Network Working Group                                       L. Fang, Ed.
Request for Comments: 4111                                    AT&T Labs.
Category: Informational                                        July 2005
Network Working Group                                       L. Fang, Ed.
Request for Comments: 4111                                    AT&T Labs.
Category: Informational                                        July 2005

Security Framework for 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 (C) The Internet Society (2005).




This document addresses security aspects pertaining to Provider-Provisioned Virtual Private Networks (PPVPNs). First, it describes the security threats in the context of PPVPNs and defensive techniques to combat those threats. It considers security issues deriving both from malicious behavior of anyone and from negligent or incorrect behavior of the providers. It also describes how these security attacks should be detected and reported. It then discusses possible user requirements for security of a PPVPN service. These user requirements translate into corresponding provider requirements. In addition, the provider may have additional requirements to make its network infrastructure secure to a level that can meet the PPVPN customer's expectations. Finally, this document defines a template that may be used to describe and analyze the security characteristics of a specific PPVPN technology.


Table of Contents


   1.  Introduction .................................................  2
   2.  Terminology ..................................................  4
   3.  Security Reference Model .....................................  4
   4.  Security Threats .............................................  6
       4.1.  Attacks on the Data Plane ..............................  7
       4.2.  Attacks on the Control Plane ...........................  9
   5.  Defensive Techniques for PPVPN Service Providers ............. 11
       5.1.  Cryptographic Techniques ............................... 12
       5.2.  Authentication ......................................... 20
       5.3.  Access Control Techniques .............................. 22
       5.4.  Use of Isolated Infrastructure ......................... 27
   1.  Introduction .................................................  2
   2.  Terminology ..................................................  4
   3.  Security Reference Model .....................................  4
   4.  Security Threats .............................................  6
       4.1.  Attacks on the Data Plane ..............................  7
       4.2.  Attacks on the Control Plane ...........................  9
   5.  Defensive Techniques for PPVPN Service Providers ............. 11
       5.1.  Cryptographic Techniques ............................... 12
       5.2.  Authentication ......................................... 20
       5.3.  Access Control Techniques .............................. 22
       5.4.  Use of Isolated Infrastructure ......................... 27
       5.5.  Use of Aggregated Infrastructure ....................... 27
       5.6.  Service Provider Quality Control Processes ............. 28
       5.7.  Deployment of Testable PPVPN Service ................... 28
   6.  Monitoring, Detection, and Reporting of Security Attacks ..... 28
   7.  User Security Requirements ................................... 29
       7.1.  Isolation .............................................. 30
       7.2.  Protection ............................................. 30
       7.3.  Confidentiality ........................................ 31
       7.4.  CE Authentication ...................................... 31
       7.5.  Integrity .............................................. 31
       7.6.  Anti-replay ............................................ 32
   8.  Provider Security Requirements ............................... 32
       8.1.  Protection within the Core Network ..................... 32
       8.2.  Protection on the User Access Link ..................... 34
       8.3.  General Requirements for PPVPN Providers ............... 36
   9.  Security Evaluation of PPVPN Technologies .................... 37
       9.1.  Evaluating the Template ................................ 37
       9.2.  Template ............................................... 37
   10. Security Considerations ...................................... 40
   11. Contributors ................................................. 41
   12. Acknowledgement .............................................. 42
   13. Normative References ......................................... 42
   14. Informative References ....................................... 43
       5.5.  Use of Aggregated Infrastructure ....................... 27
       5.6.  Service Provider Quality Control Processes ............. 28
       5.7.  Deployment of Testable PPVPN Service ................... 28
   6.  Monitoring, Detection, and Reporting of Security Attacks ..... 28
   7.  User Security Requirements ................................... 29
       7.1.  Isolation .............................................. 30
       7.2.  Protection ............................................. 30
       7.3.  Confidentiality ........................................ 31
       7.4.  CE Authentication ...................................... 31
       7.5.  Integrity .............................................. 31
       7.6.  Anti-replay ............................................ 32
   8.  Provider Security Requirements ............................... 32
       8.1.  Protection within the Core Network ..................... 32
       8.2.  Protection on the User Access Link ..................... 34
       8.3.  General Requirements for PPVPN Providers ............... 36
   9.  Security Evaluation of PPVPN Technologies .................... 37
       9.1.  Evaluating the Template ................................ 37
       9.2.  Template ............................................... 37
   10. Security Considerations ...................................... 40
   11. Contributors ................................................. 41
   12. Acknowledgement .............................................. 42
   13. Normative References ......................................... 42
   14. Informative References ....................................... 43
1. Introduction
1. 介绍

Security is an integral aspect of Provider-Provisioned Virtual Private Network (PPVPN) services. The motivation and rationale for both Provider-Provisioned Layer-2 VPN and Provider-Provisioned Layer-3 VPN services are provided by [RFC4110] and [RFC4031]. These documents acknowledge that security is an important and integral aspect of PPVPN services, for both VPN customers and VPN service providers. Both will benefit from a PPVPN Security Framework document that lists the customer and provider security requirements related to PPVPN services, and that can be used to assess how much a particular technology protects against security threats and fulfills the security requirements.


First, we describe the security threats that are relevant in the context of PPVPNs, and the defensive techniques that can be used to combat those threats. We consider security issues deriving both from malicious or incorrect behavior of users and other parties and from negligent or incorrect behavior of the providers. An important part of security defense is the detection and report of a security attack,


which is also addressed in this document. Special considerations engendered by IP mobility within PPVPNs are not in the scope of this document.


Then, we discuss the possible user and provider security requirements for a PPVPN service. Users expectations must be met for the security characteristics of a VPN service. These user requirements translate into corresponding requirements for the providers offering the service. Furthermore, providers have security requirements to protect their network infrastructure, securing it to the level required to provide the PPVPN services in addition to other services.


Finally, we define a template that may be used to describe the security characteristics of a specific PPVPN technology in a manner consistent with the security framework described in this document. It is not within the scope of this document to analyze the security properties of specific technologies. Instead, our intention is to provide a common tool, in the form of a checklist, that may be used in other documents dedicated to an in-depth security analysis of individual PPVPN technologies to describe their security characteristics in a comprehensive and coherent way, thereby providing a common ground for comparison between different technologies.


It is important to clarify that this document is limited to describing users' and providers' security requirements that pertain to PPVPN services. It is not the intention to formulate precise "requirements" on each specific technology by defining the mechanisms and techniques that must be implemented to satisfy such users' and providers' requirements.


This document is organized as follows. Section 2 defines the terminology used in the document. Section 3 defines the security reference model for security in PPVPN networks. Section 4 describes the security threats that are specific of PPVPNs. Section 5 reviews defense techniques that may be used against those threats. Section 6 describes how attacks may be detected and reported. Section 7 discusses the user security requirements that apply to PPVPN services. Section 8 describes additional security requirements on the provider to guarantee the security of the network infrastructure providing PPVPN services. In Section 9, we provide a template that may be used to describe the security characteristics of specific PPVPN technologies. Finally, Section 10 discusses security considerations.


2. Terminology
2. 术语

This document uses PPVPN-specific terminology. Definitions and details specific to PPVPN terminology can be found in [RFC4026] and [RFC4110]. The most important definitions are repeated in this section; for other definitions, the reader is referred to [RFC4026] and [RFC4110].


CE: Customer Edge device, a router or a switch in the customer network interfacing with the service provider's network.


P: Provider Router. The Provider Router is a router in the service provider's core network that does not have interfaces directly toward the customer. A P router is used to interconnect the PE routers. A P router does not have to maintain VPN state and is thus VPN unaware.


PE: Provider Edge device, the equipment in the service provider's network that interfaces with the equipment in the customer's network.


PPVPN: Provider-Provisioned Virtual Private Network, a VPN that is configured and managed by the service provider (and thus not by the customer itself).


SP: Service Provider.


VPN: Virtual Private Network, which restricts communication between a set of sites using an IP backbone shared by traffic that is not going to or coming from those sites.


3. Security Reference Model
3. 安全参考模型

This section defines a reference model for security in PPVPN networks.


A PPVPN core network is the central network infrastructure (P and PE routers) over which PPVPN services are delivered. A PPVPN core network consists of one or more SP networks. All network elements in the core are under the operational control of one or more PPVPN service providers. Even if the PPVPN core is provided by several service providers, it appears to the PPVPN users as a single zone of trust. However, several service providers providing a common PPVPN core still have to secure themselves against the other providers. PPVPN services can also be delivered over the Internet, in which case the Internet forms a logical part of the PPVPN core.


A PPVPN user is a company, institution or residential client of the PPVPN service provider.


A PPVPN service is a private network service made available by a service provider to a PPVPN user. The service is implemented using virtual constructs built on a shared PPVPN core network. A PPVPN service interconnects sites of a PPVPN user.


Extranets are VPNs in which multiple sites are controlled by different (legal) entities. Extranets are another example of PPVPN deployment scenarios wherein restricted and controlled communication is allowed between trusted zones, often via well-defined transit points.


This document defines each PPVPN as a trusted zone and the PPVPN core as another trusted zone. A primary concern is security aspects that relate to breaches of security from the "outside" of a trusted zone to the "inside" of this zone. Figure 1 depicts the concept of trusted zones within the PPVPN framework.


      +------------+                             +------------+
      | PPVPN      +-----------------------------+      PPVPN |
      | user           PPVPN                             user |
      | site       +---------------------XXX-----+       site |
      +------------+  +------------------XXX--+  +------------+
                      |   PPVPN core     | |  |
                      +------------------| |--+
                                         | |
                                         | +------\
                                         +--------/  Internet
      +------------+                             +------------+
      | PPVPN      +-----------------------------+      PPVPN |
      | user           PPVPN                             user |
      | site       +---------------------XXX-----+       site |
      +------------+  +------------------XXX--+  +------------+
                      |   PPVPN core     | |  |
                      +------------------| |--+
                                         | |
                                         | +------\
                                         +--------/  Internet

Figure 1: The PPVPN trusted zone model


In principle, the trusted zones should be separate. However, PPVPN core networks often offer Internet access, in which case a transit point (marked "XXX" in the figure) is defined.


The key requirement of a "virtual private" network (VPN) is that the security of the trusted zone of the VPN is not compromised by sharing the core infrastructure with other VPNs.


Security against threats that originate within the same trusted zone as their targets (for example, attacks from a user in a PPVPN to other users within the same PPVPN, or attacks entirely within the core network) is outside the scope of this document.


Also outside the scope are all aspects of network security that are independent of whether a network is a PPVPN network or a private


network. For example, attacks from the Internet to a web server inside a given PPVPN will not be considered here, unless the provisioning of the PPVPN network could make a difference to the security of this server.


4. Security Threats
4. 安全威胁

This section discusses the various network security threats that may endanger PPVPNs. The discussion is limited to threats that are unique to PPVPNs, or that affect PPVPNs in unique ways. A successful attack on a particular PPVPN or on a service provider's PPVPN infrastructure may cause one or more of the following ill effects:


- observation, modification, or deletion of PPVPN user data,

- 观察、修改或删除PPVPN用户数据,

- replay of PPVPN user data,

- PPVPN用户数据的回放,

- injection of non-authentic data into a PPVPN,

- 将非真实数据注入PPVPN,

- traffic pattern analysis on PPVPN traffic,

- PPVPN流量的流量模式分析,

- disruption of PPVPN connectivity, or

- PPVPN连接中断,或

- degradation of PPVPN service quality.

- PPVPN服务质量下降。

It is useful to consider that threats to a PPVPN, whether malicious or accidental, may come from different categories of sources. For example they may come from:


- users of other PPVPNs provided by the same PPVPN service provider,

- 同一PPVPN服务提供商提供的其他PPVPN的用户,

- the PPVPN service provider or persons working for it,

- PPVPN服务提供商或其工作人员,

- other persons who obtain physical access to a service provider site,

- 能够实际访问服务提供商站点的其他人员,

- other persons who use social engineering methods to influence behavior of service provider personnel,

- 使用社会工程方法影响服务提供商人员行为的其他人员,

- users of the PPVPN itself, i.e., intra-VPN threats (such threats are beyond the scope of this document), or

- PPVPN本身的用户,即VPN内部威胁(此类威胁超出本文档的范围),或

- others, i.e., attackers from the Internet at large.

- 其他,即来自互联网的攻击者。

In the case of PPVPNs, some parties may be in more advantageous positions that enable them to launch types of attacks not available to others. For example, users of different PPVPNs provided by the


same service provider may be able to launch attacks that those who are completely outside the network cannot.


Given that security is generally a compromise between expense and risk, it is also useful to consider the likelihood of different attacks. There is at least a perceived difference in the likelihood of most types of attacks being successfully mounted in different environments, such as


- in a PPVPN contained within one service provider's network, or

- 在一个服务提供商网络中包含的PPVPN中,或

- in a PPVPN transiting the public Internet.

- 在公共互联网上传输的PPVPN中。

Most types of attacks become easier to mount, and hence more likely, as the shared infrastructure that provides VPN service expands from a single service provider to multiple cooperating providers, and then to the global Internet. Attacks that may not be sufficiently likely to warrant concern in a closely controlled environment often merit defensive measures in broader, more open environments.


The following sections discuss specific types of exploits that threaten PPVPNs.


4.1. Attacks on the Data Plane
4.1. 对数据平面的攻击

This category encompasses attacks on the PPVPN user's data, as viewed by the service provider. Note that from the PPVPN user's point of view, some of this might be control plane traffic, e.g., routing protocols running from PPVPN user site to PPVPN user site via an L2 PPVPN.

此类攻击包括服务提供商查看的对PPVPN用户数据的攻击。请注意,从PPVPN用户的角度来看,其中一些可能是控制平面流量,例如,通过L2 PPVPN从PPVPN用户站点运行到PPVPN用户站点的路由协议。

4.1.1. Unauthorized Observation of Data Traffic
4.1.1. 未经授权观察数据流量

This refers to "sniffing" VPN packets and examining their contents. This can result in exposure of confidential information. It can also be a first step in other attacks (described below) in which the recorded data is modified and re-inserted, or re-inserted unchanged.


4.1.2. Modification of Data Traffic
4.1.2. 修改数据通信量

This refers to modifying the contents of packets as they traverse the VPN.


4.1.3. Insertion of Non-authentic Data Traffic: Spoofing and Replay
4.1.3. 插入非真实数据流量:欺骗和重播

This refers to the insertion into the VPN (or "spoofing") of packets that do not belong there, with the objective of having them accepted as legitimate by the recipient. Also included in this category is


the insertion of copies of once-legitimate packets that have been recorded and replayed.


4.1.4. Unauthorized Deletion of Data Traffic
4.1.4. 未经授权删除数据流量

This refers to causing packets to be discarded as they traverse the VPN. This is a specific type of Denial-of-Service attack.


4.1.5. Unauthorized Traffic Pattern Analysis
4.1.5. 非授权交通模式分析

This refers to "sniffing" VPN packets and examining aspects or meta-aspects of them that may be visible even when the packets themselves are encrypted. An attacker might gain useful information based on the amount and timing of traffic, packet sizes, source and destination addresses, etc. For most PPVPN users, this type of attack is generally considered significantly less of a concern than are the other types discussed in this section.


4.1.6. Denial-of-Service Attacks on the VPN
4.1.6. 对VPN的拒绝服务攻击

Denial-of-Service (DoS) attacks are those in which an attacker attempts to disrupt or prevent the use of a service by its legitimate users. Taking network devices out of service, modifying their configuration, or overwhelming them with requests for service are several of the possible avenues for DoS attack.


Overwhelming the network with requests for service, otherwise known as a "resource exhaustion" DoS attack, may target any resource in the network, e.g., link bandwidth, packet forwarding capacity, session capacity for various protocols, and CPU power.


DoS attacks of the resource exhaustion type can be mounted against the data plane of a particular PPVPN by attempting to insert (spoof) an overwhelming quantity of non-authentic data into the VPN from outside of that VPN. Potential results might be to exhaust the bandwidth available to that VPN or to overwhelm the cryptographic authentication mechanisms of the VPN.


Data plane resource exhaustion attacks can also be mounted by overwhelming the service provider's general (VPN-independent) infrastructure with traffic. These attacks on the general infrastructure are not usually a PPVPN-specific issue, unless the attack is mounted by another PPVPN user from a privileged position. For example, a PPVPN user might be able to monopolize network data plane resources and thus to disrupt other PPVPNs.)


4.2. Attacks on the Control Plane
4.2. 对控制飞机的攻击

This category encompasses attacks on the control structures operated by the PPVPN service provider.


4.2.1. Denial-of-Service Attacks on Network Infrastructure
4.2.1. 对网络基础设施的拒绝服务攻击

Control plane DoS attacks can be mounted specifically against the mechanisms that the service provider uses to provide PPVPNs (e.g., IPsec, MPLS) or against the general infrastructure of the service provider (e.g., P routers or shared aspects of PE routers.) Attacks against the general infrastructure are within the scope of this document only if the attack happens in relation to the VPN service; otherwise, they are not a PPVPN-specific issue.


Of special concern for PPVPNs is denial of service to one PPVPN user caused by the activities of another. This can occur, for example, if one PPVPN user's activities are allowed to consume excessive network resources of any sort that are also needed to serve other PPVPN users.


The attacks described in the following sections may each have denial of service as one of their effects. Other DoS attacks are also possible.


4.2.2. Attacks on Service Provider Equipment via Management Interfaces

4.2.2. 通过管理接口攻击服务提供商设备

This includes unauthorized access to service provider infrastructure equipment, in order, for example, to reconfigure the equipment or to extract information (statistics, topology, etc.) about one or more PPVPNs.


This can be accomplished through malicious entrance of the systems, or as an inadvertent consequence of inadequate inter-VPN isolation in a PPVPN user self-management interface. (The former is not necessarily a PPVPN-specific issue.)


4.2.3. Social Engineering Attacks on Service Provider Infrastructure

4.2.3. 对服务提供商基础设施的社会工程攻击

Attacks in which the service provider network is reconfigured or damaged, or in which confidential information is improperly disclosed, may be mounted through manipulation of service provider personnel. These types of attacks are PPVPN-specific if they affect PPVPN-serving mechanisms. It may be observed that the organizational split (customer, service provider) that is inherent in PPVPNs may make it easier to mount such attacks against provider-provisioned


VPNs than against VPNs that are self-provisioned by the customer at the IP layer.


4.2.4. Cross-Connection of Traffic between PPVPNs
4.2.4. PPVPN之间的流量交叉连接

This refers to events where expected isolation between separate PPVPNs is breached. This includes cases such as:


- a site being connected into the "wrong" VPN,

- 连接到“错误”VPN的站点,

- two or more VPNs being improperly merged,

- 两个或多个VPN未正确合并,

- a point-to-point VPN connecting the wrong two points, or

- 连接错误两点的点对点VPN,或

- any packet or frame being improperly delivered outside the VPN it is sent in.

- 任何数据包或帧被不正确地传送到它所发送的VPN之外。

Misconnection or cross-connection of VPNs may be caused by service provider or equipment vendor error, or by the malicious action of an attacker. The breach may be physical (e.g., PE-CE links misconnected) or logical (improper device configuration).


Anecdotal evidence suggests that the cross-connection threat is one of the largest security concerns of PPVPN users (or would-be users).


4.2.5. Attacks against PPVPN Routing Protocols
4.2.5. 对PPVPN路由协议的攻击

This encompasses attacks against routing protocols that are run by the service provider and that directly support the PPVPN service. In layer 3 VPNs this, typically relates to membership discovery or to the distribution of per-VPN routes. In layer 2 VPNs, this typically relates to membership and endpoint discovery. Attacks against the use of routing protocols for the distribution of backbone (non-VPN) routes are beyond the scope of this document. Specific attacks against popular routing protocols have been widely studied and are described in [RFC3889].


4.2.6. Attacks on Route Separation
4.2.6. 对路线分隔的攻击

"Route separation" refers here to keeping the per-VPN topology and reachability information for each PPVPN separate from, and unavailable to, any other PPVPN (except as specifically intended by the service provider). This concept is only a distinct security concern for layer-3 VPN types for which the service provider is involved with the routing within the VPN (i.e., VR, BGP-MPLS, routed version of IPsec). A breach in the route separation can reveal topology and addressing information about a PPVPN. It can also cause


black hole routing or unauthorized data plane cross-connection between PPVPNs.


4.2.7. Attacks on Address Space Separation
4.2.7. 地址空间分离攻击

In layer-3 VPNs, the IP address spaces of different VPNs have to be kept separate. In layer-2 VPNs, the MAC address and VLAN spaces of different VPNs have to be kept separate. A control plane breach in this addressing separation may result in unauthorized data plane cross-connection between VPNs.


4.2.8. Other Attacks on PPVPN Control Traffic
4.2.8. 对PPVPN控制流量的其他攻击

Besides routing and management protocols (covered separately in the previous sections), a number of other control protocols may be directly involved in delivering the PPVPN service (e.g., for membership discovery and tunnel establishment in various PPVPN approaches). These include but may not be limited to:


- MPLS signaling (LDP, RSVP-TE), - IPsec signaling (IKE) , - L2TP, - BGP-based membership discovery, and - Database-based membership discovery (e.g., RADIUS-based).

- MPLS信令(LDP、RSVP-TE)、IPsec信令(IKE)、L2TP、基于BGP的成员身份发现和基于数据库的成员身份发现(例如,基于RADIUS的)。

Attacks might subvert or disrupt the activities of these protocols, for example, via impersonation or DoS attacks.


5. Defensive Techniques for PPVPN Service Providers
5. PPVPN服务提供商的防御技术

The defensive techniques discussed in this document are intended to describe methods by which some security threats can be addressed. They are not intended as requirements for all PPVPN implementations. The PPVPN provider should determine the applicability of these techniques to the provider's specific service offerings, and the PPVPN user may wish to assess the value of these techniques in regard to the user's VPN requirements.


The techniques discussed here include encryption, authentication, filtering, firewalls, access control, isolation, aggregation, and other techniques.


Nothing is ever 100% secure. Defense therefore protects against those attacks that are most likely to occur or that could have the most dire consequences. Absolute protection against these attacks is seldom achievable; more often it is sufficient to make the cost of a successful attack greater than what the adversary would be willing to expend.


Successful defense against an attack does not necessarily mean that the attack must be prevented from happening or from reaching its target. In many cases, the network can instead be designed to withstand the attack. For example, the introduction of non-authentic packets could be defended against by preventing their introduction in the first place, or by making it possible to identify and eliminate them before delivery to the PPVPN user's system. The latter is frequently a much easier task.


5.1. Cryptographic Techniques
5.1. 密码技术

PPVPN defenses against a wide variety of attacks can be enhanced by the proper application of cryptographic techniques. These are the same cryptographic techniques that are applicable to general network communications. In general, these techniques can provide confidentiality (encryption) of communication between devices, authentication of the identities of the devices, and detection of a change of the protected data during transit.


Privacy is a key part (the middle name!) of any Virtual Private Network. In a PPVPN, privacy can be provided by two mechanisms: traffic separation and encryption. This section focuses on encryption; traffic separation is addressed separately.


Several aspects of authentication are addressed in some detail in a separate "Authentication" section.


Encryption adds complexity, and thus it may not be a standard offering within every PPVPN service. There are a few reasons for this. Encryption adds an additional computational burden to the devices performing encryption and decryption. This may reduce the number of user VPN connections that can be handled on a device or otherwise reduce the capacity of the device, potentially driving up the provider's costs. Typically, configuring encryption services on devices adds to the complexity of the device configuration and adds incremental labor cost. Encrypting packets typically increases packet lengths, thereby increasing the network traffic load and the likelihood of packet fragmentation, with its increased overhead. (Packet length increase can often be mitigated to some extent by data compression techniques, but with additional computational burden.) Finally, some PPVPN providers may employ enough other defensive techniques, such as physical isolation or filtering/firewall techniques, that they may not perceive additional benefit from encryption techniques.


The trust model among the PPVPN user, the PPVPN provider, and other parts of the network is a key element in determining the applicability of encryption for any specific PPVPN implementation.


In particular, it determines where encryption should be applied, as follows.


- If the data path between the user's site and the provider's PE is not trusted, then encryption may be used on the PE-CE link.

- 如果用户站点和提供商PE之间的数据路径不受信任,则可以在PE-CE链路上使用加密。

- If some part of the backbone network is not trusted, particularly in implementations where traffic may travel across the Internet or multiple provider networks, then the PE-PE traffic may be encrypted.

- 如果骨干网络的某个部分不可信,特别是在流量可能通过互联网或多个提供商网络传输的实现中,则PE-PE流量可能被加密。

- If the PPVPN user does not trust any zone outside of its premises, it may require end-to-end or CE-CE encryption service. This service fits within the scope of this PPVPN security framework when the CE is provisioned by the PPVPN provider.

- 如果PPVPN用户不信任其场所外的任何区域,则可能需要端到端或CE-CE加密服务。当PPVPN提供商提供CE时,此服务符合此PPVPN安全框架的范围。

- If the PPVPN user requires remote access to a PPVPN from a system that is not at a PPVPN customer location (for example, access by a traveler), there may be a requirement for encrypting the traffic between that system and an access point on the PPVPN or at a customer site. If the PPVPN provider provides the access point, then the customer must cooperate with the provider to handle the access control services for the remote users. These access control services are usually implemented by using encryption, as well.

- 如果PPVPN用户需要从不在PPVPN客户位置的系统远程访问PPVPN(例如,由旅行者访问),则可能需要加密该系统与PPVPN或客户站点上的接入点之间的通信量。如果PPVPN提供商提供接入点,则客户必须与提供商合作,为远程用户处理访问控制服务。这些访问控制服务通常也通过使用加密来实现。

Although CE-CE encryption provides confidentiality against third-party interception, if the PPVPN provider has complete management control over the CE (encryption) devices, then it may be possible for the provider to gain access to the user's VPN traffic or internal network. Encryption devices can potentially be configured to use null encryption, to bypass encryption processing altogether, or to provide some means of sniffing or diverting unencrypted traffic. Thus, a PPVPN implementation using CE-CE encryption has to consider the trust relationship between the PPVPN user and provider. PPVPN users and providers may wish to negotiate a service level agreement (SLA) for CE-CE encryption that will provide an acceptable demarcation of responsibilities for management of encryption on the CE devices.


The demarcation may also be affected by the capabilities of the CE devices. For example, the CE might support some partitioning of management or a configuration lock-down ability, or it might allow both parties to verify the configuration. In general, if the managed CE-CE model is used, the PPVPN user has to have a fairly high level of trust that the PPVPN provider will properly provision and manage the CE devices.


5.1.1. IPsec in PPVPNs
5.1.1. PPVPNs中的IPsec

IPsec [RFC2401] [RFC2402] [RFC2406] [RFC2407] [RFC2411] is the security protocol of choice for encryption at the IP layer (Layer 3), as discussed in [RFC3631]. IPsec provides robust security for IP traffic between pairs of devices. Non-IP traffic must be converted to IP packets, or it cannot be transported over IPsec. Encapsulation is a common conversion method.


In the PPVPN model, IPsec can be employed to protect IP traffic between PEs, between a PE and a CE, or from CE to CE. CE-to-CE IPsec may be employed in either a provider-provisioned or a user-provisioned model. The user-provisioned CE-CE IPsec model is outside the scope of this document and outside the scope of the PPVPN Working Group. Likewise, data encryption that is performed within the user's site is outside the scope of this document, as it is simply handled as user data by the PPVPN. IPsec can also be used to protect IP traffic between a remote user and the PPVPN.

在PPVPN模型中,IPsec可用于保护PE之间、PE和CE之间或从CE到CE之间的IP流量。CE到CE IPsec可以在提供者提供的模型或用户提供的模型中使用。用户提供的CE-CE IPsec模型不在本文档的范围内,也不在PPVPN工作组的范围内。同样,在用户站点内执行的数据加密不在本文档的范围内,因为PPVPN仅将其作为用户数据处理。IPsec还可用于保护远程用户和PPVPN之间的IP通信。

IPsec does not itself specify an encryption algorithm. It can use a variety of encryption algorithms with various key lengths, such as AES encryption. There are trade-offs between key length, computational burden, and the level of security of the encryption. A full discussion of these trade-offs is beyond the scope of this document. In order to assess the level of security offered by a particular IPsec-based PPVPN service, some PPVPN users may wish to know the specific encryption algorithm and effective key length used by the PPVPN provider. However, in practice, any currently recommended IPsec encryption offers enough security to substantially reduce the likelihood of being directly targeted by an attacker. Other, weaker, links in the chain of security are likely to be attacked first. PPVPN users may wish to use a Service Level Agreement (SLA) specifying the service provider's responsibility for ensuring data confidentiality rather than to analyze the specific encryption techniques used in the PPVPN service.


For many of the PPVPN provider's network control messages and some PPVPN user requirements, cryptographic authentication of messages without encryption of the contents of the message may provide acceptable security. With IPsec, authentication of messages is provided by the Authentication Header (AH) or by the Encapsulating Security Protocol (ESP) with authentication only. Where control messages require authentication but do not use IPsec, other cryptographic authentication methods are available. Message authentication methods currently considered to be secure are based on hashed message authentication codes (HMAC) [RFC2104] implemented with a secure hash algorithm such as Secure Hash Algorithm 1 (SHA-1) [RFC3174].


One recommended mechanism for providing a combination confidentiality, data origin authentication, and connectionless integrity is the use of AES in Cipher Block Chaining (CBC) Mode, with an explicit Initialization Vector (IV) [RFC3602], as the IPsec ESP.

提供组合机密性、数据源身份验证和无连接完整性的一种推荐机制是在密码块链接(CBC)模式下使用AES,并带有一个明确的初始化向量(IV)[RFC3602],如IPsec ESP。

PPVPNs that provide differentiated services based on traffic type may encounter some conflicts with IPsec encryption of traffic. As encryption hides the content of the packets, it may not be possible to differentiate the encrypted traffic in the same manner as unencrypted traffic. Although DiffServ markings are copied to the IPsec header and can provide some differentiation, not all traffic types can be accommodated by this mechanism.


5.1.2. Encryption for Device Configuration and Management
5.1.2. 用于设备配置和管理的加密

For configuration and management of PPVPN devices, encryption and authentication of the management connection at a level comparable to that provided by IPsec is desirable.


Several methods of transporting PPVPN device management traffic offer security and confidentiality.


- Secure Shell (SSH) offers protection for TELNET [STD8] or terminal-like connections to allow device configuration.

- Secure Shell(SSH)为TELNET[STD8]或类似终端的连接提供保护,以允许设备配置。

- SNMP v3 [STD62] provides encrypted and authenticated protection for SNMP-managed devices.

- SNMP v3[STD62]为SNMP管理的设备提供加密和身份验证保护。

- Transport Layer Security (TLS) [RFC2246] and the closely-related Secure Sockets Layer (SSL) are widely used for securing HTTP-based communication, and thus can provide support for most XML- and SOAP-based device management approaches.

- 传输层安全性(TLS)[RFC2246]和密切相关的安全套接字层(SSL)广泛用于保护基于HTTP的通信,因此可以支持大多数基于XML和SOAP的设备管理方法。

- As of 2004, extensive work is proceeding in several organizations (OASIS, W3C, WS-I, and others) on securing device management traffic within a "Web Services" framework. This work uses a wide variety of security models and supports multiple security token formats, multiple trust domains, multiple signature formats, and multiple encryption technologies.

- 截至2004年,多个组织(OASIS、W3C、WS-I和其他组织)正在进行大量工作,以在“Web服务”框架内保护设备管理流量。这项工作使用了多种安全模型,并支持多种安全令牌格式、多种信任域、多种签名格式和多种加密技术。

- IPsec provides the services with security and confidentiality at the network layer. With regard to device management, its current use is primarily focused on in-band management of user-managed IPsec gateway devices.

- IPsec在网络层为服务提供安全性和机密性。关于设备管理,其当前用途主要集中于用户管理的IPsec网关设备的带内管理。

5.1.3. Cryptographic Techniques in Layer-2 PPVPNs
5.1.3. 第二层PPVPN中的密码技术

Layer-2 PPVPNs will generally not be able to use IPsec to provide encryption throughout the entire network. They may be able to use IPsec for PE-PE traffic where it is encapsulated in IP packets, but IPsec will generally not be applicable for CE-PE traffic in Layer-2 PPVPNs.


Encryption techniques for Layer-2 links are widely available but are not within the scope of this document or IETF documents in general. Layer-2 encryption could be applied to the links from CE to PE, or it could be applied from CE to CE, as long as the encrypted Layer-2 packets can be handled properly by the intervening PE devices. In addition, the upper-layer traffic transported by the Layer-2 VPN can be encrypted by the user. In this case, confidentiality will be maintained; however, this is transparent to the PPVPN provider and is outside the scope of this document.


5.1.4. End-to-End vs. Hop-by-Hop Encryption Tradeoffs in PPVPNs
5.1.4. PPVPN中端到端与逐跳加密的权衡

In PPVPNs, encryption could potentially be applied to the VPN traffic at several different places. This section discusses some of the tradeoffs in implementing encryption in several different connection topologies among different devices within a PPVPN.


Encryption typically involves a pair of devices that encrypt the traffic passing between them. The devices may be directly connected (over a single "hop"), or there may be intervening devices that transport the encrypted traffic between the pair of devices. The extreme cases involve hop-by-hop encryption between every adjacent pair of devices along a given path or "end-to-end" encryption only between the end devices along a given path. To keep this discussion within the scope of PPVPNs, we consider the "end to end" case to be CE to CE rather than fully end to end.


Figure 2 depicts a simplified PPVPN topology, showing the Customer Edge (CE) devices, the Provider Edge (PE) devices, and a variable number (three are shown) of Provider core (P) devices that might be present along the path between two sites in a single VPN, operated by a single service provider (SP).



Figure 2: Simplified PPVPN topology


Within this simplified topology and assuming that P devices are not to be involved with encryption, there are four basic feasible configurations for implementing encryption on connections among the devices:


1) Site-to-site (CE-to-CE): Encryption can be configured between the two CE devices, so that traffic will be encrypted throughout the SP's network.

1) 站点到站点(CE到CE):可以在两个CE设备之间配置加密,以便在整个SP网络中对流量进行加密。

2) Provider edge-to-edge (PE-to-PE): Encryption can be configured between the two PE devices. Unencrypted traffic is received at one PE from the customer's CE; then it is encrypted for transmission through the SP's network to the other PE, where it is decrypted and sent to the other CE.

2) 提供商边缘到边缘(PE到PE):可以在两个PE设备之间配置加密。在一个PE接收来自客户CE的未加密流量;然后对其进行加密,以便通过SP的网络传输到另一个PE,在那里对其进行解密并发送到另一个CE。

3) Access link (CE-to-PE): Encryption can be configured between the CE and PE, on each side (or on only one side).

3) 接入链路(CE到PE):可以在CE和PE之间的每一侧(或仅在一侧)配置加密。

4) Configurations 2) and 3) can be combined, with encryption running from CE to PE, then from PE to PE, and then from PE to CE.

4) 配置2)和3)可以结合使用,加密从CE运行到PE,然后从PE运行到PE,然后从PE运行到CE。

Among the four feasible configurations, key tradeoffs in considering encryption include the following:


- Vulnerability to link eavesdropping: Assuming that an attacker can observe the data in transit on the links, would it be protected by encryption?

- 链接窃听漏洞:假设攻击者可以观察到链接上传输的数据,它会受到加密保护吗?

- Vulnerability to device compromise: Assuming an attacker can get access to a device (or freely alter its configuration), would the data be protected?

- 设备泄露漏洞:假设攻击者可以访问设备(或自由更改其配置),数据会受到保护吗?

- Complexity of device configuration and management: Given Nce, the number of sites per VPN customer, and Npe, the number of PEs participating in a given VPN, how many device configurations have to be created or maintained and how do those configurations scale?

- 设备配置和管理的复杂性:给定Nce、每个VPN客户的站点数量和Npe、参与给定VPN的PE数量、必须创建或维护多少设备配置以及这些配置如何扩展?

- Processing load on devices: How many encryption or decryption operations must be done, given P packets? This influences considerations of device capacity and perhaps end-to-end delay.

- 设备上的处理负载:给定P数据包,必须执行多少加密或解密操作?这会影响对设备容量和端到端延迟的考虑。

- Ability of SP to provide enhanced services (QoS, firewall, intrusion detection, etc.): Can the SP inspect the data in order to provide these services?

- SP提供增强服务(QoS、防火墙、入侵检测等)的能力:SP能否检查数据以提供这些服务?

These tradeoffs are discussed below for each configuration.


1) Site-to-site (CE-to-CE) Configurations

1) 站点到站点(CE到CE)配置

o Link eavesdropping: Protected on all links.

o 链接窃听:在所有链接上受保护。

o Device compromise: Vulnerable to CE compromise.

o 设备损坏:易受CE损坏。

o Complexity: Single administration, responsible for one device per site (Nce devices), but overall configuration per VPN scales as Nce**2.

o 复杂性:单一管理,每个站点负责一个设备(Nce设备),但每个VPN的总体配置可扩展为Nce**2。

o Processing load: on each of two CEs, each packet is either encrypted or decrypted (2P).

o 处理负载:在两个CE中的每一个上,每个数据包要么被加密,要么被解密(2P)。

o Enhanced services: Severely limited; typically only DiffServ markings are visible to SP, allowing some QoS services.

o 强化服务:严重受限;通常,SP只能看到DiffServ标记,从而允许某些QoS服务。

2) Provider edge-to-edge (PE-to-PE) Configurations

2) 提供程序边缘到边缘(PE到PE)配置

o Link eavesdropping: Vulnerable on CE-PE links; protected on SP's network links.

o 链路窃听:CE-PE链路易受攻击;在SP的网络链接上受保护。

o Device compromise: Vulnerable to CE or PE compromise.

o 设备危害:易受CE或PE危害。

o Complexity: Single administration; Npe devices to configure. (Multiple sites may share a PE device, so Npe is typically much less than Nce.) Scalability of the overall configuration depends on the PPVPN type: If the encryption is separate per VPN context, it scales as Npe**2 per customer VPN. If the encryption is per PE, it scales as Npe**2 for all customer VPNs combined.

o 复杂性:单一管理;要配置的Npe设备。(多个站点可能共享一个PE设备,因此Npe通常比Nce小得多。)总体配置的可扩展性取决于PPVPN类型:如果加密在每个VPN上下文中是独立的,则其扩展为每个客户VPN的Npe**2。如果加密为每PE,则对于所有客户VPN组合,其扩展为Npe**2。

o Processing load: On each of two PEs, each packet is either encrypted or decrypted (2P).

o 处理负载:在两个PE中的每一个上,每个数据包要么被加密,要么被解密(2P)。

o Enhanced services: Full; SP can apply any enhancements based on detailed view of traffic.

o 加强服务:全面服务;SP可以根据流量的详细视图应用任何增强功能。

3) Access link (CE-to-PE) Configuration

3) 接入链路(CE到PE)配置

o Link eavesdropping: Protected on CE-PE link; vulnerable on SP's network links.

o 链路窃听:受CE-PE链路保护;SP的网络链接上存在漏洞。

o Device compromise: Vulnerable to CE or PE compromise.

o 设备危害:易受CE或PE危害。

o Complexity: Two administrations (customer and SP) with device configuration on each side (Nce + Npe devices to configure), but as there is no mesh, the overall configuration scales as Nce.

o 复杂性:两个管理(客户和SP),每侧都有设备配置(要配置的是Nce+Npe设备),但由于没有网格,因此总体配置按Nce扩展。

o Processing load: On each of two CEs, each packet is either encrypted or decrypted. On each of two PEs, each packet is either encrypted or decrypted (4P).

o 处理负载:在两个CE中的每一个上,每个数据包要么被加密,要么被解密。在两个PEs中的每一个上,每个数据包要么被加密,要么被解密(4P)。

o Enhanced services: Full; SP can apply any enhancements based on detailed view of traffic.

o 加强服务:全面服务;SP可以根据流量的详细视图应用任何增强功能。

4) Combined Access link and PE-to-PE (essentially hop-by-hop).

4) 组合接入链路和PE到PE(基本上是逐跳)。

o Link eavesdropping: Protected on all links.

o 链接窃听:在所有链接上受保护。

o Device compromise: Vulnerable to CE or PE compromise.

o 设备危害:易受CE或PE危害。

o Complexity: Two administrations (customer and SP), with device configuration on each side (Nce + Npe devices to configure). Scalability of the overall configuration depends on the PPVPN type. If the encryption is separate per VPN context, it scales as Npe**2 per customer VPN. If the encryption is per-PE, it scales as Npe**2 for all customer VPNs combined.

o 复杂性:两个管理(客户和SP),每侧都有设备配置(需要配置Nce+Npe设备)。总体配置的可伸缩性取决于PPVPN类型。如果加密在每个VPN上下文中是独立的,那么它将按每个客户VPN扩展为Npe**2。如果加密为每PE,则对于所有客户VPN组合,其扩展为Npe**2。

o Processing load: On each of two CEs, each packet is either encrypted or decrypted. On each of two PEs, each packet is both encrypted and decrypted (6P).

o 处理负载:在两个CE中的每一个上,每个数据包要么被加密,要么被解密。在两个PE中的每一个上,每个数据包都被加密和解密(6P)。

o Enhanced services: Full; SP can apply any enhancements based on detailed view of traffic.

o 加强服务:全面服务;SP可以根据流量的详细视图应用任何增强功能。

Given the tradeoffs discussed above, a few conclusions can be reached.


- Configurations 2 and 3, which are subsets of 4, may be appropriate alternatives to 4 under certain threat models. The remainder of these conclusions compare 1 (CE-to-CE) with 4 (combined access links and PE-to-PE).

- 配置2和3是4的子集,在某些威胁模型下可能是4的合适替代方案。这些结论的其余部分将1(CE对CE)与4(组合接入链路和PE对PE)进行比较。

- If protection from link eavesdropping is most important, then configurations 1 and 4 are equivalent.

- 如果防止链路窃听是最重要的,那么配置1和4是等效的。

- If protection from device compromise is most important and the threat is to the CE devices, both cases are equivalent; if the threat is to the PE devices, configuration 1 is best.

- 如果保护设备免受危害是最重要的,并且威胁是对CE设备的,则这两种情况是等效的;如果威胁是针对PE设备,则配置1是最佳配置。

- If reducing complexity is most important and the size of the network is very small, configuration 1 is the best. Otherwise, the comparison between options 1 and 4 is relatively complex , based on a number of issues such as, how close the CE to CE communication is to a full mesh, and what tools are used for key management. Option 1 requires configuring keys for each CE-CE

- 如果降低复杂性是最重要的,并且网络的大小非常小,那么配置1是最好的。否则,选项1和选项4之间的比较相对复杂,这取决于一系列问题,如CE-to-CE通信距离完整网格有多近,以及密钥管理使用了哪些工具。选项1要求为每个CE-CE配置密钥

pair that is communicating directly. Option 4 requires configuring keys on both CE and PE devices but may offer benefit from the fact that the number of PEs is generally much smaller than the number of CEs.


Also, under some PPVPN approaches, the scaling of 4 is further improved by sharing the same PE-PE mesh across all VPN contexts. The scaling characteristics of 4 may be increased or decreased in any given situation if the CE devices are simpler to configure than the PE devices, or vice versa. Furthermore, with option 4, the impact of operational error may be significantly increased.


- If the overall processing load is a key factor, then 1 is best.

- 如果总体处理负载是一个关键因素,那么1是最好的。

- If the availability of enhanced services support from the SP is most important, then 4 is best.

- 如果SP提供的增强服务支持是最重要的,那么4是最好的。

As a quick overall conclusion, CE-to-CE encryption provides greater protection against device compromise, but it comes at the cost of enhanced services and with additional operational complexity due to the Order(n**2) scaling of the mesh.


This analysis of site-to-site vs. hop-by-hop encryption tradeoffs does not explicitly include cases where multiple providers cooperate to provide a PPVPN service, public Internet VPN connectivity, or remote access VPN service, but many of the tradeoffs will be similar.


5.2. Authentication
5.2. 认证

In order to prevent security issues from some denial-of-service attacks or from malicious misconfiguration, it is critical that devices in the PPVPN should only accept connections or control messages from valid sources. Authentication refers to methods for ensuring that message sources are properly identified by the PPVPN devices with which they communicate. This section focuses on identifying the scenarios in which sender authentication is required, and it recommends authentication mechanisms for these scenarios.


Cryptographic techniques (authentication and encryption) do not protect against some types of denial-of-service attacks, specifically, resource exhaustion attacks based on CPU or bandwidth exhaustion. In fact, the processing required to decrypt or check authentication may in some cases increase the effect of these resource exhaustion attacks. Cryptographic techniques may, however, be useful against resource exhaustion attacks based on exhaustion of state information (e.g., TCP SYN attacks).

加密技术(身份验证和加密)无法抵御某些类型的拒绝服务攻击,特别是基于CPU或带宽耗尽的资源耗尽攻击。事实上,解密或检查身份验证所需的处理在某些情况下可能会增加这些资源耗尽攻击的效果。然而,密码技术可能对基于状态信息耗尽的资源耗尽攻击(例如,TCP SYN攻击)有用。

5.2.1. VPN Member Authentication
5.2.1. VPN成员身份验证

This category includes techniques for the CEs to verify that they are connected to the expected VPN. It includes techniques for CE-PE authentication, to verify that each specific CE and PE is actually communicating with its expected peer.


5.2.2. Management System Authentication
5.2.2. 管理系统认证

Management system authentication includes the authentication of a PE to a centrally-managed directory server when directory-based "auto-discovery" is used. It also includes authentication of a CE to its PPVPN configuration server when a configuration server system is used.


5.2.3. Peer-to-Peer Authentication
5.2.3. 对等认证

Peer-to-peer authentication includes peer authentication for network control protocols (e.g., LDP, BGP), and other peer authentication (i.e., authentication of one IPsec security gateway by another).


5.2.4. Authenticating Remote Access VPN Members
5.2.4. 验证远程访问VPN成员

This section describes methods for authentication of remote access users connecting to a VPN.


Effective authentication of individual connections is a key requirement for enabling remote access to a PPVPN from an arbitrary Internet address (for instance, by a traveler).


There are several widely used standards-based protocols to support remote access authentication. These include RADIUS [RFC2865] and DIAMETER [RFC3588]. Digital certificate systems also provide authentication. In addition, there has been extensive development and deployment of mechanisms for securely transporting individual remote access connections within tunneling protocols, including L2TP [RFC2661] and IPsec.


Remote access involves connection to a gateway device, which provides access to the PPVPN. The gateway device may be managed by the user at a user site, or by the PPVPN provider at any of several possible locations in the network. The user-managed case is of limited interest within the PPVPN security framework, and it is not considered at this time.


When a PPVPN provider manages authentication at the remote access gateway, this implies that authentication databases, which are usually extremely confidential user-managed systems, will have to be


referenced in a secure manner by the PPVPN provider. This can be accomplished through proxy authentication services, which accept an encrypted authentication credential from the remote access user, pass it to the PPVPN user's authentication system, and receive a yes/no response as to whether the user has been authenticated. Thus, the PPVPN provider does not have access to the actual authentication database, but it can use it on behalf of the PPVPN user to provide remote access authentication.


Specific cryptographic techniques for handling authentication are described in the following sections.


5.2.5. Cryptographic Techniques for Authenticating Identity
5.2.5. 身份认证的密码技术

Cryptographic techniques offer several mechanisms for authenticating the identity of devices or individuals. These include the use of shared secret keys, one-time keys generated by accessory devices or software, user-ID and password pairs, and a range of public-private key systems. Another approach is to use a hierarchical Certificate Authority system to provide digital certificates.


This section describes or provides references to the specific cryptographic approaches for authenticating identity. These approaches provide secure mechanisms for most of the authentication scenarios required in operating a PPVPN.


5.3. Access Control Techniques
5.3. 访问控制技术

Access control techniques include packet-by-packet or packet flow - by - packet flow access control by means of filters and firewalls, as well as by means of admitting a "session" for a control/signaling/management protocol that is being used to implement PPVPNs. Enforcement of access control by isolated infrastructure addresses is discussed elsewhere in this document.


We distinguish between filtering and firewalls primarily by the direction of traffic flow. We define filtering as being applicable to unidirectional traffic, whereas a firewall can analyze and control both sides of a conversation.


There are two significant corollaries of this definition:


- Routing or traffic flow symmetry: A firewall typically requires routing symmetry, which is usually enforced by locating a firewall where the network topology assures that both sides of a conversation will pass through the firewall. A filter can then operate upon traffic flowing in one direction without considering traffic in the reverse direction.

- 路由或流量对称性:防火墙通常需要路由对称性,这通常通过定位防火墙来实现,其中网络拓扑确保会话双方都将通过防火墙。然后,过滤器可以对一个方向上的流量进行操作,而不考虑反向的流量。

- Statefulness: Because it receives both sides of a conversation, a firewall may be able to obtain a significant amount of information concerning that conversation and to use this information to control access. A filter can maintain some limited state information on a unidirectional flow of packets, but it cannot determine the state of the bi-directional conversation as precisely as a firewall can.

- 状态性:因为它接收会话的双方,防火墙可能能够获取有关该会话的大量信息,并使用这些信息来控制访问。过滤器可以在单向数据包流上维护一些有限的状态信息,但它不能像防火墙那样精确地确定双向对话的状态。

5.3.1. Filtering
5.3.1. 过滤

It is relatively common for routers to filter data packets. That is, routers can look for particular values in certain fields of the IP or higher level (e.g., TCP or UDP) headers. Packets that match the criteria associated with a particular filter may be either discarded or given special treatment.


In discussing filters, it is useful to separate the filter characteristics that may be used to determine whether a packet matches a filter from the packet actions that are applied to packets that match a particular filter.


o Filter Characteristics

o 滤波器特性

Filter characteristics are used to determine whether a particular packet or set of packets matches a particular filter.


In many cases, filter characteristics may be stateless. A stateless filter determines whether a particular packet matches a filter based solely on the filter definition, on normal forwarding information (such as the next hop for a packet), and on the characteristics of that individual packet. Typically, stateless filters may consider the incoming and outgoing logical or physical interface, information in the IP header, and information in higher layer headers such as the TCP or UDP header. Information in the IP header to be considered may, for example, include source and destination IP address, Protocol field, Fragment Offset, and TOS field. Filters may also consider fields in the TCP or UDP header such as the Port fields and the SYN field in the TCP header.


Stateful filtering maintains packet-specific state information to aid in determining whether a filter has been met. For example, a device might apply stateless filters to the first fragment of a fragmented IP packet. If the filter matches, then the data unit ID may be remembered, and other fragments of the same packet may then be considered to match the same filter. Stateful filtering is more commonly done in firewalls, although firewall technology may be added to routers.


o Actions Based on Filter Results

o 基于筛选结果的操作

If a packet, or a series of packets, match a specific filter, then there are a variety of actions that may be taken based on that filter match. Examples of such actions include:


- Discard

- 丢弃

In many cases, filters may be set to catch certain undesirable packets. Examples may include packets with forged or invalid source addresses, packets that are part of a DoS or DDoS attack, or packets that are trying to access forbidden resources (such as network management packets from an unauthorized source). Where such filters are activated, it is common to silently discard the packet or set of packets matching the filter. The discarded packets may also be counted and/or logged, of course.


- Set CoS

- 设置CoS

A filter may be used to set the Class of Service associated with the packet.


- Count Packets and/or Bytes

- 对数据包和/或字节进行计数

- Rate Limit

- 利率限制

In some cases, the set of packets that match a particular filter may be limited to a specified bandwidth. Packets and/or bytes would be counted and forwarded normally up to the specified limit. Excess packets may be discarded or marked (for example, by setting a "discard eligible" bit in the IP ToS field or the MPLS EXP field).

在某些情况下,与特定过滤器匹配的分组集可能被限制在指定的带宽内。数据包和/或字节的计数和转发通常会达到指定的限制。可以丢弃或标记多余的数据包(例如,通过在IP ToS字段或MPLS EXP字段中设置“丢弃合格”位)。

- Forward and Copy

- 转发和复制

It is useful in some cases not only to forward some set of packets normally, but also to send a copy to a specified other address or interface. For example, this may be used to implement a lawful intercept capability, or to feed selected packets to an Intrusion Detection System.


o Other Issues Related to Packet Filters

o 与包过滤器相关的其他问题

There may be a very wide variation in the performance impact of filtering. This may occur both due to differences between implementations, and due to differences between types or numbers


of filters deployed. For filtering to be useful, the performance of the equipment has to be acceptable in the presence of filters.


The precise definition of "acceptable" may vary from service provider to service provider and may depend on the intended use of the filters. For example, for some uses a filter may be turned on all the time in order to set CoS, to prevent an attack, or to mitigate the effect of a possible future attack. In this case it is likely that the service provider will want the filter to have minimal or no impact on performance. In other cases, a filter may be turned on only in response to a major attack (such as a major DDoS attack). In this case a greater performance impact may be acceptable to some service providers.


A key consideration with the use of packet filters is that they can provide few options for filtering packets carrying encrypted data. Because the data itself is not accessible, only packet header information or other unencrypted fields can be used for filtering.


5.3.2. Firewalls
5.3.2. 防火墙

Firewalls provide a mechanism for control over traffic passing between different trusted zones in the PPVPN model, or between a trusted zone and an untrusted zone. Firewalls typically provide much more functionality than filters, as they may be able to apply detailed analysis and logical functions to flows and not just to individual packets. They may offer a variety of complex services, such as threshold-driven denial-of-service attack protection, virus scanning, or acting as a TCP connection proxy. As with other access control techniques, the value of firewalls depends on a clear understanding of the topologies of the PPVPN core network, the user networks, and the threat model. Their effectiveness depends on a topology with a clearly defined inside (secure) and outside (not secure).


Within the PPVPN framework, traffic typically is not allowed to pass between the various user VPNs. This inter-VPN isolation is usually not performed by a firewall, but it is a part of the basic VPN mechanism. An exception to the total isolation of VPNs is the case of "extranets", which allow specific external access to a user's VPN, potentially from another VPN. Firewalls can be used to provide the services required for secure extranet implementation.


In a PPVPN, firewalls can be applied between the public Internet and user VPNs, in cases where Internet access services are offered by the provider to the VPN user sites. In addition, firewalls may be applied between VPN user sites and any shared network-based services offered by the PPVPN provider.


Firewalls may be applied to help protect PPVPN core network functions from attacks originating from the Internet or from PPVPN user sites, but typically other defensive techniques will be used for this purpose.


Where firewalls are employed as a service to protect user VPN sites from the Internet, different VPN users, and even different sites of a single VPN user, may have varying firewall requirements. The overall PPVPN logical and physical topology, along with the capabilities of the devices implementing the firewall services, will have a significant effect on the feasibility and manageability of such varied firewall service offerings.


Another consideration with the use of firewalls is that they can provide few options for handling packets carrying encrypted data. As the data itself is not accessible, only packet header information, other unencrypted fields, or analysis of the flow of encrypted packets can be used for making decisions on accepting or rejecting encrypted traffic.


5.3.3. Access Control to Management Interfaces
5.3.3. 对管理接口的访问控制

Most of the security issues related to management interfaces can be addressed through the use of authentication techniques described in the section on authentication. However, additional security may be provided by controlling access to management interfaces in other ways.


Management interfaces, especially console ports on PPVPN devices, may be configured so that they are only accessible out of band, through a system that is physically or logically separated from the rest of the PPVPN infrastructure.


Where management interfaces are accessible in-band within the PPVPN domain, filtering or firewalling techniques can be used to restrict unauthorized in-band traffic from having access to management interfaces. Depending on device capabilities, these filtering or firewalling techniques can be configured either on other devices through which the traffic might pass, or on the individual PPVPN devices themselves.


5.4. Use of Isolated Infrastructure
5.4. 使用孤立的基础设施

One way to protect the infrastructure used for support of VPNs is to separate the VPN support resources from the resources used for other purposes (such as support of Internet services). In some cases, this may require the use of physically separate equipment for VPN services, or even a physically separate network.


For example, PE-based L3 VPNs may be run on a separate backbone not connected to the Internet, or they may use separate edge routers from those used to support Internet service. Private IP addresses (local to the provider and non-routable over the Internet) are sometimes used to provide additional separation.

例如,基于PE的L3 VPN可以在未连接到Internet的单独主干上运行,或者它们可以使用与用于支持Internet服务的路由器不同的边缘路由器。专用IP地址(提供商本地地址,不可通过Internet路由)有时用于提供额外的隔离。

It is common for CE-based L3VPNs to make use of CE devices that are dedicated to one specific VPN. In many or most cases, CE-based VPNs may make use of normal Internet services to interconnect CE devices.


5.5. Use of Aggregated Infrastructure
5.5. 使用聚合基础设施

In general it is not feasible to use a completely separate set of resources for support of each VPN. One of the main reasons for VPN services is to allow sharing of resources between multiple users, including multiple VPNs. Thus, even if VPN services make use of a separate network from Internet services, there will still be multiple VPN users sharing the same network resources. In some cases, VPN services will share the use of network resources with Internet services or other services.


It is therefore important for VPN services to provide protection between resource use by different VPNs. Thus, a well-behaved VPN user should be protected from possible misbehavior by other VPNs. This requires that limits be placed on the amount of resources that can be used by any one VPN. For example, both control traffic and user data traffic may be rate limited. In some cases or in some parts of the network where a sufficiently large number of queues are available, each VPN (and, optionally, each VPN and CoS within the VPN) may make use of a separate queue. Control-plane resources such as link bandwidth and CPU and memory resources may be reserved on a per-VPN basis.


The techniques that are used to provision resource protection between multiple VPNs served by the same infrastructure can also be used to protect VPN services from Internet services.


The use of aggregated infrastructure allows the service provider to benefit from stochastic multiplexing of multiple bursty flows and may


also, in some cases, thwart traffic pattern analysis by combining the data from multiple VPNs.


5.6. Service Provider Quality Control Processes
5.6. 服务提供商质量控制流程

Deployment of provider-provisioned VPN services requires a relatively large amount of configuration by the service provider. For example, the service provider has to configure which VPN each site belongs to, as well as QoS and SLA guarantees. This large amount of required configuration leads to the possibility of misconfiguration.


It is important for the service provider to have operational processes in place to reduce the potential impact of misconfiguration. CE-to-CE authentication may also be used to detect misconfiguration when it occurs.


5.7. Deployment of Testable PPVPN Service
5.7. 可测试PPVPN服务的部署

This refers to solutions that can readily be tested for correct configuration. For example, for a point-point VPN, checking that the intended connectivity is working largely ensures that there is not connectivity to some unintended site.


6. Monitoring, Detection, and Reporting of Security Attacks
6. 监控、检测和报告安全攻击

A PPVPN service may be subject to attacks from a variety of security threats. Many threats are described in another part of this document. Many of the defensive techniques described in this document and elsewhere provide significant levels of protection from a variety of threats. However, in addition to silently employing defensive techniques to protect against attacks, PPVPN services can add value for both providers and customers by implementing security-monitoring systems that detect and report on any security attacks that occur, regardless of whether the attacks are effective.


Attackers often begin by probing and analyzing defenses, so systems that can detect and properly report these early stages of attacks can provide significant benefits.


Information concerning attack incidents, especially if available quickly, can be useful in defending against further attacks. It can be used to help identify attackers and their specific targets at an early stage. This knowledge about attackers and targets can be used to further strengthen defenses against specific attacks or attackers, or to improve the defensive services for specific targets on an as-needed basis. Information collected on attacks may also be useful in identifying and developing defenses against novel attack types.


Monitoring systems used to detect security attacks in PPVPNs will typically operate by collecting information from Provider Edge (PE), Customer Edge (CE), and/or Provider backbone (P) devices. Security monitoring systems should have the ability to actively retrieve information from devices (e.g., SNMP get) or to passively receive reports from devices (e.g., SNMP notifications). The specific information exchanged will depend on the capabilities of the devices and on the type of VPN technology. Particular care should be given to securing the communications channel between the monitoring systems and the PPVPN devices.

用于检测PPVPN中安全攻击的监控系统通常通过从提供商边缘(PE)、客户边缘(CE)和/或提供商主干(P)设备收集信息来运行。安全监控系统应能够主动从设备检索信息(如SNMP get)或被动从设备接收报告(如SNMP通知)。交换的具体信息将取决于设备的功能和VPN技术的类型。应特别注意保护监控系统和PPVPN设备之间的通信通道。

The CE, PE, and P devices should employ efficient methods to acquire and communicate the information needed by the security monitoring systems. It is important that the communication method between PPVPN devices and security monitoring systems be designed so that it will not disrupt network operations. As an example, multiple attack events may be reported through a single message, rather than allow each attack event to trigger a separate message, which might result in a flood of messages, essentially becoming a denial-of-service attack against the monitoring system or the network.


The mechanisms for reporting security attacks should be flexible enough to meet the needs of VPN service providers, VPN customers, and regulatory agencies. The specific reports will depend on the capabilities of the devices, the security monitoring system, the type of VPN, and the service level agreements between the provider and customer.


7. User Security Requirements
7. 用户安全要求

This section defines a list of security-related requirements that the users of PPVPN services may have for their PPVPN service. Typically, these translate into requirements for the provider in offering the service.


The following sections detail various requirements that ensure the security of a given trusted zone. Since in real life there are various levels of security, a PPVPN may fulfill any or all of these security requirements. This document does not state that a PPVPN must fulfill all of these requirements to be secure. As mentioned in the Introduction, it is not within the scope of this document to define the specific requirements that each VPN technology must fulfill in order to be secure.


7.1. Isolation
7.1. 隔离

A virtual private network usually defines "private" as isolation from other PPVPNs and the Internet. More specifically, isolation has several components, which are discussed in the following sections.


7.1.1. Address Separation
7.1.1. 地址分隔

A given PPVPN can use the full Internet address range, including private address ranges [RFC1918], without interfering with other PPVPNs that use PPVPN services from the same service provider(s). When Internet access is provided (e.g., by the same service provider that is offering PPVPN service), NAT functionality may be needed.


In layer-2 VPNs, the same requirement exists for the layer 2 addressing schemes, such as MAC addresses.


7.1.2. Routing Separation
7.1.2. 路由分离

A PPVPN core must maintain routing separation between the trusted zones. This means that routing information must not leak from any trusted zone to any other, unless the zones are specifically engineered this way (e.g., for Internet access.)


In layer-2 VPNs, the switching information must be kept separate between the trusted zones, so that switching information of one PPVPN does not influence other PPVPNs or the PPVPN core.


7.1.3. Traffic Separation
7.1.3. 分道行车

Traffic from a given trusted zone must never leave this zone, and traffic from another zone must never enter this zone. Exceptions are made where zones are is specifically engineered that way (e.g., for extranet purposes or Internet access.)


7.2. Protection
7.2. 保护

The common perception is that a completely separated "private" network has defined entry points and is only subject to attack or intrusion over those entry points. By sharing a common core, a PPVPN appears to lose some of these clear interfaces to networks outside the trusted zone. Thus, one of the key security requirements of PPVPN services is that they offer the same level of protection as private networks.


7.2.1. Protection against Intrusion
7.2.1. 防止入侵

An intrusion is defined here as the penetration of a trusted zone from outside. This could be from the Internet, another PPVPN, or the core network itself.


The fact that a network is "virtual" must not expose it to additional threats over private networks. Specifically, it must not add new interfaces to other parts outside the trusted zone. Intrusions from known interfaces such as Internet gateways are outside the scope of this document.


7.2.2. Protection against Denial-of-Service Attacks
7.2.2. 防止拒绝服务攻击

A denial-of-service (DoS) attack aims at making services or devices unavailable to legitimate users. In the framework of this document, only those DoS attacks are considered that are a consequence of providing network service through a VPN. DoS attacks over the standard interfaces into a trusted zone are not considered here.


The requirement is that a PPVPN is not more vulnerable against DoS attacks than it would be if the same network were private.


7.2.3. Protection against Spoofing
7.2.3. 防止欺骗

It must not be possible to violate the integrity of a PPVPN by changing the sender identification (source address, source label, etc) of traffic in transit. For example, if two CEs are connected to the same PE, it must not be possible for one CE to send crafted packets that make the PE believe those packets are coming from the other CE, thus inserting them into the wrong PPVPN.


7.3. Confidentiality
7.3. 保密性

This requirement means that data must be cryptographically secured in transit over the PPVPN core network to avoid eavesdropping.


7.4. CE Authentication
7.4. CE认证

Where CE authentication is provided, it is not possible for an outsider to install a CE and pretend to belong to a specific PPVPN to which this CE does not belong in reality.


7.5. Integrity
7.5. 诚实正直

Data in transit must be secured in such a manner that it cannot be altered or that any alteration may be detected at the receiver.


7.6. Anti-replay
7.6. 反重播

Anti-replay means that data in transit cannot be recorded and replayed later. To protect against anti-replay attacks, the data must be cryptographically secured.


Note: Even private networks do not necessarily meet the requirements of confidentiality, integrity, and anti-reply. Thus, when private and "virtually private" PPVPN services are compared, these requirements are only applicable if the comparable private service also included these services. However, the fact that VPNs operate over a shared infrastructure may make some of these requirements more important in a VPN environment than in a private network environment.


8. Provider Security Requirements
8. 提供商安全要求

In this section, we discuss additional security requirements that the provider may have in order to secure its network infrastructure as it provides PPVPN services.


The PPVPN service provider requirements defined here are the requirements for the PPVPN core in the reference model. The core network can be implemented with different types of network technologies, and each core network may use different technologies to provide the PPVPN services to users with different levels of offered security. Therefore, a PPVPN service provider may fulfill any number of the security requirements listed in this section. This document does not state that a PPVPN must fulfill all of these requirements to be secure.


These requirements are focused on 1) how to protect the PPVPN core from various attacks outside the core, including PPVPN users and non-PPVPN alike, both accidentally and maliciously, and 2) how to protect the PPVPN user VPNs and sites themselves. Note that a PPVPN core is not more vulnerable against attacks than a core that does not provide PPVPNs. However, providing PPVPN services over such a core may lead to additional security requirements, if only because most users are expecting higher security standards in a core delivering PPVPN services.


8.1. Protection within the Core Network
8.1. 核心网络内的保护
8.1.1. Control Plane Protection
8.1.1. 控制面保护

- Protocol Authentication within the Core:

- 核心内的协议身份验证:

PPVPN technologies and infrastructure must support mechanisms for authentication of the control plane. For an IP core, IGP and BGP


sessions may be authenticated by using TCP MD5 or IPsec. If an MPLS core is used, LDP sessions may be authenticated by using TCP MD5. In addition, IGP and BGP authentication should also be considered. For a core providing layer-2 services, PE to PE authentication may also be used via IPsec.

会话可以使用TCP MD5或IPsec进行身份验证。如果使用MPLS核心,则可以使用TCP MD5对LDP会话进行身份验证。此外,还应考虑IGP和BGP认证。对于提供第2层服务的核心,也可以通过IPsec使用PE-to-PE身份验证。

With the cost of authentication coming down rapidly, the application of control plane authentication may not increase the cost of implementation for providers significantly, and it will improve the security of the core. If the core is dedicated to VPN services and there are no interconnects to third parties, then it may reduce the requirement for authentication of the core control plane.


- Elements protection

- 元素保护

Here we discuss means to hide the provider's infrastructure nodes.


A PPVPN provider may make the infrastructure routers (P and PE routers) unreachable by outside users and unauthorized internal users. For example, separate address space may be used for the infrastructure loopbacks.


Normal TTL propagation may be altered to make the backbone look like one hop from the outside, but caution should be taken for loop prevention. This prevents the backbone addresses from being exposed through trace route; however, it must also be assessed against operational requirements for end-to-end fault tracing.


An Internet backbone core may be re-engineered to make Internet routing an edge function, for example, by using MPLS label switching for all traffic within the core and possibly by making the Internet a VPN within the PPVPN core itself. This helps detach Internet access from PPVPN services.


PE devices may implement separate control plane, data plane, and management plane functionality in terms of hardware and software, to improve security. This may help limit the problems when one particular area is attacked, and it may allow each plane to implement additional security measurement separately.


PEs are often more vulnerable to attack than P routers, since, by their very nature, PEs cannot be made unreachable to outside users. Access to core trunk resources can be controlled on a per-user basis by the application of inbound rate-limiting/shaping. This can be further enhanced on a per-Class of Service basis (see section 8.2.3).


In the PE, using separate routing processes for Internet and PPVPN service may help improve the PPVPN security and better protect VPN customers. Furthermore, if the resources, such as CPU and memory, may be further separated based on applications, or even on individual VPNs, it may help provide improved security and reliability to individual VPN customers.


Many of these were not particular issues when an IP core was designed to support Internet services only. Providing PPVPN services introduces new security requirements for VPN services. Similar consideration apply to L2 VPN services.

当IP核心设计为仅支持Internet服务时,其中许多问题都不是特别的问题。提供PPVPN服务为VPN服务引入了新的安全要求。类似的考虑也适用于L2 VPN服务。

8.1.2. Data Plane Protection
8.1.2. 数据平面保护

PPVPN using IPsec technologies provides VPN users with encryption of secure user data.


In today's MPLS, ATM, and Frame Relay networks, encryption is not provided as a basic feature. Mechanisms can be used to secure the MPLS data plane and to secure the data carried over the MPLS core. Additionally, if the core is dedicated to VPN services and there are no external interconnects to third party networks, then there is no obvious need for encryption of the user data plane.


Inter-working IPsec/L3 PPVPN technologies or IPsec/L2 PPVPN technologies may be used to provide PPVPN users with end-to-end PPVPN services.

可使用互操作IPsec/L3 PPVPN技术或IPsec/L2 PPVPN技术为PPVPN用户提供端到端PPVPN服务。

8.2. Protection on the User Access Link
8.2. 对用户访问链路的保护

Peer/Neighbor protocol authentication may be used to enhance security. For example, BGP MD5 authentication may be used to enhance security on PE-CE links using eBGP. In the case of an inter-provider connection, authentication/encryption mechanisms between ASes, such as IPsec, may be used.

对等/邻居协议认证可用于增强安全性。例如,BGP MD5认证可用于使用eBGP增强PE-CE链路上的安全性。在提供商间连接的情况下,可以使用ASE之间的身份验证/加密机制,例如IPsec。

WAN link address space separation for VPN and non-VPN users may be implemented to improve security in order to protect VPN customers if multiple services are provided on the same PE platform.


Firewall/Filtering: Access control mechanisms can be used to filter out any packets destined for the service provider's infrastructure prefix or to eliminate routes identified as illegitimate.


Rate limiting may be applied to the user interface/logical interfaces against DDoS bandwidth attack. This is very helpful when the PE device is supporting both VPN services and Internet services, especially when it supports VPN and Internet services on the same physical interfaces through different logical interfaces.


8.2.1. Link Authentication
8.2.1. 链路认证

Authentication mechanisms can be employed to validate site access to the PPVPN network via fixed or logical (e.g., L2TP, IPsec) connections. When the user wishes to hold the 'secret' associated to acceptance of the access and site into the VPN, then PPVPN based solutions require the flexibility for either direct authentication by the PE itself or interaction with a customer PPVPN authentication server. Mechanisms are required in the latter case to ensure that the interaction between the PE and the customer authentication server is controlled, for example, by limiting it simply to an exchange in relation to the authentication phase and with other attributes (e.g., optional filtering of RADIUS).


8.2.2. Access Routing
8.2.2. 访问路由

Mechanisms may be used to provide control at a routing protocol level (e.g., RIP, OSPF, BGP) between the CE and PE. Per-neighbor and per-VPN routing policies may be established to enhance security and reduce the impact of a malicious or non-malicious attack on the PE, in particular, the following mechanisms should be considered:


- Limiting the number of prefixes that may be advertised into the PE on a per-access basis . Appropriate action may be taken should a limit be exceeded; for example, the PE might shut down the peer session to the CE.

- 限制可在每次访问的基础上向PE播发的前缀数量。如果超过限制,可采取适当措施;例如,PE可能会关闭与CE的对等会话。

- Applying route dampening at the PE on received routing updates.

- 在收到路由更新时在PE处应用路由阻尼。

- Definition of a per-VPN prefix limit, after which additional prefixes will not be added to the VPN routing table.

- 每个VPN前缀限制的定义,在此限制之后,将不会向VPN路由表添加其他前缀。

In the case of inter-provider connection, access protection, link authentication, and routing policies as described above may be applied. Both inbound and outbound firewall/filtering mechanism may be applied between ASes. Proper security procedures must be implemented in inter-provider VPN interconnection to protect the providers' network infrastructure and their customer VPNs. This may be custom designed for each inter-Provider VPN peering connection, and both providers must agree on it.


8.2.3. Access QoS
8.2.3. 接入服务质量

PPVPN providers offering QoS-enabled services require mechanisms to ensure that individual accesses are validated against their subscribed QOS profile and are granted access to core resources that match their service profile. Mechanisms such as per-Class of Service rate limiting/traffic shaping on ingress to the PPVPN core are one option in providing this level of control. Such mechanisms may require the per-Class of Service profile to be enforced by marking, remarking, or discarding traffic that is outside of the profile.


8.2.4. Customer VPN Monitoring Tools
8.2.4. 客户VPN监控工具

End users requiring visibility of VPN-specific statistics on the core (e.g., routing table, interface status, QoS statistics) impose requirements for mechanisms at the PE both to validate the incoming user and to limit the views available to that particular user's VPN. Mechanisms should also be considered to ensure that such access cannot be used to create a DoS attack (either malicious or accidental) on the PE itself. This could be accomplished either through separation of these resources within the PE itself or via the capability to rate-limit such traffic on a per-VPN basis.


8.3. General Requirements for PPVPN Providers
8.3. PPVPN提供商的一般要求

The PPVPN providers must support the users' security requirements as listed in Section 7. Depending on the technologies used, these requirements may include the following.


- User control plane separation: Routing isolation.

- 用户控制平面隔离:路由隔离。

- User address space separation: Supporting overlapping addresses from different VPNs.

- 用户地址空间分离:支持来自不同VPN的重叠地址。

- User data plane separation: One VPN traffic cannot be intercepted by other VPNs or any other users.

- 用户数据平面分离:一个VPN流量不能被其他VPN或任何其他用户拦截。

- Protection against intrusion, DoS attacks and spoofing.

- 防止入侵、DoS攻击和欺骗。

- Access Authentication.

- 访问验证。

- Techniques highlighted through this document identify methodologies for the protection of PPVPN resources and infrastructure.

- 本文件强调的技术确定了保护PPVPN资源和基础设施的方法。

Hardware or software bugs in equipment that lead to security breaches are outside the scope of this document.


9. Security Evaluation of PPVPN Technologies
9. PPVPN技术的安全性评估

This section presents a brief template that may be used to evaluate and summarize how a given PPVPN approach (solution) measures up against the PPVPN Security Framework. An evaluation using this template should appear in the applicability statement for each PPVPN approach.


9.1. Evaluating the Template
9.1. 评估模板

The first part of the template is in the form of a list of security assertions. For each assertion the approach is assessed and one or more of the following ratings is assigned:


- The requirement is not applicable to the VPN approach because ... (fill in reason).

- 该要求不适用于VPN方法,因为。。。(填写原因)。

- The base VPN approach completely addresses the requirement by ... (fill in technique).

- 基本VPN方法完全满足以下要求。。。(填写技巧)。

- The base VPN approach partially addresses the requirement by ... (fill in technique and extent to which it addresses the requirement).

- 基本VPN方法通过以下方式部分满足了需求。。。(填写满足要求的技术和程度)。

- An optional extension to the VPN approach completely addresses the requirement by ... (fill in technique).

- VPN方法的可选扩展完全满足以下要求。。。(填写技巧)。

- An optional extension to the VPN approach partially addresses the requirement by ... (fill in technique and extent to which it addresses the requirement).

- VPN方法的可选扩展部分解决了以下要求。。。(填写满足要求的技术和程度)。

- The requirement is addressed in a way that is beyond the scope of the VPN approach. (Explain.) (One example of this would be a VPN approach in which some aspect, such as membership discovery, is done via configuration. The protection afforded to the configuration would be beyond the scope of the VPN approach.).

- 该需求的解决方式超出了VPN方法的范围。(解释。)(这方面的一个例子是VPN方法,其中某些方面(如成员身份发现)是通过配置完成的。为配置提供的保护将超出VPN方法的范围。)。

- The VPN approach does not meet the requirement.

- VPN方法不符合要求。

9.2. Template
9.2. 样板

The following assertions solicit responses of the types listed in the previous section.


1. The approach provides complete IP address space separation for each L3 VPN.

1. 该方法为每个L3 VPN提供完整的IP地址空间分离。

2. The approach provides complete L2 address space separation for each L2 VPN.

2. 该方法为每个L2 VPN提供完整的L2地址空间分离。

3. The approach provides complete VLAN ID space separation for each L2 VPN.

3. 该方法为每个L2 VPN提供完整的VLAN ID空间分离。

4. The approach provides complete IP route separation for each L3 VPN.

4. 该方法为每个L3 VPN提供完整的IP路由分离。

5. The approach provides complete L2 forwarding separation for each L2 VPN.

5. 该方法为每个L2 VPN提供完全的L2转发分离。

6. The approach provides a means to prevent improper cross-connection of sites in separate VPNs.

6. 该方法提供了一种防止不同VPN中站点之间不正确交叉连接的方法。

7. The approach provides a means to detect improper cross-connection of sites in separate VPNs.

7. 该方法提供了一种检测单独VPN中站点的不正确交叉连接的方法。

8. The approach protects against the introduction of unauthorized packets into each VPN a. in the CE-PE link, b. in a single- or multi-provider PPVPN backbone, or c. in the Internet used as PPVPN backbone.

8. 该方法可防止未经授权的数据包引入每个VPN a。在CE-PE链接中,b。在单提供商或多提供商PPVPN主干网中,或c。在Internet上用作PPVPN主干网。

9. The approach provides confidentiality (secrecy) protection for PPVPN user data a. in the CE-PE link, b. in a single- or multi-provider PPVPN backbone, or c. in the Internet used as PPVPN backbone.

9. 该方法为PPVPN用户数据a提供机密(保密)保护。在CE-PE链接中,b。在单提供商或多提供商PPVPN主干网中,或c。在Internet上用作PPVPN主干网。

10. The approach provides sender authentication for PPVPN user data. a. in the CE-PE link, b. in a single- or multi-provider PPVPN backbone, or c. in the Internet used as PPVPN backbone.

10. 该方法为PPVPN用户数据提供发送方身份验证。A.在CE-PE链接中,b。在单提供商或多提供商PPVPN主干网中,或c。在Internet上用作PPVPN主干网。

11. The approach provides integrity protection for PPVPN user data a. in the CE-PE link, b. in a single- or multi- provider PPVPN backbone, or c. in the Internet used as PPVPN backbone.

11. 该方法为PPVPN用户数据a提供完整性保护。在CE-PE链接中,b。在单提供商或多提供商PPVPN主干网中,或c。在Internet上用作PPVPN主干网。

12. The approach provides protection against replay attacks for PPVPN user data a. in the CE-PE link, b. in a single- or multi-provider PPVPN backbone, or c. in the Internet used as PPVPN backbone.

12. 该方法为PPVPN用户数据a提供了防止重播攻击的保护。在CE-PE链接中,b。在单提供商或多提供商PPVPN主干网中,或c。在Internet上用作PPVPN主干网。

13. The approach provides protection against unauthorized traffic pattern analysis for PPVPN user data a. in the CE-PE link, b. in a single- or multi-provider PPVPN backbone, or c. in the Internet used as PPVPN backbone.

13. 该方法针对PPVPN用户数据a的未授权流量模式分析提供保护。在CE-PE链接中,b。在单提供商或多提供商PPVPN主干网中,或c。在Internet上用作PPVPN主干网。

14. The control protocol(s) used for each of the following functions provides message integrity and peer authentication

14. 用于以下每个功能的控制协议提供消息完整性和对等身份验证

a. VPN membership discovery. b. Tunnel establishment. c. VPN topology and reachability advertisement: i. PE-PE. ii. PE-CE. d. VPN provisioning and management. e. VPN monitoring, attack detection, and reporting. f. Other VPN-specific control protocols, if any (list).

a. VPN成员身份发现。B隧道设施。CVPN拓扑和可达性广告:i。PE-PE。二、PE-CE。DVPN配置和管理。EVPN监控、攻击检测和报告。F其他特定于VPN的控制协议(如有)(列表)。

The following questions solicit free-form answers.


15. Describe the protection, if any, the approach provides against PPVPN-specific DoS attacks (i.e., inter-trusted-zone DoS attacks):

15. 描述该方法针对特定于PPVPN的DoS攻击(即相互信任区域DoS攻击)提供的保护(如有):

a. Protection of the service provider infrastructure against Data Plane or Control Plane DoS attacks originated in a private (PPVPN user) network and aimed at PPVPN mechanisms.

a. 保护服务提供商基础设施免受源自专用(PPVPN用户)网络并针对PPVPN机制的数据平面或控制平面DoS攻击。

b. Protection of the service provider infrastructure against Data Plane or Control Plane DoS attacks originated in the Internet and aimed at PPVPN mechanisms.

b. 保护服务提供商基础设施免受源于Internet并针对PPVPN机制的数据平面或控制平面DoS攻击。

c. Protection of PPVPN users against Data Plane or Control Plane DoS attacks originated from the Internet or from other PPVPN users and aimed at PPVPN mechanisms.

c. 保护PPVPN用户免受来自Internet或其他PPVPN用户并针对PPVPN机制的数据平面或控制平面DoS攻击。

16. Describe the protection, if any, the approach provides against unstable or malicious operation of a PPVPN user network

16. 描述该方法针对PPVPN用户网络的不稳定或恶意操作提供的保护(如有)

a. Protection against high levels of, or malicious design of, routing traffic from PPVPN user networks to the service provider network.

a. 针对从PPVPN用户网络到服务提供商网络的路由流量的高级别或恶意设计提供保护。

b. Protection against high levels of, or malicious design of, network management traffic from PPVPN user networks to the service provider network.

b. 针对从PPVPN用户网络到服务提供商网络的高级别或恶意设计的网络管理流量提供保护。

c. Protection against worms and probes originated in the PPVPN user networks, sent toward the service provider network.

c. 针对源自PPVPN用户网络、发送至服务提供商网络的蠕虫和探测的保护。

17. Is the approach subject to any approach-specific vulnerabilities not specifically addressed by this template? If so, describe the defense or mitigation, if any, that the approach provides for each.

17. 该方法是否受到本模板未明确解决的任何方法特定漏洞的影响?如果是,请描述该方法为每种方法提供的防御或缓解措施(如有)。

10. Security Considerations
10. 安全考虑

Security considerations constitute the sole subject of this memo and hence are discussed throughout. Here we recap what has been presented and explain at a very high level the role of each type of consideration in an overall secure PPVPN system. The document describes a number of potential security threats. Some of these threats have already been observed occurring in running networks; others are largely theoretical at this time.


DoS attacks and intrusion attacks from the Internet against service provider infrastructure have been seen. DoS "attacks" (typically not malicious) have also been seen in which CE equipment overwhelms PE equipment with high quantities or rates of packet traffic or routing information. Operational/provisioning errors are cited by service providers as one of their prime concerns.


The document describes a variety of defensive techniques that may be used to counter the suspected threats. All of the techniques presented involve mature and widely implemented technologies that are practical to implement.


The document describes the importance of detecting, monitoring, and reporting both successful and unsuccessful attacks. These activities are essential for "understanding one's enemy", mobilizing new defenses, and obtaining metrics about how secure the PPVPN service is. As such, they are vital components of any complete PPVPN security system.


The document evaluates PPVPN security requirements from a customer perspective and from a service provider perspective. These sections re-evaluate the identified threats from the perspectives of the various stakeholders and are meant to assist equipment vendors and service providers, who must ultimately decide what threats to protect against in any given equipment or service offering.


Finally, the document includes a template for use by authors of PPVPN technical solutions for evaluating how those solutions measure up against the security considerations presented in this memo.


11. Contributors
11. 贡献者

The following people made major contributions to writing this document: Michael Behringer, Ross Callon, Fabio Chiussi, Jeremy De Clerque, Paul Hitchen, and Paul Knignt.


Michael Behringer Cisco Village d'Entreprises Green Side, Phone: +33.49723-2652 400, Avenue Roumanille, Bat. T 3 EMail: 06410 Biot, Sophia Antipolis France

迈克尔·贝林格·思科格林赛德创业村,电话:+33.49723-2652400,巴特州鲁马尼尔大道。T 3电子邮件:mbehring@cisco.com06410比奥,索菲亚安提波利斯法国

Ross Callon Juniper Networks 10 Technology Park Drive Phone: 978-692-6724 Westford, MA 01886 EMail:

Ross Callon Juniper Networks 10 Technology Park Drive电话:978-692-6724马萨诸塞州韦斯特福德01886电子邮件

Fabio Chiussi Phone: 1 978 367-8965 Airvana EMail: 19 Alpha Road Chelmsford, Massachusetts 01824

Fabio Chiussi电话:1 978 367-8965 Airvana电子邮件:fabio@airvananet.com马萨诸塞州切姆斯福德阿尔法路19号01824

Jeremy De Clercq Alcatel Fr. Wellesplein 1, 2018 Antwerpen EMail: Belgium

Jeremy De Clercq Alcatel Fr.Welleslein 2018年1月1日安特卫普电子邮件:Jeremy.De_clercq@alcatel.be比利时

Mark Duffy Sonus Networks 250 Apollo Drive Phone: 1 978-614-8748 Chelmsford, MA 01824 EMail:

Mark Duffy Sonus Networks 250阿波罗大道电话:1 978-614-8748马萨诸塞州切姆斯福德01824电子邮件

Paul Hitchen BT BT Adastral Park Martlesham Heath Phone: 44-1473-606-344 Ipswich IP53RE EMail: UK

Paul Hitchen英国电信公司Adastral Park Martlesham Heath电话:44-1473-606-344 Ipswich IP53RE电子邮件:Paul。hitchen@bt.com英国

Paul Knight Nortel 600 Technology Park Drive Phone: 978-288-6414 Billerica, MA 01821 EMail:

Paul Knight Nortel 600 Technology Park Drive电话:978-288-6414马萨诸塞州Billerica 01821电子邮件:Paul。

12. Acknowledgement
12. 确认

The author and contributors would also like to acknowledge the helpful comments and suggestions from Paul Hoffman, Eric Gray, Ron Bonica, Chris Chase, Jerry Ash, and Stewart Bryant.


13. Normative References
13. 规范性引用文件

[RFC1918] Rekhter, Y., Moskowitz, B., Karrenberg, D., de Groot, G., and E. Lear, "Address Allocation for Private Internets", BCP 5, RFC 1918, February 1996.

[RFC1918]Rekhter,Y.,Moskowitz,B.,Karrenberg,D.,de Groot,G.,和E.Lear,“私人互联网地址分配”,BCP 5,RFC 1918,1996年2月。

[RFC2246] Dierks, T. and C. Allen, "The TLS Protocol Version 1.0", RFC 2246, January 1999.


[RFC2401] Kent, S. and R. Atkinson, "Security Architecture for the Internet Protocol", RFC 2401, November 1998.

[RFC2401]Kent,S.和R.Atkinson,“互联网协议的安全架构”,RFC 2401,1998年11月。

[RFC2402] Kent, S. and R. Atkinson, "IP Authentication Header", RFC 2402, November 1998.

[RFC2402]Kent,S.和R.Atkinson,“IP认证头”,RFC 2402,1998年11月。

[RFC2406] Kent, S. and R. Atkinson, "IP Encapsulating Security Payload (ESP)", RFC 2406, November 1998.

[RFC2406]Kent,S.和R.Atkinson,“IP封装安全有效载荷(ESP)”,RFC 2406,1998年11月。

[RFC2407] Piper, D., "The Internet IP Security Domain of Interpretation for ISAKMP", RFC 2407, November 1998.

[RFC2407]Piper,D.,“ISAKMP解释的互联网IP安全域”,RFC 2407,1998年11月。

[RFC2661] Townsley, W., Valencia, A., Rubens, A., Pall, G., Zorn, G., and B. Palter, "Layer Two Tunneling Protocol "L2TP"", RFC 2661, August 1999.

[RFC2661]汤斯利,W.,瓦伦西亚,A.,鲁本斯,A.,帕尔,G.,佐恩,G.,和B.帕尔特,“第二层隧道协议“L2TP”,RFC 26611999年8月。

[RFC2865] Rigney, C., Willens, S., Rubens, A., and W. Simpson, "Remote Authentication Dial In User Service (RADIUS)", RFC 2865, June 2000.

[RFC2865]Rigney,C.,Willens,S.,Rubens,A.,和W.Simpson,“远程认证拨入用户服务(RADIUS)”,RFC 28652000年6月。

[RFC3588] Calhoun, P., Loughney, J., Guttman, E., Zorn, G., and J. Arkko, "Diameter Base Protocol", RFC 3588, September 2003.

[RFC3588]Calhoun,P.,Loughney,J.,Guttman,E.,Zorn,G.,和J.Arkko,“直径基础协议”,RFC 3588,2003年9月。

[RFC3602] Frankel, S., Glenn, R., and S. Kelly, "The AES-CBC Cipher Algorithm and Its Use with IPsec", RFC 3602, September 2003.

[RFC3602]Frankel,S.,Glenn,R.,和S.Kelly,“AES-CBC密码算法及其在IPsec中的使用”,RFC 3602,2003年9月。

[STD62] Harrington, D., Presuhn, R., and B. Wijnen, "An Architecture for Describing Simple Network Management Protocol (SNMP) Management Frameworks", STD 62, RFC 3411, December 2002.

[STD62]Harrington,D.,Presuhn,R.,和B.Wijnen,“描述简单网络管理协议(SNMP)管理框架的体系结构”,STD 62,RFC 3411,2002年12月。

Case, J., Harrington, D., Presuhn, R., and B. Wijnen, "Message Processing and Dispatching for the Simple Network Management Protocol (SNMP)", STD 62, RFC 3412, December 2002.

Case,J.,Harrington,D.,Presohn,R.,和B.Wijnen,“简单网络管理协议(SNMP)的消息处理和调度”,STD 62,RFC 3412,2002年12月。

Levi, D., Meyer, P., and B. Stewart, "Simple Network Management Protocol (SNMP) Applications", STD 62, RFC 3413, December 2002.

Levi,D.,Meyer,P.,和B.Stewart,“简单网络管理协议(SNMP)应用”,STD 62,RFC 3413,2002年12月。

Blumenthal, U. and B. Wijnen, "User-based Security Model (USM) for version 3 of the Simple Network Management Protocol (SNMPv3)", STD 62, RFC 3414, December 2002.

Blumenthal,U.和B.Wijnen,“简单网络管理协议(SNMPv3)第3版的基于用户的安全模型(USM)”,STD 62,RFC 3414,2002年12月。

Wijnen, B., Presuhn, R., and K. McCloghrie, "View-based Access Control Model (VACM) for the Simple Network Management Protocol (SNMP)", STD 62, RFC 3415, December 2002.

Wijnen,B.,Presuhn,R.,和K.McCloghrie,“用于简单网络管理协议(SNMP)的基于视图的访问控制模型(VACM)”,STD 62,RFC 3415,2002年12月。

Presuhn, R., "Version 2 of the Protocol Operations for the Simple Network Management Protocol (SNMP)", STD 62, RFC 3416, December 2002.

Presohn,R.,“简单网络管理协议(SNMP)的协议操作第2版”,STD 62,RFC 3416,2002年12月。

Presuhn, R., "Transport Mappings for the Simple Network Management Protocol (SNMP)", STD 62, RFC 3417, December 2002.

Presohn,R.,“简单网络管理协议(SNMP)的传输映射”,STD 62,RFC 34172002年12月。

Presuhn, R., "Management Information Base (MIB) for the Simple Network Management Protocol (SNMP)", STD 62, RFC 3418, December 2002.

Presohn,R.,“简单网络管理协议(SNMP)的管理信息库(MIB)”,STD 62,RFC 3418,2002年12月。

[STD8] Postel, J. and J. Reynolds, "Telnet Protocol Specification", STD 8, RFC 854, May 1983.

[STD8]Postel,J.和J.Reynolds,“Telnet协议规范”,STD 8,RFC 854,1983年5月。

14. Informative References
14. 资料性引用

[RFC2104] Krawczyk, H., Bellare, M., and R. Canetti, "HMAC: Keyed-Hashing for Message Authentication", RFC 2104, February 1997.

[RFC2104]Krawczyk,H.,Bellare,M.,和R.Canetti,“HMAC:用于消息认证的键控哈希”,RFC 2104,1997年2月。

[RFC2411] Thayer, R., Doraswamy, N., and R. Glenn, "IP Security Document Roadmap", RFC 2411, November 1998.

[RFC2411]Thayer,R.,Doraswamy,N.,和R.Glenn,“IP安全文档路线图”,RFC 24111998年11月。

[RFC3174] Eastlake 3rd, D. and P. Jones, "US Secure Hash Algorithm 1 (SHA1)", RFC 3174, September 2001.

[RFC3174]Eastlake 3rd,D.和P.Jones,“美国安全哈希算法1(SHA1)”,RFC 3174,2001年9月。

[RFC3631] Bellovin, S., Schiller, J., and C. Kaufman, "Security Mechanisms for the Internet", RFC 3631, December 2003.

[RFC3631]Bellovin,S.,Schiller,J.,和C.Kaufman,“互联网的安全机制”,RFC 36312003年12月。

[RFC3889] Barbir, A., Murphy, S., and Y. Yang, "Generic Threats to Routing Protocols", RFC 3889, October 2004.

[RFC3889]Barbir,A.,Murphy,S.,和Y.Yang,“路由协议的一般威胁”,RFC 3889,2004年10月。

[RFC4026] Andersson, L. and T. Madsen, "Provider Provisioned Virtual Private Network (VPN) Terminology", RFC 4026, March 2005.

[RFC4026]Andersson,L.和T.Madsen,“提供商提供的虚拟专用网络(VPN)术语”,RFC 4026,2005年3月。

[RFC4031] Carugi, M. and D. McDysan, Eds., "Service Requirements for Layer 3 Provider Provisioned Virtual Private Networks (PPVPNs)", RFC 4031, April 2005.

[RFC4031]Carugi,M.和D.McDysan,编辑,“第3层提供商提供的虚拟专用网络(PPVPN)的服务要求”,RFC 4031,2005年4月。

[RFC4110] Callon, R. and M. Suzuki, "A Framework for Layer 3 Provider Provisioned Virtual Private Networks", RFC 4110, July 2005.

[RFC4110]Callon,R.和M.Suzuki,“第3层提供商提供的虚拟专用网络框架”,RFC 4110,2005年7月。

Author's Address


Luyuan Fang AT&T Labs. 200 Laurel Avenue, Room C2-3B35 Middletown, NJ 07748


Phone: 732-420-1921 EMail:


Full Copyright Statement


Copyright (C) The Internet Society (2005).


This document is subject to the rights, licenses and restrictions contained in BCP 78, and except as set forth therein, the authors retain all their rights.

本文件受BCP 78中包含的权利、许可和限制的约束,除其中规定外,作者保留其所有权利。



Intellectual Property


The IETF takes no position regarding the validity or scope of any Intellectual Property Rights or other rights that might be claimed to pertain to the implementation or use of the technology described in this document or the extent to which any license under such rights might or might not be available; nor does it represent that it has made any independent effort to identify any such rights. Information on the procedures with respect to rights in RFC documents can be found in BCP 78 and BCP 79.

IETF对可能声称与本文件所述技术的实施或使用有关的任何知识产权或其他权利的有效性或范围,或此类权利下的任何许可可能或可能不可用的程度,不采取任何立场;它也不表示它已作出任何独立努力来确定任何此类权利。有关RFC文件中权利的程序信息,请参见BCP 78和BCP 79。

Copies of IPR disclosures made to the IETF Secretariat and any assurances of licenses to be made available, or the result of an attempt made to obtain a general license or permission for the use of such proprietary rights by implementers or users of this specification can be obtained from the IETF on-line IPR repository at


The IETF invites any interested party to bring to its attention any copyrights, patents or patent applications, or other proprietary rights that may cover technology that may be required to implement this standard. Please address the information to the IETF at




Funding for the RFC Editor function is currently provided by the Internet Society.