Cisco IOS Security Configuration Guide: Securing User Services, Release 12.4

MSCHAP Version 2

The MSCHAP Version 2 feature (introduced in Cisco IOS Release 12.2(2)XB5) allows Cisco routers to utilize Microsoft Challenge Handshake Authentication Protocol Version 2 (MSCHAP V2) authentication for PPP connections between a computer using a Microsoft Windows operating system and a network access server (NAS).

For Cisco IOS Release 12.4(6)T, MSCHAP V2 now supports a new feature: AAA Support for MSCHAPv2 Password Aging. Prior to Cisco IOS Release 12.4(6)T, when Password Authentication Protocol (PAP)-based clients sent username and password values to the authentication, authorization, and accounting (AAA) subsystem, AAA generated an authentication request to the RADIUS server. If the password expired, the RADIUS server replied with an authentication failure message. The reason for the authentication failure was not passed back to AAA subsystem; thus, users were denied access because of authentication failure but were not informed why they were denied access.

The Password Aging feature, available in Cisco IOS Release 12.4(6)T, notifies crypto-based clients that the password has expired and provides a generic way for the user to change the password. The Password Aging feature supports only crypto-based clients.

Finding Feature Information

Your software release may not support all the features documented in this module. For the latest feature information and caveats, see the release notes for your platform and software release. To find information about the features documented in this module, and to see a list of the releases in which each feature is supported, see the "Feature Information for MSCHAP Version 2" section.

Use Cisco Feature Navigator to find information about platform support and Cisco IOS and Catalyst OS software image support. To access Cisco Feature Navigator, go to http://tools.cisco.com/ITDIT/CFN/jsp/index.jsp. An account on Cisco.com is not required.

Contents

•Prerequisites for MSCHAP Version 2

•Restrictions for MSCHAP Version 2

•Information About MSCHAP Version 2

•How to Configure MSCHAP Version 2

•Configuration Examples

•Additional References

•Feature Information for MSCHAP Version 2

Prerequisites for MSCHAP Version 2

•Configure an interface type and enter interface configuration mode by using the interface command.

•Configure the interface for PPP encapsulation by using the encapsulation command.

•Be sure that the client operating system supports all MSCHAP V2 capabilities.

•For Cisco IOS Release 12.4(6)T, the Password Aging feature only supports RADIUS authentication for crypto-based clients.

•To ensure that the MSCHAP Version 2 features correctly interpret the authentication failure attributes sent by the RADIUS server, you must configure the ppp max-bad-auth command and set the number of authentication retries at two or more.

•In order for the MSCHAP Version 2 feature to support the ability to change a password, the authentication failure attribute, which is sent by the RADIUS server, must be correctly interpreted as described in "Configuring MSCHAP V2 Authentication" section.

In addition, the radius server vsa send authentication command must be configured, allowing the RADIUS client to send a vendor-specific attribute to the RADIUS server. The Change Password feature is supported only for RADIUS authentication.

•The Microsoft Windows 2000, Microsoft Windows XP, and Microsoft Windows NT operating systems have a known caveat that prevents the Change Password feature from working. You must download a patch from Microsoft at the following URL:

http://support.microsoft.com/default.aspx?scid=kb;en-us;Q326770

For more information on completing these tasks, see the section "PPP Configuration" in the
Cisco IOS Dial Technologies Configuration Guide, Release 12.4T. The RADIUS server must be configured for authentication. Refer to vendor-specific documentation for information on configuring RADIUS authentication on the RADIUS server.

Restrictions for MSCHAP Version 2

•MSCHAP V2 authentication is not compatible with MSCHAP V1 authentication.

•The change password option is supported only for RADIUS authentication and is not available for local authentication.

Information About MSCHAP Version 2

MSCHAP V2 authentication is the default authentication method used by the Microsoft Windows 2000 operating system. Cisco routers that support this authentication method enable Microsoft Windows 2000 operating system users to establish remote PPP sessions without configuring an authentication method on the client.

MSCHAP V2 authentication introduced an additional feature not available with MSCHAP V1 or standard CHAP authentication: the Change Password feature. This features allows the client to change the account password if the RADIUS server reports that the password has expired.

Note MSCHAP V2 authentication is an updated version of MSCHAP that is similar to but incompatible with MSCHAP Version 1 (V1). MSCHAP V2 introduces mutual authentication between peers and a Change Password feature.

How to Configure MSCHAP Version 2

See the following sections for configuration tasks for the MSCHAP Version 2 feature.

•"Configuring MSCHAP V2 Authentication" section (required)

•"Verifying MSCHAP V2 Configuration" section (optional)

•"Configuring Password Aging for Crypto-Based Clients" section (optional)

Configuring MSCHAP V2 Authentication

To configure the NAS to accept MSCHAP V2 authentication for local or RADIUS authentication and to allow proper interpretation of authentication failure attributes and vendor-specific RADIUS attributes for RADIUS authentication, use the following commands beginning in global configuration mode.

SUMMARY STEPS

1. enable

2. configure terminal

3. radius-server vsa send authentication

4. interface type number

5. ppp max-bad-auth number

6. ppp authentication ms-chap-v2

7. end

	Command	Purpose
Step 1	enable Example: Router> enable	Enables privileged EXEC mode. •Enter your password if prompted.
Step 2	configure terminal Example: Router# configure terminal	Enters global configuration mode.
Step 3	radius-server vsa send authentication Example: Router(config)# radius-server vsa send authentication	Configures the NAS to recognize and use vendor-specific attributes.
Step 4	interface type number Example: Router(config)# interface FastEthernet 0/1	Configures an interface type and enters interface configuration mode.
Step 5	ppp max-bad-auth number Example: Router(config-if)# ppp max-bad-auth 2	Configures a point-to-point interface to reset immediately after an authentication failure or within a specified number of authentication retries. •The default value for the number argument is 0 seconds (immediately). •The range is between 0 and 255. Note The number argument must be set to a value of at least 2 for authentication failure attributes to be interpreted by the NAS.
Step 6	ppp authentication ms-chap-v2 Example: Router(config-if)# ppp authentication ms-chap-v2	Enables MSCHAP V2 authentication on a NAS.
Step 7	end Example: Router(config-if)# end	Returns to privileged EXEC mode.

Verifying MSCHAP V2 Configuration

To verify that the MSCHAP Version 2 feature is configured properly, perform the following steps.

SUMMARY STEPS

1. show running-config interface type number

2. debug ppp negotiation

3. debug ppp authentication

DETAILED STEPS

Configuring Password Aging for Crypto-Based Clients

The AAA security services facilitate a variety of login authentication methods. Use the aaa authentication login command to enable AAA authentication no matter which of the supported login authentication methods you decide to use. With the aaa authentication login command, you create one or more lists of authentication methods that are tried at login. These lists are applied using the login authentication line configuration command.

After the RADIUS server requests a new password, AAA queries the crypto client, which in turn prompts the user to enter a new password.

To configure login authentication and password aging for crypto-based clients, use the following commands beginning in global configuration mode.

Note The AAA Password Expiry infrastructure notifies the Easy VPN client that the password has expired and provides a generic way for the user to change the password. Please use RADIUS-server domain-stripping feature wisely in combination with AAA password expiry support.

SUMMARY STEPS

1. enable

2. configure terminal

3. aaa new-model

4. aaa authentication login {default | list-name} passwd-expiry method1 [method2...]

5. crypto map map-name client authentication list list-name

crypto map map-name client authentication list 
list-name

Router(config)# crypto map clientmap client 
authentication list userauthen

Configuration Examples

This section provides the following configuration examples:

•"Configuring Local Authentication: Example" section

•"Configuring RADIUS Authentication: Example" section

•"Configuring Password Aging with Crypto Authentication: Example" section

Configuring Local Authentication: Example

The following example configures PPP on an asynchronous interface and enables MSCHAP V2 authentication locally:

interface Async65

  ip address 10.0.0.2 255.0.0.0

  encapsulation ppp

  async mode dedicated

  no peer default ip address

  ppp max-bad-auth 3

  ppp authentication ms-chap-v2

  username client password secret

Configuring RADIUS Authentication: Example

The following example configures PPP on an asynchronous interface and enables MSCHAP V2 authentication via RADIUS:

interface Async65

  ip address 10.0.0.2 255.0.0.0

  encapsulation ppp

  async mode dedicated

  no peer default ip address

  ppp max-bad-auth 3

  ppp authentication ms-chap-v2

  exit

aaa authentication ppp default group radius

 radius-server host 10.0.0.2 255.0.0.0

 radius-server key secret

 radius-server vsa send authentication

Configuring Password Aging with Crypto Authentication: Example

The following example configures password aging by using AAA with a crypto-based client:

aaa authentication login userauthen passwd-expiry group radius

!

aaa session-id common

!

crypto isakmp policy 3

 encr 3des

 authentication pre-share

 group 2

!

crypto isakmp client configuration group 3000client

 key cisco123

 dns 10.1.1.10

 wins 10.1.1.20

 domain cisco.com

 pool ippool

 acl 153

!

crypto ipsec transform-set myset esp-3des esp-sha-hmac 

!

crypto dynamic-map dynmap 10

 set transform-set myset 

!

crypto map clientmap client authentication list userauthen

!

radius-server host 10.140.15.203 auth-port 1645 acct-port 1646

radius-server domain-stripping prefix-delimiter $

radius-server key cisco123

radius-server vsa send authentication

radius-server vsa send authentication 3gpp2

!

end

Additional References

The following sections provide references related to the MSCHAP Version 2 feature.

Related Documents

Standards

MIBs

RFCs

Technical Assistance

Feature Information for MSCHAP Version 2

Table 1 lists the release history for this feature.

Not all commands may be available in your Cisco IOS software release. For release information about a specific command, see the command reference documentation.

Use Cisco Feature Navigator to find information about platform support and software image support. Cisco Feature Navigator enables you to determine which Cisco IOS and Catalyst OS software images support a specific software release, feature set, or platform. To access Cisco Feature Navigator, go to http://tools.cisco.com/ITDIT/CFN/jsp/index.jsp. An account on Cisco.com is not required.

Note Table 1 lists only the Cisco IOS software release that introduced support for a given feature in a given Cisco IOS software release train. Unless noted otherwise, subsequent releases of that Cisco IOS software release train also support that feature.

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