Networking Software (IOS & NX-OS)

Table Of Contents

DHCP Server RADIUS Proxy

Finding Feature Information

Contents

Prerequisites for DHCP Server RADIUS Proxy

Restrictions for DHCP Server RADIUS Proxy

Information About DHCP Server RADIUS Proxy

DHCP Server RADIUS Proxy Overview

DHCP Server RADIUS Proxy Architecture

DHCP Server and RADIUS Translations

RADIUS Profiles for DHCP Server RADIUS Proxy

How to Configure DHCP Server RADIUS Proxy

Configuring the DHCP Server for RADIUS-based Authorization

Monitoring and Maintaining the DHCP Server

Configuration Examples for DHCP Server Radius Proxy

Configuring the DHCP Server: Example

Configuring RADIUS Profiles: Example

Additional References

Related Documents

Standards

MIBs

RFCs

Technical Assistance

Feature Information for DHCP Server RADIUS Proxy

Glossary

DHCP Server RADIUS Proxy

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First Published: May 2, 2005

Last Updated: June 25, 2009

The Dynamic Host Configuration Protocol (DHCP) Server RADIUS Proxy is a RADIUS-based address assignment mechanism in which a DHCP server authorizes remote clients and allocates addresses based on replies from a RADIUS server.

Finding Feature Information

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 DHCP Server RADIUS Proxy" section.

Use Cisco Feature Navigator to find information about platform support and Cisco IOS XE software image support. To access Cisco Feature Navigator, go to http://www.cisco.com/go/cfn. An account on Cisco.com is not required.

Contents

•Prerequisites for DHCP Server RADIUS Proxy

•Restrictions for DHCP Server RADIUS Proxy

•Information About DHCP Server RADIUS Proxy

•How to Configure DHCP Server RADIUS Proxy

•Configuration Examples for DHCP Server Radius Proxy

•Additional References

•Feature Information for DHCP Server RADIUS Proxy

•Glossary

Prerequisites for DHCP Server RADIUS Proxy

Before you can configure the DHCP Server RADIUS Proxy, you must be running DHCPv4 or a later version. For information about release and platform support, see the "Feature Information for DHCP Server RADIUS Proxy" section.

Restrictions for DHCP Server RADIUS Proxy

The DHCP Server RADIUS Proxy supports only one address authorization pool on the router.

Information About DHCP Server RADIUS Proxy

Before you configure the DHCP Server RADIUS Proxy, you should understand the following concepts:

•DHCP Server RADIUS Proxy Overview

•DHCP Server RADIUS Proxy Architecture

•DHCP Server and RADIUS Translations

•RADIUS Profiles for DHCP Server RADIUS Proxy

DHCP Server RADIUS Proxy Overview

The DHCP Server RADIUS Proxy feature is an address allocation mechanism for RADIUS-based authorization of DHCP leases. This feature supports DHCP options 60 and 121.

1. The DHCP server passes client information to a RADIUS server.

2. The RADIUS server returns all required information to the DHCP server as RADIUS attributes.

3. The DHCP server translates the RADIUS attributes into DHCP options, and sends this information back to RADIUS in a DHCP OFFER message.

4. DHCP binding is synchronized after the RADIUS server authorizes the client session.

If a local pool and an authorization pool are configured on the router, the DHCP server can assign addresses from both pools for different client interfaces.

DHCP Server RADIUS Proxy Architecture

The allocation of addresses in a DHCP and RADIUS solution occurs as follows:

1. The client accesses the network from a residential gateway and sends a DHCP DISCOVER broadcast message to the relay agent. The DHCP DISCOVER message contains the client IP address, hostname, vendor class identifier, and client identifier.

2. The relay agent sends a DHCP DISCOVER unicast message containing the following information to the router:

–Relay agent information (option 82) with the remote ID suboption containing the inner and outer VLAN IDs

–Client information in the DHCP DISCOVER packet

The router determines the address of the DHCP server from the IP helper address on the interface that receives the DHCP packet.

3. RADIUS receives an access-request message to translate the DHCP options to RADIUS attributes.

4. RADIUS responds with an access-accept message, and delivers the following attributes to the DHCP server:

–Framed-IP-Address

–Framed-IP-Netmask

–Session-Timeout

–Session-Duration

5. The DHCP server sends an OFFER unicast message containing the following translations from the RADIUS server access-accept message to the client:

–Framed-IP-Address inserted into the DHCP header.

–Framed-IP-Netmask inserted into DHCP option 1 (subnet mask).

–Session-Timeout inserted into DHCP option 51 (IP address lease time).

–Framed-Route that is translated from the standard Cisco Framed-Route format into DHCP option 121 or the DHCP default gateway option (if the network and netmask are appropriate for a default route).

–A copy of relay agent information (option 82). Before the DHCP client receives the packet, the relay removes option 82.

–T1 time set to the Session-Timeout and T2 time set to the Session-Duration.

6. The client returns a formal request for the offered IP address to the DHCP server in a DHCP REQUEST broadcast message.

7. The DHCP confirms that the IP address is allocated to the client by returning a DHCP ACK unicast message containing lease information and the DHCP options to the client.

8. A RADIUS server accounting request starts, followed by a RADIUS server accounting response that is used by the AAA subsystem.

When a RADIUS server attribute is not present in an access-accept message, the corresponding DHCP option is not sent to the DHCP client. If the required information to produce a particular RADIUS server attribute is not available to the DHCP server, the DHCP server does not include information in the RADIUS packet. Non-inclusion can be in the form of not sending an attribute (if there is no information at all), or omitting information from the attribute (in the case of CLI-based format strings).

If a DHCP option is provided to the DHCP server but is invalid, the DHCP server may not transmit the corresponding RADIUS attribute in the access-request, or may transmit an invalid RADIUS server attribute.

DHCP Server and RADIUS Translations

Table 1 lists the translations of DHCP options in a DHCP DISCOVER message to attributes in a RADIUS server access-request message.

Table 1 DCHP DISCOVER to RADIUS Access-Request Translations

DHCP DISCOVER	RADIUS Access-Request
Virtual MAC address of the residential gateway	User-Name
Not Applicable	User-Password as configured on the DHCP server
Gateway address of the relay agent (giaddr field of a DHCP packet)	NAS-identifier
Hostname	Cisco AV pair client-hostname that equals the value of DHCP option 12
Vendor class	Cisco AV pair dhcp-vendor-class that equals a hexadecimal-encoded value of DHCP option 60
Client identifier	Cisco AV pair dhcp-client-id that equals the hexadecimal-encoded value of DHCP option 61
DHCP relay information option that can contain VLAN parameter on the D-router	Cisco AV pair dhcp-relay-info that equals the hexadecimal-encoded value of DHCP option 82

Table 2 lists the translations of attributes in a RADIUS server access-accept message to DHCP options in a DHCP OFFER message.

Table 2 RADIUS Access-Accept to DHCP OFFER Translations

RADIUS Access-Accept	DHCP OFFER
Framed-IP-Address	IP address of the residential gateway
Framed-IP-Netmask	Subnet mask (option 1)
Session-Timeout	IP address lease time (option 51)
Cisco AV pair session-duration in seconds, where seconds is greater than or equal to the number of seconds in the Session-Timeout attribute.	Provides session control on the DHCP server. This attribute is not transmitted to the DHCP client.
Framed-Route (RADIUS attribute 22). One route for each DHCP option is allowed with a maximum of 16 Framed-Route options for a RADIUS packet.	Contains up to 16 classless routes in one option (option 121)

RADIUS Profiles for DHCP Server RADIUS Proxy

When you configure RADIUS server user profiles for DHCP server RADIUS proxy, use the following guidelines:

•The Session-Timeout attribute must contain a value, in seconds. If this attribute is not present, the DHCP OFFER is not sent to the client.

•A RADIUS user profile must contain the following attributes:

–Framed-IP-Address

–Framed-IP-Netmask

–Framed-Route

–Session-Timeout

–Session-Duration—Session-Duration is the Cisco AV pair session-duration = seconds, where seconds is the maximum time for the duration of a lease including all renewals. The value for Session-Duration must be greater than or equal to the Session-Timeout attribute value, and it cannot be zero.

•Additional RADIUS server attributes are allowed but are not required. The DHCP server ignores additional attributes that it does not understand. If a RADIUS server user profile contains a required attribute that is empty, the DHCP server does not generate the DHCP options.

How to Configure DHCP Server RADIUS Proxy

This section contains the following tasks:

•Configuring the DHCP Server for RADIUS-based Authorization

•Monitoring and Maintaining the DHCP Server

Configuring the DHCP Server for RADIUS-based Authorization

Perform this task on the DHCP server to configure address allocation for RADIUS-based authorization of DHCP leases.

SUMMARY STEPS

1. enable

2. configure terminal

3. service dhcp

4. aaa new-model

5. aaa group server radius group-name

6. server ip-address [auth-port port-number] [acct-port port-number]

7. exit

8. aaa authorization network method-list-name group server-group-name

9. aaa accounting network method-list-name start-stop group server-group-name

10. ip dhcp pool name

11. accounting method-list-name

12. authorization method method-list-name

13. authorization shared-password password

14. authorization username string

15. exit

16. interface type slot/subslot/port[.subinterface]

17. encapsulation dot1q vlan-id second-dot1q {any | vlan-id [,vlan-id [-vlan-id]]}

18. ip address address mask

19. no shutdown

20. radius-server host ip-address [auth-port port-number] [acct-port port-number]

21. radius-server key {0 string | 7 string | string}

22. exit

DETAILED STEPS

	Command or Action	Purpose
Step 1	enable Example: Router> enable	Enables privileged EXEC mode. •Enter your password if prompted.
Step 2	configure terminal Example: Router# configure terminal	Enters global configuration mode.
Step 3	service dhcp Example: Router(config)# service dhcp	Enables DHCP server and relay agent features on the router. By default, these features are enabled on the router.
Step 4	aaa new-model Example: Router(config)# aaa new-model	Enables the authentication, authorization, and accounting (AAA) access control system.
Step 5	aaa group server radius group-name Example: Router(config)# aaa group server radius group1	Specifies the name of the server host list to group RADIUS server hosts. Enters server-group configuration mode. group-name—Character string to name the server group. The following words cannot be used as group name: •auth-guest •enable •guest •if-authenticated •if-needed •krb5 •krb-instance •krb-telnet •line •local •none •radius •rcmd •tacacs •tacacsplus
Step 6	server ip-address [auth-port port-number] [acct-port port-number] Example: Router(config-sg)# server 10.1.1.1 auth-port 1700 acct-port 1701	Specifies the IP address of the RADIUS server host for the defined server group. Repeat this command for each RADIUS server host to associate with the server group. •ip-address—IP address of the RADIUS server host. •auth-port port-number—(Optional) Specifies the UDP destination port for authentication requests. Default value is 1645. •acct-port port-number—(Optional) Specifies the UDP destination port for accounting requests. Default value is 1646.
Step 7	exit Example: Router(config-sg)# exit	Exits server-group configuration mode.
Step 8	aaa authorization network method-list-name group group-name Example: Router(config)# aaa authorization network auth1 group group1	Specifies the methods list and server group for DHCP authorization. •method-list-name—Character string to name the authorization methods list. •group—Specifies a server group. •group-name—Name of the server group to apply to DHCP authorization.
Step 9	aaa accounting network method-list-name start-stop group group-name Example: Router(config)# aaa accounting network acct1 start-stop group group1	Specifies that AAA accounting runs for all network service requests. •method-list-name—Character string to name the accounting methods list. •start-stop—Sends a start accounting notice at the beginning of a process and a stop accounting notice at the end of a process. The start accounting record is sent in the background. The requested user process begins regardless of whether or not the start accounting notice is received by the accounting server. •group—Specifies a server group. •group-name—Name of the server group to apply to DHCP accounting.
Step 10	ip dhcp pool name Example: Router(config)# ip dhcp pool pool1	Specifies a name for the DHCP server address pool. Enters DHCP pool configuration mode. •name—Name of the pool.
Step 11	accounting method-list-name Example: Router(config-dhcp)# accounting acct1	Enables DHCP accounting. •method-list-name—Name of the accounting methods list.
Step 12	authorization method method-list-name Example: Router(config-dhcp)# authorization method auth1	Enables DHCP authorization. •method-list-name—Name of the authorization methods list.
Step 13	authorization shared-password password Example: Router(config-dhcp)# authorization shared-password cisco	Specifies the password that is configured in the RADIUS user profile.
Step 14	authorization username string Example: Router(config-dhcp)# authorization username %%c-user1	Specifies the parameters that RADIUS sends to a DHCP server when downloading configuration information for a DHCP client. The string command argument contains the following formatting characters to insert DHCP client information: •%c-—Ethernet address of the DHCP client (chaddr field) •%i-—Inner VLAN ID from the DHCP relay information (option 82) •%o-—Outer VLAN ID from the DHCP relay information (option 82) •%p—Port number from the DHCP relay information (option 82) •%g—Gateway address of the DHCP relay agent (giaddr field) •%%—Transmits the percent sign (%) character in the string sent to the RADIUS server Note The percent (%) is a marker to insert the DHCP client information associated with the specified character. The % is not sent to the RADIUS server unless you specify the %% character.
Step 15	exit Example: Router(config-dhcp)# exit	Exits DHCP pool configuration mode.
Step 16	interface type slot/subslot/port[.subinterface] Example: Router(config)# interface ethernet 1/10.0	Configures an interface or subinterface that allows the DHCP client to obtain an IP address from the DHCP server. Enters interface or subinterface configuration mode.
Step 17	encapsulation dot1q vlan-id second-dot1q {any | vlan-id [,vlan-id [-vlan-id]]} Example: Router(config-subif)# encapsulation dot1q 100 second-dot1q 200	(Optional) Enables IEEE 802.1Q encapsulation of traffic on a subinterface in a virtual LAN (VLAN). •vlan-id—VLAN ID, integer in the range 1 to 4094. To separate the starting and ending VLAN ID values that are used to define a range of VLAN IDs, enter a hyphen. (Optional) To separate each VLAN ID range from the next range, enter a comma. •second-dot1q—Supports the IEEE 802.1Q-in-Q VLAN Tag Termination feature to configure an inner VLAN ID. •any—Any second tag in the range 1 to 4094.
Step 18	ip address address mask Example: Router(config-if)# ip address 192.168.1.1 255.255.255.0	Specifies an IP address for an interface or subinterface. •address is the IP address of the interface or subinterface. •mask is the subnet address for the IP address.
Step 19	no shutdown Example: Router(config-if)# no shutdown	Enables the interface or subinterface.
Step 20	radius-server host ip-address [auth-port port-number] [acct-port port-number] Example: Router(config)# radius-server host 10.1.1.1	Specifies a RADIUS server host. •ip-address is the IP address of the RADIUS server host. •auth-port port-number—(Optional) Specifies the UDP destination port for authentication requests. Default value is 1645. •acct-port port-number—(Optional) Specifies the UDP destination port for accounting requests. Default value is 1646.
Step 21	radius-server key {0 string | 7 string | string} Example: Router(config)# radius-server key cisco	Specifies the authentication and encryption key for all RADIUS communications between the router and the RADIUS daemon. •0 string—Specifies an unencrypted (cleartext) shared key •7 string—Specifies a hidden shared key. Note Any key you enter must match the key on the RADIUS daemon. All leading spaces are ignored, but spaces within and at the end of the key are used. If you use spaces in your key, do not enclose the key in quotation marks unless the quotation marks are part of the key.
Step 22	exit	Exits global configuration mode.

Monitoring and Maintaining the DHCP Server

Perform this task to verify and monitor DHCP server information:

SUMMARY STEPS

1. enable

2. debug ip dhcp server packet

3. debug ip dhcp server events

4. show ip dhcp binding [address]

5. show ip dhcp server statistics

6. show ip dhcp pool [name]

7. show ip route dhcp [address]

DETAILED STEPS

	Command or Action	Purpose
Step 1	enable Example: Router> enable	Enables privileged EXEC mode. •Enter your password if prompted.
Step 2	debug ip dhcp server packet Example: Router# debug ip dhcp server packet	(Optional) Enables DHCP server debugging.
Step 3	debug ip dhcp server events Example: Router# debug ip dhcp server events	(Optional) Reports DHCP server events, such as address assignments and database updates.
Step 4	show ip dhcp binding [address] Example: Router# show ip dhcp binding	(Optional) Displays a list of all bindings created on a specific DHCP server. •Use the show ip dhcp binding command to display the IP addresses that have already been assigned. Verify that the address pool has not been exhausted. If necessary, re-create the pool to create a larger pool of addresses. •Use the show ip dhcp binding command to display the lease expiration date and time of the IP address of the host.
Step 5	show ip dhcp server statistics Example: Router# show ip dhcp server statistics	(Optional) Displays count information about server statistics and messages sent and received.
Step 6	show ip dhcp pool [name] Example: Router# show ip dhcp pool	(Optional) Displays the routes added to the routing table by the DHCP server and relay agent.
Step 7	show ip route dhcp [address] Example: Router# show ip route dhcp [address]	(Optional) Displays information about DHCP address pools.

Configuration Examples for DHCP Server Radius Proxy

This section provides the following configuration examples:

•Configuring the DHCP Server: Example

•Configuring RADIUS Profiles: Example

Configuring the DHCP Server: Example

The following example shows how to configure a DHCP server for RADIUS-based authorization of DHCP leases. In this example, DHCP clients can attach to Ethernet interface 4/0/1 and Ethernet subinterface 4/0/3.10. The username string (%c-user1) specifies that the RADIUS server sends the Ethernet address of DHCP client named user1 to the DHCP server.

Router> enable

Router# configure terminal

Router(config)# service dhcp

Router(config)# aaa new-model

Router(config)# aaa group server radius rad1

Router(config-sg)# server 10.1.1.1

Router(config-sg)# server 10.1.5.10

Router(config-sg)# exit 

Router(config)# aaa authorization network auth1 group group1

Router(config)# aaa accounting network acct1 start-stop group group1

Router(config)# aaa session-id common

Router(config)# ip dhcp database tftp://172.16.1.1/router-dhcp write-delay 100 timeout 5

!

Router(config)# ip dhcp pool pool_common

Router(config-dhcp)# accounting acct1

Router(config-dhcp)# authorization method auth1

Router(config-dhcp)# authorization shared-password cisco

Router(config-dhcp)# authorization username %c-user1

Router(config-dhcp)# exit

! 

Router(config)# interface ethernet4/0/1

Router(config-if)# ip address 15.0.0.1 255.255.255.0

Router(config-if)# exit

Router(config-if)# interface ethernet4/0/3.10 

Router(config-if)# encapsulation dot1q 100 second-dot1q 200

Router(config-if)# ip address 10.1.1.1 255.255.255.0

Router(config-if)# exit

Router(config)# radius-server host 10.1.3.2

Router(config)# radius-server key cisco

Router(config)# exit

Configuring RADIUS Profiles: Example

The following example shows how to configure a typical RADIUS user profile to send attributes in an access-accept message to the DHCP server:

DHCP-00059A3C7800 Password = "metta"

Service-Type = Framed,

Framed-Ip-Address = 10.3.4.5,

Framed-Netmask = 255.255.255.0,

Framed-Route = "0.0.0.0 0.0.0.0 10.3.4.1",

Session-Timeout = 3600,

Cisco:Cisco-Avpair = "session-duration=7200"

Additional References

The following sections provide references related to the DHCP Server RADIUS Proxy feature.

Related Documents

Related Topic	Document Title
DHCP relay configuration	Configuring the Cisco IOS XE DHCP Relay Agent
DHCP commands: complete command syntax, command mode, command history, defaults, usage guidelines, and examples	Cisco IOS IP Addressing Services Command Reference

Standards

Standards	Title
No new or modified standards are supported by this functionality.	—

MIBs

MIBs	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: http://www.cisco.com/go/mibs

RFCs

RFCs	Title
No new or modified RFCs are supported by this feature, and support for existing RFCs was not modified by this feature.	—

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.

http://www.cisco.com/techsupport

Feature Information for DHCP Server RADIUS Proxy

Table 3 lists the release history for this feature.

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

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Note Table 3 lists only the Cisco IOS XE software release that introduced support for a given feature in a given Cisco IOS XE software release train. Unless noted otherwise, subsequent releases of that Cisco IOS XE software release train also support that feature.

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Table 3 Feature Information for the Cisco IOS XE DHCP Relay Agent

Feature Name	Releases	Feature Configuration Information
DHCP Server RADIUS Proxy	Cisco IOS XE  Release 2.4	DHCP Server RADIUS Proxy enables a server to authorize remote clients and allocate addresses based on replies from the server. In Cisco IOS XE 2.4, this feature was introduced on the Cisco ASR 1000 Series Aggregation Services Routers. The following commands were modified by this feature: authorization method (dhcp), authorization shared-password, authorization username (dhcp).

Glossary

client—A host trying to configure its interface (obtain an IP address) using DHCP or BOOTP protocols.

DHCP—Dynamic Host Configuration Protocol.

giaddr—Gateway IP address. The giaddr field of the DHCP message provides the DHCP server with information about the IP address subnet on which the client is to reside. It also provides the DHCP server with an IP address where the response messages are to be sent.

MPLS—Multiprotocol Label Switching. Emerging industry standard upon which tag switching is based.

relay agent—A router that forwards DHCP and BOOTP messages between a server and a client on different subnets.

server—DHCP or BOOTP server.

VPN—Virtual Private Network. Enables IP traffic to use tunneling to travel securely over a public TCP/IP network.

VRF—VPN routing and forwarding instance. A VRF consists of an IP routing table, a derived forwarding table, a set of interfaces that use the forwarding table, and a set of rules and routing protocols that determine what goes into the forwarding table. In general, a VRF includes the routing information that defines a customer VPN site that is attached to a PE router. Each VPN instantiated on the PE router has its own VRF.

Cisco and the Cisco Logo are trademarks of Cisco Systems, Inc. and/or its affiliates in the U.S. and other countries. A listing of Cisco's trademarks can be found at www.cisco.com/go/trademarks. Third party trademarks mentioned are the property of their respective owners. The use of the word partner does not imply a partnership relationship between Cisco and any other company. (1005R)

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.

© 2005-2009 Cisco Systems, Inc. All rights reserved.