Authentication, Authorization, and Accounting Configuration Guide, Cisco IOS Release 15SY
Bias-Free Language
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Authentication provides a method to identify users, which includes the login and password dialog, challenge and response,
messaging support, and encryption, depending on the selected security protocol. Authentication is the way a user is identified
prior to being allowed access to the network and network services.
Finding Feature Information
Your software release may not support all the features documented in this module. For the latest caveats and feature information,
see Bug Search Tool and 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 table.
Use Cisco Feature Navigator to find information about platform support and Cisco software image support. To access Cisco Feature
Navigator, go to www.cisco.com/go/cfn. An account on Cisco.com is not required.
Prerequisites for Configuring Authentication
The Cisco IOS XE implementation of authentication is divided into AAA Authentication and non-authentication methods. Cisco
recommends that, whenever possible, AAA security services be used to implement authentication.
Restrictions for Configuring Authentication
The number of AAA method lists that can be configured is 250.
Web authentication is not supported on Cisco IOS XE software.
Information About Configuring Authentication
The following sections describe how AAA authentication is configured by defining a named list of authentication methods and
then applying that list to various interfaces. This section also describes how AAA authentication is handled by using RADIUS
Change in Authorization (CoA):
Named Method Lists for Authentication
To configure AAA authentication, you must first define a named list of authentication methods, and then apply that list to
various interfaces. The method list defines the types of authentication to be performed and the sequence in which they will
be performed; it must be applied to a specific interface before any of the defined authentication methods will be performed.
The only exception is the default method list (which is named “default”). The default method list is automatically applied
to all interfaces except those that have a named method list explicitly defined. A defined method list overrides the default
method list.
A method list is a sequential list describing the authentication methods to be queried in order to authenticate a user. Method
lists enable you to designate one or more security protocols to be used for authentication, thus ensuring a backup system
for authentication in case the initial method fails. Cisco IOS XE software uses the first listed method to authenticate users.
If that method fails to respond, the Cisco IOS XE software selects the next authentication method listed in the method list.
This process continues until there is successful communication with a listed authentication method, or all methods defined
in the method list are exhausted.
It is important to note that the Cisco IOS XE software attempts authentication with the next listed authentication method
only when there is no response from the previous method. If authentication fails at any point in this cycle--meaning that
the security server or local username database responds by denying the user access--the authentication process stops and no
other authentication methods are attempted.
Note
The number of AAA method lists that can be configured is 250.
Method Lists and Server Groups
A server group is a way to group existing RADIUS or TACACS+ server hosts for use in method lists. The figure below shows
a typical AAA network configuration that includes four security servers: R1 and R2 are RADIUS servers and T1 and T2 are TACACS+
servers. R1 and R2 make up the group of RADIUS servers. T1 and T2 make up the group of TACACS+ servers.
Figure 1. Typical AAA Network Configuration
Using server groups, you can specify a subset of the configured server hosts and use them for a particular service. For example,
server groups allow you to define R1 and R2 as a server group, and define T1 and T2 as a separate server group. For example,
you can specify R1 and T1 in the method list for authentication login, while specifying R2 and T2 in the method list for PPP
authentication.
Server groups also can include multiple host entries for the same server, as long as each entry has a unique identifier.
The combination of an IP address and a UDP port number creates a unique identifier, allowing different ports to be individually
defined as RADIUS hosts providing a specific AAA service. In other words, this unique identifier enables RADIUS requests to
be sent to different UDP ports on a server at the same IP address. If two different host entries on the same RADIUS server
are configured for the same service--for example, authentication--the second host entry configured acts as failover backup
to the first one. Using this example, if the first host entry fails to provide accounting services, the network access server
will try the second host entry configured on the same device for accounting services. (The RADIUS host entries will be tried
in the order in which they are configured.)
For more information about configuring server groups and about configuring server groups based on Dialed Number Identification
Service (DNIS) numbers, refer to the “Configuring RADIUS” or “Configuring TACACS+” chapter.
Method List Examples
Suppose the system administrator has decided on a security solution where all interfaces will use the same authentication
methods to authenticate PPP connections. In the RADIUS group, R1 is contacted first for authentication information, then if
there is no response, R2 is contacted. If R2 does not respond, T1 in the TACACS+ group is contacted; if T1 does not respond,
T2 is contacted. If all designated servers fail to respond, authentication falls to the local username database on the access
server itself. To implement this solution, the system administrator would create a default method list by entering the following
command:
aaa authentication ppp default group radius group tacacs+ local
In this example, “default” is the name of the method list. The protocols included in this method list are listed after the
name, in the order they are to be queried. The default list is automatically applied to all interfaces.
When a remote user attempts to dial in to the network, the network access server first queries R1 for authentication information.
If R1 authenticates the user, it issues a PASS response to the network access server and the user is allowed to access the
network. If R1 returns a FAIL response, the user is denied access and the session is terminated. If R1 does not respond, then
the network access server processes that as an ERROR and queries R2 for authentication information. This pattern would continue
through the remaining designated methods until the user is either authenticated or rejected, or until the session is terminated.
It is important to remember that a FAIL response is significantly different from an ERROR. A FAIL means that the user has
not met the criteria contained in the applicable authentication database to be successfully authenticated. Authentication
ends with a FAIL response. An ERROR means that the security server has not responded to an authentication query. Because of
this, no authentication has been attempted. Only when an ERROR is detected will AAA select the next authentication method
defined in the authentication method list.
Suppose the system administrator wants to apply a method list only to a particular interface or set of interfaces. In this
case, the system administrator creates a named method list and then applies this named list to the applicable interfaces.
The following example shows how the system administrator can implement an authentication method that will be applied only
to interface 3:
aaa authentication ppp default group radius group tacacs+ local
aaa authentication ppp apple group radius group tacacs+ local none
interface async 3
ppp authentication chap apple
In this example, “apple” is the name of the method list, and the protocols included in this method list are listed after the
name in the order in which they are to be performed. After the method list has been created, it is applied to the appropriate
interface. Note that the method list name (apple) in both the AAAand PPP authentication commands must match.
In the following example, the system administrator uses server groups to specify that only R2 and T2 are valid servers for
PPP authentication. To do this, the administrator must define specific server groups whose members are R2 (172.16.2.7) and
T2 (172.16.2.77), respectively. In this example, the RADIUS server group “rad2only” is defined as follows using the aaa group server command:
aaa group server radius rad2only
server 172.16.2.7
The TACACS+ server group “tac2only” is defined as follows using the aaa group server command:
aaa group server tacacs+ tac2only
server 172.16.2.77
The administrator then applies PPP authentication using the server groups. In this example, the default methods list for PPP
authentication follows this order: group rad2only , group tac2only , and local :
aaa authentication ppp default group rad2only group tac2only local
About RADIUS Change of Authorization
A standard RADIUS interface is typically used in a pulled model, in which the request originates from a device attached to
a network and the response is sent from the queried servers. The Cisco software supports the RADIUS CoA request defined in
RFC 5176 that is used in a pushed model, in which the request originates from the external server to the device attached to
the network, and enables the dynamic reconfiguring of sessions from external authentication, authorization, and accounting
(AAA) or policy servers.
Use the following per-session CoA requests:
Session reauthentication
Session termination
Session termination with port shutdown
Session termination with port bounce
Security and Password
Accounting
CoA Requests
CoA requests, as described in RFC 5176, are used in a pushed model to allow for session identification, host reauthentication,
and session termination. The model comprises one request (CoA-Request) and two possible response codes:
CoA acknowledgment (ACK) [CoA-ACK]
CoA non-acknowledgment (NAK) [CoA-NAK]
The request is initiated from a CoA client (typically a RADIUS or policy server) and directed to the device that acts as
a listener.
RFC 5176 Compliance
The Disconnect Request message, which is also referred to as Packet of Disconnect (POD), is supported by the device for a
session termination.
The following table shows the IETF attributes that are supported for the RADIUS Change of Authorization (CoA) feature.
Table 1. Supported IETF Attributes
Attribute Number
Attribute Name
24
State
31
Calling-Station-ID
44
Acct-Session-ID
80
Message-Authenticator
101
Error-Cause
The following table shows the possible values for the Error-Cause attribute.
Table 2. Error-Cause Values
Value
Explanation
201
Residual Session Context Removed
202
Invalid EAP Packet (Ignored)
401
Unsupported Attribute
402
Missing Attribute
403
NAS Identification Mismatch
404
Invalid Request
405
Unsupported Service
406
Unsupported Extension
407
Invalid Attribute Value
501
Administratively Prohibited
502
Request Not Routable (Proxy)
503
Session Context Not Found
504
Session Context Not Removable
505
Other Proxy Processing Error
506
Resources Unavailable
507
Request Initiated
508
Multiple Session Selection Unsupported
CoA Request Response Code
The CoA Request Response code can be used to issue a command to the device. The supported commands are listed in the “CoA
Request Commands” section.
The packet format for a CoA Request Response code as defined in RFC 5176 consists of the following fields: Code, Identifier,
Length, Authenticator, and Attributes in the Type:Length:Value (TLV) format.
The Attributes field is used to carry Cisco VSAs.
Session Identification
For disconnect and CoA requests targeted at a particular session, the device locates the session based on one or more of
the following attributes:
Calling-Station-Id (IETF attribute #31, which contains the host MAC address)
Unless all session identification attributes included in the CoA message match the session, the device returns a Disconnect-NAK
or CoA-NAK with the “Invalid Attribute Value” error-code attribute.
Note
A CoA NAK message is not sent for all CoA requests with a key mismatch. The message is sent only for the first three requests
for a client. After that, all the packets from that client are dropped. When there is a key mismatch, the response authenticator
sent with the CoA NAK message is calculated from a dummy key value.
CoA ACK Response Code
If an authorization state is changed successfully, a positive acknowledgment (ACK) is sent. The attributes returned within
a CoA ACK can vary based on the CoA Request.
CoA NAK Response Code
A negative acknowledgment (NAK) indicates a failure to change the authorization state and can include attributes that indicate
the reason for the failure.
CoA Request Commands
The commands supported on the device are shown in the table below. All CoA commands must include the session identifier between
the device and the CoA client.
Table 3. CoA Request Commands Supported on the Device
This is a standard disconnect request that does not require a VSA
Session Reauthentication
To initiate session reauthentication, the authentication, authorization, and accounting (AAA) server sends a standard CoA-Request
message that contains a Cisco VSA and one or more session identification attributes. The Cisco VSA is in the form of Cisco:Avpair=“subscriber:command=reauthenticate”.
The current session state determines the device’s response to the message in the following scenarios:
If the session is currently authenticated by IEEE 802.1x, the device responds by sending an Extensible Authentication Protocol over LAN (EAPoL)-RequestId message to the server.
If the session is currently authenticated by MAC authentication bypass (MAB), the device sends an access request to the server,
passing the same identity attributes used for the initial successful authentication.
If session authentication is in progress when the device receives the command, the device terminates the process and restarts
the authentication sequence, starting with the method configured to be attempted first.
Session Termination
A CoA Disconnect-Request terminates the session without disabling the host port. CoA Disconnect-Request termination causes
reinitialization of the authenticator state machine for the specified host, but does not restrict the host’s access to the
network. If the session cannot be located, the device returns a Disconnect-NAK message with the “Session Context Not Found”
error-code attribute. If the session is located, the device terminates the session. After the session has been completely
removed, the device returns a Disconnect-ACK message.
To restrict a host’s access to the network, use a CoA Request with the Cisco:Avpair=“subscriber:command=disable-host-port”
VSA. This command is useful when a host is known to cause problems on the network and network access needs to be immediately
blocked for the host. If you want to restore network access on the port, reenable it using a non-RADIUS mechanism.
CoA Request Disable Host Port
The RADIUS server CoA disable port command administratively shuts down the authentication port that is hosting a session,
resulting in session termination. This command is useful when a host is known to cause problems on the network and network
access needs to be immediately blocked for the host. If you want to restore network access on the port, reenable it using
a non-RADIUS mechanism. This command is carried in a standard CoA-Request message that has the following VSA:
Because this command is session-oriented, it must be accompanied by one or more of the session identification attributes
described in the “Session Identification” section. If the device cannot locate the session, it returns a CoA-NAK message with
the “Session Context Not Found” error-code attribute. If the device locates the session, it disables the hosting port and
returns a CoA-ACK message.
If the device fails before returning a CoA-ACK to the client, the process is repeated on the new active device when the request
is re-sent from the client. If the device fails after returning a CoA-ACK message to the client but before the operation is
complete, the operation is restarted on the new active device.
To ignore the RADIUS server CoA disable port command, see the “Configuring the Device to Ignore Bounce and Disable RADIUS
CoA Requests” section.
CoA Request Bounce Port
A RADIUS server CoA bounce port sent from a RADIUS server can cause a link flap on an authentication port, which triggers
DHCP renegotiation from one or more hosts connected to this port. This incident can occur when there is a VLAN change and
the endpoint is a device (such as a printer) that does not have a mechanism to detect a change on this authentication port.
The CoA bounce port is carried in a standard CoA-Request message that contains the following VSA:
Because this command is session-oriented, it must be accompanied by one or more of the session identification attributes
described in the Session Identification. If the session cannot be located, the device returns a CoA-NAK message with the “Session
Context Not Found” error-code attribute. If the session is located, the device disables the hosting port for a period of 10
seconds, reenables it (port-bounce), and returns a CoA-ACK.
To ignore the RADIUS server CoA bounce port, see the “Configuring the Device to Ignore Bounce and Disable RADIUS CoA Requests”
section.
Domain Stripping
You can remove the domain name from the username received at the global level by using the
radius-server domain-stripping command. When the
radius-server domain-stripping command is configured, all the AAA requests with “user@example.com” go to the remote RADIUS server with the reformatted username
“user.” The domain name is removed from the request.
Note
Domain stripping will not be done in a TACACS configuration.
The AAA Broadcast Accounting feature allows accounting information to be sent to multiple AAA servers at the same time, that
is, accounting information can be broadcast to one or more AAA servers simultaneously. This functionality allows you to send
accounting information to private and public AAA servers. It also provides redundant billing information for voice applications.
The Domain Stripping feature allows domain stripping to be configured at the server group level.
Per-server group configuration overrides the global configuration. If domain stripping is not enabled globally, but it is
enabled in a server group, then it is enabled only for that server group. Also, if virtual routing and forwarding (VRF)-specific
domain stripping is configured globally and in a server group for a different VRF, domain stripping is enabled in both the
VRFs. VRF configurations are taken from server-group configuration mode. If server-group configurations are disabled in global
configuration mode but are available in server-group configuration mode, all configurations in server-group configuration
mode are applicable.
After the domain stripping and broadcast accounting are configured, you can create separate accounting records as per the
configurations.
How to Configure AAA Authentication Methods
Note
AAA features are not available until you enable AAA globally using the
aaa new-model command.
For authentication configuration examples using the commands in this chapter, refer to the Authentication Examples.
Configuring Login Authentication Using AAA
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
theaaa 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.
To configure login authentication by using AAA, use the following commands beginning in global configuration mode:
Enters line configuration mode for the lines to which you want to apply the authentication list.
Step 4
Router(config-line)#
login authentication
Example:
{default | list-name}
Applies the authentication list to a line or set of lines.
What to do next
The
list-name is a character string used to name the list you are creating. The method argument refers to the actual method the authentication
algorithm tries. The additional methods of authentication are used only if the previous method returns an error, not if it
fails. To specify that the authentication should succeed even if all methods return an error, specify
none as the final method in the command line.
For example, to specify that authentication should succeed even if (in this example) the TACACS+ server returns an error,
enter the following command:
aaa authentication login default group tacacs+ none
Note
Because the
none keyword enables
any user logging in to successfully authenticate, it should be used only as a backup method of authentication.
To create a default list that is used when a named list is
not specified in the
login authentication command, use the
default keyword followed by the methods that are to be used in default situations. The default method list is automatically applied
to all interfaces.
For example, to specify RADIUS as the default method for user authentication during login, enter the following command:
aaa authentication login default group radius
The table below lists the supported login authentication methods.
Table 4. AAA Authentication Login Methods
Keyword
Description
enable
Uses the enable password for authentication.
krb5
Uses Kerberos 5 for authentication.
krb5-telnet
Uses Kerberos 5 Telnet authentication protocol when using Telnet to connect to the router. If selected, this keyword must
be listed as the first method in the method list.
line
Uses the line password for authentication.
local
Uses the local username database for authentication.
local-case
Uses case-sensitive local username authentication.
none
Uses no authentication.
group radius
Uses the list of all RADIUS servers for authentication.
group tacacs+
Uses the list of all TACACS+ servers for authentication.
group group-name
Uses a subset of RADIUS or TACACS+ servers for authentication as defined by the
aaa group server radius or
aaa group server tacacs+ command.
Note
The
login command only changes username and privilege level but does not execute a shell; therefore autocommands will not be executed.
To execute autocommands under this circumstance, you need to establish a Telnet session back into the router (loop-back).
Make sure that the router has been configured for secure Telnet sessions if you choose to implement autocommands this way.
Login Authentication Using Enable Password
Use the aaa authentication login command with the enable method keyword to specify the enable password as the login authentication method. For example, to specify the enable password as
the method of user authentication at login when no other method list has been defined, enter the following command:
aaa authentication login default enable
Before you can use the enable password as the login authentication method, you need to define the enable password. For more
information about defining enable passwords, refer to the chapter “Configuring Passwords and Privileges.”
Login Authentication Using Kerberos
Authentication via Kerberos is different from most other authentication methods: the user’s password is never sent to the
remote access server. Remote users logging in to the network are prompted for a username. If the key distribution center (KDC)
has an entry for that user, it creates an encrypted ticket granting ticket (TGT) with the password for that user and sends
it back to the router. The user is then prompted for a password, and the router attempts to decrypt the TGT with that password.
If it succeeds, the user is authenticated and the TGT is stored in the user’s credential cache on the router.
While krb5 does use the KINIT program, a user does not need to run the KINIT program to get a TGT to authenticate to the router.
This is because KINIT has been integrated into the login procedure in the Cisco IOS XE implementation of Kerberos.
Use the aaa authentication login command with the krb5 method
keyword to specify Kerberos as the login authentication method. For example, to specify Kerberos as the method of user authentication
at login when no other method list has been defined, enter the following command:
aaa authentication login default krb5
Before you can use Kerberos as the login authentication method, you need to enable communication with the Kerberos security
server. For more information about establishing communication with a Kerberos server, refer to the chapter “Configuring Kerberos.”
Login Authentication Using Line Password
Use the
aaa authentication login command with the
line method keyword to specify the line password as the login authentication method. For example, to specify the line password as the
method of user authentication at login when no other method list has been defined, enter the following command:
aaa authentication login default line
Before you can use a line password as the login authentication method, you need to define a line password. For more information
about defining line passwords, refer to the Configuring Line Password Protection.
Login Authentication Using Local Password
Use the
aaa authentication login command with the
local method keyword to specify that the Cisco router or access server will use the local username database for authentication. For example,
to specify the local username database as the method of user authentication at login when no other method list has been defined,
enter the following command:
aaa authentication login default local
For information about adding users into the local username database, refer to the Establishing Username Authentication.
Login Authentication Using Group RADIUS
Use the aaa authentication login command with the group radius method to specify RADIUS as the login authentication method. For example, to specify RADIUS as the method of user authentication
at login when no other method list has been defined, enter the following command:
aaa authentication login default group radius
Before you can use RADIUS as the login authentication method, you need to enable communication with the RADIUS security server.
For more information about establishing communication with a RADIUS server, refer to the chapter “Configuring RADIUS.”
Configuring RADIUS Attribute 8 in Access Requests
After you have used the
aaa authentication login command to specify RADIUS and your login host has been configured to request its IP address from the NAS, you can send attribute
8 (Framed-IP-Address) in access-request packets by using the
radius-server attribute 8 include-in-access-req command in global configuration mode. This command makes it possible for NAS to provide the RADIUS server a hint of the user
IP address in advance for user authentication. For more information about attribute 8, refer to the appendix “RADIUS Attributes”
at the end of the book.
Login Authentication Using Group TACACS
Use the aaa authentication login command with the group tacacs+ method to specify TACACS+ as the login authentication method. For example, to specify TACACS+ as the method of user authentication
at login when no other method list has been defined, enter the following command:
aaa authentication login default group tacacs+
Before you can use TACACS+ as the login authentication method, you need to enable communication with the TACACS+ security
server. For more information about establishing communication with a TACACS+ server, refer to the chapter “Configuring TACACS+.”
Login Authentication Using group group-name
Use the aaa authentication login command with the group group-name method to specify a subset of RADIUS or TACACS+ servers to use as the login authentication method. To specify and define
the group name and the members of the group, use the aaa group server command. For example, use the aaa group server command to first define the members of group loginrad :
aaa group server radius loginrad
server 172.16.2.3
server 172.16.2 17
server 172.16.2.32
This command specifies RADIUS servers 172.16.2.3, 172.16.2.17, and 172.16.2.32 as members of the group loginrad.
To specify group loginrad as the method of user authentication at login when no other method list has been defined, enter the following command:
aaa authentication login default group loginrad
Before you can use a group name as the login authentication method, you need to enable communication with the RADIUS or TACACS+
security server. For more information about establishing communication with a RADIUS server, refer to the chapter “Configuring
RADIUS.” For more information about establishing communication with a TACACS+ server, refer to the chapter “Configuring TACACS+.”
Configuring PPP Authentication Using AAA
Many users access network access servers through dialup via async or ISDN. Dialup via async or ISDN bypasses the CLI completely;
instead, a network protocol (such as PPP or ARA) starts as soon as the connection is established.
The AAA security services facilitate a variety of authentication methods for use on serial interfaces running PPP. Use the
aaa authentication ppp command to enable AAA authentication no matter which of the supported PPP authentication methods you decide to use.
To configure AAA authentication methods for serial lines using PPP, use the following commands in global configuration mode:
Applies the authentication list to a line or set of lines. In this command,
protocol1 and
protocol2 represent the following protocols: CHAP, MS-CHAP, and PAP. PPP authentication is attempted first using the first authentication
method, specified by
protocol1. If
protocol1 is unable to establish authentication, the next configured protocol is used to negotiate authentication.
What to do next
With theaaa authentication ppp command, you create one or more lists of authentication methods that are tried when a user tries to authenticate via PPP.
These lists are applied using the
ppp authentication line configuration command.
To create a default list that is used when a named list is
not specified in the
ppp authentication command, use the
default keyword followed by the methods you want used in default situations.
For example, to specify the local username database as the default method for user authentication, enter the following command:
aaa authentication ppp default local
The
list-name is any character string used to name the list you are creating. The method argument refers to the actual method the authentication
algorithm tries. The additional methods of authentication are used only if the previous method returns an error, not if it
fails. To specify that the authentication should succeed even if all methods return an error, specify
none as the final method in the command line.
For example, to specify that authentication should succeed even if (in this example) the TACACS+ server returns an error,
enter the following command:
aaa authentication ppp default group tacacs+ none
Note
Because
none allows all users logging in to authenticate successfully, it should be used as a backup method of authentication.
The table below lists the supported login authentication methods.
Table 5. AAA Authentication PPP Methods
Keyword
Description
if-needed
Does not authenticate if user has already been authenticated on a TTY line.
krb5
Uses Kerberos 5 for authentication (can only be used for PAP authentication).
local
Uses the local username database for authentication.
local-case
Uses case-sensitive local username authentication.
none
Uses no authentication.
group radius
Uses the list of all RADIUS servers for authentication.
group tacacs+
Uses the list of all TACACS+ servers for authentication.
group group-name
Uses a subset of RADIUS or TACACS+ servers for authentication as defined by the
aaa group server radius or
aaa group server tacacs+ command.
PPP Authentication Using Kerberos
Use the aaa authentication ppp command with the krb5 method
keyword to specify Kerberos as the authentication method for use on interfaces running PPP. For example, to specify Kerberos
as the method of user authentication when no other method list has been defined, enter the following command:
aaa authentication ppp default krb5
Before you can use Kerberos as the PPP authentication method, you need to enable communication with the Kerberos security
server. For more information about establishing communication with a Kerberos server, refer to the chapter “Configuring Kerberos”.
Note
Kerberos login authentication works only with PPP PAP authentication.
PPP Authentication Using Local Password
Use the
aaa authentication ppp command with the
method keyword
local to specify that the Cisco router or access server will use the local username database for authentication. For example, to
specify the local username database as the method of authentication for use on lines running PPP when no other method list
has been defined, enter the following command:
aaa authentication ppp default local
For information about adding users into the local username database, refer to the Establishing Username Authentication.
PPP Authentication Using Group RADIUS
Use the aaa authentication ppp command with the group radius method to specify RADIUS as the login authentication method. For example, to specify RADIUS as the method of user authentication
at login when no other method list has been defined, enter the following command:
aaa authentication ppp default group radius
Before you can use RADIUS as the PPP authentication method, you need to enable communication with the RADIUS security server.
For more information about establishing communication with a RADIUS server, refer to the chapter “Configuring RADIUS.”
Configuring RADIUS Attribute 44 in Access Requests
After you have used the
aaa authentication ppp command with the
group radius method to specify RADIUS as the login authentication method, you can configure your device to send attribute 44 (Acct-Session-ID)
in access-request packets by using the
radius-server attribute 44 include-in-access-req command in global configuration mode. This command allows the RADIUS daemon to track a call from the beginning to the end.
PPP Authentication Using Group TACACS
Use the aaa authentication ppp command with the group tacacs+ method to specify TACACS+ as the login authentication method. For example, to specify TACACS+ as the method of user authentication
at login when no other method list has been defined, enter the following command:
aaa authentication ppp default group tacacs+
Before you can use TACACS+ as the PPP authentication method, you need to enable communication with the TACACS+ security server.
For more information about establishing communication with a TACACS+ server, refer to the chapter “Configuring TACACS+.”
PPP Authentication Using group group-name
Use the aaa authentication ppp command with the group group-name method to specify a subset of RADIUS or TACACS+ servers to use as the login authentication method. To specify and define
the group name and the members of the group, use the aaa group server command. For example, use the aaa group server command to first define the members of group ppprad :
aaa group server radius ppprad
server 172.16.2.3
server 172.16.2 17
server 172.16.2.32
This command specifies RADIUS servers 172.16.2.3, 172.16.2.17, and 172.16.2.32 as members of the group ppprad.
To specify group ppprad as the method of user authentication at login when no other method list has been defined, enter the following command:
aaa authentication ppp default group ppprad
Before you can use a group name as the PPP authentication method, you need to enable communication with the RADIUS or TACACS+
security server. For more information about establishing communication with a RADIUS server, refer to the chapter “Configuring
RADIUS”. For more information about establishing communication with a TACACS+ server, refer to the chapter “Configuring TACACS+.”
Configuring AAA Scalability for PPP Requests
You can configure and monitor the number of background processes allocated by the PPP manager in the network access server
(NAS) to deal with AAA authentication and authorization requests. The AAA Scalability feature enables you to configure the
number of processes used to handle AAA requests for PPP, thus increasing the number of users that can be simultaneously authenticated
or authorized.
To allocate a specific number of background processes to handle AAA requests for PPP, use the following command in global
configuration mode:
Command
Purpose
Router(config)# aaa processes number
Allocates a specific number of background processes to handle AAA authentication and authorization requests for PPP.
The argument number defines the number of background processes earmarked to process AAA authentication and authorization requests for PPP and
can be configured for any value from 1 to 2147483647. Because of the way the PPP manager handles requests for PPP, this argument
also defines the number of new users that can be simultaneously authenticated. This argument can be increased or decreased
at any time.
Note
Allocating additional background processes can be expensive. You should configure the minimum number of background processes
capable of handling the AAA requests for PPP.
Configuring ARAP Authentication Using AAA
Using theaaa authentication arap command, you can create one or more lists of authentication methods that are tried when AppleTalk Remote Access Protocol
(ARAP) users attempt to log in to the device. These lists are used with the
arap authentication line configuration command.
Use the following commands starting in global configuration mode:
SUMMARY STEPS
Device(config)#
aaa new-model
Device(config)#
aaa authentication arap
Device(config)#
line number
Device(config-line)#
autoselect arap
Device(config-line)#
autoselect during-login
Device(config-line)#
arap authentication list-name
Device(config-line)#
end
DETAILED STEPS
Command or Action
Purpose
Step 1
Device(config)#
aaa new-model
Enables AAA globally.
Step 2
Device(config)#
aaa authentication arap
Example:
Enables authentication for ARAP users.
Step 3
Device(config)#
line number
(Optional) Changes to line configuration mode.
Step 4
Device(config-line)#
autoselect arap
(Optional) Enables autoselection of ARAP.
Step 5
Device(config-line)#
autoselect during-login
(Optional) Starts the ARAP session automatically at user login.
Step 6
Device(config-line)#
arap authentication list-name
(Optional—not needed if
default is used in the
aaa authentication arap command) Enables TACACS+ authentication for ARAP on a line.
Step 7
Device(config-line)#
end
Returns to the privileged EXEC mode.
What to do next
The
list-name is any character string used to name the list you are creating. The
method argument refers to the actual list of methods the authentication algorithm tries, in the sequence entered.
To create a default list that is used when a named list is
not specified in the
arap authentication command, use the
default keyword followed by the methods you want to use in default situations.
The additional methods of authentication are used only if the previous method returns an error, not if it fails. To specify
that the authentication should succeed even if all methods return an error, specify
none as the final method in the command line.
Note
Because
none allows all users logging in to be authenticated, it should be used as a backup method of authentication.
The following table lists the supported login authentication methods.
Table 6. AAA Authentication ARAP Methods
Keyword
Description
auth-guest
Allows guest logins only if the user has already logged in to EXEC mode.
guest
Allows guest logins.
line
Uses the line password for authentication.
local
Uses the local username database for authentication.
local-case
Uses case-sensitive local username authentication.
group radius
Uses the list of all RADIUS servers for authentication.
group tacacs+
Uses the list of all TACACS+ servers for authentication.
group group-name
Uses a subset of RADIUS or TACACS+ servers for authentication as defined by the
aaa group server radius or
aaa group server tacacs+ command.
For example, to create a default AAA authentication method list used with ARAP, use the following command:
aaa authentication arap default if-needed none
To create the same authentication method list for ARAP and name the list
MIS-access, use the following command:
aaa authentication arap MIS-access if-needed none
This section includes the following sections:
ARAP Authentication Allowing Authorized Guest Logins
Use the aaa authentication arap command with the auth-guest keyword to allow guest logins only if the user has already successfully logged in to the EXEC. This method must be the first
listed in the ARAP authentication method list but it can be followed by other methods if it does not succeed. For example,
to allow all authorized guest logins--meaning logins by users who have already successfully logged in to the EXEC--as the
default method of authentication, using RADIUS only if that method fails, enter the following command:
aaa authentication arap default auth-guest group radius
Note
By default, guest logins through ARAP are disabled when you initialize AAA. To allow guest logins, you must use the aaa authentication arap command with either the guest or the auth-guest keyword.
ARAP Authentication Allowing Guest Logins
Use the aaa authentication arap command with the guest keyword to allow guest logins. This method must be the first listed in the ARAP authentication method list but it can be
followed by other methods if it does not succeed. For example, to allow all guest logins as the default method of authentication,
using RADIUS only if that method fails, enter the following command:
aaa authentication arap default guest group radius
ARAP Authentication Using Line Password
Use the
aaa authentication arap command with the
method keyword
line to specify the line password as the authentication method. For example, to specify the line password as the method of ARAP
user authentication when no other method list has been defined, enter the following command:
aaa authentication arap default line
Before you can use a line password as the ARAP authentication method, you need to define a line password. For more information
about defining line passwords, refer to the section Configuring Line Password Protection in this chapter.
ARAP Authentication Using Local Password
Use the
aaa authentication arap command with the
methodkeyword
local to specify that the Cisco router or access server will use the local username database for authentication. For example, to
specify the local username database as the method of ARAP user authentication when no other method list has been defined,
enter the following command:
aaa authentication arap default local
For information about adding users to the local username database, refer to the Establishing Username Authentication.
ARAP Authentication Using Group RADIUS
Use the aaa authentication arap command with the group radius method to specify RADIUS as the ARAP authentication method. For example, to specify RADIUS as the method of user authentication
at login when no other method list has been defined, enter the following command:
aaa authentication arap default group radius
Before you can use RADIUS as the ARAP authentication method, you need to enable communication with the RADIUS security server.
For more information about establishing communication with a RADIUS server, refer to the chapter “Configuring RADIUS.”
ARAP Authentication Using Group TACACS
Use the aaa authentication arap command with the group tacacs+ method to specify TACACS+ as the ARAP authentication method. For example, to specify TACACS+ as the method of user authentication
at login when no other method list has been defined, enter the following command:
aaa authentication arap default group tacacs+
Before you can use TACACS+ as the ARAP authentication method, you need to enable communication with the TACACS+ security server.
For more information about establishing communication with a TACACS+ server, refer to the chapter “Configuring TACACS+.”
ARAP Authentication Using Group group-name
Use the aaa authentication arap command with the group group-name method to specify a subset of RADIUS or TACACS+ servers to use as the ARAP authentication method. To specify and define the
group name and the members of the group, use the aaa group server command. For example, use the aaa group server command to first define the members of group araprad :
aaa group server radius araprad
server 172.16.2.3
server 172.16.2 17
server 172.16.2.32
This command specifies RADIUS servers 172.16.2.3, 172.16.2.17, and 172.16.2.32 as members of the group araprad.
To specify group araprad as the method of user authentication at login when no other method list has been defined, enter the following command:
aaa authentication arap default group araprad
Before you can use a group name as the ARAP authentication method, you need to enable communication with the RADIUS or TACACS+
security server. For more information about establishing communication with a RADIUS server, refer to the chapter “Configuring
RADIUS.” For more information about establishing communication with a TACACS+ server, refer to the chapter “Configuring TACACS+.”
Configuring NASI Authentication Using AAA
Using theaaa authentication nasi command, you can create one or more lists of authentication methods that are tried when NetWare Asynchronous Services Interface
(NASI) users attempt to log in to the device. These lists are used with the
nasi authentication line configuration command.
To configure NASI authentication using AAA, use the following commands starting in global configuration mode:
(Optional--not needed if
default is used in the
aaa authentication nasi command) Enables authentication for NASI on a line.
Step 5
Device(config-line)#
end
Returns to the privileged EXEC mode.
What to do next
The
list-name is any character string used to name the list you are creating. The
method argument refers to the actual list of methods that the authentication algorithm tries, in the sequence entered.
To create a default list that is used when a named list is
not specified in the
aaa authentication nasi command, use the
default keyword followed by the methods you want to use in default situations.
The additional methods of authentication are used only if the previous method returns an error, not if it fails. To specify
that the authentication should succeed even if all methods return an error, specify
none as the final method in the command line.
Note
Because
none allows all users logging in to be authenticated, it should be used as a backup method of authentication.
The table below lists the supported NASI authentication methods.
Table 7. AAA Authentication NASI Methods
Keyword
Description
enable
Uses the enable password for authentication.
line
Uses the line password for authentication.
local
Uses the local username database for authentication.
local-case
Uses case-sensitive local username authentication.
none
Uses no authentication.
group radius
Uses the list of all RADIUS servers for authentication.
group tacacs+
Uses the list of all TACACS+ servers for authentication.
group group-name
Uses a subset of RADIUS or TACACS+ servers for authentication as defined by the
aaa group server radius or
aaa group server tacacs+ command.
NASI Authentication Using Enable Password
Use the
aaa authentication nasi command with the keyword
enable to specify the enable password as the authentication method. For example, to specify the enable password as the method of
NASI user authentication when no other method list has been defined, use the following command:
aaa authentication nasi default enable
Before you can use the enable password as the authentication method, you need to define the enable password. For more information
about defining enable passwords, refer to the chapter “Configuring Passwords and Privileges.”
NASI Authentication Using Line Password
Use the
aaa authentication nasi command with the
method keyword
line to specify the line password as the authentication method. For example, to specify the line password as the method of NASI
user authentication when no other method list has been defined, enter the following command:
aaa authentication nasi default line
Before you can use a line password as the NASI authentication method, you need to define a line password. For more information
about defining line passwords, refer to the Configuring Line Password Protection.
NASI Authentication Using Local Password
Use the
aaa authentication nasi command with the
method keyword
local to specify that the Cisco router or access server will use the local username database for authentication information. For
example, to specify the local username database as the method of NASI user authentication when no other method list has been
defined, enter the following command:
aaa authentication nasi default local
For information about adding users to the local username database, refer to the Establishing Username Authentication.
NASI Authentication Using Group RADIUS
Use the aaa authentication nasi command with the group radius method to specify RADIUS as the NASI authentication method. For example, to specify RADIUS as the method of NASI user authentication
when no other method list has been defined, enter the following command:
aaa authentication nasi default group radius
Before you can use RADIUS as the NASI authentication method, you need to enable communication with the RADIUS security server.
For more information about establishing communication with a RADIUS server, refer to the chapter “Configuring RADIUS.”
NASI Authentication Using Group TACACS
Use the aaa authentication nasi command with the group tacacs+ method keyword to specify TACACS+ as the NASI authentication method. For example, to specify TACACS+ as the method of NASI user
authentication when no other method list has been defined, enter the following command:
aaa authentication nasi default group tacacs+
Before you can use TACACS+ as the authentication method, you need to enable communication with the TACACS+ security server.
For more information about establishing communication with a TACACS+ server, refer to the chapter “Configuring TACACS+.”
NASI Authentication Using group group-name
Use the aaa authentication nasi command with the group group-name method to specify a subset of RADIUS or TACACS+ servers to use as the NASI authentication method. To specify and define the
group name and the members of the group, use the aaa group server command. For example, use the aaa group server command to first define the members of group nasirad :
aaa group server radius nasirad
server 172.16.2.3
server 172.16.2 17
server 172.16.2.32
This command specifies RADIUS servers 172.16.2.3, 172.16.2.17, and 172.16.2.32 as members of the group nasirad.
To specify group nasirad as the method of user authentication at login when no other method list has been defined, enter the following command:
aaa authentication nasi default group nasirad
Before you can use a group name as the NASI authentication method, you need to enable communication with the RADIUS or TACACS+
security server. For more information about establishing communication with a RADIUS server, refer to the chapter “Configuring
RADIUS”. For more information about establishing communication with a TACACS+ server, refer to the chapter “Configuring TACACS+.”
Specifying the Amount of Time for Login Input
The timeout login response command allows you to specify how long the system will wait for login input (such as username and password) before timing
out. The default login value is 30 seconds; with thetimeout login response command, you can specify a timeout value from 1 to 300 seconds. To change the login timeout value from the default of 30
seconds, use the following command in line configuration mode:
Specifies how long the system will wait for login information before timing out.
Enabling Password Protection at the Privileged Level
Use the
aaa authentication enable default command to create a series of authentication methods that are used to determine whether a user can access the privileged
EXEC command level. You can specify up to four authentication methods. The additional methods of authentication are used only
if the previous method returns an error, not if it fails. To specify that the authentication should succeed even if all methods
return an error, specify
none as the final method in the command line.
Use the following command in global configuration mode:
Enables user ID and password checking for users requesting privileged EXEC level.
Note
All
aaa authentication enable default requests sent by the router to a RADIUS server include the username “$enab15$.” Requests sent to a TACACS+ server will include
the username that is entered for login authentication.
The method argument refers to the actual list of methods the authentication algorithm tries, in the sequence entered. the
table below lists the supported enable authentication methods.
Uses the list of all RADIUS hosts for authentication.
Note
The RADIUS method does not work on a per-username basis.
group tacacs+
Uses the list of all TACACS+ hosts for authentication.
group group-name
Uses a subset of RADIUS or TACACS+ servers for authentication as defined by the
aaa group server radius or
aaa group server tacacs+ command.
Changing the Text Displayed at the Password Prompt
Use the aaa authentication password-prompt command to change the default text that the Cisco IOS XE software displays when prompting a user to enter a password. This
command changes the password prompt for the enable password as well as for login passwords that are not supplied by remote
security servers. The no form of this command returns the password prompt to the following default value:
Password:
The aaa authentication password-prompt command does not change any dialog that is supplied by a remote TACACS+ or RADIUS server.
The aaa authentication password-prompt command works when RADIUS is used as the login method. You will be able to see the
password prompt defined in the command shown even when the RADIUS server is unreachable. The aaa authentication password-prompt
command does not work with TACACS+. TACACS+ supplies the NAS with the password prompt to display to the users. If the TACACS+
server is reachable, the NAS gets the password prompt from the server and uses that prompt instead of the one defined in the
aaa authentication password-prompt command. If the TACACS+ server is not reachable, the password prompt defined in the aaa
authentication password-prompt command may be used.
Use the following command in global configuration mode:
Changes the default text displayed when a user is prompted to enter a password.
Preventing an Access Request with a Blank Username from Being Sent to the RADIUS Server
The following configuration steps provide the ability to prevent an Access Request with a blank username from being sent to
the RADIUS server. This functionality ensures that unnecessary RADIUS server interaction is avoided, and RADIUS logs are kept
short.
Note
The aaa authentication suppress null-username command is available beginning in Cisco IOS XE Release 2.4.
Prevents an Access Request with a blank username from being sent to the RADIUS server.
Configuring Message Banners for AAA Authentication
AAA supports the use of configurable, personalized login and failed-login banners. You can configure message banners that
will be displayed when a user logs in to the system to be authenticated using AAA and when, for whatever reason, authentication
fails.
Configuring a Login Banner
To configure a banner that is displayed when a user logs in (replacing the default message for login), perform the following
task:
Before you begin
To create a login banner, you must configure a delimiting character that notifies the system that the following text string
must be displayed as the banner, and then the text string itself. The delimiting character is repeated at the end of the text
string to signify the end of the banner. The delimiting character can be any single character in the extended ASCII character
set, but once defined as the delimiter, that character cannot be used in the text string for the banner.
After you have configured a login banner, you must complete basic authentication configuration using AAA if you have not already
done so. For information about the different types of AAA authentication available, please refer to “Configuring Authentication”
in the
Authentication, Authorization, and Accounting Configuration Guide.
Configuring a Failed-Login Banner
To configure a message that is displayed when a user login fails (replacing the default message for failed login), perform
the following task:
Before you begin
To create a failed-login banner, you must configure a delimiting character, which notifies the system that the following
text string must be displayed as the banner, and then configure the text string itself. The delimiting character is repeated
at the end of the text string to signify the end of the failed-login banner. The delimiting character can be any single character
in the extended ASCII character set, but once defined as the delimiter, that character cannot be used in the text string making
up the banner.
Creates a message to be displayed when a user login fails.
Step 3
Device(config)#
end
Returns to privileged EXEC mode.
What to do next
After you have configured a failed-login banner, you must complete basic authentication configuration using AAA if you have
not already done so. For information about the different types of AAA authentication available, please refer to “Configuring
Authentication” in the
Authentication, Authorization, and Accounting Configuration Guide.
Configuring AAA Packet of Disconnect
Packet of disconnect (POD) terminates connections on the network access server (NAS) when particular session attributes are
identified. By using session information obtained from AAA, the POD client residing on a UNIX workstation sends disconnect
packets to the POD server running on the network access server. The NAS terminates any inbound user session with one or more
matching key attributes. It rejects requests when required fields are missing or when an exact match is not found.
To configure POD, perform the following tasks in global configuration mode:
Declares a RADIUS host that uses a vendor-proprietary version of RADIUS.
Enabling Double Authentication
Depending on the Cisco release, PPP sessions could be authenticated only by using a single authentication method: either
PAP or CHAP. Double authentication requires remote users to pass a second stage of authentication (after CHAP or PAP authentication)
before gaining network access.
This second (“double”) authentication requires a password that is known to the user but
not stored on the user’s remote host. Therefore, the second authentication is specific to a user, not to a host. This provides
an additional level of security that will be effective even if information from the remote host is stolen. In addition, this
also provides greater flexibility by allowing customized network privileges for each user.
The second stage authentication can use one-time passwords such as token card passwords, which are not supported by CHAP.
If one-time passwords are used, a stolen user password is of no use to the perpetrator.
How Double Authentication Works
With double authentication, there are two authentication/authorization stages. These two stages occur after a remote user
dials in and a PPP session is initiated.
In the first stage, the user logs in using the remote host name; CHAP (or PAP) authenticates the remote host, and then PPP
negotiates with AAA to authorize the remote host. In this process, the network access privileges associated with the remote
host are assigned to the user.
Note
We suggest that the network administrator restrict authorization at this first stage to allow only Telnet connections to
the local host.
In the second stage, the remote user must Telnet to the network access server to be authenticated. When the remote user logs
in, the user must be authenticated with AAA login authentication. The user then must enter the
access-profile command to be reauthorized using AAA. When this authorization is complete, the user has been double authenticated, and can
access the network according to per-user network privileges.
The system administrator determines what network privileges remote users will have after each stage of authentication by
configuring appropriate parameters on a security server. To use double authentication, the user must activate it by issuing
the
access-profile command.
Caution
Double authentication can cause certain undesirable events if multiple hosts share a PPP connection to a network access server,
as shown in the figure below. First, if a user, Bob, initiates a PPP session and activates double authentication at the network
access server (per the figure below), any other user will automatically have the same network privileges as Bob until Bob’s
PPP session expires. This happens because Bob’s authorization profile is applied to the network access server’s interface
during the PPP session and any PPP traffic from other users will use the PPP session Bob established. Second, if Bob initiates
a PPP session and activates double authentication, and then--before Bob’s PPP session has expired--another user, Jane, executes
the
access-profile command (or, if Jane Telnets to the network access server and
autocommand access-profile is executed), a reauthorization will occur and Jane’s authorization profile will be applied to the interface--replacing Bob’s
profile. This can disrupt or halt Bob’s PPP traffic, or grant Bob additional authorization privileges Bob should not have.
Figure 2. Possibly Risky Topology: Multiple Hosts Share a PPP Connection to a Network Access Server
Configuring Double Authentication
To configure double authentication, you must complete the following steps:
Enable AAA by using the
aaa-new model global configuration command. For more information about enabling AAA, refer to the chapter “AAA Overview.”
Use the
aaa authentication command to configure your network access server to use login and PPP authentication method lists, then apply those method
lists to the appropriate lines or interfaces.
Use the
aaa authorization command to configure AAA network authorization at login. For more information about configuring network authorization, refer
to the “Configuring Authorization” chapter.
Configure security protocol parameters (for example, RADIUS or TACACS+). For more information about RADIUS, refer to the
chapter “Configuring RADIUS”. For more information about TACACS+, refer to the chapter “Configuring TACACS+.”
Use access control list AV pairs on the security server that the user can connect to the local host only by establishing
a Telnet connection.
(Optional) Configure the
access-profile command as an autocommand. If you configure the autocommand, remote users will not have to manually enter the
access-profile command to access authorized rights associated with their personal user profile.
Note
If the
access-profile command is configured as an autocommand, users will still have to Telnet to the local host and log in to complete double
authentication.
Follow these rules when creating the user-specific authorization statements (These rules relate to the default behavior of
the
access-profile command):
Use valid AV pairs when configuring access control list AV pairs on the security server.
If you want remote users to use the interface’s existing authorization (that which existed prior to the second stage authentication/authorization),
but you want them to have different access control lists (ACLs), you should specify
only ACL AV pairs in the user-specific authorization definition. This might be desirable if you set up a default authorization
profile to apply to the remote host, but want to apply specific ACLs to specific users.
When these user-specific authorization statements are later applied to the interface, they can either be
added to the existing interface configuration or they can
replace the existing interface configuration--depending on which form of the
access-profile command is used to authorize the user. You should understand how the
access-profile command works before configuring the authorization statements.
If you will be using ISDN or Multilink PPP, you must also configure virtual templates at the local host.
To troubleshoot double authentication, use the
debug aaa per-user debug command. For more information about this command, refer to the
Cisco IOS Debug Command Reference .
Accessing the User Profile After Double Authentication
In double authentication, when a remote user establishes a PPP link to the local host using the local host name, the remote
host is CHAP (or PAP) authenticated. After CHAP (or PAP) authentication, PPP negotiates with AAA to assign network access
privileges associated with the remote host to the user. (We suggest that privileges at this stage be restricted to allow the
user to connect to the local host only by establishing a Telnet connection.)
When the user needs to initiate the second phase of double authentication, establishing a Telnet connection to the local host,
the user enters a personal username and password (different from the CHAP or PAP username and password). This action causes
AAA reauthentication to occur according to the personal username/password. The initial rights associated with the local host,
though, are still in place. By using the access-profile command, the rights associated with the local host are replaced by or merged with those defined for the user in the user’s
profile.
To access the user profile after double authentication, use the following command in EXEC configuration mode:
Accesses the rights associated for the user after double authentication.
If you configured the access-profile command to be executed as an autocommand, it will be executed automatically after the remote user logs in.
Enabling Automated Double Authentication
You can make the double authentication process easier for users by implementing automated double authentication. Automated
double authentication provides all of the security benefits of double authentication, but offers a simpler, more user-friendly
interface for remote users. With double authentication, a second level of user authentication is achieved when the user Telnets
to the network access server or router and enters a username and password. With automated double authentication, the user
does not have to Telnet to the network access server; instead the user responds to a dialog box that requests a username and
password or personal identification number (PIN). To use the automated double authentication feature, the remote user hosts
must be running a companion client application.
Note
Automated double authentication, like the existing double authentication feature, is for Multilink PPP ISDN connections only.
Automated double authentication cannot be used with other protocols such as X.25 or SLIP.
Automated double authentication is an enhancement to the existing double authentication feature. To configure automated double
authentication, you must first configure double authentication by completing the following steps:
Enable AAA by using the
aaa-new model global configuration command.
Use the
aaa authentication command to configure your network access server to use login and PPP authentication method lists, then apply those method
lists to the appropriate lines or interfaces.
Use the
aaa authorization command to configure AAA network authorization at login. For more information about configuring network authorization, refer
to the chapter “Configuring Authorization.”
Configure security protocol parameters (for example, RADIUS or TACACS+). For more information about RADIUS, refer to the
chapter “Configuring RADIUS”. For more information about TACACS+, refer to the chapter “Configuring TACACS+.”
Use access control list AV pairs on the security server that the user can connect to the local host only by establishing
a Telnet connection.
Configure the
access-profile command as an autocommand. If you configure the autocommand, remote users will not have to manually enter the
access-profile command to access authorized rights associated with their personal user profile. To learn about configuring autocommands,
refer to the
autocommand command in the
CiscoIOS Dial Technologies Command Reference , Release 12.2.
Note
If the
access-profile command is configured as an autocommand, users will still have to Telnet to the local host and log in to complete double
authentication.
Follow these rules when creating the user-specific authorization statements (These rules relate to the default behavior of
the
access-profile command):
Use valid AV pairs when configuring access control list AV pairs on the security server.
If you want remote users to use the interface’s existing authorization (that which existed prior to the second stage authentication/authorization),
but you want them to have different access control lists (ACLs), you should specify
only ACL AV pairs in the user-specific authorization definition. This might be desirable if you set up a default authorization
profile to apply to the remote host, but want to apply specific ACLs to specific users.
When these user-specific authorization statements are later applied to the interface, they can either be
added to the existing interface configuration, or
replace the existing interface configuration--depending on which form of the
access-profile command is used to authorize the user. You should understand how the
access-profile command works before configuring the authorization statements.
If you will be using ISDN or Multilink PPP, you must also configure virtual templates at the local host.
To troubleshoot double authentication, use the
debug aaa per-user debug command. For more information about this command, refer to the
Cisco IOS Debug Command Reference .
After you have configured double authentication, you are ready to configure the automation enhancement.
Configuring Automated Double Authentication
To configure automated double authentication, use the following commands, starting in global configuration mode.
SUMMARY STEPS
Router(config)# ip trigger-authentication
Do one of the following:
Router(config)# interface bri number
Router(config)# interface serial number:23
Router(config-if)# ip trigger-authentication
DETAILED STEPS
Command or Action
Purpose
Step 1
Router(config)# ip trigger-authentication
Example:
[timeout seconds] [port number]
Enables automation of double authentication.
Step 2
Do one of the following:
Router(config)# interface bri number
Router(config)# interface serial number:23
Selects an ISDN BRI or ISDN PRI interface and enter the interface configuration mode.
Step 3
Router(config-if)# ip trigger-authentication
Applies automated double authentication to the interface.
Troubleshooting Automated Double Authentication
To troubleshoot automated double authentication, use the following commands in privileged EXEC mode:
SUMMARY STEPS
Router# show ip trigger-authentication
Router# clear ip trigger-authentication
Router# debug ip trigger-authentication
DETAILED STEPS
Command or Action
Purpose
Step 1
Router# show ip trigger-authentication
Displays the list of remote hosts for which automated double authentication has been attempted (successfully or unsuccessfully).
Step 2
Router# clear ip trigger-authentication
Clears the list of remote hosts for which automated double authentication has been attempted. (This clears the table displayed
by the show ip trigger-authentication command.)
Step 3
Router# debug ip trigger-authentication
Displays debug output related to automated double authentication.
Configuring the Dynamic Authorization Service for RADIUS CoA
Use the following procedure to enable the router as an
authentication, authorization, and accounting (AAA) server for dynamic
authorization service to support the CoA functionality that pushes the policy
map in an input and output direction.
Sets up the local AAA server for dynamic authorization service,
which must be enabled to support the CoA functionality to push the policy map
in an input and output direction and enter dynamic authorization local server
configuration mode. In this mode, the RADIUS application commands are
configured.
Configures the IP address or hostname of the AAA server client.
Use the optional
server-key keyword and
string argument to configure the server
key at the “client” level.
Note
Configuring the server key at the client level overrides the
server key configured at the global level.
(Optional) Configures username domain options for the RADIUS
application.
The
delimiter keyword specifies the domain
delimiter. One of the following options can be specified for the
character argument:
@ ,
/ ,
$ ,
% ,
\ ,
# or
-
The
stripping keyword compares the incoming
username with the names oriented to the left of the
@ domain delimiter.
The
right-to-left keyword terminates the
string at the first delimiter going from right to left.
Step 7
port
{port-num}
Example:
Router(config-locsvr-da-radius)# port 3799
Configures UDP port 3799 for CoA requests.
Configuring a Device to Ignore Bounce and Disable RADIUS CoA Requests
When an authentication port is authenticated with multiple hosts and there is a Change of Authorization (CoA) request for
one host to flap on this port or one host session to be terminated on this port, the other hosts on this port are also affected.
Thus, an authenticated port with multiple hosts can trigger a DHCP renegotiation from one or more hosts in the case of a flap,
or it can administratively shut down the authentication port that is hosting the session for one or more hosts.
Perform the following steps to configure the device to ignore RADIUS server Change of Authorization (CoA) requests in the
form of a bounce port command or disable port command.
SUMMARY STEPS
enable
configure terminal
aaa new-model
authentication command bounce-port ignore
authentication command disable-port ignore
end
DETAILED STEPS
Command or Action
Purpose
Step 1
enable
Example:
Device> enable
Enables privileged EXEC mode.
Enter your password if prompted.
Step 2
configure terminal
Example:
Device# configure terminal
Enters global configuration mode.
Step 3
aaa new-model
Example:
Device(config)# aaa new-model
Enables authentication, authorization, and accounting (AAA) globally.
(Optional) Configures the device to ignore a RADIUS server bounce port command that causes a host to link flap on an authentication
port, which causes DHCP renegotiation from one or more hosts connected to this port.
(Optional) Configures the device to ignore a RADIUS server CoA disable port command that administratively shuts down the
authentication port that hosts one or more host sessions.
The shutting down of the port causes session termination.
Step 6
end
Example:
Device(config)# end
Returns to privileged EXEC mode.
Configuring Domain Stripping at the Server Group Level
Configures domain stripping at the server group level.
Step 5
end
Example:
Device(config-sg-radius)# end
Exits server group RADIUS configuration mode and returns to the privileged EXEC mode.
Non-AAA Authentication Methods
Configuring Line Password Protection
You can This task is used to provide access control on a terminal line by entering the password and establishing password
checking.
Note
If you configure line password protection and then configure TACACS or extended TACACS, the TACACS username and password take
precedence over line passwords. If you have not yet implemented a security policy, we recommend that you use AAA.
Assigns a password to a terminal or other device on a line. The password checker is case sensitive and can include spaces;
for example, the password “Secret” is different from the password “secret,” and “two words” is an acceptable password.
Step 5
login
Example:
Router(config-line)# login
Enables password checking at login.
You can disable line password verification by disabling password checking by using the no version of this command.
Note
The login command only changes username and privilege level but it does not execute a shell; therefore autocommands will not be executed.
To execute autocommands under this circumstance, you need to establish a Telnet session back into the router (loop-back).
Make sure that the router has been configured for secure Telnet sessions if you choose to implement autocommands this way.
Establishing Username Authentication
You can create a username-based authentication system, which is useful in the following situations:
To provide a TACACS-like username and encrypted password-authentication system for networks that cannot support TACACS
To provide special-case logins: for example, access list verification, no password verification, autocommand execution at
login, and “no escape” situations
To establish username authentication, use the following commands in global configuration mode as needed for your system configuration:
SUMMARY STEPS
Do one of the following:
Router(config)#
username name [nopassword |
password password |
password encryption-typeencryptedpassword]
Router(config)#
username name [access-class number]
Router(config)#
username name [privilege level]
Router(config)#
username name [autocommand command]
Router(config)#
username name [noescape ] [nohangup ]
DETAILED STEPS
Command or Action
Purpose
Step 1
Do one of the following:
Router(config)#
username name [nopassword |
password password |
password encryption-typeencryptedpassword]
Router(config)#
username name [access-class number]
Establishes username authentication with encrypted passwords.
or
(Optional) Establishes username authentication by access list.
Step 2
Router(config)#
username name [privilege level]
(Optional) Sets the privilege level for the user.
Step 3
Router(config)#
username name [autocommand command]
(Optional) Specifies a command to be executed automatically.
Step 4
Router(config)#
username name [noescape ] [nohangup ]
(Optional) Sets a “no escape” login environment.
What to do next
The keyword
noescape prevents users from using escape characters on the hosts to which they are connected. The
nohangup feature does not disconnect after using the autocommand.
Caution
Passwords will be displayed in clear text in your configuration unless you enable the
service password-encryption command. For more information about the
service password-encryption command, refer to the
Cisco IOS Security Command Reference.
Enabling CHAP or PAP Authentication
One of the most common transport protocols used in Internet service providers’ (ISPs’) dial solutions is the Point-to-Point
Protocol (PPP). Traditionally, remote users dial in to an access server to initiate a PPP session. After PPP has been negotiated,
remote users are connected to the ISP network and to the Internet.
Because ISPs want only customers to connect to their access servers, remote users are required to authenticate to the access
server before they can start up a PPP session. Normally, a remote user authenticates by typing in a username and password
when prompted by the access server. Although this is a workable solution, it is difficult to administer and awkward for the
remote user.
A better solution is to use the authentication protocols built into PPP. In this case, the remote user dials in to the access
server and starts up a minimal subset of PPP with the access server. This does not give the remote user access to the ISP’s
network--it merely allows the access server to talk to the remote device.
PPP currently supports two authentication protocols: Password Authentication Protocol (PAP) and Challenge Handshake Authentication
Protocol (CHAP). Both are specified in RFC 1334 and are supported on synchronous and asynchronous interfaces. Authentication
via PAP or CHAP is equivalent to typing in a username and password when prompted by the server. CHAP is considered to be more
secure because the remote user’s password is never sent across the connection.
PPP (with or without PAP or CHAP authentication) is also supported in dialout solutions. An access server utilizes a dialout
feature when it initiates a call to a remote device and attempts to start up a transport protocol such as PPP.
See the
Cisco IOS XE Dial Technologies Configuration Guide , Release 2 for more information about CHAP and PAP.
Note
To use CHAP or PAP, you must be running PPP encapsulation.
When CHAP is enabled on an interface and a remote device attempts to connect to it, the access server sends a CHAP packet
to the remote device. The CHAP packet requests or “challenges” the remote device to respond. The challenge packet consists
of an ID, a random number, and the host name of the local router.
When the remote device receives the challenge packet, it concatenates the ID, the remote device’s password, and the random
number, and then encrypts all of it using the remote device’s password. The remote device sends the results back to the access
server, along with the name associated with the password used in the encryption process.
When the access server receives the response, it uses the name it received to retrieve a password stored in its user database.
The retrieved password should be the same password the remote device used in its encryption process. The access server then
encrypts the concatenated information with the newly retrieved password--if the result matches the result sent in the response
packet, authentication succeeds.
The benefit of using CHAP authentication is that the remote device’s password is never transmitted in clear text. This prevents
other devices from stealing it and gaining illegal access to the ISP’s network.
CHAP transactions occur only at the time a link is established. The access server does not request a password during the
rest of the call. (The local device can, however, respond to such requests from other devices during a call.)
When PAP is enabled, the remote router attempting to connect to the access server is required to send an authentication request.
If the username and password specified in the authentication request are accepted, the Cisco IOS XE software sends an authentication
acknowledgment.
After you have enabled CHAP or PAP, the access server will require authentication from remote devices dialing in to the access
server. If the remote device does not support the enabled protocol, the call will be dropped.
To use CHAP or PAP, you must perform the following tasks:
Enable PPP encapsulation.
Enable CHAP or PAP on the interface.
For CHAP, configure host name authentication and the secret or password for each remote system with which authentication
is required.
Enabling PPP Encapsulation
To enable PPP encapsulation, use the following command in interface configuration mode:
Command
Purpose
Router(config-if)# encapsulation ppp
Enables PPP on an interface.
Enabling PAP or CHAP
To enable CHAP or PAP authentication on an interface configured for PPP encapsulation, use the following command in interface
configuration mode:
Defines the authentication protocols supported and the order in which they are used. In this command, protocol1, protocol2
represent the following protocols: CHAP, MS-CHAP, and PAP. PPP authentication is attempted first using the first authentication
method, which is protocol1. If protocol1 is unable to establish authentication, the next configured protocol is used to negotiate authentication.
If you configure ppp authentication chap on an interface, all incoming calls on that interface that initiate a PPP connection will have to be authenticated using
CHAP; likewise, if you configure ppp authentication pap , all incoming calls that start a PPP connection will have to be authenticated via PAP. If you configure ppp authentication chap pap , the access server will attempt to authenticate all incoming calls that start a PPP session with CHAP. If the remote device
does not support CHAP, the access server will try to authenticate the call using PAP. If the remote device does not support
either CHAP or PAP, authentication will fail and the call will be dropped. If you configure ppp authentication pap chap , the access server will attempt to authenticate all incoming calls that start a PPP session with PAP. If the remote device
does not support PAP, the access server will try to authenticate the call using CHAP. If the remote device does not support
either protocol, authentication will fail and the call will be dropped. If you configure the ppp authentication command with the callin keyword, the access server will only authenticate the remote device if the remote device initiated the call.
Authentication method lists and the one-time keyword are only available if you have enabled AAA--they will not be available if you are using TACACS or extended TACACS.
If you specify the name of an authentication method list with the ppp authentication command, PPP will attempt to authenticate the connection using the methods defined in the specified method list. If AAA is
enabled and no method list is defined by name, PPP will attempt to authenticate the connection using the methods defined as
the default. The ppp authentication command with the one-time keyword enables support for one-time passwords during authentication.
The if-needed keyword is only available if you are using TACACS or extended TACACS. The ppp authentication command with the if-needed keyword means that PPP will only authenticate the remote device via PAP or CHAP if they have not yet authenticated during
the life of the current call. If the remote device authenticated via a standard login procedure and initiated PPP from the
EXEC prompt, PPP will not authenticate via CHAP if ppp authentication chap if-needed is configured on the interface.
Caution
If you use a list-name that has not been configured with the aaa authentication ppp command, you disable PPP on the line.
For information about adding a username entry for each remote system from which the local router or access server requires authentication, see the Establishing Username Authentication.
Inbound and Outbound Authentication
PPP supports two-way authentication. Normally, when a remote device dials in to an access server, the access server requests
that the remote device prove that it is allowed access. This is known as inbound authentication. At the same time, the remote
device can also request that the access server prove that it is who it says it is. This is known as outbound authentication.
An access server also does outbound authentication when it initiates a call to a remote device.
Enabling Outbound PAP Authentication
To enable outbound PAP authentication, use the following command in interface configuration mode:
Command
Purpose
Router(config-if)# ppp pap sent-username usernamepassword password
Enables outbound PAP authentication.
The access server uses the username and password specified by the ppp pap sent-username command to authenticate itself whenever it initiates a call to a remote device or when it has to respond to a remote device’s
request for outbound authentication.
Refusing PAP Authentication Requests
To refuse PAP authentication from peers requesting it, meaning that PAP authentication is disabled for all calls, use the
following command in interface configuration mode:
Command
Purpose
Router(config-if)# ppp pap refuse
Refuses PAP authentication from peers requesting PAP authentication.
If the refuse keyword is not used, the router will not refuse any PAP authentication challenges received from the peer.
Creating a Common CHAP Password
For remote CHAP authentication only, you can configure your router to create a common CHAP secret password to use in response
to challenges from an unknown peer; for example, if your router calls a rotary of routers (either from another vendor, or
running an older version of the Cisco IOS software) to which a new (that is, unknown) router has been added. The ppp chap password command allows you to replace several username and password configuration commands with a single copy of this command on
any dialer interface or asynchronous group interface.
To enable a router calling a collection of routers to configure a common CHAP secret password, use the following command in
interface configuration mode:
Command
Purpose
Router(config-if)# ppp chap password secret
Enables a router calling a collection of routers to configure a common CHAP secret password.
Refusing CHAP Authentication Requests
To refuse CHAP authentication from peers requesting it, meaning that CHAP authentication is disabled for all calls, use the
following command in interface configuration mode:
Command
Purpose
Router(config-if)# ppp chap refuse [callin ]
Refuses CHAP authentication from peers requesting CHAP authentication.
If the callin keyword is used, the router will refuse to answer CHAP authentication challenges received from the peer, but will still require
the peer to answer any CHAP challenges the router sends.
If outbound PAP has been enabled (using the ppp pap sent-username command), PAP will be suggested as the authentication method in the refusal packet.
Delaying CHAP Authentication Until Peer Authenticates
To specify that the router will not authenticate to a peer requesting CHAP authentication until after the peer has authenticated
itself to the router, use the following command in interface configuration mode:
Command
Purpose
Router(config-if)# ppp chap wait secret
Configures the router to delay CHAP authentication until after the peer has authenticated itself to the router.
This command (which is the default) specifies that the router will not authenticate to a peer requesting CHAP authentication
until the peer has authenticated itself to the router. The no ppp chap wait commandspecifies that the router will respond immediately to an authentication challenge.
Using MS-CHAP
Microsoft Challenge Handshake Authentication Protocol (MS-CHAP) is the Microsoft version of CHAP and is an extension of RFC
1994. Like the standard version of CHAP, MS-CHAP is used for PPP authentication; in this case, authentication occurs between
a PC using Microsoft Windows NT or Microsoft Windows 95 and a Cisco device or access server acting as a network access server.
MS-CHAP differs from the standard CHAP as follows:
MS-CHAP is enabled by negotiating CHAP Algorithm 0x80 in LCP option 3, Authentication Protocol.
The MS-CHAP Response packet is in a format designed to be compatible with Microsoft Windows NT 3.5 and 3.51, Microsoft Windows
95, and Microsoft LAN Manager 2.x. This format does not require the authenticator to store a clear or reversibly encrypted password.
MS-CHAP provides an authenticator-controlled authentication retry mechanism.
MS-CHAP provides an authenticator-controlled change password mechanism.
MS-CHAP defines a set of “reason-for failure” codes returned in the Failure packet message field.
Depending on the security protocols you have implemented, PPP authentication using MS-CHAP can be used with or without AAA
security services. If you have enabled AAA, PPP authentication using MS-CHAP can be used in conjunction with both TACACS+
and RADIUS. The table below lists the vendor-specific RADIUS attributes (IETF Attribute 26) that enable RADIUS to support
MS-CHAP.
Table 9. Vendor-Specific RADIUS Attributes for MS-CHAP
Vendor-ID
Number
Vendor-Type
Number
Vendor-Proprietary Attribute
Description
311
11
MSCHAP-Challenge
Contains the challenge sent by a network access server to an MS-CHAP user. It can be used in both Access-Request and Access-Challenge
packets.
211
11
MSCHAP-Response
Contains the response value provided by a PPP MS-CHAP user in response to the challenge. It is only used in Access-Request
packets. This attribute is identical to the PPP CHAP Identifier.
Defining PPP Authentication using MS-CHAP
To define PPP authentication using MS-CHAP, use the following commands in interface configuration mode:
If you configure ppp authentication ms-chap on an interface, all incoming calls on that interface that initiate a PPP connection will have to be authenticated using
MS-CHAP. If you configure the ppp authentication command with the callin keyword, the access server will only authenticate the remote device if the remote device initiated the call.
Authentication method lists and the one-time keyword are only available if you have enabled AAA--they will not be available if you are using TACACS or extended TACACS.
If you specify the name of an authentication method list with the ppp authentication command, PPP will attempt to authenticate the connection using the methods defined in the specified method list. If AAA is
enabled and no method list is defined by name, PPP will attempt to authenticate the connection using the methods defined as
the default. The ppp authentication command with the one-time keyword enables support for one-time passwords during authentication.
The if-needed keyword is only available if you are using TACACS or extended TACACS. The ppp authentication command with the if-needed keyword means that PPP will only authenticate the remote device via MS-CHAP if that device has not yet authenticated during
the life of the current call. If the remote device authenticated through a standard login procedure and initiated PPP from
the EXEC prompt, PPP will not authenticate through MS-CHAP if ppp authentication chap if-needed is configured.
Note
If PPP authentication using MS-CHAP is used with username authentication, you must include the MS-CHAP secret in the local
username/password database. For more information about username authentication, refer to the “Establish Username Authentication”
section.
Authentication Examples
RADIUS Authentication Examples
This section provides two sample configurations using RADIUS.
The following example shows how to configure the router to authenticate and authorize using RADIUS:
aaa authentication login radius-login group radius local
aaa authentication ppp radius-ppp if-needed group radius
aaa authorization exec default group radius if-authenticated
aaa authorization network default group radius
line 3
login authentication radius-login
interface serial 0
ppp authentication radius-ppp
The lines in this sample RADIUS authentication and authorization configuration are defined as follows:
The aaa authentication login radius-login group radius local command configures the router to use RADIUS for authentication
at the login prompt. If RADIUS returns an error, the user is authenticated using the local database.
The aaa authentication ppp radius-ppp if-needed group radius command configures the Cisco IOS XE software to use PPP authentication
using CHAP or PAP if the user has not already logged in. If the EXEC facility has authenticated the user, PPP authentication
is not performed.
The aaa authorization exec default group radius if-authenticated command queries the RADIUS database for information that
is used during EXEC authorization, such as autocommands and privilege levels, but only provides authorization if the user
has successfully authenticated.
The aaa authorization network default group radius command queries RADIUS for network authorization, address assignment, and
other access lists.
The login authentication radius-login command enables the radius-login method list for line 3.
The ppp authentication radius-ppp command enables the radius-ppp method list for serial interface 0.
The following example shows how to configure the router to prompt for and verify a username and password, authorize the user’s
EXEC level, and specify it as the method of authorization for privilege level 2. In this example, if a local username is entered
at the username prompt, that username is used for authentication.
If the user is authenticated using the local database, EXEC authorization using RADIUS will fail because no data is saved
from the RADIUS authentication. The method list also uses the local database to find an autocommand. If there is no autocommand,
the user becomes the EXEC user. If the user then attempts to issue commands that are set at privilege level 2, TACACS+ is
used to attempt to authorize the command.
aaa authentication login default group radius local
aaa authorization exec default group radius local
aaa authorization command 2 default group tacacs+ if-authenticated
radius-server host 172.16.71.146 auth-port 1645 acct-port 1646
radius-server attribute 44 include-in-access-req
radius-server attribute 8 include-in-access-req
The lines in this sample RADIUS authentication and authorization configuration are defined as follows:
The aaa authentication login default group radius local command specifies that the username and password are verified by RADIUS
or, if RADIUS is not responding, by the router’s local user database.
The aaa authorization exec default group radius local command specifies that RADIUS authentication information be used to
set the user’s EXEC level if the user authenticates with RADIUS. If no RADIUS information is used, this command specifies
that the local user database be used for EXEC authorization.
The aaa authorization command 2 default group tacacs+ if-authenticated command specifies TACACS+ authorization for commands
set at privilege level 2, if the user has already successfully authenticated.
The radius-server host 172.16.71.146 auth-port 1645 acct-port 1646 command specifies the IP address of the RADIUS server host,
the UDP destination port for authentication requests, and the UDP destination port for accounting requests.
The radius-server attribute 44 include-in-access-req command sends RADIUS attribute 44 (Acct-Session-ID) in access-request
packets.
The radius-server attribute 8 include-in-access-req command sends RADIUS attribute 8 (Framed-IP-Address) in access-request
packets.
TACACS Authentication Examples
The following example shows how to configure TACACS+ as the security protocol to be used for PPP authentication:
aaa new-model
aaa authentication ppp test group tacacs+ local
interface serial 0
ppp authentication chap pap test
tacacs-server host 192.0.2.3
tacacs-server key goaway
The lines in this sample TACACS+ authentication configuration are defined as follows:
The
aaa new-model command enables the AAA security services.
The
aaa authentication command defines a method list, “test,” to be used on serial interfaces running PPP. The keywordsgroup tacacs+ means that authentication will be done through TACACS+. If TACACS+ returns an ERROR of some sort during authentication, the
keyword
local indicates that authentication will be attempted using the local database on the network access server.
The
interface command selects the line.
The
ppp authentication command applies the test method list to this line.
The
tacacs-server host command identifies the TACACS+ daemon as having an IP address of 192.0.2.3.
The
tacacs-server key command defines the shared encryption key to be “goaway.”
The following example shows how to configure AAA authentication for PPP:
aaa authentication ppp default if-needed group tacacs+ local
In this example, the keyword
default means that PPP authentication is applied by default to all interfaces. The
if-needed keyword means that if the user has already authenticated by going through the ASCII login procedure, then PPP is not necessary
and can be skipped. If authentication is needed, the keywords
group tacacs+ means that authentication will be done through TACACS+. If TACACS+ returns an ERROR of some sort during authentication, the
keyword
local indicates that authentication will be attempted using the local database on the network access server.
The following example shows how to create the same authentication algorithm for PAP, but it calls the method list “MIS-access”
instead of “default”:
aaa authentication ppp MIS-access if-needed group tacacs+ local
interface serial 0
ppp authentication pap MIS-access
In this example, because the list does not apply to any interfaces (unlike the default list, which applies automatically
to all interfaces), the administrator must select interfaces to which this authentication scheme should apply by using the
interface command. The administrator must then apply this method list to those interfaces by using the
ppp authentication command.
Kerberos Authentication Examples
To specify Kerberos as the login authentication method, use the following command:
aaa authentication login default krb5
To specify Kerberos authentication for PPP, use the following command:
aaa authentication ppp default krb5
AAA Scalability Example
The following example shows a general security configuration using AAA with RADIUS as the security protocol. In this example,
the network access server is configured to allocate 16 background processes to handle AAA requests for PPP.
aaa new-model
radius-server host alcatraz
radius-server key myRaDiUSpassWoRd
radius-server configure-nas
username root password ALongPassword
aaa authentication ppp dialins group radius local
aaa authentication login admins local
aaa authorization network default group radius local
aaa accounting network default start-stop group radius
aaa processes 16
line 1 16
autoselect ppp
autoselect during-login
login authentication admins
modem dialin
interface group-async 1
group-range 1 16
encapsulation ppp
ppp authentication pap dialins
The lines in this sample RADIUS AAA configuration are defined as follows:
The aaa new-model command enables AAA network security services.
The radius-server host command defines the name of the RADIUS server host.
The radius-server key command defines the shared secret text string between the network access server and the RADIUS server host.
The radius-server configure-nas command defines that the Cisco router or access server will query the RADIUS server for static routes and IP pool definitions
when the device first starts up.
The username command defines the username and password to be used for the PPP Password Authentication Protocol (PAP) caller identification.
The aaa authentication ppp dialins group radius local command defines the authentication method list “dialins,” which specifies that RADIUS authentication, then (if the RADIUS
server does not respond) local authentication will be used on serial lines using PPP.
The aaa authentication login admins local command defines another method list, “admins,” for login authentication.
The aaa authorization network default group radius local command is used to assign an address and other network parameters to the RADIUS user.
The aaa accounting network default start-stop group radius command tracks PPP usage.
The aaa processes command allocates 16 background processes to handle AAA requests for PPP.
The line command switches the configuration mode from global configuration to line configuration and identifies the specific lines
being configured.
The autoselect ppp command allows a PPP session to start up automatically on these selected lines.
The autoselect during-login command is used to display the username and password prompt without pressing the Return key. After the user logs in, the
autoselect function (in this case, PPP) begins.
The login authentication admins command applies the “admins” method list for login authentication.
Themodem dialin command configures modems attached to the selected lines to only accept incoming calls.
The interface group-async command selects and defines an asynchronous interface group.
The group-range command defines the member asynchronous interfaces in the interface group.
Theencapsulation ppp command sets PPP as the encapsulation method used on the specified interfaces.
Theppp authentication pap dialins command applies the “dialins” method list to the specified interfaces.
Example: Configuring Login and Failed-Login Banners for AAA Authentication
The following example shows how to configure a login banner that is displayed when a user logs in to the system, (in this
case, the phrase “Unauthorized Access Prohibited”). The asterisk (*) is used as the delimiting character. RADIUS is specified
as the default login authentication method.
This configuration displays the following login banner:
Unauthorized Access Prohibited
Username:
The following example shows how to configure a failed-login banner that is displayed when a user tries to log in to the system
and fails, (in this case, the phrase “Failed login. Try again”). The asterisk (*) is used as the delimiting character. RADIUS
is specified as the default login authentication method.
The following example shows how to configure POD (packet of disconnect), which terminates connections on the network access
server (NAS) when particular session attributes are identified.
The examples in this section illustrate possible configurations to be used with double authentication. Your configurations
could differ significantly, depending on your network and security requirements.
Note
These configuration examples include specific IP addresses and other specific information. This information is for illustration
purposes only: your configuration will use different IP addresses, different usernames and passwords, and different authorization
statements.
Configuration of the Local Host for AAA with Double Authentication Examples
These two examples show how to configure a local host to use AAA for PPP and login authentication, and for network and EXEC
authorization. An example each is shown for RADIUS and for TACACS+.
In both the examples, the first three lines configure AAA with a specific server as the AAA server. The next two lines configure
AAA for PPP and login authentication, and the last two lines configure network and EXEC authorization. The last line is necessary
only if the
access-profile command will be executed as an autocommand.
The following example shows device configuration with a RADIUS AAA server:
aaa new-model
radius-server host secureserver
radius-server key myradiuskey
aaa authentication ppp default group radius
aaa authentication login default group radius
aaa authorization network default group radius
aaa authorization exec default group radius
The following example shows device configuration with a TACACS+ server:
aaa new-model
tacacs-server host security
tacacs-server key mytacacskey
aaa authentication ppp default group tacacs+
aaa authentication login default group tacacs+
aaa authorization network default group tacacs+
aaa authorization exec default group tacacs+
Configuration of the AAA Server for First-Stage PPP Authentication and Authorization Example
This example shows a configuration on the AAA server. A partial sample AAA configuration is shown for RADIUS.
TACACS+ servers can be configured similarly. (See the Complete Configuration with TACACS Example.)
This example defines authentication/authorization for a remote host named “hostx” that will be authenticated by CHAP in the
first stage of double authentication. Note that the ACL AV pair limits the remote host to Telnet connections to the local
host. The local host has the IP address 10.0.0.2.
The following example shows a partial AAA server configuration for RADIUS:
Configuration of the AAA Server for Second-Stage Per-User Authentication and Authorization Examples
This section contains partial sample AAA configurations on a RADIUS server. These configurations define authentication and
authorization for a user (Pat) with the username “patuser,” who will be user-authenticated in the second stage of double authentication.
TACACS+ servers can be configured similarly. (See the Complete Configuration with TACACS Example.)
Three examples show sample RADIUS AAA configurations that could be used with each of the three forms of the
access-profile command.
The first example shows a partial sample AAA configuration that works with the default form (no keywords) of the
access-profile command. Note that only ACL AV pairs are defined. This example also sets up the
access-profile command as an autocommand.
The second example shows a partial sample AAA configuration that works with the
access-profile merge form of the
access-profile command. This example also sets up the
access-profile merge command as an autocommand.
The third example shows a partial sample AAA configuration that works with the
access-profile replace form of the
access-profile command. This example also sets up the
access-profile replace command as an autocommand.
This example shows TACACS+ authorization profile configurations both for the remote host (used in the first stage of double
authentication) and for specific users (used in the second stage of double authentication). This TACACS+ example contains
approximately the same configuration information as shown in the previous RADIUS examples.
This sample configuration shows authentication/authorization profiles on the TACACS+ server for the remote host “hostx” and
for three users, with the usernames “pat_default,” “pat_merge,” and “pat_replace.” The configurations for these three usernames
illustrate different configurations that correspond to the three different forms of the
access-profile command. The three user configurations also illustrate setting up the autocommand for each form of the
access-profile command.
The figure below shows the topology. The example that follows the figure shows a TACACS+ configuration file.
Figure 3. Example Topology for Double Authentication
This sample configuration shows authentication/authorization profiles on the TACACS+ server for the remote host “hostx” and
for three users, with the usernames “pat_default,” “pat_merge,” and “pat_replace.”
key = “mytacacskey”
default authorization = permit
#-----------------------------Remote Host (BRI)-------------------------
#
# This allows the remote host to be authenticated by the local host
# during fist-stage authentication, and provides the remote host
# authorization profile.
#
#-----------------------------------------------------------------------
user = hostx
{
login = cleartext “welcome”
chap = cleartext “welcome”
service = ppp protocol = lcp {
interface-config=”ip unnumbered fastethernet 0"
}
service = ppp protocol = ip {
# It is important to have the hash sign and some string after
# it. This indicates to the NAS that you have a per-user
# config.
inacl#3=”permit tcp any 172.21.114.0 0.0.0.255 eq telnet”
inacl#4=”deny icmp any any”
route#5=”10.0.0.0 255.0.0.0"
route#6=”10.10.0.0 255.0.0.0"
}
service = ppp protocol = ipx {
# see previous comment about the hash sign and string, in protocol = ip
inacl#3=”deny any”
}
}
#------------------- “access-profile” default user “only acls” ------------------
#
# Without arguments, access-profile removes any access-lists it can find
# in the old configuration (both per-user and per-interface), and makes sure
# that the new profile contains ONLY access-list definitions.
#
#--------------------------------------------------------------------------------
user = pat_default
{
login = cleartext “welcome”
chap = cleartext “welcome”
service = exec
{
# This is the autocommand that executes when pat_default logs in.
autocmd = “access-profile”
}
service = ppp protocol = ip {
# Put whatever access-lists, static routes, whatever
# here.
# If you leave this blank, the user will have NO IP
# access-lists (not even the ones installed prior to
# this)!
inacl#3=”permit tcp any host 10.0.0.2 eq telnet”
inacl#4=”deny icmp any any”
}
service = ppp protocol = ipx {
# Put whatever access-lists, static routes, whatever
# here.
# If you leave this blank, the user will have NO IPX
# access-lists (not even the ones installed prior to
# this)!
}
}
#--------------------- “access-profile merge” user ---------------------------
#
# With the 'merge' option, first all old access-lists are removed (as before),
# but then (almost) all AV pairs are uploaded and installed. This will allow
# for uploading any custom static routes, sap-filters, and so on, that the user
# may need in his or her profile. This needs to be used with care, as it leaves
# open the possibility of conflicting configurations.
#
#-----------------------------------------------------------------------------
user = pat_merge
{
login = cleartext “welcome”
chap = cleartext “welcome”
service = exec
{
# This is the autocommand that executes when pat_merge logs in.
autocmd = “access-profile merge”
}
service = ppp protocol = ip
{
# Put whatever access-lists, static routes, whatever
# here.
# If you leave this blank, the user will have NO IP
# access-lists (not even the ones installed prior to
# this)!
inacl#3=”permit tcp any any”
route#2=”10.0.0.0 255.255.0.0"
route#3=”10.1.0.0 255.255.0.0"
route#4=”10.2.0.0 255.255.0.0"
}
service = ppp protocol = ipx
{
# Put whatever access-lists, static routes, whatever
# here.
# If you leave this blank, the user will have NO IPX
# access-lists (not even the ones installed prior to
# this)!
}
}
#--------------------- “access-profile replace” user ----------------------------
#
# With the 'replace' option, ALL old configuration is removed and ALL new
# configuration is installed.
#
# One caveat: access-profile checks the new configuration for address-pool and
# address AV pairs. As addresses cannot be renegotiated at this point, the
# command will fail (and complain) when it encounters such an AV pair.
# Such AV pairs are considered to be “invalid” for this context.
#-------------------------------------------------------------------------------
user = pat_replace
{
login = cleartex
t
“
welcome
”
chap = cleartext “welcome”
service = exec
{
# This is the autocommand that executes when pat_replace logs in.
autocmd = “access-profile replace”
}
service = ppp protocol = ip
{
# Put whatever access-lists, static routes, whatever
# here.
# If you leave this blank, the user will have NO IP
# access-lists (not even the ones installed prior to
# this)!
inacl#3=”permit tcp any any”
inacl#4=”permit icmp any any”
route#2=”10.10.0.0 255.255.0.0"
route#3=”10.11.0.0 255.255.0.0"
route#4=”10.12.0.0 255.255.0.0"
}
service = ppp protocol = ipx
{
# put whatever access-lists, static routes, whatever
# here.
# If you leave this blank, the user will have NO IPX
# access-lists (not even the ones installed prior to
# this)!
}
}
Automated Double Authentication Example
This example shows a complete configuration file with automated double authentication configured. The configuration commands
that apply to automated double authentication are preceded by descriptions with a double asterisk (**).
Current configuration:
!
version 11.3
no service password-encryption
!
hostname myrouter
!
!
! **The following AAA commands are used to configure double authentication:
!
! **The following command enables AAA:
aaa new-model
! **The following command enables user authentication via the RADIUS AAA server:
!
aaa authentication login default none
aaa authentication ppp default group radius
! **The following command causes the remote user’s authorization profile to be
! downloaded from the AAA server to the router when required:
!
aaa authorization network default group radius
!
enable password mypassword
!
ip host blue 172.21.127.226
ip host green 172.21.127.218
ip host red 172.21.127.114
ip domain-name example.com
ip name-server 172.16.2.75
!
!
interface FastEthernet0/0/0
ip address 172.21.127.186 255.255.255.248
no ip route-cache
no ip mroute-cache
no keepalive
ntp disable
no cdp enable
!
interface Virtual-Template1
ip unnumbered loopback0
no ip route-cache
no ip mroute-cache
!
! **The following command specifies that device authentication occurs via PPP CHAP:
ppp authentication chap
!
router eigrp 109
network 172.21.0.0
no auto-summary
!
ip default-gateway 172.21.127.185
no ip classless
ip route 172.21.127.114 255.255.255.255 172.21.127.113
! **Virtual profiles are required for double authentication to work:
virtual-profile virtual-template 1
dialer-list 1 protocol ip permit
no cdp run
! **The following command defines where the TACACS+ AAA server is:
tacacs-server host 172.16.57.35 port 1049
tacacs-server timeout 90
! **The following command defines the key to use with TACACS+ traffic (required):
tacacs-server key mytacacskey
snmp-server community public RO
!
line con 0
exec-timeout 0 0
login authentication console
line aux 0
transport input all
line vty 0 4
exec-timeout 0 0
password lab
!
end
The lines in this sample RADIUS AAA configuration are defined as follows:
The aaa new-model command enables AAA network security services.
The aaa authentication login admins local command defines another method list, “admins”, for login authentication.
The aaa authentication ppp dialins group radius local command defines the authentication method list “dialins,” which specifies that RADIUS authentication then (if the RADIUS
server does not respond) local authentication will be used on serial lines using PPP.
The aaa authorization network default group radius local command is used to assign an address and other network parameters to the RADIUS user.
The aaa accounting network default start-stop group radius command tracks PPP usage.
The username command defines the username and password to be used for the PPP Password Authentication Protocol (PAP) caller identification.
The radius-server host command defines the name of the RADIUS server host.
The radius-server key command defines the shared secret text string between the network access server and the RADIUS server host.
The interface group-async command selects and defines an asynchronous interface group.
The group-range command defines the member asynchronous interfaces in the interface group.
Theencapsulation ppp command sets PPP as the encapsulation method used on the specified interfaces.
Theppp authentication ms-chap dialins command selects MS-CHAP as the method of PPP authentication and applies the “dialins” method list to the specified interfaces.
The line command switches the configuration mode from global configuration to line configuration and identifies the specific lines
being configured.
The autoselect ppp command allows a PPP session to start up automatically on these selected lines.
The autoselect during-login command is used to display the username and password prompt without pressing the Return key. After the user logs in, the
autoselect function (in this case, PPP) begins.
The login authentication admins command applies the “admins” method list for login authentication.
Themodem dialin command configures modems attached to the selected lines to only accept incoming calls.
Additional References
The following sections provide references related to the Configuring Authentication feature.
Related Documents
Related Topic
Document Title
Authorization
Configuring Authorization in the
Cisco IOS XE Security Configuration Guide: Securing User Services, Release 2.
Accounting
Configuring Accounting in the
Cisco IOS XE Security Configuration Guide: Securing User Service , Release 2.
Security commands
Cisco IOS Security Command Reference
Standards
Standard
Title
No new or modified standards are supported by this feature, and support for existing standards has not been modified by this
feature.
--
MIBs
MIB
MIBs Link
No new or modified MIBs are supported by this feature, and support for existing MIBs has not been modified by this feature.
To locate and download MIBs for selected platforms, Cisco IOS XE software releases, and feature sets, use Cisco MIB Locator
found at the following URL:
Criteria for Evaluating AAA Protocols for Network Access
Technical Assistance
Description
Link
The Cisco Support website provides extensive online resources, including documentation and tools for troubleshooting and
resolving technical issues with Cisco products and technologies.
To receive security and technical information about your products, you can subscribe to various services, such as the Product
Alert Tool (accessed from Field Notices), the Cisco Technical Services Newsletter, and Really Simple Syndication (RSS) Feeds.
Access to most tools on the Cisco Support website requires a Cisco.com user ID and password.
Feature Information for Configuring Authentication
The following table provides release information about the feature or features described in this module. This table lists
only the software release that introduced support for a given feature in a given software release train. Unless noted otherwise,
subsequent releases of that software release train also support that feature.
Use Cisco Feature Navigator to find information about platform support and Cisco software image support. To access Cisco
Feature Navigator, go to www.cisco.com/go/cfn. An account on Cisco.com is not required.
Table 10. Feature Information for Configuring Authentication
Feature Name
Releases
Feature Information
AAA Method Lists Enhancement
Cisco IOS XE Release 2.1
This feature allows you to enable fallback methods for authentication, authorization or accounting. The fallback methods
could include trying groups of RADIUS or TACACS+ servers or a local database in some cases.
In Cisco IOS XE Release 2.1, this feature was introduced on the Cisco ASR 1000 Series Aggregation Services Routers.
The following command was introduced or modified:
aaa authentication ppp .
AAA Per-User Scalability
Cisco IOS XE Release 2.3
The AAA Per-User Scalability feature supports two RADIUS VSAs for
ip vrf and
ip unnumbered commands and creates subvirtual access interfaces if specified instead of full VA interface to achieve higher scalability.
In Cisco IOS XE Release 2.3, this feature was introduced on the Cisco ASR 1000 Series Aggregation Services Routers.
Challege Handshake Authentication Protocol (CHAP)
Cisco IOS XE Release 2.1
PPP currently supports two authentication protocols: Password Authentication Protocol (PAP) and Challenge Handshake Authentication
Protocol (CHAP). Both are specified in RFC 1334 and are supported on synchronous and asynchronous interfaces. Authentication
via PAP or CHAP is equivalent to typing in a username and password when prompted by the server. CHAP is considered to be more
secure because the remote user’s password is never sent across the connection.
In Cisco IOS XE Release 2.1, this feature was introduced on the Cisco ASR 1000 Series Aggregation Services Routers.
The following commands were introduced or modified:
ppp authentication ,ppp chap password ,ppp chap refuse .
Domain Stripping at the Server Group Level
Cisco IOS XE Release 3.4S
The Domain Stripping feature allows domain stripping to be configured at the server group level. Per-server group configuration
overrides the global configuration.
The following sections provide information about this feature:
The following command was introduced:
domain-stripping .
Double Authentication
Cisco IOS XE Release 2.1
In Cisco IOS XE Release 2.1, this feature was introduced on the Cisco ASR 1000 Series Aggregation Services Routers.
The following commands were introduced or modified:
aaa authentication ,aaa authorization ,access-profile .
Message Banners for AAA Authentication
Cisco IOS XE Release 2.1
In Cisco IOS XE Release 2.1, this feature was introduced on the Cisco ASR 1000 Series Aggregation Services Routers.
The following command was introduced:
aaa authentication banner .
MS-CHAP Version 1
Cisco IOS XE Release 2.1
Microsoft Challenge Handshake Authentication Protocol (MS-CHAP) is the Microsoft version of CHAP and is an extension of RFC
1994. Like the standard version of CHAP, MS-CHAP is used for PPP authentication; in this case, authentication occurs between
a PC using Microsoft Windows NT or Microsoft Windows 95 and a Cisco router or access server acting as a network access server.
In Cisco IOS XE Release 2.1, this feature was introduced on the Cisco ASR 1000 Series Aggregation Services Routers.
The following commands were introduced or modified:
ppp authentication .
Password Authentication Protocol (PAP)
Cisco IOS XE Release 2.1
PPP currently supports two authentication protocols: Password Authentication Protocol (PAP) and Challenge Handshake Authentication
Protocol (CHAP). Both are specified in RFC 1334 and are supported on synchronous and asynchronous interfaces. Authentication
via PAP or CHAP is equivalent to typing in a username and password when prompted by the server. CHAP is considered to be more
secure because the remote user’s password is never sent across the connection.
In Cisco IOS XE Release 2.1, this feature was introduced on the Cisco ASR 1000 Series Aggregation Services Routers.
The following commands were introduced or modified:
ppp authentication ,
ppp pap sent-username ,ppp pap refuse .
RADIUS—CLI to Prevent Sending of Access Request with a Blank Username
Cisco IOS XE Release 2.4
This authentication feature prevents an Access Request with a blank username from being sent to the RADIUS server. This functionality
ensures that unnecessary RADIUS server interaction is avoided, and RADIUS logs are kept short.
In Cisco IOS XE Release 2.4, this feature was introduced on the Cisco ASR 1000 Series Aggregation Services Routers.
The following command was introduced:
aaa authentication suppress null-username .
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