, if any.
Since the VR approach is based on standard router operations, there
are no VPN-specific control protocols defined for the VR model.
The following questions solicit free-form answers.
15. Describe the protection, if any, the approach provides against
PPVPN-specific DOS attacks (i.e. Inter-trusted-zone DOS attacks):
a. Protection of the service provider infrastructure against Data
Plane or Control Plane DOS attacks originated in a private
(PPVPN user) network and aimed at PPVPN mechanisms.
In the VR approach, the service provider-managed VRs typically appear
to the PPVPN users to be a single router connecting all of the VPN
sites.
The VRs should be configured to allow only three types of traffic
from the user VPN sites:
- routing protocols
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- data packets destined for another site within the same VPN as the
originating site
- data packets with non-VPN destinations, if permitted by the Service
Provider.
This configuration serves to prevent most types of control plane
attacks, since any type of direct connection from a VPN site to the
VR's management functions using protocols such as SNMP, ftp, tftp,
rlogin, rsh, etc., should be disallowed. The VR allows the same
types of configurations as are common on physical routers to enforce
this kind of configuration.
A control plane attack might still be able to attempt to use the
first type of traffic, while a data plane attack might use the latter
two. These cases are discussed below.
A control plane attack might consist of the CE device sending
improper routing information to the VR. This could consist of
unauthorized or malformed routes, rapid announcement and/or
withdrawal of proper routes, or some combination of these. Since the
VR has the same mechanisms as a physical router, the VR can use well-
known routing security features to provide protection against this
kind of attack, including route filters and route flap damping, or it
could be configured with the allowable routes for the specific VPN
site, and not accept routing updates from the site. The VPN
mechanisms in the VR do not make it more susceptible to control plane
attacks such as those based on routing protocols.
A data plane attack on the VR would consist of a CE transmitting a
large amount of traffic to the VR. Since the VR has all of the
mechanisms of a physical router, it can be configured to handle the
traffic using the same techniques as any Service Provider router.
The VPN mechanisms in the VR do not make it more susceptible to DoS
attacks based on traffic flooding.
The VR architecture used in the PE devices provides for isolation of
the operation of the VRs configured on it. Thus measures taken to
defend against excessive traffic from one VPN site should not be able
to affect the operation of other VRs in that PE, or elsewhere in the
network.
b. Protection of the service provider infrastructure against Data
Plane or Control Plane DOS attacks originated in the Internet
and aimed at PPVPN mechanisms.
Both data plane and control plane DoS attacks which originate in the
Internet can be prevented by overall design of Service Provider
network, for instance by the use of filtering to block any packets
destined to internal SP devices such as VRs. Internal SP devices may
also be configured with private or non-routable addresses to help
prevent access from the Internet. The VPN mechanisms in the VR do
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not make it more susceptible to DoS attacks from the Internet. Since
VRs have the capabilities of physical routers, they can use the
techniques available to Service Provider routers to provide various
protective measures.
c. Protection of PPVPN users against Data Plane or Control Plane
DOS attacks originated from the Internet or from other PPVPN
users and aimed at PPVPN mechanisms.
The VR model completely supports protection of PPVPN users from
either data plane or control plane DoS attacks directly from the
Internet, unless Internet connectivity is specifically configured for
an individual VPN. Since inter-VR links are tunneled, there is no
opportunity for non-VPN traffic, such as Internet traffic, to be
introduced into the VPN.
If an individual VPN includes PPVPN-mediated Internet connectivity as
a configured option, then the VR(s) providing the Internet access
should be configured with appropriate firewall policies to protect
against Dos (and other) attacks.
The mechanisms discussed above in (15.a) and (15.b) for protection of
the Service Provider infrastructure from VPN-based and Internet-based
DoS attacks also serve to protect other VPNs from attacks from these
sources. The VPN mechanisms used in the VR approach do not make it
more susceptible to propagating DoS attacks among VPNs, since the
basic VR architecture defines effective separation of all PE
resources among the VRs.
Attacks from one VPN site toward another VPN site in the same VPN are
outside the scope of the VR approach, although the VR model makes it
possible to configure firewall protections including internal attack
protection at each VR if this service is desired.
16. Describe the protection, if any, the approach provides against
unstable or malicious operation of a PPVPN user network:
a. Protection against high levels of, or malicious design of,
routing traffic from PPVPN user networks to the service
provider network.
This is discussed in the response to (15.a) above. Since the VR has
the same mechanisms as a physical router, the VR can use well-known
routing security features to provide protection against this kind of
attack, including route filters and route flap damping, or it could
be configured with the allowable routes for the specific VPN site,
and not accept routing updates from the site.
b. Protection against high levels of, or malicious design of,
network management traffic from PPVPN user networks to the
service provider network.
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Since the VR approach imbues each VR with the capabilities of
physical routers, including filtering and firewall functionality, the
VRs should be configured by the Service Provider with appropriate
filters to block network management traffic directed at any Service
Provider system. Network management traffic from PPVPN users does
not have any privileged access to the Service Provider network
outside of the VR-VR tunnels, so they will be blocked by the same
mechanisms which prevent this kind of attack from anywhere in the
Internet.
c. Protection against worms and probes originated in the PPVPN
user networks, sent towards the service provider network.
Similar to the filtering capabilities which the VR and use to block
network management traffic, the VR can be configured to block any
kind of traffic directed at any component of the service provider
network. Since the traffic originating in PPVPN user networks is
contained in tunnels after it is received at the VR serving any
particular VPN site, the VR approach makes it fairly simple to
prevent traffic originating in PPVPN user networks from being able to
reach any Service Provider device. Worms or probes from PPVPN users
do not have any privileged access to the Service Provider network
outside of the VR-VR tunnels, so they will be blocked by the same
mechanisms which prevent this kind of attack from anywhere in the
Internet.
17. Is the approach subject to any approach-specific vulnerabilities
not specifically addressed by this template? If so describe the
defense or mitigation, if any, the approach provides for each.
The authors are not aware of any VR-specific vulnerabilities not
addressed by this template.
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References
Informative References
[PPVPNVR] Ould-Brahim, H., et al., "Network based IP VPN
Architecture using Virtual Routers", work in progress.
[FRAMEWORK] R. Callon, et al., "A Framework for Layer 3 Provider
Provisioned Virtual Private Networks," RFC 4410.
[REQTS] McDysan, D., et al., "Service requirements for Layer 3
Provider Provisioned Virtual Private Networks", RFC 4031.
[SEC-FRMWK] Fang, L., et al., "Security Framework for Provider
Provisioned Virtual Private Networks", RFC 4111.
[RFC2685] Fox B., et al, "Virtual Private Networks Identifier", RFC
2685, September 1999.
[RADIUS-DIS] Heinanen J., "Using Radius for PE-Based VPN Discovery",
work in progress.
[VPN-BGP] Ould-Brahim, H., et al, "Using BGP as an Auto-Discovery
Mechanism for Network-based VPNs", work in progress.
[RFC1918] Rekhter, Y. et al., "Address Allocation for Private
Internets," RFC 1918, February 1996.
[RFC2547bis] Rosen E., et al, "BGP/MPLS VPNs", RFC 4364.
[RFC2764] Gleeson, B., et al., "A Framework for IP Based Virtual
Private Networks", RFC 2764, February 2000.
[L3-VERIF] Bonica, R. et al., "CE-to-CE Member Verification for
Layer 3 VPNs",work in progress.
[VR-MIB] Seltzer, E et al., ” Virtual Router Management Information
Base Using SMIv2”, work in progress
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Acknowledgments
The authors of this draft would like to acknowledge the suggestions
and comments received from the entire Layer 3 Applicability Statement
Design Team formed in the PPVPN working group. Besides the authors,
the members of the design team include Marco Carugi, Eric Rosen,
Jeremy De Clercq, Luyuan Fang, Dave McDysan, Cliff Wang, Olivier
Paridaens, Tom Nadeau, Yakov Rekhter and Rick Wilder. Thanks are also
due to the authors of [PPVPNVR], especially Hamid Ould-Brahim. Many
thanks are due to the constructive comments made by Ross Callon and
Mark Duffy.
Author's Addresses
Ananth Nagarajan
Juniper Networks
E-mail: ananth@juniper.net
Muneyoshi Suzuki
NTT Information Sharing Platform Labs.
3-9-11, Midori-cho,
Musashino-shi, Tokyo 180-8585, Japan
Email: suzuki.muneyoshi@lab.ntt.co.jp
Junichi Sumimoto
NTT Communications Corporation
3-20-2 Nishi-Shinjuku,
Shinjuku-ku, Tokyo 163-1421, Japan
E-mail: j.sumimoto@ntt.com
Paul Knight
Nortel Networks
600 Technology Park Drive
Billerica, MA 01821
+1-978-288-6414
E-mail: paul.knight@nortel.com
Benson Schliesser
SAVVIS Communications
1 Savvis Parkway
St. Louis, MO 63017 USA
+1-877-203-1097
Email: bensons@savvis.net
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Full Copyright Statement
Copyright (C) The Internet Society (2006). All Rights Reserved.
This document is subject to the rights, licenses and restrictions
contained in BCP 78, and except as set forth therein, the authors
retain all their rights.
This document and the information contained herein are provided on an
"AS IS" basis and THE CONTRIBUTOR, THE ORGANIZATION HE/SHE REPRESENTS
OR IS SPONSORED BY (IF ANY), THE INTERNET SOCIETY AND THE INTERNET
ENGINEERING TASK FORCE DISCLAIM ALL WARRANTIES, EXPRESS OR IMPLIED,
INCLUDING BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF THE
INFORMATION HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED
WARRANTIES OF MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE.
Acknowledgement:
Funding for the RFC Editor function is currently provided by the
Internet Society.
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