Table Of Contents
RADIUS NAS-IP-Address Attribute Configurability
First Published: November 19, 2003Last Updated: September 22, 2009
The RADIUS NAS-IP-Address Attribute Configurability feature allows an arbitrary IP address to be configured and used as RADIUS attribute 4, NAS-IP-Address, without changing the source IP address in the IP header of the RADIUS packets. This feature may be used for situations in which service providers are using a cluster of small network access servers (NASs) to simulate a large NAS to improve scalability. This feature allows the NASs to behave as a single RADIUS client from the perspective of the RADIUS server.
Finding Feature Information
Your software release may not support all the features documented in this module. For the latest feature information and caveats, see the release notes for your platform and software release. To find information about the features documented in this module, and to see a list of the releases in which each feature is supported, see the "Feature Information for RADIUS NAS-IP-Address Attribute Configurability" section.
Use Cisco Feature Navigator to find information about platform support and Cisco IOS and Catalyst OS software image support. To access Cisco Feature Navigator, go to http://tools.cisco.com/ITDIT/CFN/jsp/index.jsp. An account on Cisco.com is not required.
Prerequisites for RADIUS NAS-IP-Address Attribute Configurability
The following requirements are necessary before configuring this feature:
•Experience with IP Security (IPSec) and configuring both RADIUS servers and authentication, authorization, and accounting (AAA) is necessary.
•RADIUS server and AAA lists must be configured.
Restrictions for RADIUS NAS-IP-Address Attribute Configurability
The following restrictions apply if a cluster of RADIUS clients are being used to simulate a single RADIUS client for scalability. Solutions, or workarounds, to the restrictions are also provided.
•RADIUS attribute 44, Acct-Session-Id, may overlap among sessions from different NASs.
There are two solutions. Either the radius-server attribute 44 extend-with-addr or radius-server unique-ident command can be used on NAS routers to specify different prepending numbers for different NAS routers.
•RADIUS server-based IP address pool for different NASs must be managed.
The solution is to configure different IP address pool profiles for different NASs on the RADIUS server. Different NASs use different pool usernames to retrieve them.
•RADIUS request message for sessions from different NASs must be differentiated.
One of the solutions is to configure different format strings for RADIUS attribute 32, NAS-Identifier, using the radius-server attribute 32 include-in-access-req command on different NASs.
Information About RADIUS NAS-IP-Address Attribute Configurability
To simulate a large NAS RADIUS client using a cluster of small NAS RADIUS clients, as shown in Figure 1, a Network Address Translation (NAT) or Port Address Translation (PAT) device is inserted in a network. The device is placed between a cluster of NASs and the IP cloud that is connected to a RADIUS server. When RADIUS traffic from different NASs goes through the NAT or PAT device, the source IP addresses of the RADIUS packets are translated to a single IP address, most likely an IP address on a loopback interface on the NAT or PAT device. Different User Datagram Protocol (UDP) source ports are assigned to RADIUS packets from different NASs. When the RADIUS reply comes back from the server, the NAT or PAT device receives it, uses the destination UDP port to translate the destination IP address back to the IP address of the NAS, and forwards the reply to the corresponding NAS.
Figure 1 demonstrates how the source IP addresses of several NASs are translated to a single IP address as they pass through the NAT or PAT device on the way to the IP cloud.
Figure 1 NAS Addresses Translated to a Single IP Address
RADIUS servers normally check the source IP address in the IP header of the RADIUS packets to track the source of the RADIUS requests and to maintain security. The NAT or PAT solution satisfies these requirements because only a single source IP address is used even though RADIUS packets come from different NAS routers.
However, when retrieving accounting records from the RADIUS database, some billing systems use RADIUS attribute 4, NAS-IP-Address, in the accounting records. The value of this attribute is recorded on the NAS routers as their own IP addresses. The NAS routers are not aware of the NAT or PAT that runs between them and the RADIUS server; therefore, different RADIUS attribute 4 addresses will be recorded in the accounting records for users from the different NAS routers. These addresses eventually expose different NAS routers to the RADIUS server and to the corresponding billing systems.
Using the RADIUS NAS-IP-Address Attribute Configurability Feature
The RADIUS NAS-IP-Address Attribute Configurability feature allows you to freely configure an arbitrary IP address as RADIUS NAS-IP-Address, RADIUS attribute 4. By manually configuring the same IP address, most likely the IP address on the loopback interface of the NAT or PAT device, for all the routers, you can hide a cluster of NAS routers behind the NAT or PAT device from the RADIUS server.
How to Configure RADIUS NAS-IP-Address Attribute Configurability
This section contains the following procedures:
Configuring RADIUS NAS-IP-Address Attribute Configurability
Before configuring the RADIUS NAS-IP-Address Attribute Configurability feature, you must have configured the RADIUS servers or server groups and AAA method lists.
To configure the RADIUS NAS-IP-Address Attribute Configurability feature, perform the following steps.
2. configure terminal
3. radius-server attribute 4 ip-address
Monitoring and Maintaining RADIUS NAS-IP-Address Attribute Configurability
To monitor the RADIUS attribute 4 address that is being used inside the RADIUS packets, use the debug radius command.
2. debug radius
Command or Action Purpose
Enables privileged EXEC mode.
•Enter your password if prompted.
Router# debug radius
Displays information associated with RADIUS.
The following sample output is from the debug radius command:Router# debug radiusRADIUS/ENCODE(0000001C): acct_session_id: 29RADIUS(0000001C): sendingRADIUS(0000001C): Send Access-Request to 10.0.0.10:1645 id 21645/17, len 81RADIUS: authenticator D0 27 34 C0 F0 C4 1C 1B - 3C 47 08 A2 7E E1 63 2FRADIUS: Framed-Protocol  6 PPP RADIUS: User-Name  18 "firstname.lastname@example.org"RADIUS: CHAP-Password  19 *RADIUS: NAS-Port-Type  6 Virtual RADIUS: Service-Type  6 Framed RADIUS: NAS-IP-Address  6 10.0.0.21UDP: sent src=10.1.1.1(21645), dst=10.0.0.10(1645), length=109UDP: rcvd src=10.0.0.10(1645), dst=10.1.1.1(21645), length=40RADIUS: Received from id 21645/17 10.0.0.10:1645, Access-Accept, len 32RADIUS: authenticator C6 99 EC 1A 47 0A 5F F2 - B8 30 4A 4C FF 4B 1D F0RADIUS: Service-Type  6 Framed RADIUS: Framed-Protocol  6 PPP RADIUS(0000001C): Received from id 21645/17
Configuration Examples for RADIUS NAS-IP-Address Attribute Configurability
This section provides the following configuration example:
Configuring a RADIUS NAS-IP-Address Attribute Configurability: Example
The following example shows that IP address 10.0.0.21 has been configured as the RADIUS NAS-IP-Address attribute:radius-server attribute 4 10.0.0.21radius-server host 10.0.0.10 auth-port 1645 acct-port 1646 key cisco
The following sections provide references related to RADIUS NAS-IP-Address Attribute Configurability.
Related Topic Document Title
"Authentication, Authorization, and Accounting (AAA)" section of Cisco IOS Security Configuration Guide: Securing User Services
"Configuring RADIUS" module.
MIBs MIBs Link
No new or modified MIBs are supported by this feature.
To locate and download MIBs for selected platforms, Cisco IOS releases, and feature sets, use Cisco MIB Locator found at the following URL:
Feature Information for RADIUS NAS-IP-Address Attribute Configurability
Table 1 lists the release history for this feature.
Not all commands may be available in your Cisco IOS software release. For release information about a specific command, see the command reference documentation.
Use Cisco Feature Navigator to find information about platform support and software image support. Cisco Feature Navigator enables you to determine which Cisco IOS and Catalyst OS software images support a specific software release, feature set, or platform. To access Cisco Feature Navigator, go to http://tools.cisco.com/ITDIT/CFN/jsp/index.jsp. An account on Cisco.com is not required.
Note Table 1 lists only the Cisco IOS software release that introduced support for a given feature in a given Cisco IOS software release train. Unless noted otherwise, subsequent releases of that Cisco IOS software release train also support that feature.
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Any Internet Protocol (IP) addresses and phone numbers used in this document are not intended to be actual addresses and phone numbers. Any examples, command display output, network topology diagrams, and other figures included in the document are shown for illustrative purposes only. Any use of actual IP addresses or phone numbers in illustrative content is unintentional and coincidental.
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