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IETF RFC 4031
Service Requirements for Layer 3 Provider Provisioned Virtual Private Networks (PPVPNs)
Last modified on Tuesday, April 12th, 2005
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Network Working Group M. Carugi, Ed.
Request for Comments: 4031 Nortel Networks
Category: Informational D. McDysan, Ed.
MCI
April 2005
Service Requirements for Layer 3
Provider Provisioned Virtual Private Networks (PPVPNs)
 Status of This Memo
This memo provides information for the Internet community. It does
not specify an Internet standard of any kind. Distribution of this
memo is unlimited.
Copyright Notice
Copyright © The Internet Society (2005).
Abstract
This document provides requirements for Layer 3 Virtual Private
Networks (L3VPNs). It identifies requirements applicable to a number
of individual approaches that a Service Provider may use to provision
a Virtual Private Network (VPN) service. This document expresses a
service provider perspective, based upon past experience with IP-
based service offerings and the ever-evolving needs of the customers
of such services. Toward this end, it first defines terminology and
states general requirements. Detailed requirements are expressed
from a customer perspective as well as that of a service provider.
Table of Contents
1. Introduction. . . . . . . . . . . . . . . . . . . . . . . . . 3
1.1. Scope of This Document. . . . . . . . . . . . . . . . . 4
1.2. Outline . . . . . . . . . . . . . . . . . . . . . . . . 5
2. Contributing Authors. . . . . . . . . . . . . . . . . . . . . 5
3. Definitions . . . . . . . . . . . . . . . . . . . . . . . . . 5
3.1. Virtual Private Network . . . . . . . . . . . . . . . . 6
3.2. Users, Sites, Customers, and Agents . . . . . . . . . . 6
3.3. Intranets, Extranets, and VPNs. . . . . . . . . . . . . 6
3.4. Networks of Customer and Provider Devices . . . . . . . 7
3.5. Access Networks, Tunnels, and Hierarchical Tunnels. . . 7
3.6. Use of Tunnels and Roles of CE and PE in L3VPNs . . . . 8
3.6.1. PE-Based L3VPNs and Virtual Forwarding
Instances . . . . . . . . . . . . . . . . . . . 8
3.6.2. CE-Based L3VPN Tunnel Endpoints and Functions . 10
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RFC 4031 Service Requirements for L3 PPVPNs April 2005
3.7. Customer and Provider Network Management. . . . . . . . 10
4. Service Requirements Common to Customers and Service
Providers . . . . . . . . . . . . . . . . . . . . . . . . . . 11
4.1. Isolated Exchange of Data and Routing Information . . . 11
4.2. Addressing. . . . . . . . . . . . . . . . . . . . . . . 12
4.3. Quality of Service. . . . . . . . . . . . . . . . . . . 12
4.3.1. QoS Standards . . . . . . . . . . . . . . . . . 12
4.3.2. Service Models. . . . . . . . . . . . . . . . . 13
4.4. Service Level Specification and Agreements. . . . . . . 14
4.5. Management. . . . . . . . . . . . . . . . . . . . . . . 14
4.6. Interworking. . . . . . . . . . . . . . . . . . . . . . 15
5. Customer Requirements . . . . . . . . . . . . . . . . . . . . 15
5.1. VPN Membership (Intranet/Extranet). . . . . . . . . . . 15
5.2. Service Provider Independence . . . . . . . . . . . . . 16
5.3. Addressing. . . . . . . . . . . . . . . . . . . . . . . 16
5.4. Routing Protocol Support. . . . . . . . . . . . . . . . 16
5.5. Quality of Service and Traffic Parameters . . . . . . . 16
5.5.1. Application Level QoS Objectives. . . . . . . . 17
5.5.2. DSCP Transparency . . . . . . . . . . . . . . . 17
5.6. Service Level Specification/Agreement . . . . . . . . . 18
5.7. Customer Management of a VPN. . . . . . . . . . . . . . 18
5.8. Isolation . . . . . . . . . . . . . . . . . . . . . . . 18
5.9. Security. . . . . . . . . . . . . . . . . . . . . . . . 19
5.10. Migration Impact. . . . . . . . . . . . . . . . . . . . 19
5.11. Network Access. . . . . . . . . . . . . . . . . . . . . 19
5.11.1. Physical/Link Layer Technology. . . . . . . . . 20
5.11.2. Temporary Access. . . . . . . . . . . . . . . . 20
5.11.3. Sharing of the Access Network . . . . . . . . . 20
5.11.4. Access Connectivity . . . . . . . . . . . . . . 20
5.12. Service Access. . . . . . . . . . . . . . . . . . . . . 23
5.12.1. Internet Access . . . . . . . . . . . . . . . . 23
5.12.2. Hosting, Application Service Provider . . . . . 24
5.12.3. Other Services. . . . . . . . . . . . . . . . . 24
5.13. Hybrid VPN Service Scenarios. . . . . . . . . . . . . . 24
6. Service Provider Network Requirements . . . . . . . . . . . . 24
6.1. Scalability . . . . . . . . . . . . . . . . . . . . . . 24
6.2. Addressing. . . . . . . . . . . . . . . . . . . . . . . 25
6.3. Identifiers . . . . . . . . . . . . . . . . . . . . . . 25
6.4. Discovering VPN Related Information . . . . . . . . . . 26
6.5. SLA and SLS Support . . . . . . . . . . . . . . . . . . 26
6.6. Quality of Service (QoS) and Traffic Engineering. . . . 27
6.7. Routing . . . . . . . . . . . . . . . . . . . . . . . . 27
6.8. Isolation of Traffic and Routing. . . . . . . . . . . . 28
6.9. Security. . . . . . . . . . . . . . . . . . . . . . . . 28
6.9.1. Support for Securing Customer Flows . . . . . . 28
6.9.2. Authentication Services . . . . . . . . . . . . 29
6.9.3. Resource Protection . . . . . . . . . . . . . . 30
6.10. Inter-AS (SP)VPNs . . . . . . . . . . . . . . . . . . . 30
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6.10.1. Routing Protocols . . . . . . . . . . . . . . . 31
6.10.2. Management. . . . . . . . . . . . . . . . . . . 31
6.10.3. Bandwidth and QoS Brokering . . . . . . . . . . 31
6.10.4. Security Considerations . . . . . . . . . . . . 32
6.11. L3VPN Wholesale . . . . . . . . . . . . . . . . . . . . 32
6.12. Tunneling Requirements. . . . . . . . . . . . . . . . . 33
6.13. Support for Access and Backbone Technologies. . . . . . 33
6.13.1. Dedicated Access Networks . . . . . . . . . . . 34
6.13.2. On-Demand Access Networks . . . . . . . . . . . 34
6.13.3. Backbone Networks . . . . . . . . . . . . . . . 35
6.14. Protection, Restoration . . . . . . . . . . . . . . . . 35
6.15. Interoperability. . . . . . . . . . . . . . . . . . . . 35
6.16. Migration Support . . . . . . . . . . . . . . . . . . . 36
7. Service Provider Management Requirements. . . . . . . . . . . 36
7.1. Fault Management. . . . . . . . . . . . . . . . . . . . 37
7.2. Configuration Management. . . . . . . . . . . . . . . . 37
7.2.1. Configuration Management for PE-Based VPNs. . . 38
7.2.2. Configuration Management for CE-Based VPNs. . . 39
7.2.3. Provisioning Routing. . . . . . . . . . . . . . 39
7.2.4. Provisioning Network Access . . . . . . . . . . 39
7.2.5. Provisioning Security Services. . . . . . . . . 40
7.2.6. Provisioning VPN Resource Parameters. . . . . . 40
7.2.7. Provisioning Value-Added Service Access . . . . 40
7.2.8. Provisioning Hybrid VPN Services. . . . . . . . 41
7.3. Accounting. . . . . . . . . . . . . . . . . . . . . . . 41
7.4. Performance Management. . . . . . . . . . . . . . . . . 42
7.4.1. Performance Monitoring. . . . . . . . . . . . . 42
7.4.2. SLA and QoS Management Features . . . . . . . . 42
7.5. Security Management . . . . . . . . . . . . . . . . . . 43
7.5.1. Resource Access Control . . . . . . . . . . . . 43
7.5.2. Authentication. . . . . . . . . . . . . . . . . 43
7.6. Network Management Techniques . . . . . . . . . . . . . 44
8. Security Considerations . . . . . . . . . . . . . . . . . . . 44
9. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 45
10. References. . . . . . . . . . . . . . . . . . . . . . . . . . 45
10.1. Normative References. . . . . . . . . . . . . . . . . . 45
10.2. Informative References. . . . . . . . . . . . . . . . . 46
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 49
Full Copyright Statement . . . . . . . . . . . . . . . . . . . . . 50
1. Introduction
This section describes the scope and outline of the document.
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 ([RFC 2119]).
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1.1. Scope of This Document
This document provides requirements specific to Layer 3 Virtual
Private Networks (L3VPN). (Requirements that are generic to L2 and L3
VPNs are contained in [RFC 3809].)
This document identifies requirements that may apply to one or more
individual approaches that a Service Provider may use to provision a
Layer 3 (e.g., IP) VPN service. It makes use of the terminology and
common components for Layer 3 VPNs as defined in [L3VPN-FR] and of
the generic VPN terminology defined in
[PPVPN-TERM].
The specification of technical means to provide L3VPN services is
outside the scope of this document. Other documents are intended to
cover this aspect, such as the L3 VPN framework document [L3VPN-FR]
and several sets of documents, one for each technical approach for
providing L3VPN services.
Technical approaches targeted by this document include the network-
based (PE-based) L3VPN category (aggregated routing VPNs [2547bis]
and virtual routers [PPVPN-VR]) and the CE-based L3VPNs category
[CE-PPVPN][IPSEC-PPVPN]. The document distinguishes L3VPN categories
as to where the endpoints of tunnels exist, as detailed in the L3VPN
framework document [L3VPN-FR]. Terminology describing whether
equipment faces a customer or the service provider network is used to
define the various types of L3VPN solutions.
This document is intended as a "checklist" of requirements, providing
a consistent way to evaluate and document how well each approach
satisfies specific requirements. The applicability statement
documents for each approach should present the results of this
evaluation. This document is not intended to compare one approach to
another.
This document provides requirements from several points of view. It
begins with some considerations from a point of view common to
customers and service providers not covered in the generic provider
provisioned VPN requirement document [RFC 3809], continues with a
customer perspective, and concludes with specific needs of a Service
Provider (SP).
The following L3VPN deployment scenarios are considered within this
document:
1. Internet-wide: VPN sites attached to arbitrary points in the
Internet.
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2. Single SP/single AS: VPN sites attached to the network of a
single provider within the scope of a single AS.
3. Single SP/multiple ASes: VPN sites attached to the network of a
single provider consisting of multiple ASes.
4. Cooperating SPs: VPN sites attached to networks of different
providers that cooperate with each other to provide the VPN
service.
The above deployment scenarios have many requirements in common.
These include SP requirements for security, privacy, manageability,
interoperability, and scalability, including service provider
projections for number, complexity, and rate of change of customer
VPNs over the next several years. When requirements apply to a
specific deployment scenario, the above terminology is used to state
the context of those particular requirements.
1.2. Outline
The outline of the rest of the document is as follows: Section 2
lists the contributing authors. Section 3 provides definitions of
terms and concepts. Section 4 provides requirements common to both
customers and service providers that are not covered in the generic
provider provisioned VPN requirement document [RFC 3809]. Section 5
states requirements from a customer perspective. Section 6 states
network requirements from a service provider perspective. Section 7
states service provider management requirements. Section 8 describes
security considerations. Section 9 lists acknowledgments. Section
10 provides a list of references cited herein. Section 11 lists the
authors' addresses.
2. Contributing Authors
This document is the combined effort of the two co-editors and the
following contributing authors:
Luyuan Fang
Ananth Nagarajan
Junichi Sumimoto
Rick Wilder
3. Definitions
This section provides the definition of terms and concepts used
throughout the document. Terminology used herein is taken from
[PPVPN-TERM] and [L3VPN-FR].
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3.1. Virtual Private Network
"L3 Virtual Private Network" (L3VPN) refers to the L3 communication
between a set of sites making use of a shared network infrastructure.
"Provider Provisioned VPN" (PPVPN) refers to VPNs for which the
service provider participates in management and provisioning of the
VPN.
3.2. Users, Sites, Customers, and Agents
User: A user is an entity (e.g., a human being using a host, a
server, or a system) authorized to use a VPN service.
Site: A site is a set of users that have mutual L3 (i.e., IP)
reachability without use of a specific service provider network. A
site may consist of a set of users that are in geographic proximity.
Note that a topological definition of a site (e.g., all users at a
specific geographic location) may not always conform to this
definition. For example, two geographic locations connected via
another provider's network would also constitute a single site as
communication between the two locations does not involve the use of
the service provider offering the L3 VPN service.
Customer: A single organization, corporation, or enterprise that
administratively controls a set of sites.
Agent: A set of users designated by a customer who has the
authorization to manage a customer's VPN service offering.
3.3. Intranets, Extranets, and VPNs
Intranet: An intranet restricts communication to a set of sites that
belong to one customer. An example is branch offices at different
sites that require communication with a headquarters site.
Extranet: An extranet allows the specification of communication
between a set of sites that belong to different customers. In other
words, two or more organizations have access to a specified set of
each other's sites. Examples of extranets include multiple companies
cooperating in joint software development, a service provider having
access to information from the vendors' corporate sites, different
companies, or universities participating in a consortium. An
extranet often has further restrictions on reachability, for example,
at a host and individual transport level.
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RFC 4031 Service Requirements for L3 PPVPNs April 2005
Note that an intranet or extranet can exist across a single service
provider network with one or more ASes, or across multiple service
provider networks.
L3 Virtual Private Network (L3VPN): An alternative definition of VPN
refers to a specific set of sites that have been configured to allow
communication as either an intranet or an extranet. Note that a site
is a member of at least one VPN and may be a member of many VPNs.
3.4. Networks of Customer and Provider Devices
L3VPNs are composed of the following types of devices.
Customer Edge (CE) device: A CE device faces the users at a customer
site. The CE has an access connection to a PE device. It may be a
router or a switch that allows users at a customer site to
communicate over the access network with other sites in the VPN. In
a CE-based L3VPN, as intended in this document (provider-provisioned
CE-based VPN), the service provider manages (at least partially) the
CE device.
Provider Edge (PE) device: A PE device faces the provider network on
one side and attaches via an access connection over one or more
access networks to one or more CE devices. It participates in the
Packet Switched Network (PSN) in performing routing and forwarding
functions.
Note that the definitions of Customer Edge and Provider Edge do not
necessarily describe the physical deployment of equipment on customer
premises or a provider point of presence.
Provider (P) device: A device within a provider network that
interconnects PE (or other P) devices but does not have any direct
attachment to CE devices. The P router does not keep VPN state and
is VPN unaware [PPVPN-TERM].
Packet Switched Network (PSN): A (IP or MPLS [RFC 3031]) network
through which the tunnels supporting the VPN services are set up
[PPVPN-TERM].
Service Provider (SP) network: An SP network is a set of
interconnected PE and P devices administered by a single service
provider in one or more ASes.
3.5. Access Networks, Tunnels, and Hierarchical Tunnels
VPNs are built between CEs by using access networks, tunnels, and
hierarchical tunnels across a PSN.
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Access connection: An access connection provides connectivity between
a CE and a PE. This includes dedicated physical circuits, virtual
circuits (such as Frame Relay), ATM, Ethernet (V)LAN, or IP tunnels
(e.g., IPsec, L2TP [RFC 2661]).
Access network: An access network provides access connections between
CE and PE devices. It may be a TDM network, an L2 network (e.g., FR,
ATM, and Ethernet), or an IP network over which access is tunneled
(e.g., by using L2TP).
Tunnel: A tunnel between two entities is formed by encapsulating
packets within another encapsulating header for the purposes of
transmission between those two entities in support of a VPN
application. Examples of protocols commonly used for tunneling are
GRE, IPsec, IP-in-IP tunnels, and MPLS.
Hierarchical Tunnel: Encapsulating one tunnel within another forms a
hierarchical tunnel. The innermost tunnel protocol header defines a
logical association between two entities (e.g., between CEs or PEs)
[VPNTUNNEL]. Note that the tunneling protocols need not be the same
at different levels in a hierarchical tunnel.
3.6. Use of Tunnels and Roles of CE and PE in L3 VPNs
This section summarizes the points where tunnels terminate and the
functions implemented in the CE and PE devices that differentiate the
two major categories of L3VPNs for which requirements are stated,
namely PE-based and CE-based L3VPNs. See the L3VPN framework
document for more detail [L3VPN-FR].
3.6.1. PE-Based L3VPNs and Virtual Forwarding Instances
In a PE-based L3VPN service, a customer site receives IP layer (i.e.,
layer 3) service from the SP. The PE is attached via an access
connection to one or more CEs. The PE forwards user data packets
based on information in the IP layer header, such as an IPv4 or IPv6
destination address. The CE sees the PE as a layer 3 device such as
an IPv4 or IPv6 router.
Virtual Forwarding Instance (VFI): In a PE-based L3VPN service, the
PE contains a VFI for each L3 VPN that it serves. The VFI terminates
tunnels for interconnection with other VFIs and also terminates
access connections for accommodating CEs. VFI contains information
regarding how to forward data received over the CE-PE access
connection to VFIs in other PEs supporting the same L3VPN. The VFI
includes the router information base and the forwarding information
base for an L3VPN [L3VPN-FR]. A VFI enables router functions
dedicated to serving a particular VPN, such as separation of
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RFC 4031 Service Requirements for L3 PPVPNs April 2005
forwarding and routing and support for overlapping address spaces.
Routing protocols in the PEs and the CEs interact to populate the
VFI.
The following narrative and figures provide further explanation of
the way PE devices use tunnels and hierarchical tunnels. Figure 1.1
illustrates the case where a PE uses a separate tunnel for each VPN.
As shown in the figure, the tunnels provide communication between the
VFIs in each of the PE devices.
+----------+ +----------+
+-----+ |PE device | |PE device | +-----+
| CE | | | | | | CE |
| dev | Access | +------+ | | +------+ | Access | dev |
| of | conn. | |VFI of| | Tunnel | |VFI of| | conn. | of |
|VPN A|----------|VPN A |==================|VPN A |----------|VPN A|
+-----+ | +------+ | | +------+ | +-----+
| | | |
+-----+ Access | +------+ | | +------+ | Access +-----+
|CE | conn. | |VFI of| | Tunnel | |VFI of| | conn. | CE |
| dev |----------|VPN B |==================|VPN B |----------| dev |
| of | | +------+ | | +------+ | | of |
|VPN B| | | | | |VPN B|
+-----+ +----------+ +----------+ +-----+
Figure 1.1. PE Usage of Separate Tunnels to Support VPNs
Figure 1.2 illustrates the case where a single hierarchical tunnel is
used between PE devices to support communication for VPNs. The
innermost encapsulating protocol header provides the means for the PE
to determine the VPN for which the packet is directed.
+----------+ +----------+
+-----+ |PE device | |PE device | +-----+
| CE | | | | | | CE |
| dev | Access | +------+ | | +------+ | Access | dev |
| of | conn. | |VFI of| | | |VFI of| | conn. | of |
|VPN A|----------|VPN A | | Hierarchical | |VPN A |----------|VPN A|
+-----+ | +------+\| Tunnel |/+------+ | +-----+
| >==============< |
+-----+ Access | +------+/| |\+------+ | Access +-----+
| CE | conn. | |VFI of| | | |VFI of| | conn. | CE |
| dev |----------|VPN B | | | |VPN B |----------| dev |
| of | | +------+ | | +------+ | | of |
|VPN B| | | | | |VPN B|
+-----+ +----------+ +----------+ +-----+
Figure 1.2. PE Usage of Shared Hierarchical Tunnels to Support VPNs
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3.6.2. CE-Based L3VPN Tunnel Endpoints and Functions
Figure 1.3 illustrates the CE-based L3VPN reference model. In this
configuration, typically a single level of tunnel (e.g., IPsec)
terminates at pairs of CEs. Usually, a CE serves a single customer
site, and therefore the forwarding and routing is physically separate
from all other customers. Furthermore, the PE is not aware of the
membership of specific CE devices to a particular VPN. Hence, the
VPN functions are implemented with provisioned configurations on the
CE devices, and the shared PE and P network is used to only provide
the routing and forwarding that supports the tunnel endpoints on
between CE devices. The tunnel topology connecting the CE devices
may be a full or partial mesh, depending on VPN customer requirements
and traffic patterns.
+---------+ +--------------------------------+ +---------+
| | | | | |
| | | +------+ +------+ : +------+
+------+ : | | | | | | : | CE |
| CE | : | | | P | | PE | : |device|
|device| : +------+ Tunnel |router| |device| : | of |
| of |=:================================================:=|VPN A|
|VPN A| : | | +------+ +------+ : +------+
+------+ : | PE | | | : |
+------+ : |device| | | : |
| CE | : | | Tunnel +------+ : +------+
|device|=:================================================:=| CE |
| of | : +------+ | PE | : |device|
|VPN B| : | | |device| : | of |
+------+ : | | +----------+ +----------+ | | : |VPN B|
| : | | | Customer | | Network | +------+ : +------+
|Customer | | |management| |management| | | : |
|interface| | | function | | function | | |Customer |
| | | +----------+ +----------+ | |interface|
| | | | | |
+---------+ +--------------------------------+ +---------+
| Access | |<-------- SP network(s) ------->| | Access |
| network | | | | network |
Figure 1.3. CE-Based L3VPN
3.7. Customer and Provider Network Management
Customer Network Management Function: A customer network management
function provides the means for a customer agent to query or
configure customer-specific information, or to receive alarms
regarding his or her VPN. Customer-specific information includes
data related to contact, billing, site, access network, IP address,
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and routing protocol parameters. It may use a combination of
proprietary network management system, SNMP manager, or directory
service (e.g., LDAP [RFC 3377] [RFC 2251]).
Provider Network Management Function: A provider network management
function provides many of the same capabilities as a customer network
management system across all customers. This would not include
customer confidential information, such as keying material. The
intent of giving the provider a view comparable to that of the
customer is to aid in troubleshooting and problem resolution. Such a
system also provides the means to query, configure, or receive alarms
regarding any infrastructure supporting the L3VPN service. It may
use a combination of proprietary network management system, SNMP
manager, or directory service (e.g., LDAP [RFC 3377] [RFC 2251]).
4. Service Requirements Common to Customers and Service Providers
Many of the requirements that apply to both the customer and the
provider and are of an otherwise general nature, or that apply to
both L2 and L3VPNs, are described in [RFC 3809]. This section
contains requirements that are not covered in [RFC 3809] and that are
specific to L3VPNs.
4.1. Isolated Exchange of Data and Routing Information
A mechanism must be provided for isolating the distribution of
reachability information to only those sites associated with a VPN.
L3VPN solutions shall define means that prevent routers in a VPN from
interacting with unauthorized entities and that avoid introducing
undesired routing information that could corrupt the VPN routing
information base [VPN-CRIT].
A means must be provided to constrain or isolate the distribution of
addressed data to only those VPN sites determined by either routing
data and/or configuration.
A single site shall be capable of being in multiple VPNs. The VPN
solution must ensure that traffic is exchanged only with sites in the
same VPN.
The internal structure of a VPN should not be advertised or
discoverable from outside that VPN.
Note that isolation of forwarded data or exchange of reachability
information to only those sites that are part of a VPN may be viewed
as a form of security - for example, [Y.1311.1], [MPLSSEC].
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4.2. Addressing
IP addresses must be unique within the set of sites reachable from
the VPNs of which a particular site is a member.
A VPN solution must support IPv4 and IPv6 as both the encapsulating
and encapsulated protocol.
If a customer has private or non-unique IP addresses, then a VPN
service SHOULD be capable of translating such customer private or
non-unique IP addresses for communicating with IP systems having
public addresses.
4.3. Quality of Service
To the extent possible, L3VPN QoS should be independent of the access
network technology.
4.3.1. QoS Standards
A non-goal of the L3VPN WG effort (as chartered) is the development
of new protocols or extension of existing ones. An L3VPN shall be
able to support QoS in one or more of the following already defined
modes:
- Best Effort (mandatory support for all L3VPN types)
- Aggregate CE Interface Level QoS ("hose" level QoS)
- Site-to-site ("pipe" level QoS)
- Intserv (i.e., RSVP) signaled
- Diffserv marked
- Across packet-switched access networks
Note that all cases involving QoS may require that the CE and/or PE
perform shaping and/or policing.
L3VPN CEs should be capable of supporting integrated services
(Intserv) for certain customers in support of session applications,
such as switched voice or video. Intserv-capable CE devices shall
support the following Internet standards:
- Resource reSerVation Protocol (RSVP) [RFC 2205]
- Guaranteed Quality of Service providing a strict delay bound
[RFC 2212]
- Controlled Load Service providing performance equivalent to that
of an unloaded network [RFC 2211]
Carugi & McDysan Standards Track PAGE 12
RFC 4031 Service Requirements for L3 PPVPNs April 2005
L3VPN CE and PE should be capable of supporting differentiated
service (Diffserv). Diffserv-capable L3VPN CE and PE shall support
the following per hop behavior (PHB) [RFC 2475] types:
- Expedited Forwarding (EF) - The departure rate of an aggregate
class of traffic from a device that must equal or exceed a
configured rate [RFC 3246].
- Assured Forwarding (AF) - A means for a provider Diffserv (DS)
domain to offer different levels of forwarding assurances for IP
packets received from a customer DS domain. Four AF classes are
defined, where each AF class implies allocation in each DS node of
a certain amount of forwarding resources (e.g., buffer space and
bandwidth) [RFC 2597].
A CE or PE device supporting an L3VPN service may classify a packet
for a particular Intserv or Diffserv service based on one or more of
the following IP header fields: protocol ID, source port number,
destination port number, destination address, or source address.
For a specifiable set of Internet traffic, L3VPN devices should
support Random Early Detection (RED) to provide graceful degradation
in the event of network congestion.
4.3.2. Service Models
A service provider must be able to offer QoS service to a customer
for at least the following generic service types: managed-access VPN
service or edge-to-edge QoS VPN service [RFC 3809]. More detail
specific to L3VPNs is provided below.
A managed-access L3VPN service provides QoS on the access connection
between the CE and the PE. For example, diffserv would be enabled
only on the CE router and the customer-facing ports of the PE router.
Note that this service would not require Diffserv implementation in
the SP backbone. The SP may use policing for inbound traffic at the
PE. The CE may perform shaping for outbound traffic. Another
example of a managed-access L3VPN service is when the SP performs the
packet classification and diffserv marking. An SP may provide
several packet classification profiles that customers may select or
may offer custom profiles based on customer specific requirements.
In general, more complex QoS policies should be left to the customer
for implementation.
An edge-to-edge QoS VPN service provides QoS from edge device to edge
device. The edge device may be either PE or CE, depending on the
service demarcation point between the provider and the customer.
Such a service may be provided across one or more provider backbones.
Carugi & McDysan Standards Track PAGE 13
RFC 4031 Service Requirements for L3 PPVPNs April 2005
The CE requirements for this service model are the same as the
managed access VPN service. However, in this service QoS is provided
from one edge of the SP network(s) to the other.
4.4. Service-Level Specification and Agreements
A generic discussion of SLAs is provided in [RFC 3809]. Additionally,
SLS measurements for quality based on the DiffServ scheme SHOULD be
based on the following classification:
- A Point-to-Point SLS [Y.1311.1], sometimes also referred to as
the "Pipe" model, defines traffic parameters in conjunction
with the QoS objectives for traffic exchanged between a pair
of VPN sites (i.e., points). A Point-to-Point SLS is
analogous to the SLS typically supported over point-to-point
Frame Relay or ATM PVCs or an edge-to-edge MPLS tunnel. The
set of SLS specifications to all other reachable VPN sites
would define the overall Point-to-Point SLS for a specific
site.
- A Point-to-Cloud SLS [Y.1311.1], sometimes also referred to as
the "Hose" model, defines traffic parameters in conjunction
with the QoS objectives for traffic exchanged between a CE and
a PE for traffic destined to a set (either all or a subset) of
other sites in the VPN (i.e., the cloud), as applicable. In
other words, a point-to-cloud SLS defines compliance in terms
of all packets transmitted from a given VPN site toward the SP
network on an aggregate basis (i.e., regardless of the
destination VPN site of each packet).
- A Cloud-to-Point SLS (a case not covered by this SLS is where
flows originating from multiple sources may congest the
interface toward a specific site).
Traffic parameters and actions SHOULD be defined for packets to and
from the demarcation between the service provider and the site. For
example, policing may be defined on ingress, and shaping on egress.
4.5. Management
An SP and its customers MUST be able to manage the capabilities and
characteristics of their VPN services. To the extent possible,
automated operations and interoperability with standard management
platforms SHOULD be supported.
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RFC 4031 Service Requirements for L3 PPVPNs April 2005
The ITU-T Telecommunications Management Network (TMN) model has the
following generic requirements structure:
O Engineer, deploy, and manage the switching, routing, and
transmission resources supporting the service, from a network
perspective (network element management).
O Manage the VPN networks deployed over these resources (network
management).
o Manage the VPN service (service management).
o Manage the VPN business, mainly provisioning administrative and
accounting information related to the VPN service customers
(business management).
Service management should include the TMN 'FCAPS' functionalities, as
follows: Fault, Configuration, Accounting, Provisioning, and
Security, as detailed in section 7.
4.6. Interworking
Interworking scenarios among different solutions providing L3VPN
services is highly desirable. See the L3VPN framework document for
more details on interworking scenarios [L3VPN-FR]. Interworking
SHOULD be supported in a scalable manner.
Interworking scenarios MUST at least consider traffic and routing
isolation, security, QoS, access, and management aspects. This
requirement is essential of network migration, to ensure service
continuity among sites belonging to different portions of the
network.
5. Customer Requirements
This section captures additional requirements from a customer
perspective.
5.1. VPN Membership (Intranet/Extranet)
When an extranet is formed, a customer agent from each of the
organizations first approves addition of a site to an extranet VPN as
a business decision between the parties involved. The solution
SHOULD provide a means for these organizations to control extranet
communication involving the L3VPN exchange of traffic and routing
information.
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RFC 4031 Service Requirements for L3 PPVPNs April 2005
5.2. Service Provider Independence
Customers MAY require VPN service that spans multiple administrative
domains or service provider networks. Therefore, a VPN service MUST
be able to span multiple AS and SP networks, but still act and appear
as a single, homogeneous VPN from a customer point of view.
A customer might also start with a VPN provided in a single AS with a
certain SLA but then ask for an expansion of the service, spanning
multiple ASes/SPs. In this case, as well as for all kinds of multi-
AS/SP VPNs, VPN service SHOULD be able to deliver the same SLA to all
sites in a VPN regardless of the AS/SP to which it homes.
5.3. Addressing
A customer requires support from an L3VPN for the following
addressing IP assignment schemes:
o Customer-assigned, non-unique, or [RFC 1918] private addresses
o Globally unique addresses obtained by the customer
o Globally unique addresses statically assigned by the L3VPN service
provider
o On-demand, dynamically assigned IP addresses (e.g., DHCP),
irrespective of whether the access is temporary (e.g., remote) or
permanent (e.g., dedicated)
In the case of combined L3VPN service with non-unique or private
addresses and Internet access, mechanisms that permit the exchange of
traffic between the customer's address space and the global unique
Internet address space MAY be supported. For example, NAT is
employed by many customers and by some service providers today to
meet this need. A preferred solution would be to assign unique
addresses, either IPv4 or IPv6; however, some customers do not want
to renumber their networks.
5.4. Routing Protocol Support
There SHOULD be no restriction on the routing protocols used between
CE and PE routers, or between CE routers. At least the following
protocols MUST be supported: static routing, IGP protocols such as
RIP, OSPF, IS-IS, and BGP [L3VPN-FR].
5.5. Quality of Service and Traffic Parameters
QoS is expected to be an important aspect of an L3VPN service for
some customers. QoS requirements cover scenarios involving an
intranet, an extranet, and shared access between a VPN site and the
Internet.
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RFC 4031 Service Requirements for L3 PPVPNs April 2005
5.5.1. Application-Level QoS Objectives
A customer is concerned primarily that the L3VPN service provides his
or her applications with the QoS and level of traffic so that the
applications perform acceptably. Voice, interactive video, and
multimedia applications are expected to require the most stringent
QoS. These real-time applications are sensitive to delay, delay
variation, loss, availability, and/or reliability. Another set of
applications, including some multimedia and interactive video
applications, high-performance web browsing, and file transfer
intensive applications, requires near real time performance.
Finally, best effort applications are not sensitive to degradation,
that is they are elastic and can adapt to conditions of degraded
performance.
The selection of appropriate QoS and service type to meet specific
application requirements is particularly important to deal with
periods of congestion in an SP network. Sensitive applications will
likely select per-flow Integrated service (Intserv) with precise SLA
guarantees measured on a per-flow basis. On the other hand, non-
sensitive applications will likely rely on a Diffserv class-based
QoS.
The fundamental customer application requirement is that an L3VPN
solution MUST support both the Intserv QoS model for selected
individual flows and Diffserv for aggregated flows.
A customer application SHOULD experience consistent QoS independent
of the access network technology used at different sites connected to
the same VPN.
5.5.2. DSCP Transparency
The Diffserv Code Point (DSCP) set by a user as received by the
ingress CE SHOULD be capable of being relayed transparently to the
egress CE (see section 2.6.2 of [RFC 3270] and [Y.1311.1]). Although
RFC 2475 states that interior or boundary nodes within a DS domain
can change the DSCP, customer VPNs MAY have other requirements, such
as
o applications that use the DSCP in a manner differently from the
DSCP solution supported by the SP network(s),
o customers using more DSCPs within their sites than the SP
network(s) supports,
o support for a carrier's carrier service in which one SP is the
customer of another L3VPN SP. Such an SP should be able to resell
VPN service to his or her VPN customers independently of the DSCP
mapping solution supported by the carrier's carrier SP.
Carugi & McDysan Standards Track PAGE 17
RFC 4031 Service Requirements for L3 PPVPNs April 2005
Note that support for DSCP transparency has no implication on the QoS
or SLA requirements. If an SP supports DSCP transparency, then that
SP needs to carry only the DSCP values across its domain but MAY map
the received DSCP to some other value for QoS support across its
domain.
5.6. Service-Level Specification/Agreement
Most customers simply want their applications to perform well. An
SLA is a vehicle for customer recourse in the event that SP(s) do not
perform or manage a VPN service well in a measurable sense.
Therefore, when purchasing service under an SLA, a customer agent
MUST have access to the measures from the SP(s) that support the SLA.
5.7. Customer Management of a VPN
A customer MUST have a means to view the topology, operational state,
order status, and other parameters associated with his or her VPN.
Most aspects of management information about CE devices and customer
attributes of an L3VPN manageable by an SP SHOULD be capable of being
configured and maintained by an authenticated, authorized customer
agent. However, some aspects, such as encryption keys, SHALL NOT be
readable nor writable by management systems.
A customer agent SHOULD be able to make dynamic requests for changes
to traffic parameters. A customer SHOULD be able to receive real-
time response from the SP network in response to these requests. One
example of such service is a "Dynamic Bandwidth management"
capability that enables real-time response to customer requests for
changes of allocated bandwidth allocated to his or her VPN
[Y.1311.1].
A customer who may not be able to afford the resources to manage his
own sites SHOULD be able to outsource the management of the entire
VPN to the SP(s) supporting the VPN network.
5.8. Isolation
These features include traffic and routing information exchange
isolation, similar to that obtained in VPNs based on Layer 1 and
Layer 2 (e.g., private lines, FR, or ATM) [MPLSSEC].
Carugi & McDysan Standards Track PAGE 18
RFC 4031 Service Requirements for L3 PPVPNs April 2005
5.9. Security
The suite of L3VPN solutions SHOULD support a range of security
related features. Higher levels of security services, such as edge-
to-edge encryption, authentication, or replay attack, should be
supported. More details on customer requirements for security are
described in [VPNSEC].
Security in an L3VPN service SHOULD be as transparent as possible to
the customer, with the obvious exception of support for remote or
temporary user access, as detailed in section 5.11.2.
L3VPN customers MUST be able to deploy their own internal security
mechanisms in addition to those deployed by the SP, in order to
secure specific applications or traffic at a granularity finer than
that on a site-to-site basis.
If a customer requires QoS support in an L3VPN, then this request
MUST be communicated to the SP either by using unencrypted fields or
via an agreed security association. For example, applications could
send RSVP messages in support of Intserv either in the clear or
encrypted with a key negotiated with the SP. Another case is that
where applications using an IPsec tunnel could copy the DSCP from the
encrypted IP header to the header of the tunnel's IP header.
5.10. Migration Impact
Often, customers are migrating from an already deployed private
network toward one or more L3VPN solutions. A typical private
network scenario is CE routers connected via real or virtual
circuits. Ideally, minimal incremental cost SHOULD result during the
migration period. Furthermore, if necessary, any disruption of
service SHOULD also be minimized.
A range of scenarios of customer migration MUST be supported. Full
migration of all sites MUST be supported. Support for cases of
partial migration is highly desirable [Y.1311.1] - that is, legacy
private network sites that belong to the L3VPN service SHOULD still
have L3 reachability to the sites that migrate to the L3VPN service.
5.11. Network Access
Every L3 packet exchanged between the customer and the SP over the
access connection MUST appear as it would on a private network
providing an equivalent service to that offered by the L3VPN.
Carugi & McDysan Standards Track PAGE 19
RFC 4031 Service Requirements for L3 PPVPNs April 2005
5.11.1. Physical/Link Layer Technology
L3VPNs SHOULD support a broad range of physical and link-layer access
technologies, such as PSTN, ISDN, xDSL, cable modem, leased line,
Ethernet, Ethernet VLAN, ATM, Frame Relay, Wireless local loop, and
mobile radio access. The capacity and QoS achievable may be
dependent on the specific access technology in use.
5.11.2. Temporary Access
The VPN service offering SHOULD allow both permanent and temporary
access to one or more L3VPNs for authenticated users across a broad
range of access technologies. Support for remote or temporary VPN
access SHOULD include ISDN, PSTN dial-in, xDSL, or access via another
SP network. The customer SHOULD be able to choose from alternatives
for authentication of temporary access users. Choices for access
authentication are SP-provided, third-party, or customer-provided
authentication.
A significant number of VPN users may not be permanently attached to
one VPN site: in order to limit access to a VPN to authorized users,
it is first necessary to authenticate them. Authentication SHALL
apply as configured by the customer agent and/or SP where a specific
user may be part of one or more VPNs. The authentication function
SHOULD be used to invoke all actions necessary to join a user to the
VPN automatically.
A user SHOULD be able to access an L3VPN via a network having generic
Internet access.
Mobile users may move within an L3VPN site. Mobile users may also
have temporary connections to different L3VPN sites within the same
VPN. Authentication SHOULD be provided in both of these cases.
5.11.3. Sharing of the Access Network
In a PE-based L3VPN, if the site shares the access network with other
traffic (e.g., access to the Internet), then data security in the
access network is the responsibility of the L3VPN customer.
5.11.4. Access Connectivity
Various types of physical connectivity scenarios MUST be supported,
such as multi-homed sites, backdoor links between customer sites, and
devices homed to two or more SP networks. L3VPN solutions SHOULD
support at least the types of physical or link-layer connectivity
arrangements shown in Figure 2.1. Support for other physical
connectivity scenarios with arbitrary topology is desirable.
Carugi & McDysan Standards Track PAGE 20
RFC 4031 Service Requirements for L3 PPVPNs April 2005
Access arrangements with multiple physical or logical paths from a CE
to other CEs and PEs MUST support redundancy and SHOULD support load
balancing. Resiliency uses redundancy to provide connectivity
between a CE site and other CE sites and, optionally, other services.
Load balancing provides a means to perform traffic engineering so
that capacity on redundant links is used to achieve improved
performance during periods when the redundant component(s) are
available.
For multi-homing to a single SP, load balancing capability SHOULD be
supported by the PE across the CE to PE links. For example, in case
(a), load balancing SHOULD be provided by the two PEs over the two
links connecting to the single CE. In case (c), load balancing
SHOULD be provided by the two PEs over the two links connecting to
the two CEs.
In addition, the load-balancing parameters (e.g., the ratio of
traffic on the multiple load-balanced links, or the preferred link)
SHOULD be provisionable based on customer's requirements. The load-
balancing capability may also be used to achieve resiliency in the
event of access connectivity failures. For example, in case (b) a CE
may connect to two different SPs via diverse access networks.
Resiliency MAY be further enhanced as shown in case (d), where CEs
connected via a "back door" connection connect to different SPs.
Furthermore, arbitrary combinations of the above methods, with a few
examples shown in cases (e) and (f), should be supportable by any
L3VPN approach.
For multi-homing to multiple SPs, load balancing capability MAY also
be supported by the PEs in the different SPs (clearly, this is a more
complex type of load balancing to realize, requiring policy and
service agreements between the SPs to interoperate).
Carugi & McDysan Standards Track PAGE 21
RFC 4031 Service Requirements for L3 PPVPNs April 2005
+---------------- +---------------
| |
+------+ +------+
+---------| PE | +---------| PE |
| |router| | |router| SP network
| +------+ | +------+
+------+ | +------+ |
| CE | | | CE | +---------------
|device| | SP network |device| +---------------
+------+ | +------+ |
| +------+ | +------+
| | PE | | | PE |
+---------|router| +---------|router| SP network
+------+ +------+
| |
+---------------- +---------------
(a) (b)
+---------------- +---------------
| |
+------+ +------+ +------+ +------+
| CE |-----| PE | | CE |-----| PE |
|device| |router| |device| |router| SP network
+------+ +------+ +------+ +------+
| | | |
| Backdoor | | Backdoor +---------------
| link | SP network | link +---------------
| | | |
+------+ +------+ +------+ +------+
| CE | | PE | | CE | | PE |
|device|-----|router| |device|-----|router| SP network
+------+ +------+ +------+ +------+
| |
+---------------- +---------------
(c) (d)
Carugi & McDysan Standards Track PAGE 22
RFC 4031 Service Requirements for L3 PPVPNs April 2005
+---------------- +---------------
| |
+------+ +------+ +------+ +------+
| CE |-----| PE | | CE |-----| PE |
|device| |router| |device| |router| SP network
+------+\\ +------+ +------+\\ +------+
| \\ | | \\ |
|Back \\ | |Back \\
+---------------
|door \\ | SP network |door \\
+---------------
|link \\ | |link \\ |
+------+ +------+ +------+ +------+
| CE | | PE | | CE | | PE |
|device|-----|router| |device|-----|router| SP network
+------+ +------+ +------+ +------+
| |
+---------------- +---------------
(e) (f)
Figure 2.1. Representative types of access arrangements
5.12. Service Access
Customers MAY also require access to other services, as described in
this section.
5.12.1. Internet Access
Customers SHOULD be able to have L3VPN and Internet access across the
same access network for one or more of the customer's sites.
Customers SHOULD be able to direct Internet traffic from the set of
sites in the L3VPN to one or more customer sites that have firewalls,
other security-oriented devices, and/or NATs that process all traffic
between the Internet and the customer's VPN.
L3 VPN Customers SHOULD be able to receive traffic from the Internet
addressed to a publicly accessible resource that is not part of the
VPN, such as an enterprise's public web server.
As stated in section 5.3, if a customer L3VPN employs private or
non-unique IP addresses, then network address translation (NAT) or a
similar mechanism MUST be provided either by the customer or the SP
in order to allow traffic exchange with devices outside the
customer's L3VPN.
Carugi & McDysan Standards Track PAGE 23
RFC 4031 Service Requirements for L3 PPVPNs April 2005
5.12.2. Hosting, Application Service Provider
A customer SHOULD be able to access hosting, other application
services, or other Application Service Providers (ASP) over an L3
L3VPN service. This MAY require that an ASP participate in one or
more VPNs with the customers that use such a service.
5.12.3. Other Services
In conjunction with a VPN service, a customer MAY also wish to have
access to other services, such as DNS, FTP, HTTP, NNTP, SMTP, LDAP,
VoIP, NAT, LDAP, Videoconferencing, Application sharing, E-business,
Streaming, E-commerce, Directory, Firewall, etc. The resources that
implement these services could be physically dedicated to each VPN.
If the resources are logically shared, then they MUST have access
separated and isolated between VPNs in a manner consistent with the
L3VPN solution to meet this requirement.
5.13. Hybrid VPN Service Scenarios
Intranet or extranet customers have a number of reasons for wanting
hybrid networks that involve more than one VPN solution type. These
include migration, mergers, extranet customers with different VPN
types, the need for different capabilities between different sets of
sites, temporary access, and different availability of VPN solutions
as provided by different service providers.
The framework and solution approaches SHOULD include provisions for
interworking, interconnection, and/or reachability between different
L3VPN solutions in a way that does not overly complicate
provisioning, management, scalability, or performance.
6. Service Provider Network Requirements
This section describes requirements from a service provider
perspective.
6.1. Scalability
[RFC 3809] lists projections of L3VPN sizing and scalability
requirements and metrics related to specific solutions.
Carugi & McDysan Standards Track PAGE 24
RFC 4031 Service Requirements for L3 PPVPNs April 2005
6.2. Addressing
As described in section 4.2, SPs MUST have support for public and
private IP addresses, IPv4 and IPv6, for both unicast and multicast.
In order to support this range of addressing schemes, SPs require the
following support from L3VPN solutions.
An L3VPN solution MUST be able to assign blocks of addresses from its
own public IP address space to L3VPN customer sites so that
advertisement of routes to other SPs and other sites aggregates
efficiently.
An L3VPN solution MUST be able to use address assignments made by a
customer. These customer-assigned addresses may be public or
private.
If private IP addresses are used, an L3VPN solution MUST provide a
means for an SP to translate such addresses to public IP addresses
for communication with other VPNs by using overlapping addresses or
the Internet.
6.3. Identifiers
A number of identifiers MAY be necessary for SP use in management,
control, and routing protocols. Requirements for at least the
following identifiers are known.
An SP domain MUST be uniquely identified at least within the set of
all interconnected SP networks when supporting a VPN that spans
multiple SPs. Ideally, this identifier should be globally unique
(e.g., an AS number).
An identifier for each VPN SHOULD be unique, at least within each
SP's network. Ideally, the VPN identifier SHOULD be globally unique
to support the case where a VPN spans multiple SPs (e.g., [RFC 2685]).
A CE device SHOULD have a unique identifier, at least within each
SP's network.
A PE device SHOULD have a unique identifier, at least within each
SP's network.
The identifier of a device interconnecting SP networks MUST be unique
within the set of aforementioned networks.
Each site interface SHOULD have a unique identifier, at least within
each PE router supporting such an interface.
Carugi & McDysan Standards Track PAGE 25
RFC 4031 Service Requirements for L3 PPVPNs April 2005
Each tunnel SHOULD have a unique identifier, at least within each
router supporting the tunnel.
6.4. Discovering VPN Related Information
Configuration of CE and PE devices is a significant task for a
service provider. Solutions SHOULD strive to contain methods that
dynamically allow VPN information to be discovered (or learned) by
the PE and/or CE to reduce configuration complexity. The following
specific requirements apply to intra- and inter-provider VPNs
[VPNDISC].
Every device involved in a VPN SHALL be able to identify and
authenticate itself to other devices in the VPN. After learning the
VPN membership, the devices SHOULD be able to exchange configuration
information securely. The VPN information MUST include at least the
IP address of the PE and may be extensible to provide additional
information.
Each device in a VPN SHOULD be able to determine which other devices
belong to the same VPN. Such a membership discovery scheme MUST
prevent unauthorized access and allow authentication of the source.
Distribution of VPN information SHOULD be limited to those devices
involved in that VPN.
In the case of a PE-based VPN, a solution SHOULD support the means
for attached CEs to authenticate each other and verify that the SP's
VPN network is correctly configured.
The mechanism SHOULD respond to VPN membership changes in a timely
manner. This is no longer than the provisioning timeframe, typically
on the order of minutes, and could be as short as the timeframe
required for "rerouting", typically on the order of seconds.
Dynamically creating, changing, and managing multiple VPN assignments
to sites and/or customers is another aspect of membership that MUST
be addressed in an L3VPN solution.
6.5. SLA and SLS Support
Typically, a Service Provider offering an L3VPN service commits to
specific Service Level Specifications (SLS) as part of a contract
with the customer, as described in section 4.4 and [RFC 3809]. Such a
Service Level Agreement (SLA) implies SP requirements for measuring
Specific Service Level Specifications (SLS) for quality,
availability, response time, and configuration intervals.
Carugi & McDysan Standards Track PAGE 26
RFC 4031 Service Requirements for L3 PPVPNs April 2005
6.6. Quality of Service (QoS) and Traffic Engineering
A significant aspect of an L3VPN is support for QoS. Since an SP has
control over the provisioning of resources and configuration of
parameters in at least the PE and P devices and, in some cases, in
the CE device as well, the onus is on the SP to provide either
managed QoS access service, or edge-to-edge QoS service, as defined
in section 4.3.2.
Each L3VPN approach MUST describe the traffic engineering techniques
available for an SP to meet the QoS objectives. These descriptions
of traffic engineering techniques SHOULD quantify scalability and
achievable efficiency. Traffic engineering support MAY be on an
aggregate or per-VPN basis.
QoS policies MUST not be impacted by security mechanisms. For
example, Diffserv policies MUST not be impacted by the use of IPSec
tunnels using the mechanisms explained in RFC 2983 [RFC 2983].
As stated in RFC 2475, a mapping function from customer provided
Diffserv marking to marking used in an SP network should be provided
for L3 VPN services.
If a customer requires DSCP transparency, as described in section
5.5.2, an L3VPN service MUST deliver the same value of DSCP field in
the IP header received from the customer to the egress demarcation of
the destination.
6.7. Routing
The distribution of reachability and routing policy SHOULD be
constrained to the sites that are members of the VPN.
Optionally, the exchange of such information MAY use some form of
authentication (e.g., MD5).
Functions to isolate the SP network and customer VPNs from anomalous
routing behavior from a specific set of customer sites SHOULD be
provided. Examples of such functions are controls for route flap
dampening, filters that accept only prefixes configured for a
specific CE, a maximum number of routes accepted for each CE, or a
maximum rate at which route updates can be received from a CE.
When VPN customers use overlapping non-unique IP addresses, the
solution MUST define a means to distinguish between such overlapping
addresses on a per-VPN basis.
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Furthermore, the solution SHOULD provide an option that either allows
or prevents advertisement of VPN routes to the Internet.
Ideally, the choice of an SP's IGP SHOULD not depend on the routing
protocol(s) used between PE and CE routers in a PE-based VPN.
Furthermore, it is desirable that an SP SHOULD have a choice
regarding the IGP routing protocol.
The additional routing burden that an SP must carry should be
articulated in each specific L3VPN solution.
6.8. Isolation of Traffic and Routing
The internal structure of an L3VPN network SHOULD not be visible to
outside networks (e.g., the Internet or any connected VPN).
From a high-level SP perspective, a PE-based L3VPN MUST isolate the
exchange of traffic and routing information to only those sites that
are authenticated and authorized members of a VPN.
In a CE-based VPN, the tunnels that connect the sites effectively
meet this isolation requirement if both traffic and routing
information flow over the tunnels.
An L3VPN solution SHOULD provide a means to meet L3VPN QoS SLA
requirements that isolates VPN traffic from the effects of traffic
offered by non-VPN customers. Also, L3VPN solutions SHOULD provide a
means to isolate the effects that traffic congestion produced by
sites as part of one VPN can have on another VPN.
6.9. Security
This section contains requirements related to securing customer
flows; providing authentication services for temporary, remote, or
mobile users; and protecting service provider resources involved in
supporting an L3VPN. More detailed security requirements are
provided in [VPNSEC].
6.9.1. Support for Securing Customer Flows
In order to meet the general requirement for providing a range of
security options to a customer, each L3VPN solution MUST clearly
spell out the configuration options that can work together and how
they can do so.
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When a VPN solution operates over a part of the Internet, it should
support a configurable option to support one or more of the following
standard IPsec methods for securing a flow for a specified subset of
a customer's VPN traffic:
o Confidentiality, so that only authorized devices can decrypt it
o Integrity, to ensure that the data has not been altered
o Authentication, to ensure that the sender is indeed who he or she
claims to be
o Replay attack prevention.
The above functions SHOULD be applicable to "data traffic" of the
customer, which includes the traffic exchanged between sites between
temporary users and sites, and even between temporary users. It
SHOULD also be possible to apply these functions to "control
traffic", such as routing protocol exchanges, that are not
necessarily perceived by the customer but are nevertheless essential
to maintain his or her VPN.
Furthermore, such security methods MUST be configurable between
different end points, such as CE-CE, PE-PE, and CE-PE. It is also
desirable to configure security on a per-route or per-VPN basis
[VPNSEC].
A VPN solution MAY support one or more encryption schemes, including
AES, and 3DES. Encryption, decryption, and key management SHOULD be
included in profiles as part of the security management system.
6.9.2. Authentication Services
A service provider MUST provide authentication services in support of
temporary user access requirements, as described in section 5.11.2.
Furthermore, traffic exchanged within the scope of VPN MAY involve
several categories of equipment that must cooperate to provide the
service [Y.1311.1]. These network elements can be CE, PE, firewalls,
backbone routers, servers, management stations, etc. These network
elements learn about each other's identity, either via manual
configuration or via discovery protocols, as described in section
6.4. When network elements must cooperate, these network elements
SHALL authenticate peers before providing the requested service.
This authentication function MAY also be used to control access to
network resources.
The peer identification and authentication function described above
applies only to network elements participating in the VPN. Examples
include:
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- traffic between a CE and a PE,
- traffic between CEs belonging to the same VPN,
- CE or PE routers dealing with route announcements for a VPN,
- policy decision point [RFC 3198] and a network element, and
- management station and an SNMP agent.
For a peer authentication function, each L3VPN solution SHOULD
describe where necessary, how it shall be implemented, how secure it
must be, and the way to deploy and maintain identification and
authentication information necessary to operate the service.
6.9.3. Resource Protection
Recall from the definitions in section 3.3 that a site can be part of
an intranet with sites from the only same organization, can be part
of an extranet involving sites from other organizations, can have
access to the Internet, or can have any combination of these scopes
of communication. Within these contexts, a site might be subject to
various attacks coming from different sources. Potential sources of
attack include:
- users connected to the supporting public IP backbone,
- users from the Internet, and
- users from temporary sites belonging to the intranet and/or
extranet VPN the site is part of.
Security threats and risks that a site may encounter include the
following:
- Denial of service, for example mail spamming, access connection
congestion, TCP SYN attacks, and ping attacks
- Intrusion attempts, which may eventually lead to denial of service
(e.g., a Trojan horse attack).
Additional threat scenarios are defined in [VPNSEC]. An L3VPN
solution MUST state how it addresses each potential threat scenario.
The devices in the L3VPN network must provide some means of reporting
intrusion attempts to the service provider resources.
6.10. Inter-AS (SP)VPNs
The scenario for VPNs spanning multiple Autonomous Systems (AS) or
Service Providers (SP) requires standard solutions. The scenario
where multiple ASes are involved is the most general case and is
therefore the one described here. The scenarios of concern are the
CE-based and PE-based L3VPNs defined in section 3.
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In each scenario, all applicable SP requirements, such as traffic and
routing isolation, SLAs, management, security, and provisioning.
MUST be preserved across adjacent ASes. The solutions MUST describe
the inter-SP network interface, encapsulation method(s), routing
protocol(s), and all applicable parameters [VPNIW].
An essential pre-condition for an inter-AS VPN is an agreement
between the ASes involved that spells out at least trust, economic,
and management responsibilities.
The overall scalability of the VPN service MUST allow the L3VPN
service to be offered across potentially hundreds of SPs, with the
overall scaling parameters per SP given in [RFC 3809].
6.10.1. Routing Protocols
If the link between ASes is not trusted, routing protocols running
between those ASes MUST support some form of authentication. For
example, the TCP option for carrying an MD5 digest may be used to
enhance security for BGP [RFC 2385].
BGP MUST be supported as the standard inter-AS routing protocol to
control the path taken by L3VPN traffic.
6.10.2. Management
The general requirements for managing a single AS apply to a
concatenation of ASes. A minimum subset of such capabilities as
follows:
- Diagnostic tools (e.g., ping, traceroute)
- Secured access to one AS management system by another
- Configuration request and status query tools
- Fault notification and trouble-tracking tools
6.10.3. Bandwidth and QoS Brokering
When a VPN spans multiple ASes, a brokering mechanism is desired that
requests certain SLA parameters, such as bandwidth and QoS, from the
other domains and/or networks involved in transferring traffic to
various sites. Although bandwidth and QoS brokering across multiple
ASes is not common in today's networks, these may be desirable for
maintaining SLAs in inter-AS VPNs. This section describes
requirements for features that would facilitate these mechanisms.
The objective is that a solution SHOULD be able to determine whether
a set of ASes can establish and guarantee uniform QoS in support of
an L3VPN.
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The brokering mechanism can be a manual one, for example, in which
one provider requests from another a specific set of bandwidth and
QoS parameters for traffic going to and from a specific set of sites.
The mechanism could also be an automated one where a device
dynamically requests and receives certain bandwidth and SLA/QoS
parameters. For instance, in the case of an L3VPN over MPLS, a PE
may negotiate the label for different traffic classes to reach a PE
residing in a neighboring AS. Or, it might be a combination of both.
For additional detailed requirements on the automated approach, see
[TE-INTERAS].
Brokering on a per VPN basis is not desirable as this approach would
not scale. A solution MUST provide some means to aggregate QoS and
bandwidth brokering requests between ASes. One method could be for
SPs to make an agreement specifying the maximum amount of bandwidth
for specific QoS parameters for all VPN customers using the SP
network. Alternatively, such aggregation might be on a per
hierarchical tunnel basis between PE routers in different ASes
supporting an L3VPN service [TE-INTERAS].
6.10.4. Security Considerations
If a tunnel traverses multiple SP networks and passes through an
unsecured SP, POP, NAP, or IX, then security mechanisms MUST be
employed. These security mechanisms include encryption,
authentication, and resource protection, as described in section 6.9,
and security management, as covered in section 7.5. For example, a
provider should consider using both authentication and encryption for
a tunnel used as part of an L3VPN that traverses another service
provider's network.
6.11. L3VPN Wholesale
The architecture MUST support the possibility of one service provider
offering VPN service to another service provider. Another example is
when one service provider sells L3VPN service at wholesale to another
service provider, who then resells that VPN service to his or her
customers.
The wholesaler's VPN MUST be transparent to the addressing and
routing used by the reseller.
Support for additional levels of hierarchy (for example, three levels
at which a reseller can again resell the VPN service to yet another
VPN provider) SHOULD be provided.
The Carrier's Carrier scenario is the term used in this document for
this category of L3VPN wholesale (although some scenarios of Inter-
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AS/Inter-Provider VPN could possibly fall in this L3VPN wholesale
category, too). Various carrier's carrier scenarios should be
supported, such as when
- the customer carriers do not operate L3VPN services for their
clients;
- the customer carriers operate L3VPN services for their clients,
but these services are not linked with the L3VPN service offered
by the Carrier's Carrier and
- the customer carriers operate L3VPN services for their clients,
and these services are linked with the L3VPN service offered by
the Carrier's Carrier ("Hierarchical VPNs" scenario).
6.12. Tunneling Requirements
Connectivity between CE sites or PE devices in the backbone SHOULD
use a range of tunneling technologies, such as L2TP, IPSEC, GRE, IP-
in-IP, and MPLS.
To set up tunnels between routers, every router MUST support static
configuration for tunneling and MAY support a tunnel setup protocol.
If employed, a tunnel establishment protocol SHOULD be capable of
conveying information such as the following:
- Relevant identifiers
- QoS/SLA parameters
- Restoration parameters
- Multiplexing identifiers
- Security parameters
There MUST be a means to monitor the following aspects of tunnels:
- Statistics, such as amount of time spent in the up and down state.
- Count of transitions between the up and down state.
- Events, such as transitions between the up and down states.
The tunneling technology used by the VPN Service Provider and its
associated mechanisms for tunnel establishment, multiplexing, and
maintenance MUST meet the requirements on scaling, isolation,
security, QoS, manageability, etc.
6.13. Support for Access and Backbone Technologies
This section describes requirements for aspects of access and
backbone network technologies from an SP point of view.
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Some SPs MAY desire that a single network infrastructure suffices for
all services, public IP, VPNs, traffic engineering, and
differentiated services [L2VPN].
6.13.1. Dedicated Access Networks
Ideally, the L3VPN service SHOULD be independent of physical, link
layer, or even network technology of the access network. However,
the characteristics of access networks MUST be accounted for when the
QoS aspects of SLAs for VPN service offerings are specified.
6.13.2. On-Demand Access Networks
Service providers SHOULD be able to support temporary user access, as
described in section 5.11.2, by using dedicated or dial-in access
network technology.
L3VPN solutions MUST support the case where a VPN user directly
accesses the VPN service through an access network connected to the
service provider. They MUST also describe how they can support the
case where one or more other service provider networks are used for
access to the service provider supporting the L3VPN service.
Ideally, all information necessary to identify and authenticate users
for an intranet SHOULD be stored and maintained by the customer. In
an extranet, one customer SHOULD be able to maintain the
authentication server, or the customers involved in the extranet MAY
choose to outsource the function to a service provider.
Identification and authentication information could be made available
to the service provider for controlling access, or the service
provider may query a customer maintained server. Furthermore, one SP
may act as access for the SP providing the VPN service. If the
access SP performs identification and authentication on behalf of the
VPN SP, an agreement MUST be reached on a common specification.
Support for at least the following authentication protocols SHALL be
supported: PAP, CHAP, and EAP, as they are currently used in a wide
range of equipment and services.
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6.13.3. Backbone Networks
Ideally, the backbone interconnecting SP, PE, and P devices SHOULD be
independent of physical and link layer technology. Nevertheless, the
characteristics of backbone technology MUST be taken into account
when specifying the QoS aspects of SLAs for VPN service offerings.
6.14. Protection, Restoration
When primary and secondary access connections are available, an L3VPN
solution MUST provide restoration of access connectivity whenever the
primary access link from a CE site to a PE fails. This capability
SHOULD be as automatic as possible, that is, the traffic should be
directed over the secondary link soon after failure of the primary
access link is detected. Furthermore, reversion to the primary link
SHOULD be dynamic, if configured to do so [VPN-NEEDS].
As mentioned in section 5.11.4, in the case of multi-homing, the load
balancing capability MAY be used to achieve a degree of redundancy in
the network. In the case of failure of one or more (but not all) of
the multi-homed links, the load balancing parameters MAY be
dynamically adjusted to redirect the traffic rapidly from the failed
link(s) to the surviving links. Once the failed link(s) is (are)
restored, the original provisioned load balancing ratio SHOULD be
restored to its value prior to the failure.
An SP SHOULD be able to deploy protection and restoration mechanisms
within his or her backbone infrastructure to increase reliability and
fault tolerance of the VPN service offering. These techniques SHOULD
be scalable, and therefore should strive not to perform such function
in the backbone on a per-VPN basis.
Appropriate measurements and alarms that indicate how well network
protection and restoration mechanisms are performing MUST be
supported.
6.15. Interoperability
Service providers are interested in interoperability in at least the
following scenarios:
- Facilitating use of PE and managed CE devices within a single SP
network.
- Implementing L3VPN services across two or more interconnected SP
networks.
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- Achieving interworking or interconnection between customer sites
using different L3VPN approaches or different implementations of
the same approach.
Each approach MUST describe whether any of the above objectives can
be met. If an objective can be met, the approach MUST describe how
such interoperability could be achieved. In particular, the approach
MUST describe the inter-solution network interface, encapsulation
method(s), routing protocol(s), security, isolation, management, and
all other applicable aspects of the overall VPN solution provided
[VPNIW].
6.16. Migration Support
Service providers MUST have a graceful means to migrate a customer
with minimal service disruption on a site-by-site basis to an L3VPN
approach.
If L3VPN approaches can interwork or interconnect, then service
providers MUST have a graceful means to migrate a customer with
minimal service disruption on a site-by-site basis whenever
interworking or interconnection is changed.
7. Service Provider Management Requirements
A service provider MUST have a means to view the topology,
operational state, order status, and other parameters associated with
each customer's VPN. Furthermore, an SP MUST have a means to view
the underlying logical and physical topology, operational state,
provisioning status, and other parameters associated with the
equipment providing the VPN service(s) to its customers.
Currently, proprietary methods are often used to manage VPNs. The
additional expense associated with operators using multiple
proprietary management methods (e.g., command line interface (CLI)
languages) to access such systems is undesirable. Therefore, devices
SHOULD provide standards-based interfaces wherever feasible.
The remainder of this section presents detailed SP management
requirements for a Network Management System (NMS) in the traditional
fault, configuration, accounting, performance, and security (FCAPS)
management categories. Much of this text was adapted from ITU-T
Y.1311.1.
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7.1. Fault Management
Support for fault management includes:
- indication of customers impacted by failure,
- fault detection (incidents reports, alarms and failure
visualization),
- fault localization (analysis of alarms reports and diagnostics),
- incident recording or logs (creation and follow-through of trouble
tickets), and
- corrective actions (traffic, routing, and resource allocation).
As PE-based VPNs rely on a common network infrastructure, the NMS
MUST provide a means to inform the provider of the VPN customers
impacted by a failure in the infrastructure. The NMS SHOULD provide
pointers to the related customer configuration information to aid in
fault isolation and determining corrective action.
Detecting faults caused by configuration errors is desirable, because
these may cause VPN service failure or may disrupt other requirements
(e.g., traffic and routing isolation). This is a likely case of
compromised security [VPNSEC]. Detection of such errors is
inherently difficult because the problem involves more than one node
and may reach across a global perspective. One approach could be a
protocol that systematically checks whether all constraints and
consistency checks hold among tunnel configuration parameters at the
various end points.
A capability to verify L3 reachability within a VPN MUST be provided
for diagnostic purposes.
A capability to verify the parameter configuration of a device
supporting an L3VPN MUST be provided for diagnostic purposes.
7.2. Configuration Management
Overall, the NMS must support a configuration necessary to realize
the desired L3-reachability of an L3VPN. Toward this end, an NMS
MUST provide configuration management to provision at least the
following L3VPN components: PE,CE, hierarchical tunnels, access
connections, routing, and QoS, as detailed in this section. If
shared access to the Internet is provided, then this option MUST also
be configurable.
As VPN configuration and topology are highly dependent on a
customer's organization, provisioning systems MUST address a broad
range of customer-specific requirements. The NMS MUST ensure that
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RFC 4031 Service Requirements for L3 PPVPNs April 2005
these devices and protocols are provisioned consistently and
correctly.
Provisioning for adding or removing sites SHOULD be as localized and
automated as possible.
Configuration management for VPNs, according to service templates
defined by the provider MUST be supported. A service template
contains fields that, when used, yield a definite service requirement
or policy. For example, a template for an IPSec tunnel would contain
fields such as tunnel end points, authentication modes, encryption
and authentication algorithms, pre-shared keys (if any), and traffic
filters. An SLA template would contain fields such as delay, jitter,
and throughput and packet loss thresholds, as well as end points over
which the SLA has to be satisfied. In general, a customer's service
order can be regarded as a set of instantiated service templates.
This set can, in turn, be regarded as the logical service
architecture of the customer's VPN.
Service templates can also be used by the provider to define the
service architecture of the provider's own network. For example,
OSPF templates could contain fields such as the subnets that form a
particular area, the area identifier, and the area type. BGP service
template could contain fields that, when used, would yield a BGP
policy, such as for expressing a preference about an exit router for
a particular destination.
The set of service templates SHOULD be comprehensive in that it can
capture all service orders in some meaningful sense.
The provider SHOULD provide means to translate service templates into
device configurations so that associated services can be provisioned.
Finally, the approach SHOULD provide means to check whether a service
order is correctly provisioned. This would represent one method of
diagnosing configuration errors. Configuration errors can arise due
to a variety of reasons: manual configuration, intruder attacks, and
conflicting service requirements.
7.2.1. Configuration Management for PE-Based VPNs
Requirements for configuration management unique to a PE-based VPN
are as follows:
o The NMS MUST support configuration of at least the following
aspects of L3 PE routers: intranet and extranet membership, CE
routing protocol for each access connection, routing metrics, and
tunnels.
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RFC 4031 Service Requirements for L3 PPVPNs April 2005
o The NMS SHOULD use identifiers for SPs, L3VPNs, PEs, CEs,
hierarchical tunnels, and access connections, as described in
section 6.3.
o Tunnels MUST be configured between PE and P devices. This
requires coordination of identifiers of tunnels, hierarchical
tunnels, VPNs, and any associated service information, for
example, a QoS/SLA service.
o Routing protocols running between PE routers and CE devices MUST
be configured per VPN.
o For multicast service, multicast routing protocols MUST also be
configurable.
o Routing protocols running between PE routers and between PE and P
routers MUST also be configured.
o The configuration of a PE-based L3VPN MUST be coordinated with the
configuration of the underlying infrastructure, including Layer 1
and 2 networks interconnecting components of an L3VPN.
7.2.2. Configuration Management for CE-Based VPN
Requirements for configuration management unique to a CE-based VPN
are as follows:
o Tunnels MUST be configured between CE devices. This requires
coordination of identifiers of tunnels, VPNs, and any associated
service information, for example, a QoS/SLA service.
o Routing protocols running between PE routers and CE devices MUST
be configured. For multicast service, multicast routing protocols
MUST also be configurable.
7.2.3. Provisioning Routing
A means for a service provider to provision parameters for the IGP
for an L3VPN MUST be provided. This includes link level metrics,
capacity, QoS capability, and restoration parameters.
7.2.4. Provisioning Network Access
A service provider MUST have the means to provision network access
between SP-managed PE and CE, as well as the case where the customer
manages the CE.
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7.2.5. Provisioning Security Services
When a security service is requested, an SP MUST have the means to
provision the entities and associated parameters involved with the
service. For example, for IPsec service, tunnels, options, keys, and
other parameters must be provisioned at either the CE or the PE. In
the case of an intrusion detection service, the filtering and
detection rules must be provisioned on a VPN basis.
7.2.6. Provisioning VPN Resource Parameters
A service provider MUST have a means to provision resources
associated with VPN services dynamically. For example, in a PE-based
service, the number and size of virtual switching and forwarding
table instances must be provisionable.
Dynamic VPN resource assignment is crucial for coping with the
frequent change requests from customers (e.g., sites joining or
leaving a VPN), as well as for achieving scalability. The PEs SHOULD
be able to dynamically assign the VPN resources dynamically. This
capability is especially important for dial and wireless VPN
services.
If an SP supports a "Dynamic Bandwidth management" service, then the
provisioning system MUST be able to make requested changes within the
ranges and bounds specified in the SLA. Examples of SLA parameters
are response time and probability of being able to service such a
request.
7.2.7. Provisioning Value-Added Service Access
An L3VPN service provides controlled access between a set of sites
over a common backbone. However, many service providers also offer a
range of value-added services. (for example, Internet access,
firewall services, intrusion protection, IP telephony and IP Centrex,
application hosting, and backup). It is outside of the scope of this
document to define whether and how these different services interact
with the VPN to solve issues such as addressing, integrity, and
security. However, the VPN service MUST be able to provide access to
these various types of value-added services.
A VPN service SHOULD allow the SP to supply the customer with
different kinds of standard IP services, such as DNS, NTP, and
RADIUS, that are needed for ordinary network operation and
management. The provider SHOULD be able to provide IP services to
multiple VPN customers.
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A firewall function MAY be required to restrict access to the L3VPN
from the Internet [Y.1311].
A managed firewall service MUST be carrier grade. For redundancy and
failure recovery, a means for firewall fail-over should be provided.
Managed firewall services that may be provided include dropping
specified protocol types, intrusion protection, and traffic-rate
limiting against malicious attacks.
Managed firewalls MUST be supported on a per-VPN basis, although
multiple VPNs may be supported by the same physical device (e.g., in
a PE-based solution). Managed firewalls SHOULD be provided at the
major access point(s) for the L3VPN. Managed firewall services may
be embedded in CE or PE device or implemented in standalone devices.
The NMS SHOULD allow a customer to outsource the management of an IP
networking service to the SP providing the VPN or to a third party.
The NMS SHOULD support collection of information necessary for
optimal allocation of IP services in response to customer orders.
Reachability to and from the Internet to sites within a VPN MUST be
configurable by an SP. This could be controlled by configuring
routing policy to control distribution of VPN routes advertised to
the Internet.
7.2.8. Provisioning Hybrid VPN Services
Configuration of interworking or interconnection between L3VPN
solutions SHOULD be also supported. Ensuring that security and
end-to-end QoS issues are provided consistently SHOULD be addressed.
7.3. Accounting
Many service providers require collection of measurements regarding
resource usage for accounting purposes. The NMS MAY need to
correlate accounting information with performance and fault
management information to produce billing that takes into account SLA
provisions for periods of time when the SLS is not met.
An L3VPN solution MUST describe how the following accounting
functions can be provided:
- Measurements of resource utilization.
- collection of accounting information.
- storage and administration of measurements.
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Some providers may require near - real time reporting of measurement
information and may offer this as part of a customer network
management service.
If an SP supports a "Dynamic Bandwidth management" service, then the
dates, times, amounts, and interval required to perform requested
bandwidth allocation change(s) MUST be traceable for monitoring and
accounting purposes.
Solutions should state compliance with accounting requirements, as
described in section 1.7 of RFC 2975 [RFC 2975].
7.4. Performance Management
Performance management MUST support functions involved with
monitoring and collecting performance data for devices, facilities,
and services, as well as determining conformance to SLS, such as QoS
and availability measurements.
Performance management SHOULD also support analysis of important
aspects of an L3VPN, such as bandwidth utilization, response time,
availability, QoS statistics, and trends based on collected data.
7.4.1. Performance Monitoring
The NMS MUST monitor device behavior to evaluate performance metrics
associated with an SLA. Different measurement techniques may be
necessary depending on the service for which an SLA is provided.
Example services are QoS, security, multicast, and temporary access.
These techniques MAY be either intrusive or non-intrusive depending
on the parameters being monitored.
The NMS MUST also monitor aspects of the VPN not directly associated
with an SLA, such as resource utilization, state of devices, and
transmission facilities, as well as control of monitoring resources
such as probes and remote agents at network access points used by
customers and mobile users.
7.4.2. SLA and QoS Management Features
The NMS SHOULD support SLAs between an SP and the various VPN
customers according to the corresponding SLSes by measurement of the
indicators defined within the context of the SLA, on a regular basis.
The NMS SHOULD use the QoS parameter measurement definitions,
techniques, and methods as defined by the IETF IP Performance Metrics
(IPPM) working group for delay, loss, and delay variation.
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The NMS SHOULD support allocation and measurement of end-to-end QoS
requirements to QoS parameters for one or more VPN network(s).
Devices supporting L3VPN SLAs SHOULD have real-time performance
measurements that have indicators and threshold crossing alerts.
Such thresholds should be configurable.
7.5. Security Management
The security management function of the NMS MUST include management
features to guarantee the security of devices, access connections,
and protocols within the L3VPN network(s), as well as the security of
customer data and control as described in section 6.9.
7.5.1. Resource Access Control
Resource access control determines the privileges that a user has to
access particular applications and VPN network resources. Without
such control, only the security of the data and control traffic is
protected, leaving the devices providing the L3VPN network
unprotected. Access control capabilities protect these devices to
ensure that users have access only to the resources and applications
they are authorized to use.
In particular, access to the routing and switching resources managed
by the SP MUST be tightly controlled to prevent and/or effectively
mitigate a malicious attack. More detailed requirements in this area
are described in [VPNSEC].
7.5.2. Authentication
Authentication is the process of verifying that the sender is
actually who he or she claims to be. The NMS MUST support standard
methods for authenticating users attempting to access management
services.
Scalability is critical, as the number of nomadic/mobile clients is
increasing rapidly. The authentication scheme implemented for such
deployments MUST be manageable for large numbers of users and VPN
access points.
Strong authentication schemes SHALL be supported to ensure the
security of both VPN access point-to-VPN access point (e.g., PE to
PE in a PE-based case) and client-to-VPN access point (e.g., CE-to-PE
in a PE-based case) communications. This is particularly important
for preventing VPN access point spoofing, a situation where an
attacker tries to convince a PE or CE that the attacker is the VPN
access point. If an attacker can convince a PE or CE device of this,
Carugi & McDysan Standards Track PAGE 43
RFC 4031 Service Requirements for L3 PPVPNs April 2005
then that device will send VPN traffic to the attacker (who could
forward it to the true access point after compromising
confidentiality or integrity). In other words, a non-authenticated
VPN AP can be spoofed with a man-in-the-middle attack, because the
endpoints never verify each other. A weakly authenticated VPN AP may
be subject to such an attack. Strongly authenticated VPN APs are not
subject to such attacks, because the man-in-the-middle cannot be
authenticated as the real AP due to the strong authentication
algorithms.
7.6. Basis and Presentation Techniques of Management Information
Each L3VPN solution approach MUST specify the management information
bases (MIB) modules for the network elements involved in L3VPN
services. This is an essential requirement in network provisioning.
The approach SHOULD identify any information not contained in a
standard MIB related to FCAPS that is necessary to meet a generic
requirement.
An IP VPN (Policy) Information model, when available, SHOULD reuse
the policy information models being developed in parallel for
specific IP network capabilities [IM-REQ]. This includes the QoS
Policy Information Model [QPIM] and the IPSEC Configuration Policy
Model [IPSECIM]. The IP VPN Information model SHOULD provide the OSS
with adequate "hooks" to correlate service level specifications with
traffic data collected from network elements. The use of policies
includes rules that control corrective actions taken by OSS
components responsible for monitoring the network and ensuring that
it meets service requirements.
Additional requirements on VPN information models are given in
reference [IM-PPVPN]. In particular, an information model MUST allow
an SP to change VPN network dimensions with minimal influence on
provisioning issues. The adopted model SHOULD be applicable to both
small/medium size and large-scale L3VPN scenarios.
Some service providers MAY require systems that visually, audibly, or
logically present FCAPS information to internal operators and/or
customers.
8. Security Considerations
Security considerations occur at several levels and dimensions within
L3VPNs, as detailed within this document. This section provides a
summary with references to detailed supporting information
[L3VPN-SEC] [VPNSEC].
Carugi & McDysan Standards Track PAGE 44
RFC 4031 Service Requirements for L3 PPVPNs April 2005
The requirements in this document separate traditional notions of
security requirements, such as integrity, confidentiality, and
authentication, from issues such as isolating (or separating) the
exchange of VPN data and control traffic between specific sets of
sites (as defined in sections 3.3 and 4.1). Further detail on
security requirements is given from the customer and service provider
perspectives in sections 5.9 and 6.9, respectively. Further detail
on data and control traffic isolation requirements are given from the
customer and service provider perspectives in sections 5.1 and 6.8,
respectively.
Furthermore, requirements regarding management of security from a
service provider perspective are described in section 7.5.
9. Acknowledgements
The authors of this document would like to acknowledge the
contributions from the people who launched the work on VPN
requirements inside ITU-T SG13 and the authors of the original IP VPN
requirements and framework document [RFC 2764], as well as Tom
Worster, Ron Bonica, Sanjai Narain, Muneyoshi Suzuki, Tom Nadeau,
Nail Akar, Derek Atkins, Bryan Gleeson, Greg Burns, and Frederic Le
Garrec. The authors are also grateful to the helpful suggestions and
direction provided by the technical advisors, Alex Zinin, Scott
Bradner, Bert Wijnen, and Rob Coltun. Finally, the authors wish to
acknowledge the insights and requirements gleaned from the many
documents listed in the references section. Citations to these
documents were made only where the authors believed that additional
insight could be obtained from reading the source document.
10. References
10.1. Normative References
[RFC 3377] Hodges, J. and R. Morgan, "Lightweight Directory Access
Protocol (v3): Technical Specification", RFC 3377,
September 2002.
[RFC 1918] Rekhter, Y., Moskowitz, B., Karrenberg, D., de Groot,
G., and E. Lear, "Address Allocation for Private
Internets", BCP 5, RFC 1918, February 1996.
[RFC 2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
[RFC 2205] Braden, R., Zhang, L., Berson, S., Herzog, S., and S.
Jamin, "Resource ReSerVation Protocol (RSVP) -- Version
1 Functional Specification", RFC 2205, September 1997.
Carugi & McDysan Standards Track PAGE 45
RFC 4031 Service Requirements for L3 PPVPNs April 2005
[RFC 2211] Wroclawski, J., "Specification of the Controlled-Load
Network Element Service", RFC 2211, September 1997.
[RFC 2212] Shenker, S., Partridge, C., and R. Guerin,
"Specification of Guaranteed Quality of Service", RFC
2212, September 1997.
[RFC 2251] Wahl, M., Howes, T., and S. Kille, "Lightweight
Directory Access Protocol (v3)", RFC 2251, December
1997.
[RFC 2475] Blake, S., Black, D., Carlson, M., Davies, E., Wang,
Z., and W. Weiss, "An Architecture for Differentiated
Service", RFC 2475, December 1998.
[RFC 2597] Heinanen, J., Baker, F., Weiss, W., and J. Wroclawski,
"Assured Forwarding PHB Group", RFC 2597, June 1999.
[RFC 2661] Townsley, W., Valencia, A., Rubens, A., Pall, G., Zorn,
G., and B. Palter, "Layer Two Tunneling Protocol
"L2TP"", RFC 2661, August 1999.
[RFC 2685] Fox, B. and B. Gleeson, "Virtual Private Networks
Identifier", RFC 2685, September 1999.
[RFC 3246] Davie, B., Charny, A., Bennet, J.C., Benson, K., Le
Boudec, J., Courtney, W., Davari, S., Firoiu, V., and
D. Stiliadis, "An Expedited Forwarding PHB (Per-Hop
Behavior)", RFC 3246, March 2002.
[RFC 3270] Le Faucheur, F., Wu, L., Davie, B., Davari, S.,
Vaananen, P., Krishnan, R., Cheval, P., and J.
Heinanen, "Multi-Protocol Label Switching (MPLS)
Support of Differentiated Services", RFC 3270, May
2002.
[RFC 3809] Nagarajan, A., "Generic Requirements for Provider
Provisioned Virtual Private Networks (PPVPN)", RFC
3809, June 2004.
10.2. Informative References
[2547bis] Rosen, E., Rekhter, Y. et al., "BGP/MPLS VPNs", Work in
Progress.
[IM-PPVPN] Lago, P., et al., "An Information Model for Provider
Provisioned Virtual Private Networks", Work in
Progress.
Carugi & McDysan Standards Track PAGE 46
RFC 4031 Service Requirements for L3 PPVPNs April 2005
[IM-REQ] Iyer, M., et al., "Requirements for an IP VPN Policy
Information Model", Work in Progress.
[IPSECIM] Jason, J., "IPsec Configuration Policy Model", Work in
Progress.
[CE-PPVPN] De Clercq, J., Paridaens, O., Krywaniuk, A., Wang, C.,
"An Architecture for Provider Provisioned CE-based
Virtual Private Networks using IPsec", Work in
Progress.
[IPSEC-PPVPN] Gleeson, B., "Uses of IPsec with Provider Provisioned
VPNs", Work in Progress.
[L2VPN] Rosen, E., et al., "An Architecture for L2VPNs", Work
in Progress.
[MPLSSEC] Behringer, M., "Analysis of the Security of the MPLS
Architecture", Work in Progress.
[PPVPN-TERM] Andersson, L., Madsen, T., "PPVPN Terminology", Work in
Progress.
[L3VPN-SEC] Fang, L., et al., "Security Framework for Provider
Provisioned Virtual Private Networks", Work in
Progress.
[L3VPN-FR] Callon, R., Suzuki, M., et al. "A Framework for Layer 3
Provider Provisioned Virtual Private Networks", Work in
Progress.
[PPVPN-VR] Knight, P., Ould-Brahim, H., Gleeson, B., "Network
based IP VPN Architecture using Virtual Routers", Work
in Progress.
[QPIM] Snir, Ramberg, Strassner, Cohen and Moore, "Policy QoS
Information Model", Work in Progress.
[RFC 2385] Heffernan, A., "Protection of BGP Sessions via the TCP
MD5 Signature Option", RFC 2385, August 1998.
[RFC 2764] Gleeson, B., Lin, A., Heinanen, J., Armitage, G., and
A. Malis, "A Framework for IP Based Virtual Private
Networks", RFC 2764, February 2000.
[RFC 2975] Aboba, B., Arkko, J., and D. Harrington, "Introduction
to Accounting Management", RFC 2975, October 2000.
Carugi & McDysan Standards Track PAGE 47
RFC 4031 Service Requirements for L3 PPVPNs April 2005
[RFC 2983] Black, D., "Differentiated Services and Tunnels", RFC
2983, October 2000.
[RFC 3031] Rosen, E., Viswanathan, A., and R. Callon,
"Multiprotocol Label Switching Architecture", RFC 3031,
January 2001.
[RFC 3198] Westerinen, A., Schnizlein, J., Strassner, J.,
Scherling, M., Quinn, B., Herzog, S., Huynh, A.,
Carlson, M., Perry, J., and S. Waldbusser, "Terminology
for Policy-Based Management", RFC 3198, November 2001.
[TE-INTERAS] Zhang, R., Vasseur, J.P., "MPLS Inter-AS Traffic
Engineering requirements", Work in Progress.
[VPNDISC] Squire, M. et al., "VPN Discovery Discussions and
Options", Work in Progress.
[VPNIW] Kurakami, H., et al., "Provider-Provisioned VPNs
Interworking", Work in Progress.
[VPNSEC] De Clercq, J., et al., "Considerations about possible
security extensions to BGP/MPLS VPN", Work in Progress.
[VPNTUNNEL] Worster, T., et al., "A PPVPN Layer Separation: VPN
Tunnels and Core Connectivity", Work in Progress.
[VPN-CRIT] Yu, J., Jou, L., Matthews, A ., Srinivasan, V.,
"Criteria for Evaluating VPN Implementation
Mechanisms", Work in Progress.
[VPN-NEEDS] Jacquenet, C., "Functional needs for the deployment of
an IP VPN service offering : a service provider
perspective", Work in Progress.
[Y.1311.1] Carugi, M. (editor), "Network Based IP VPN over MPLS
architecture", Y.1311.1 ITU-T Recommendation, July
2001.
[Y.1311] Knightson, K. (editor), "Network based VPNs - Generic
Architecture and Service Requirements", Y.1311 ITU-T
Recommendation, March 2002.
Carugi & McDysan Standards Track PAGE 48
RFC 4031 Service Requirements for L3 PPVPNs April 2005
Authors' Addresses
Marco Carugi (co-editor)
Nortel Networks
Parc d'activites de Magny-Chateaufort
Les Jeunes Bois - MS CTF 32B5 - Chateaufort
78928 YVELINES Cedex 9 - FRANCE
EMail: marco.carugi@nortel.com
Dave McDysan (co-editor)
MCI
22001 Loudoun County Parkway
Ashburn, VA 20147, USA
EMail: dave.mcdysan@mci.com
Luyuan Fang
AT&T
200 Laurel Ave - Room C2-3B35
Middletown, NJ 07748 USA
EMail: Luyuanfang@att.com
Ananth Nagarajan
Juniper Networks
EMail: ananth@juniper.net
Junichi Sumimoto
NTT Communications Corporation
3-20-2 Nishi-Shinjuku, Shinjuku-ku, Tokyo 163-1421, Japan
EMail: j.sumimoto@ntt.com
Rick Wilder
Alcatel
EMail: rick.wilder@alcatel.com
Carugi & McDysan Standards Track PAGE 49
RFC 4031 Service Requirements for L3 PPVPNs April 2005
Full Copyright Statement
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Carugi & McDysan Standards Track PAGE 50
Service Requirements for Layer 3 Provider Provisioned Virtual Private Networks (PPVPNs)
RFC TOTAL SIZE: 118568 bytes
PUBLICATION DATE: Tuesday, April 12th, 2005
LEGAL RIGHTS: The IETF Trust (see BCP 78)
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