Home > Articles > Networking > Voice/IP Communications

IPSec Authentication and Authorization Models

📄 Contents

  1. Extended Authentication (XAUTH) and Mode Configuration (MODE-CFG)
  2. Mode-Configuration (MODECFG)
  3. Easy VPN (EzVPN)
  4. Digital Certificates for IPSec VPNs
  5. Summary
  • Print
  • + Share This
This chapter covers IPSec features and mechanisms that are primarily targeted at the authentication of remote access users. You'll learn about XAUTH, which provides extended authentication for IPSec telecommuters by using authentication schemes such as RADIUS. MODECFG uses a push model to push attributes to the IPSec client.
This chapter is from the book

This chapter is from the book

For more information on Security, visit our Security Reference Guide or sign up for our Security Newsletter

Telecommuting is increasingly becoming a part of everyday life, and IPSec connectivity is arguably the most popular connection method that telecommuters use to connect to a VPN across the public Internet. Given that telecommuters can be anywhere in the Internet, the successful completion of authorization and authentication is critical for granting access to the VPN. This chapter explores authentication and authorization models for the IPSec telecommuter.

Extended Authentication (XAUTH) and Mode Configuration (MODE-CFG)

Authentication schemes such as Remote Authentication Dial-In User Service (RADIUS) and SecureID are commonly used for providing secure remote access. It is highly desirable to leverage these authentication mechanisms for IPSec remote access. But Internet Key Exchange (IKE) protocol, which you learned about in Chapter 2, "IPSec Overview," does not provide a method to leverage these unidirectional authentication schemes. Extended Authentication, commonly referred to as XAUTH, was developed to leverage these legacy authentication schemes with IKE.

XAUTH provides an additional level of authentication by allowing the IPSec gateway to request extended authentication from remote users, thus forcing remote users to respond with their credentials before being allowed access to the VPN. It should be noted that XAUTH functions by first forming an IKE phase 1 SA using conventional IKE, and then by extending the IKE exchange to include additional user authentication exchanges. Figure 4-1 shows an XAUTH exchange using a generic username and password authentication scheme.

04fig01.gif

Figure 4-1 Extended Authentication (XAUTH) Exchange

As shown in Figure 4-1, XAUTH uses a Request/Reply mechanism to provide the extended authentication. The XAUTH process is terminated, either when the gateway starts a SET/ACK exchange, which includes an XAUTH_STATUS attribute, or when the remote device sends a XAUTH_STATUS attribute in a REPLY message.

The XAUTH protocol defines four message types that are exchanged between the remote user and the IPSec gateway. These messages carry various attributes for the extended authentication process to work. The four XAUTH message types are:

  • ISAKMP_CFG_REQUEST
  • ISAKMP_CFG_REPLY
  • ISAKMP_CFG_SET
  • ISAKMP_CFG_ACK

A description of the XAUTH message types follows:

  • ISAKMP_CFG_REQUEST— This message is sent from the IPSec gateway to the IPSec client requesting extended authentication of the client.
  • ISAKMP_CFG_REPLY— This message must contain the filled-in authentication attributes that were requested by the gateway or, if the proper authentication attributes cannot be retrieved, this message must contain the XAUTH_STATUS attribute with a value of FAIL.
  • ISAKMP_CFG_SET— This message is sent from the gateway and is used only to state the success or failure of the authentication.
  • ISAKMP_CFG_ACK— This message is sent from the IPSec client, acknowledging receipt of the authentication result.

The XAUTH message types defined above carry various attributes. A brief description of the attributes is shown in Table 4-1.

Table 4-1. XAUTH Attributes

Attribute

Description

XAUTH_TYPE

This attribute describes the type of extended authentication method requested. Four authentication methods are defined in the protocol: Generic, RADIUS_CHAP, One Time password (OTP), and Secure ID. This is an optional attribute for the ISAKMP_CFG_REQUEST and ISAKMP_CFG_REPLY messages. The XAUTH_TYPE in a REPLY must be identical to the XAUTH_TYPE in the REQUEST. However, an XAUTH transaction may have multiple REQUEST/REPLY pairs with different XAUTH_TYPE values in each pair.

XAUTH_USER_NAME

The username may be any unique identifier of the user, such as a login name, an email address, or a X.500 Distinguished Name.

XAUTH_USER_PASSWORD

The user's password.

XAUTH_PASSCODE

A token card's passcode.

XAUTH_MESSAGE

A textual message from the gateway to the IPSec client. The message may contain a textual challenge or instruction.

XAUTH_CHALLENGE

A challenge string sent from the gateway to the IPSec client to be included in its calculation of a password. This attribute should be sent only in an ISAKMP_CFG_REQUEST message. Typically, the XAUTH_TYPE attribute dictates how the receiving device should handle the challenge. For example, RADIUS-CHAP uses the challenge to hide the password.

XAUTH_STATUS

A variable that is used to denote authentication success (OK=1) or failure (FAIL=0). This attribute must be sent in the ISAKMP_CFG_SET message, in which case it may be set to either OK or FAIL, and may be sent in a REPLY message by a remote peer, in which case it must be set to FAIL.

When a remote access user connects to an IPSec gateway and XAUTH is required by the gateway, configuration on the gateway initiates the XAUTH messages before IKE phase 2 negotiation begins. If the remote access client does not have support for the authentication method requested by the gateway, the client would send back a REPLY with the XAUTH_STATUS attribute set to FAIL, thus failing the authentication.

Example 4-1 shows the configuration of XAUTH using the RADIUS/AAA authentication method.

Example 4-1. Cisco IOS XAUTH Configuration on the IPSec Gateway

vpn-gw1-east#
!
hostname vpn-gw1-east
!
username ezvpn password 0 east
username ezvpn1@vpngroup password 0 ezvpn1east                                        

   username ezvpn2@vpngroup password 0 ezvpn2east                                        
aaa new-model
!
aaa authentication login vpn local                                                    
aaa authorization network vpn local
aaa session-id common
ip subnet-zero
!
crypto isakmp policy 1
 encr 3des
 authentication pre-share
 group 2
crypto isakmp keepalive 10 10
!
crypto ipsec transform-set vpn esp-3des esp-sha-hmac
!
crypto dynamic-map dynamic 1
 set transform-set vpn
 reverse-route remote-peer 9.1.1.33
!
!
crypto map vpn client authentication list vpn                                         
crypto map vpn isakmp authorization list vpn
crypto map vpn client configuration address respond
crypto map vpn 3 ipsec-isakmp dynamic dynamic

The addition of the following command on the crypto map enables XAUTH and triggers the XAUTH transaction after IKE phase 1 and before IKE phase 2:

crypto map map-name client authentication list list-name

As you learned in Chapter 2, "IPSec Overview," a very common deployment scenario for IPSec telecommuters is the use of IKE pre-shared key authentication with Aggressive Mode. The primary motivation for this scenario is that the IP address of an IPSec remote access user connecting to an IPSec gateway over the public Internet is typically not known in advance to the gateway. In most deployments using pre-shared keys, a single shared group key is used for all users of the VPN. What this means is that without employing some form of additional user authentication, there is no way to verify that the person connecting with that VPN client is indeed a valid user.

Imagine, for example, a situation where a laptop with a VPN client is stolen—because the VPN client is already configured with a valid group key, anyone with the laptop can connect to the VPN without any problems, as no further authentication is required! Extended Authentication (XAUTH) is widely employed to address this serious security gap. XAUTH forces users to identify themselves with a user id and a password after the group pre-shared key has been verified.

XAUTH is also referred to as "two factor authentication." The password could be a "one-time password" (for example, from a SecureID card) adding further security to such a deployment. Although the usage of XAUTH is very common and desired for the telecommuter scenario using pre-shared keys and Aggressive Mode, it can also be used with Main Mode and other authentication methods such as digital certificates. It is important to note that although XAUTH is deployed very commonly, it has not been established as a standard by the IPSec working group in the IETF, which means that it may present interoperability issues among different vendor implementations.

  • + Share This
  • 🔖 Save To Your Account

InformIT Promotional Mailings & Special Offers

I would like to receive exclusive offers and hear about products from InformIT and its family of brands. I can unsubscribe at any time.

Overview


Pearson Education, Inc., 221 River Street, Hoboken, New Jersey 07030, (Pearson) presents this site to provide information about products and services that can be purchased through this site.

This privacy notice provides an overview of our commitment to privacy and describes how we collect, protect, use and share personal information collected through this site. Please note that other Pearson websites and online products and services have their own separate privacy policies.

Collection and Use of Information


To conduct business and deliver products and services, Pearson collects and uses personal information in several ways in connection with this site, including:

Questions and Inquiries

For inquiries and questions, we collect the inquiry or question, together with name, contact details (email address, phone number and mailing address) and any other additional information voluntarily submitted to us through a Contact Us form or an email. We use this information to address the inquiry and respond to the question.

Online Store

For orders and purchases placed through our online store on this site, we collect order details, name, institution name and address (if applicable), email address, phone number, shipping and billing addresses, credit/debit card information, shipping options and any instructions. We use this information to complete transactions, fulfill orders, communicate with individuals placing orders or visiting the online store, and for related purposes.

Surveys

Pearson may offer opportunities to provide feedback or participate in surveys, including surveys evaluating Pearson products, services or sites. Participation is voluntary. Pearson collects information requested in the survey questions and uses the information to evaluate, support, maintain and improve products, services or sites, develop new products and services, conduct educational research and for other purposes specified in the survey.

Contests and Drawings

Occasionally, we may sponsor a contest or drawing. Participation is optional. Pearson collects name, contact information and other information specified on the entry form for the contest or drawing to conduct the contest or drawing. Pearson may collect additional personal information from the winners of a contest or drawing in order to award the prize and for tax reporting purposes, as required by law.

Newsletters

If you have elected to receive email newsletters or promotional mailings and special offers but want to unsubscribe, simply email information@informit.com.

Service Announcements

On rare occasions it is necessary to send out a strictly service related announcement. For instance, if our service is temporarily suspended for maintenance we might send users an email. Generally, users may not opt-out of these communications, though they can deactivate their account information. However, these communications are not promotional in nature.

Customer Service

We communicate with users on a regular basis to provide requested services and in regard to issues relating to their account we reply via email or phone in accordance with the users' wishes when a user submits their information through our Contact Us form.

Other Collection and Use of Information


Application and System Logs

Pearson automatically collects log data to help ensure the delivery, availability and security of this site. Log data may include technical information about how a user or visitor connected to this site, such as browser type, type of computer/device, operating system, internet service provider and IP address. We use this information for support purposes and to monitor the health of the site, identify problems, improve service, detect unauthorized access and fraudulent activity, prevent and respond to security incidents and appropriately scale computing resources.

Web Analytics

Pearson may use third party web trend analytical services, including Google Analytics, to collect visitor information, such as IP addresses, browser types, referring pages, pages visited and time spent on a particular site. While these analytical services collect and report information on an anonymous basis, they may use cookies to gather web trend information. The information gathered may enable Pearson (but not the third party web trend services) to link information with application and system log data. Pearson uses this information for system administration and to identify problems, improve service, detect unauthorized access and fraudulent activity, prevent and respond to security incidents, appropriately scale computing resources and otherwise support and deliver this site and its services.

Cookies and Related Technologies

This site uses cookies and similar technologies to personalize content, measure traffic patterns, control security, track use and access of information on this site, and provide interest-based messages and advertising. Users can manage and block the use of cookies through their browser. Disabling or blocking certain cookies may limit the functionality of this site.

Do Not Track

This site currently does not respond to Do Not Track signals.

Security


Pearson uses appropriate physical, administrative and technical security measures to protect personal information from unauthorized access, use and disclosure.

Children


This site is not directed to children under the age of 13.

Marketing


Pearson may send or direct marketing communications to users, provided that

  • Pearson will not use personal information collected or processed as a K-12 school service provider for the purpose of directed or targeted advertising.
  • Such marketing is consistent with applicable law and Pearson's legal obligations.
  • Pearson will not knowingly direct or send marketing communications to an individual who has expressed a preference not to receive marketing.
  • Where required by applicable law, express or implied consent to marketing exists and has not been withdrawn.

Pearson may provide personal information to a third party service provider on a restricted basis to provide marketing solely on behalf of Pearson or an affiliate or customer for whom Pearson is a service provider. Marketing preferences may be changed at any time.

Correcting/Updating Personal Information


If a user's personally identifiable information changes (such as your postal address or email address), we provide a way to correct or update that user's personal data provided to us. This can be done on the Account page. If a user no longer desires our service and desires to delete his or her account, please contact us at customer-service@informit.com and we will process the deletion of a user's account.

Choice/Opt-out


Users can always make an informed choice as to whether they should proceed with certain services offered by InformIT. If you choose to remove yourself from our mailing list(s) simply visit the following page and uncheck any communication you no longer want to receive: www.informit.com/u.aspx.

Sale of Personal Information


Pearson does not rent or sell personal information in exchange for any payment of money.

While Pearson does not sell personal information, as defined in Nevada law, Nevada residents may email a request for no sale of their personal information to NevadaDesignatedRequest@pearson.com.

Supplemental Privacy Statement for California Residents


California residents should read our Supplemental privacy statement for California residents in conjunction with this Privacy Notice. The Supplemental privacy statement for California residents explains Pearson's commitment to comply with California law and applies to personal information of California residents collected in connection with this site and the Services.

Sharing and Disclosure


Pearson may disclose personal information, as follows:

  • As required by law.
  • With the consent of the individual (or their parent, if the individual is a minor)
  • In response to a subpoena, court order or legal process, to the extent permitted or required by law
  • To protect the security and safety of individuals, data, assets and systems, consistent with applicable law
  • In connection the sale, joint venture or other transfer of some or all of its company or assets, subject to the provisions of this Privacy Notice
  • To investigate or address actual or suspected fraud or other illegal activities
  • To exercise its legal rights, including enforcement of the Terms of Use for this site or another contract
  • To affiliated Pearson companies and other companies and organizations who perform work for Pearson and are obligated to protect the privacy of personal information consistent with this Privacy Notice
  • To a school, organization, company or government agency, where Pearson collects or processes the personal information in a school setting or on behalf of such organization, company or government agency.

Links


This web site contains links to other sites. Please be aware that we are not responsible for the privacy practices of such other sites. We encourage our users to be aware when they leave our site and to read the privacy statements of each and every web site that collects Personal Information. This privacy statement applies solely to information collected by this web site.

Requests and Contact


Please contact us about this Privacy Notice or if you have any requests or questions relating to the privacy of your personal information.

Changes to this Privacy Notice


We may revise this Privacy Notice through an updated posting. We will identify the effective date of the revision in the posting. Often, updates are made to provide greater clarity or to comply with changes in regulatory requirements. If the updates involve material changes to the collection, protection, use or disclosure of Personal Information, Pearson will provide notice of the change through a conspicuous notice on this site or other appropriate way. Continued use of the site after the effective date of a posted revision evidences acceptance. Please contact us if you have questions or concerns about the Privacy Notice or any objection to any revisions.

Last Update: November 17, 2020