1、BSI Standards PublicationBS ISO/IEC 27033-5:2013Information technology Security techniques NetworksecurityPart 5: Securing communications acrossnetworks using Virtual Private Networks(VPNs)BS ISO/IEC 27033-5:2013 BRITISH STANDARDNational forewordThis British Standard is the UK implementation of ISO/
2、IEC27033-5:2013. It supersedes BS ISO/IEC 18028-5:2006 which iswithdrawn.The UK participation in its preparation was entrusted to TechnicalCommittee IST/33, IT - Security techniques.A list of organizations represented on this committee can beobtained on request to its secretary.This publication does
3、 not purport to include all the necessaryprovisions of a contract. Users are responsible for its correctapplication. The British Standards Institution 2013. Published by BSI StandardsLimited 2013ISBN 978 0 580 65102 1ICS 35.040Compliance with a British Standard cannot confer immunity fromlegal oblig
4、ations.This British Standard was published under the authority of theStandards Policy and Strategy Committee on 31 August 2013.Amendments issued since publicationDate Text affectedBS ISO/IEC 27033-5:2013Information technology Security techniques Network security Part 5: Securing communications acros
5、s networks using Virtual Private Networks (VPNs)Technologies de linformation Techniques de scurit - Scurit de rseau Partie 5: Scurit des communications au travers des rseaux utilisant des rseaux privs virtuels (VPNs) ISO/IEC 2013INTERNATIONAL STANDARDISO/IEC27033-5First edition2013-08-01Reference nu
6、mberISO/IEC 27033-5:2013(E)BS ISO/IEC 27033-5:2013ISO/IEC 27033-5:2013(E)ii ISO/IEC 2013 All rights reservedCOPYRIGHT PROTECTED DOCUMENT ISO/IEC 2013All rights reserved. Unless otherwise specified, no part of this publication may be reproduced or utilized otherwise in any form or by any means, elect
7、ronic or mechanical, including photocopying, or posting on the internet or an intranet, without prior written permission. Permission can be requested from either ISO at the address below or ISOs member body in the country of the requester.ISO copyright officeCase postale 56 CH-1211 Geneva 20Tel. + 4
8、1 22 749 01 11Fax + 41 22 749 09 47E-mail copyrightiso.orgWeb www.iso.orgPublished in SwitzerlandBS ISO/IEC 27033-5:2013ISO/IEC 27033-5:2013(E) ISO/IEC 2013 All rights reserved iiiContents PageForeword iv1 Scope . 12 Normative references 13 Terms and definitions . 14 Abbreviations. 25 Document struc
9、ture 26 Overview . 26.1 Introduction 26.2 Types of VPNs 37 Security Threats 48 Security Requirements 58.1 Overview 58.2 Confidentiality . 58.3 Integrity 68.4 Authenticity . 68.5 Authorization . 68.6 Availability 68.7 Tunnel Endpoint Security 69 Security Controls 69.1 Security aspects 69.2 Virtual ci
10、rcuits . 710 Design Techniques 710.1 Overview 710.2 Regulatory and legislative aspects . 810.3 VPN management aspects . 810.4 VPN architectural aspects 810.5 VPN technical considerations 1111 Guidelines for Product Selection 1211.1 Carrier protocol selection . 1211.2 VPN appliances 12Bibliography .1
11、4BS ISO/IEC 27033-5:2013ISO/IEC 27033-5:2013(E)ForewordISO (the International Organization for Standardization) and IEC (the International Electrotechnical Commission) form the specialized system for worldwide standardization. National bodies that are members of ISO or IEC participate in the develop
12、ment of International Standards through technical committees established by the respective organization to deal with particular fields of technical activity. ISO and IEC technical committees collaborate in fields of mutual interest. Other international organizations, governmental and non-governmenta
13、l, in liaison with ISO and IEC, also take part in the work. In the field of information technology, ISO and IEC have established a joint technical committee, ISO/IEC JTC 1.International Standards are drafted in accordance with the rules given in the ISO/IEC Directives, Part 2.The main task of the jo
14、int technical committee is to prepare International Standards. Draft International Standards adopted by the joint technical committee are circulated to national bodies for voting. Publication as an International Standard requires approval by at least 75 % of the national bodies casting a vote.Attent
15、ion is drawn to the possibility that some of the elements of this document may be the subject of patent rights. ISO and IEC shall not be held responsible for identifying any or all such patent rights.ISO/IEC 27033 was prepared by Joint Technical Committee ISO/IEC JTC 1, Information technology, Subco
16、mmittee SC 27, IT security techniques.This first edition cancels and replaces ISO/IEC 18028-5:2006, which has been technically revised.ISO/IEC 27033 consists of the following parts, under the general title Information technology Security techniques Network security: Part 1: Overview and concepts Par
17、t 2: Guidelines for the design and implementation of network security Part 3: Reference networking scenarios Threats, design techniques and control issues Part 4: Securing communications between networks using security gateways Part 5: Securing communications across networks using Virtual Private Ne
18、tworks (VPNs) Part 6: Securing wireless IP network access(Note that there may be other parts. Examples of possible topics to be covered by parts include local area networks, wide area networks, broadband networks, web hosting, Internet email, and routed access to third-party organizations. The main
19、clauses of all such parts should be Risks, Design Techniques, and Control Issues.)iv ISO/IEC 2013 All rights reservedBS ISO/IEC 27033-5:2013INTERNATIONAL STANDARD ISO/IEC 27033-5:2013(E)Information technology Security techniques Network security Part 5: Securing communications across networks using
20、Virtual Private Networks (VPNs)1 ScopeThis part of ISO/IEC 27033 gives guidelines for the selection, implementation, and monitoring of the technical controls necessary to provide network security using Virtual Private Network (VPN) connections to interconnect networks and connect remote users to net
21、works.2 Normative referencesThe following documents, in whole or in part, are normatively referenced in this document and are indispensable for its application. For dated references, only the edition cited applies. For undated references, the latest edition of the referenced document (including any
22、amendments) applies.ISO/IEC 27001:2005, Information technology Security techniques Information security management systems RequirementsISO/IEC 27002:2005, Information technology Security techniques Code of practice for information security managementISO/IEC 27005:2011, Information technology Securit
23、y techniques Information security risk managementISO/IEC 27033-1:2009, Information technology Security techniques Network security Part 1: Overview and concepts3 Terms and definitionsFor the purposes of this document, the terms and definitions given in ISO/IEC 7498 (all parts), ISO/IEC 27000, ISO/IE
24、C 27001, ISO/IEC 27002, ISO/IEC 27005, and ISO/IEC 27033-1 apply. ISO/IEC 2013 All rights reserved 1BS ISO/IEC 27033-5:2013ISO/IEC 27033-5:2013(E)4 AbbreviationsFor the purposes of this document, the abbreviated terms given in ISO/IEC 27033-1 and the following apply.AH Authentication HeaderESP Encap
25、sulating Security PayloadIKE Internet Key ExchangeIPsec Internet Protocol SecurityISAKMP Internet Security Association and Key Management ProtocolL2F Layer Two Forwarding (Protocol)LDP Label Distribution ProtocolMPPE Microsoft Point-to-Point EncryptionMPLS Multi-protocol Label SwitchingNAS Network A
26、rea StorageOSI Open Systems InterconnectionPPP Point-to-Point ProtocolPPTP Point-to-Point Tunneling ProtocolSSL Secure Sockets LayerVPLS Virtual Private LAN ServiceVPWS Virtual Private Wire ServiceWAN Wide Area Network5 Document structureThe structure of ISO/IEC 27033-5 comprises: an overview of VPN
27、s (see clause 6), security threats associated with VPNs (see clause 7), security requirements derived from threat analysis for VPNs (see clause 8), security controls associated with typical network scenarios and network technology areas using VPNs (see clause 9), various design techniques for VPNs (
28、see clause 10).6 Overview6.1 IntroductionVPNs have developed rapidly as a means of inter-connecting networks and as a method of connecting remote users to networks.2 ISO/IEC 2013 All rights reservedBS ISO/IEC 27033-5:2013ISO/IEC 27033-5:2013(E)There exists a broad range of definitions for VPNs. In t
29、heir simplest form, they provide a mechanism for establishing a secure data channel or channels over an existing network or point-to-point connection. They are assigned to the exclusive use of a restricted user group, and can be established and removed dynamically, as needed. The hosting network may
30、 be private or public.An example representation of a VPN, with the secure data channel connecting an end user to a gateway across a public network and a secure data channel connecting two gateways across a public network, is shown in Figure 1 below.User Attacker 2 Attacker 1 Gateway VPN between User
31、 and Gateway Public Network Figure 1 Example representations of a VPNRemote access using a VPN is implemented over the top of a normal point-to-point connection. The normal point-to-point connection between the local user and the remote locations is established first. Some VPNs are provided as a man
32、aged service, in which secure, reliable connectivity, management and addressing, equivalent to that on a private network, are provided on a shared infrastructure. Additional security controls, as indicated in this standard, may therefore need to be taken into account to strengthen the VPN.The data a
33、nd code transiting a VPN should be restricted to the organization using the VPN and should be kept separate from other users of the underlying network. It should not be possible for data and code belonging to other users to access the same VPN channel. The level of trust in the confidentiality and o
34、ther security aspects of the organization owning or providing the VPN should be taken into consideration when evaluating the extent of additional security controls that may be required.6.2 Types of VPNsAs stated above, there are multiple ways of expressing types of VPN.Architecturally, VPNs comprise
35、 of either: a single point-to-point connection (e.g. client device remotely accessing an organizations network via a site gateway, or a site gateway connecting to another site gateway), or a point-to-cloud connection (e.g. implemented by MPLS technology).From an OSI Basic Reference Model perspective
36、, there are three main types of VPN: Layer 2 VPNs offer a simulated LAN facility, using VPN connections running over a hosting network (e.g. a providers network) to link sites of an organization or to provide a remote connection to an organization. Typical provider offerings in this area include Vir
37、tual Private Wire Service (VPWS), ISO/IEC 2013 All rights reserved 3BS ISO/IEC 27033-5:2013ISO/IEC 27033-5:2013(E)which provides a simulated “wires only connection”, or Virtual Private LAN Service (VPLS), which provides a more complete simulated LAN service. Layer 3 VPNs offer a simulated WAN facili
38、ty, again using VPNs running over a network infrastructure. These offerings provide sites with simulated “OSI Network Layer” connectivity. A basic attraction here is the ability to use private IP addressing schemes over a public infrastructure, a practice that would not be permitted over a “normal”
39、public IP connection. Whilst private addresses can be used over public networks via NAT (Network Address Translation), this can complicate IPsec VPN establishment and use, although there are work-arounds available. Higher Layer VPNs are used for securing transactions across public networks. They typ
40、ically provide a secure channel between communicating applications, thus ensuring data confidentiality and integrity during the transaction. This type may also be known as a Layer 4 VPN because the VPN connection is usually established over TCP which is a Layer 4 protocol.7 Security ThreatsFor the f
41、oreseeable future, organizations can expect increasingly sophisticated attacks to be mounted against their systems. Attempts at unauthorized access can be malicious, for example leading to a Denial-of-Service attack, the misuse of resources, or the access to valuable information.Generally speaking t
42、hreats against a VPN can be in the form of Intrusions or Denial of Service (DoS).Intrusions happen when an outsider or malicious perpetrator takes control over part of your network; this can be a computer or other networking device (including mobile devices).Intrusions may come from any location tha
43、t has connectivity to your/the network. These attacks can come from other VPNs, the internet or the service provider core itself. The protection against these types of attacks comes from the ability to filter unwanted traffic from unwanted sources on networks ingress points. One of the typical examp
44、les of intrusion is the unauthorized access to the secure tunnel by an unauthorized entity.This can be difficult in some VPN design models which lack centralization as all sites connect to each other without traffic control.DoS attacks are another type of threat against a VPN. Both DoS attacks and i
45、ntrusions can come from another VPN, the internet or the service provider core The main difference between the two types of attacks is that for DoS attacks the attacker needs to get access or have control over one of your pieces of equipment.DoS attacks against the service provider devices can also
46、cause a denial of service to some parts of your VPN. Although it might be hard to sometimes protect your network against DoS attacks, the main protection against them lies in the good network design of the VPN.Security issues for VPNs include: address space and routing separation between VPNs carrie
47、d over the label switched network; ensuring that the internal structure of the label switched network core is not visible to outside networks (e.g. to limit information available to a potential attacker); providing resistance to denial of service attacks; providing resistance to unauthorized access
48、attacks; protecting against label spoofing (although whilst it may be possible to insert wrong labels into a label switched network from the outside, because of address separation the spoofed packet would only harm the VPN from which the spoofed packet originated).4 ISO/IEC 2013 All rights reservedB
49、S ISO/IEC 27033-5:2013ISO/IEC 27033-5:2013(E)8 Security Requirements8.1 OverviewThe primary security objective of a VPN is protection from unauthorized access. VPNs could therefore be used to fulfill wider network security objectives: to safeguard information in networks, in systems connected to networks, and the services used by them, to protect the supporting network infrastructure, to protect network management systems.To achieve the objectives outlined in the paragraph above,
