Table Of Contents

Configuring the NAS for RADIUS

Global Configuration

Authentication on the NAS

Excluding Ports

Authorization on the NAS

Accounting on the NAS

Sample Configuration for a Cisco 2509 Using RADIUS with Accounting Enabled

Sample Configuration for an ISP Using a Cisco AS5200

CHAP-Challenge Attribute

RADIUS Tunneling

RADIUS Tunneling in a Multivendor LAC Environment

Configuring the NAS for RADIUS

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Configuration for the network access server (NAS) using the Remote Access Dial-In User Service (RADIUS) protocol is similar to configuration for the Terminal Access Controller Access Control System (TACACS+) protocol.

This chapter describes:

• Global Configuration

• Authentication on the NAS

• Authorization on the NAS

• Accounting on the NAS

• Sample Configuration for a Cisco 2509 Using RADIUS with Accounting Enabled

• Sample Configuration for an ISP Using a Cisco AS5200

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Note The information in this chapter applies to Cisco NASes; however, you can use the CiscoSecure Access Control Server (ACS) with other vendors' NASes. See your manufacturer's documentation for more specific information on configuring your NAS. Configure your NAS for RADIUS as you would normally; no special configuration is required.

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For complete information about a specific Cisco IOS release or more detailed configurations, see the Router Products Configuration Guide or the Configuration Fundamentals Configuration Guide publication. (See "References and Recommended Reading.")

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Note For a sample configuration, see the "Sample Configuration for a Cisco 2509 Using RADIUS with Accounting Enabled" section and the "Sample Configuration for an ISP Using a Cisco AS5200" section. For more ready-to-use configurations, see the chapter "NAS Configuration Examples," in the CiscoSecure ACS 2.3 for UNIX Reference Guide for sample configurations that you can apply directly to your own NAS or modify according to your needs.

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Global Configuration

The first steps in configuring the NAS are:

1. Enable RADIUS.

2. Specify the list of CiscoSecure ACSs that will provide AAA services for the NAS.

3. Configure the encryption key that is used to encrypt the data transfer between the NAS and the CiscoSecure ACS.

To begin global configuration, enter the following commands, using the correct IP address of the CiscoSecure ACSes and your own encryption key:

Router(config)# aaa new-model

Router(config)# radius-server host 144.1.12.100

Router(config)# radius-server host 144.1.200.250

Router(config)# radius-server key arachnid

The word "arachnid" is the encryption key shared between the NAS and the CiscoSecure ACS. The encryption key should be kept secret to protect the privacy of passwords sent between the CiscoSecure ACS and the NAS during the authentication process.

For backup purposes, you can specify multiple CiscoSecure ACSes by repeating the radius-server host command.

For a RADIUS-enabled NAS to use a CiscoSecure ACS, it must be added to the list of available RADIUS-enabled NASes in the NASes page of that ACS's Java-based CiscoSecure Administrator advanced configuration program.

Authentication on the NAS

The authentication configuration builds a set of authentication lists, each of which can be used for different purposes within the NAS. The syntax of the command is as follows:

aaa authentication login list_name method1 [method2] [method3] [method4]

aaa authentication PPP list_name method1 [method2] [method3] [method4]

As you can see, the AAA server requires an authentication for PPP in addition to an authentication for login before it will work properly.

Each of these command lines supports several arguments. A list name and one authentication method are required. Additional authentication methods are optional.

Each of the authentication methods is listed in Table 11-1.

Table 11-1 NAS Authentication Methods 

Method	Meaning
enable	Use the enable password.
line	Use the line password.
local	Use the NAS internal username database.
none	Use no authentication.
RADIUS	Use RADIUS authentication.

In the following example, system administrators must use RADIUS authentication. If a CiscoSecure ACS is not available, use the NAS's local user database password. However, all other users must use only RADIUS:

aaa authentication login default radius

aaa authentication login admin radius local

To configure authentication at login on all lines on a 16-port NAS, enter the following commands:

line console 0

login authentication admin

line aux 0

login authentication admin

line vty 0 4

login authentication default

line 1 16

login authentication default

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Caution If you do not include the enable method for system administrator logins, you will no longer be able to log in to your NAS unless you have a functioning CiscoSecure ACS appropriately configured with usernames and passwords. The addition of the enable method ensures that you will still be able to log in to the router if the router cannot contact a CiscoSecure ACS. The NAS will test the enable method only if it cannot contact a CiscoSecure ACS.

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Excluding Ports

NAS ports can be excluded from using the CiscoSecure ACS by creating a separate authentication method list that does not include RADIUS as an authentication method. Depending on your needs, you create a separate authentication method list to fixed ports that do not need authentication, authorization, and accounting (AAA) services, or for all the vty ports.

In the following example, only the first two vty ports and the console are enabled for AAA services in the NAS configuration:

aaa new-model

aaa authentication login admin radius local

aaa authentication login no_radius line

radius-server host 144.251.1.1

radius-server key arachnid

! The console and VTY lines 0 & 1 use RADIUS

line console 0

login authentication admin

line vty 0 1

login authentication admin

! VTY Lines 2 - 4 do not use RADIUS

line vty 2 4

login authentication no_radius

Authorization on the NAS

The NAS can use a CiscoSecure ACS to authorize specific commands by individual users. To authorize specific commands, you must use the following command syntax to specify which commands and actions will require authorization checks:

aaa authorization {network | connection | exec | commands level} methods 

The four items that can be checked for authorization are listed in Table 11-2.

Table 11-2 Checkable Authorization Items on the NAS 

Keyword	Authorization Check
network	Check authorization for all network activities including SLIP, PPP, PPP network control protocols, and ARAP.
connection	Check authorization for outbound Telnet and rlogin.
exec	Determine if the user is allowed to run an EXEC shell when logging into the NAS. This keyword might cause the CiscoSecure ACS to return user profile information such as autocommand information.
commands level	Check authorization for all commands at the specified privilege level level. Valid levels are 1 through 15. Level 1 is normal user EXEC commands. Level 15 is normal privileged level.

The methods you can specify are listed in Table 11-3.

Table 11-3 Authorization Methods on the NAS 

Method	Meaning
radius	Requests authorization information from the CiscoSecure ACS.
if-authenticated	Allows the user to access the requested function if the user is authenticated. Note that you are either authenticated or not, so this should be the last method in the list.
none	No authorization is performed.
local	Uses the local database for authorization.

Using the command syntax specified above, you can configure the NAS to restrict the set of commands that an individual user can execute. To require that all commands entered by users at privilege level 1 be checked for ACS authorization, enter the following command:

aaa authorization commands 1 radius

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Caution When you enter this command in your NAS, you will be permitted to execute only NAS commands that are allowed by your CiscoSecure ACS. Therefore, make sure you have configured an authenticated user who is authorized to run commands on the CiscoSecure ACS.

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To require that the system administrators be authorized at level 15, enter the following command:

aaa authorization commands 15 radius if-authenticated

This command uses RADIUS authorization level 15, but if problems arise you can switch off the CiscoSecure ACS and the authorization will then be granted to anyone who is authenticated.

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Note The NAS will test the if-authenticated method only if it cannot contact a CiscoSecure ACS.

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Accounting on the NAS

The NAS must be specifically configured to send accounting records to the CiscoSecure ACS. Several types of accounting records are available. Use the following command syntax to configure accounting on the NAS:

aaa accounting {system | network | connection | exec | command level} {start-stop | 
wait-start | stop-only} radius

The first set of keywords allows you to specify accounting of the events listed in Table 11-4.

Table 11-4 Accounting Events on the NAS 

Event Type	Meaning
system	Enables accounting for all system-level events not associated with users, such as reloads
network	Enables accounting for all network-related requests, including SLIP, PPP, PPP network control protocols, and ARAP
connection	Enables accounting for outbound Telnet and rlogin
exec	Enables accounting for EXEC processes (user shells)
command level	Enables accounting for all commands at the specified privilege level

You can specify when accounting records are to be sent by using the second set of keywords, which are listed in Table 11-5.

Table 11-5 Accounting Record Keywords on the NAS 

Keyword	Meaning
stop-only	The NAS sends a stop record accounting notice at the end of the specified activity or event (command, EXEC shell, and so on).
start-stop	The NAS sends a start record accounting notice at the beginning of a process and a stop record at the end of the process. The start accounting record is sent in the background. The requested user process begins regardless of whether or not the start accounting record was acknowledged by the accounting server.
wait-start	This keyword causes both a start and stop accounting record to be sent to the accounting server. However, the requested user service does not begin until the start accounting record is acknowledged. A stop accounting record is also sent.

Use the following commands to record accounting information on NAS system events, network connections, outbound connections, EXEC operations, and commands at level 1 and level 15:

aaa accounting system start-stop radius

aaa accounting network start-stop radius

aaa accounting connection start-stop radius

aaa accounting exec stop-only radius

aaa accounting command 1 stop-only radius

aaa accounting command 15 wait-start radius 

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Note Stop records contain elapsed time for connections and EXEC sessions.

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Note The aaa accounting command 0 start-stop command is not implemented in Cisco IOS Release 11.0. Check the release notes for your Cisco IOS release to determine whether it has been implemented.

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Sample Configuration for a Cisco 2509 Using RADIUS with Accounting Enabled

The following is a sample configuration for a Cisco 2509 router using RADIUS with the accounting feature enabled:

Current configuration:

!

version 11.2

service udp-small-servers

service tcp-small-servers

!

hostname as2509

!

aaa new-model

aaa authentication local-override

aaa authentication login default radius

aaa authentication login no_radius local

aaa authentication enable default enable

aaa authentication ppp default radius

aaa authorization exec radius if-authenticated

aaa authorization network radius

aaa accounting exec start-stop radius

aaa accounting network start-stop radius

aaa accounting system start-stop radius

enable password secure

!

username cisco password 7 03175E08131D24

username therzog password 7 09404B1D14001E1C59

username root password 7 070C285F4D06

ip address-pool local

chat-script cisco-default ABORT ERROR "" "AT Z" OK "ATDT \T" TIMEOUT 30 \c CONNECT \c

chat-script usr-courier-veverything "" "AT&FS0=1&C1&D2&H1&R2&N14&B1&W"

chat-script factory-default "" "AT&F"

!

interface Ethernet0

ip address 200.200.200.44 255.255.255.0

no mop enabled

!

interface Serial0

no ip address

shutdown

!

interface Serial1

no ip address

shutdown

!

interface Async1

ip unnumbered Ethernet0

encapsulation ppp

sync mode interactive

peer default ip address 200.200.200.58

no cdp enable

ppp authentication chap pap

!

interface Async2

ip unnumbered Ethernet0

encapsulation ppp

async mode interactive

peer default ip address pool pool1

no cdp enable

ppp authentication pap chap

!

interface Group-Async1

ip unnumbered Ethernet0

encapsulation ppp

no cdp enable

group-range 3 8

!

ip local pool pool1 200.200.200.50 200.200.200.57

no ip classless

!

radius-server host 200.200.200.41

radius-server key as2509abcd

!

line con 0

session-timeout 10 

exec-timeout 30 0

login authentication no_radius

transport preferred none

line 1

autoselect during-login

autoselect ppp

script startup usr-courier-veverything

script reset usr-courier-veverything

modem InOut

modem autoconfigure type usr_courier

transport input all

rxspeed 115200

txspeed 115200

flowcontrol hardware

line 2

autoselect ppp

script startup usr-courier-veverything

script reset usr-courier-veverything

modem InOut

modem autoconfigure type usr_courier

transport input all

rxspeed 115200

txspeed 115200

flowcontrol hardware

line 3 8

transport input all

rxspeed 115200

txspeed 115200

flowcontrol hardware

line aux 0

transport preferred none

transport input all

line vty 0

exec-timeout 0 0

width 102

transport preferred none

line vty 1

exec-timeout 0 0

length 35

width 127

transport preferred none

line vty 2 4

exec-timeout 0 0

transport preferred none

!

end

as2509#

Sample Configuration for an ISP Using a Cisco AS5200

The following sample configuration for a Cisco AS5200 is typical of one that can be used by an Internet service provider (ISP) with a RADIUS installation. This configuration includes AAA, allowing the ISP to have centralized user management as well as accounting records necessary for billing:

!

version 11.1

service udp-small-servers

service tcp-small-servers

!

hostname isdn-14

!

aaa new-model

aaa authentication login default Radius

aaa authentication login console line

aaa authentication login secure radius local

aaa authentication login vty line

aaa authentication ppp default Radius

aaa authentication ppp secure if-needed radius local

aaa authorization exec radius

aaa authorization network radius

aaa accounting exec start-stop radius

aaa accounting network start-stop radius

!

username backup password radiusISdown

ip radius source-interface Ethernet0

rlogin trusted-remoteuser-source local

rlogin trusted-localuser-source radius

isdn switch-type primary-5ess

!

controller T1 0

framing esf

clock source line primary

linecode b8zs

pri-group timeslots 1-24

!

controller T1 1

framing esf

clock source line secondary

linecode b8zs

pri-group timeslots 1-24

!

interface Loopback0

ip address 171.68.187.254 255.255.255.0

!

interface Ethernet0

ip address 172.16.25.15 255.255.255.224

!

interface Serial0

no ip address

shutdown

!

interface Serial1

no ip address

shutdown

!

interface Serial0:23

ip unnumbered Loopback0

encapsulation ppp

isdn incoming-voice modem

peer default ip address pool default

dialer rotary-group 1

dialer-group 1

!

interface Serial1:23

ip unnumbered Loopback0

encapsulation ppp

isdn incoming-voice modem

peer default ip address pool default

dialer rotary-group 1

dialer-group 1

!

interface Group-Async1

ip unnumbered Loopback0

ip tcp header-compression passive

encapsulation ppp

async mode interactive

peer default ip address pool default

dialer-group 1

ppp authentication chap pap secure

group-range 1 48

!

interface Dialer1

ip unnumbered Loopback0

encapsulation ppp

peer default ip address pool default

ppp multilink

ppp authentication chap pap secure

dialer-group 1

!

ip local pool default 171.68.187.1 171.68.187.48

ip domain-name cisco.com

ip name-server 171.68.10.70

no ip classless

async-bootp dns-server 171.68.10.70

!

radius-server host 172.16.72.41

radius-server host 172.16.72.42

radius-server timeout 3

radius-server key MYSECRET

!

dialer-list 1 protocol ip permit

!

line con 0

login authentication console

password cisco

line 1 48

session-timeout 15  output

autoselect during-login

autoselect ppp

login authentication secure

modem InOut

transport input all

line aux 0

line vty 0 4

login authentication vty

password secret

!

end

CHAP-Challenge Attribute

CiscoSecure ACS for UNIX supports the CHAP-Challenge(60) RADIUS attribute.

RADIUS Tunneling

CiscoSecure ACS supports the following attributes for use with RADIUS tunneling.

Table 11-6 RADIUS Tunneling Attributes Supported by CiscoSecure ACS

Name	ID#	Type
Tunnel-Type	64	Enumeration	Indicates the tunneling protocol(s) to be used: L2TP or L2F. l2F is used if this attribute is not set.
Tunnel-Medium-Type	65	Enumeration	Indicates transport medium type to use when creating a tunnel. IP is used if this attribute is not set.
Tunnel-Server-Endpoint	67	String	Indicates the address of the server end of the tunnel. The value can be an IP, X.25, or Frame Relay address and is converted based on the value of Tunnel-Medium-Type attribute. For now, the IP address or the hostname of LNS is valid for this attribute.
Tunnel-Password	69	String	Contains a password to be used to authenticate to a remote server. Must be converted into different AAA attributes based on the value of Tunnel-Type. Decrypt to retrieve the information by using the algorithm defined in the RFC.
Tunnel-Assignment-ID	82	String	Indicate to the tunnel initiator the particular tunnel to which a session is to be assigned.

RADIUS Tunneling in a Multivendor LAC Environment

To use RADIUS tunneling in a multivendor L2TP Access Concentrator (LAC) environment in which the non-Cisco LAC sends a fully qualified name in the form of user@domain_name (one that might incorporate 3Com LACs, for example), follow these additional configuration steps. This allows CiscoSecure ACS for UNIX to handle fully qualified names in the form of user@domain_name.

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Step 1 Install CiscoSecure ACS for UNIX according to the instructions in the CiscoSecure ACS 2.3 for UNIX Installation Guide.

Step 2 Edit the CSU.cfg file and set config_remote_domain_authen to 1.

Step 3 Start CiscoSecure ACS.

Step 4 Using the graphical user interface (GUI), Click AAA->Domain and enter the name of the remote domain(s) in the LAC CiscoSecure ACS AAA server field.

Step 5 Click AAA->Re-Initialize to reinitialize the AAA server.

Step 6 Set up the remote domain profiles as follows:

•Specify password=no_password.

•Do not specify User-Password (attribute 2) as a check item.

•In reply_attributes, specify User-Service-Type (attribute 6) to be Outbound-User (5).

For example:

     user = l2tp.com{

     password = no_password 

     radius=Cisco12.05 {

     reply_attributes= {

     6=5

     64=:1:3

     65=:1:1

     67=:1:"204.183.122.143"

     69=:1:"tunpass"

     82=:1:"sp_lac"

     }

     }

     }

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