Cisco Prime Access Registrar 9.2 Reference Guide

Use Case Example

When HA receives an RRQ from a PDSN, it authenticates the RRQ by using a MN-HA shared key. If the HA does not have the MN-HA shared key, it retrieves the MN-HA shared key from the Prime Access Registrar server by sending an Access-Request packet containing the 3GPP2 vendor-specific attribute (VSA) CDMA-MN-HA-SPI, the Security Parameter Index (SPI attribute).

The Prime Access Registrar server then sends the CDMA-MN-HA-Shared-Key corresponding to the user if the user has successfully authenticated subject to the following rules:

1. If there is an incoming SPI and no configured SPI, the Prime Access Registrar server authenticates the user as usual and does not include a configured shared-key (if there is one) in the reply.

2. If the incoming SPI does not match the configured SPI, the Prime Access Registrar server authenticates the user as usual, but does not include the configured shared-key (if there is one) in the reply.

3. If the incoming SPI matches the configured SPI, but there is no shared-key configured, the Prime Access Registrar server proceeds with normal authentication. Since there is no shared-key, it will not be included in the reply.

4. If the incoming SPI matches the configured SPI and a configured shared-key exists, the Prime Access Registrar server proceeds to encrypt the MCD5 shared-key and include it in the Access-Accept.

The key to including the shared key in an Access-Accept is in matching the values of the SPI attribute.

Configuring User Attributes

Prime Access Registrar server supports user-specific attributes which enables the Prime Access Registrar server to return attributes on a per-user or per-group basis without having to use profiles.

Configuring the User Attributes

To configure a user with the CDMA-MN-HA-SPI VSA to request a MN-HA shared key:

Step 1 Log into the Prime Access Registrar server and launch aregcmd.

Log in as a user with administrative rights such as user admin.

Step 2 Change directory to the attribute directory of the user.

cd /Radius/UserLists/Default/bob/Attributes

Step 3 Set the CDMA-MN-HA-SPI VSA to the appropriate shared-key value.

set CDMA-MN-HA-SPI 1124

Step 4 Set the CDMA-MN-HA-SPI VSA to the appropriate shared-key value.

set CDMA-MN-HA-Shared-Key secret112

Step 5 Validate and save your changes.

validate

save

Home-Agent Resource Manager

Prime Access Registrar supports dynamic HA assignment with a new resource manager type called home-agent. You configure the home-agent resource manager with a list of IP addresses. The Prime Access Registrar server assigns those addresses to clients whose request dictionary has the right attributes to indicate that an assignment should be done. This is similar to the ip-dynamic resource manager.

Unlike the ip-dynamic resource manager, HAs are not exclusively allocated to an individual session but are shared among a set of sessions.

Load Balancing

The goal of dynamic HA assignment is to have load balancing among HAs. The Prime Access Registrar server achieves this by evenly distributing mobile clients among HAs. At the same time, the Prime Access Registrar server ensures that the same HA is always assigned to the same Mobile IP client for the same session.

Configuring the Home Agent Resource Manager

To create a new resource manager using the aregcmd command:

Step 1 Use the cd command to change to the Radius /ResourceManagers level.

--> cd /Radius/ResourceManagers

[ //localhost/Radius/ResourceManagers ]

Entries 0 to 0 from 0 total entries
Current filter: <all>


Step 2 Use the add command to specify the name of a resource manager to create.

--> add home-agent-pool

--> Added home-agent-pool


Step 3 Use the cd command to change to the Radius /ResourceManagers/home-agent-pool level.

--> cd home-agent-pool

[ //localhost/Radius/ResourceManagers/home-agent-pool ]

Name = home-agent-pool
Description =
Type =

Step 4 Use the set command to set the resource manager type to home-agent.

--> set type home-agent

Step 5 Use the ls command to view the subdirectories under home-agent-pool.

--> ls

[ //localhost/Radius/ResourceManagers/home-agent-pool ]

Name = home-agent-pool
Description =
Type = home-agent
Home-Agent-IPAddresses/

Step 6 Use the cd command to change to the Radius/ResourceManagers/home-agent-pool/Home-Agent-IPAddresses level.

--> cd Home-Agent-IPAddresses

[ //localhost/Radius/ResourceManagers/home-agent-pool/Home-Agent-IPAddresses ]

Step 7 Use the add command to add a single IP address or a range of IP addresses.

--> add 209.165.200.200-209.165.200.254

--> Added 209.165.200.200-209.165.200.254

Querying and Releasing Sessions

The aregcmd program has been modified to support a new filter for query-session and release-session. You can use this filter to restrict a request (either query or release) to just the sessions with a given home-agent IP address. For example, consider the following command line.

--> query-session /radius with-home-agent 10.10.10.1

This command line will return all sessions that have a home-agent resource equal to the IP address 10.10.10.1.

Querying sessions using aregcmd displays the home-agent resource in each session as:

HA ddd.ddd.ddd.ddd

where each ddd is a decimal number from 0-255.

Access Request Requirements

When the home-agent resource manager receives an Access-Request that contains a CDMA-HA-IP-Addr attribute, the home-agent resource manager checks the response dictionary to see if it already has a CDMA-HA-IP-Addr attribute. If it does, then the Mobile IP client has been assigned a HA address already and the resource manager does not need to do anything.

If the value of the CDMA-HA-IP-Addr attribute in the request dictionary is 0.0.0.0, the home-agent resource manager assigns a HA and puts a new CDMA-HA-IP-Addr attribute whose value is the IP address of the HA in the response dictionary.

If the value of the CDMA-HA-IP-Addr attribute is not 0.0.0.0, the Mobile IP client has been assigned a HA address already. The home-agent resource manager copies the attribute (with its value) from the request dictionary into the response dictionary.

The Prime Access Registrar server might select the session manager based on the domain (using the rule engine, dynamic properties, or scripting), and it allows each session manager to have its own home-agent resource manager.

New 3GPP2 VSAs in the Cisco Prime Access Registrar Dictionary

Prime Access Registrar supports 3GPP2 vendor-specfic attributes (VSAs) in the vendor-specific dictionary in /Radius/Advanced/Attribute Dictionary.

Note There is no planned support for the Accounting-Container (3GPP2/6) attribute because it has different syntax than other vendor-specfic attributes (VSAs) and requires special processing.

SWa Access Authentication and Authorization

The SWa reference point is defined between a non-3GPP IP access and a 3GPP AAA server or between a non-3GPP IP access and a 3GPP AAA proxy.

The SWa access authentication and authorization procedure includes the following steps:

1. The 3GPP AAA server issues an unsolicited re-auth request towards the untrusted non-3GPP access, indicating that both re-authentication and re-authorization of the user is needed.

2. Upon receipt of such a request, the untrusted non-3GPP access responds to the request and indicates the disposition of the request. This procedure is mapped to the Diameter command codes Re-Auth-Request and Re-Auth-Answer.

3. Upon receiving the re-auth request, the untrusted non-3GPP access immediately invokes the SWa authentication and authorization procedure requesting the identity of the user through EAP and using DER/DEA commands, with the same session-ID.

4. If the re-authentication of the user is not successful, the untrusted non-3GPP access detaches the user.

STa Access Authentication and Authorization

The STa reference point is defined between a non-3GPP access network and a 3GPP AAA Server or between a non-3GPP access network and a 3GPP AAA Proxy.

Prime Access Registrar decides whether a non-3GPP access network is trusted or untrusted by using the access authentication and authorization procedure executed between the non-3GPP access network and the 3GPP AAA server. This is implemented by the STa and SWa reference points sharing the same Diameter application and partly sharing the same authentication and authorization procedure. The STa and SWa reference points are clearly distinguished after the exchange of the first authentication and authorization messages, during which trusted/untrusted decision is made by the 3GPP AAA server and this decision is communicated to the non-3GPP access network.

The trusted non-3GPP access authentication and authorization requires DiaEAP with EAP-AKA or EAP-AKA`. Prime Access Registrar implements the STa access authentication and authorization procedure based on the mobility parameters transported by the non-3GPP access network to the 3GPP AAA server.

This procedure follows the SWa authentication and authorization procedure, with the following differences:

• Information elements that reflect information about the user's service request and about the access network are mandatorily included in the authentication and authorization request.
• The information elements that describe the user's subscription profile are downloaded to the non-3GPP access network.

SWm Access Authentication and Authorization

The SWm reference point is defined between the ePDG and the 3GPP AAA server or between the ePDG and the 3GPP AAA proxy. It is used to authenticate and authorize a UE by transporting mobility parameters that are needed for the S2b interface. In particular this information may include the Packet Data Network (PDN) GW identity(s) and Access Point Name (APN(s)) currently allocated to a UE during a previous attach in a 3GPP access.

The SWm reference point performs authentication and authorization based on the reuse of the DER/DEA command set defined in the Diameter EAP application. The SWm access authentication and authorization procedure includes the following steps:

• The UE transmits a ‘tunnel establishment request’ message to the ePDG in order to establish a connection to the PDN.
• The ePDG initiates access authentication and authorization request to the 3GPP AAA server.
• During the access authentication and authorization procedure, the ePDG provides mobility parameters of the UE to the 3GPP AAA Server.
• The 3GPP AAA server performs IP mobility mode selection appropriately and upon successful authorization, it returns mobilty mode information back to the ePDG.

SWd Access Authentication and Authorization

The SWd reference point is defined between a 3GPP AAA proxy and a 3GPP AAA server. The SWd interface is used in roaming scenarios where the 3GPP AAA proxy is located in the visited network and the 3GPP AAA server is located in the home network. The 3GPP AAA proxy acts as a Diameter proxy agent and forwards Diameter commands between the Diameter client and the Diameter server.

When used in connection with an STa reference point, the SWd interface supports the trusted non-3GPP access authentication and authorization procedure. For this procedure, the 3GPP AAA proxy forwards the Diameter commands received from the 3GPP AAA server and the trusted non-3GPP access network as a stateful Diameter proxy.

When used in connection with the SWm reference point, the SWd interface supports the untrusted non-3GPP access authentication and authorization procedure. For this procedure, the 3GPP AAA proxy forwards the Diameter commands received from the 3GPP AAA server and the ePDG as a stateful Diameter proxy.

SWx Authentication Procedure

The SWx is a reference point defined between a HSS and a 3GPP AAA server. It is used in AAA server registration of a new user.

The authentication procedure includes the following steps:

1. The 3GPP AAA server registers the current 3GPP AAA server address in the HSS for a given user when a new subscriber has been authenticated by the 3GPP AAA server.

2. The 3GPP AAA server informs the HSS about the current PDN GW identity and APN being used for a given UE, or that a certain PDN GW and APN pair is no longer used.

3. Accordingly, the 3GPP AAA server may de-register the currently registered 3GPP AAA server in the HSS for a given user and purge any related non-3GPP user status data in the HSS. This occurs if the UE for some reason has been disconnected from the non-3GPP access.

HSS Initiated Update of User Profile

The subscriber profile management procedures over SWx include the subscriber profile push and the subscriber profile request. The SWx reference point enables the following:

• Indication to the 3GPP AAA server of change of non-3GPP subscriber profile within HSS.
• Activation and deactivation of the subscriber and equipment trace in the PDN GW.

This procedure is used between the 3GPP AAA Server and the HSS and is invoked by the HSS during the following circumstances:

• When the subscriber profile has been modified and needs to be sent to the 3GPP AAA Server. This may happen due to a modification in the HSS.
• To update the 3GPP AAA Server with the identity of a dynamically allocated PDN GW, which is included in the APN-Configuration AVP in the user profile as a result of the first PDN connection establishment associated with an APN over 3GPP access.

This procedure is mapped to the Diameter command codes Push-Profile-Request (PPR) and Push-Profile-Answer (PPA). An IMSI Range based mechanism is provided to select the HSS server. In the CLI, if the MultiplePeersPolicy is IMSIRangeBased, then the ranges are configured as a list and from them the HSS server is selected.

S6b Authentication and Authorization Procedure

The S6b reference point is defined between a PDN GW and a 3GPP AAA server (for non-roaming case, or roaming with home routed traffic to PDN GW in home network) and between a PDN GW and a 3GPP AAA proxy.The S6b interface protocol is based on Diameter. It uses the Diameter base protocol and also supports Diameter EAP application. The EAP methods EAP-AKA and EAP-AKA` are used.

The authentication and authorization procedure includes the following steps:

1. The S6b interface enables authentication and authorization between the UE and the 3GPP AAA server/proxy.

2. When the UE performs the DSMIPv6 initial attach, it runs an IKEv2 exchange with the PDN GW. In this exchange, EAP AKA is used for UE authentication over IKEv2. The PDN GW acts as an IKEv2 responder and an EAP pass-through authenticator for this authentication.

3. The S6b authentication and authorization procedure is invoked by the PDN GW after receiving an IKE_SA_AUTH message from the UE. The S6b reference point performs authentication based on reuse of the DER/DEA command set defined in Diameter EAP.

3GPP Call Flows

When Prime Access Registrar receives an authentication or authorization request from any of the access points, it sends the packet to the rules and policy engine for processing. The rules and policies are added in the configuration of Prime Access Registrar. Client, vendor, and server scripting points are provided in order to modify any AVPs in the packet or to decide upon the type of service that the packet requires. For example, if the service is Radius-to-Diameter translation, Prime Access Registrar performs the translation of Radius packet to Diameter packet and sends it to the remote server. The service also has scripting points that can be used to modify the incoming packets. Once authentication or authorization is done for the packet session management can be performed for the packet by storing the user sessions in a session cache, if the authentication or authorization is successful. The server, client, vendor, and service outgoing scripting points can be used to modify the response packet.

Figure 6-2 depicts the call flows implemented for 3GPP.

Figure 6-2 3GPP Call Flows

This topic contains the following sections:

• CLI for 3GPP Authorization
• CLI for 3GPP Reverse Authorization

CLI for 3GPP Authorization

Following is the CLI for 3GPP authorization service:

CLI for 3GPP Reverse Authorization

3GPP reverse authorization is used during RADIUS to Diameter translation. You can set the corresponding parameter to TRUE during the RADIUS to Diameter conversion. In this case, the request command mapping must not be defined because a new diameter request is created from the radius request by the 3GPP reverse authorization service. For more information about RADIUS<->Diameter translations, see “Diameter” chapter of the Cisco Prime Access Registrar 9.2 User Guide.

Following is the CLI for 3GPP reverse authorization service:

Voice over Wi-Fi (VoWiFi) Location Based Authentication

Prime Access Registrar allows or blocks access to voice over Wi-Fi (VoWiFi) based on location information of the user equipment (UE). Prime Access Registrar uses Sh interface for fetching the location information of the UE. The workflow is as given below:

1. UE tries to establish connection to VoWiFi.

2. Request reaches Prime Access Registrar server.

3. Upon successful authentication, Prime Access Registrar sends a User Data Repository (UDR) request to HSS through Sh interface.

4. If HSS has the location information, it sends a User-Data-Answer (UDA) response to Prime Access Registrar through Sh interface in XML format.

a. The UDA response contains a User-Data AVP, which contains location information of the UE.

b. The AVP has various attributes including E-UTRANCellGlobalId, which carries the location information of the UE.

5. If HSS doesn’t have the location information, it sends an Insert-Subscription-Data-Request (IDR) to the Mobility Management Entity (MME)/Serving GPRS Support Node (SGSN) requesting for the user identity information.

6. The MME/SGSN sends the user identity information to the HSS through an Insert-Subscription-Data-Answer (IDA) response.

7. The HSS communicates the received data to Prime Access Registrar through Sh interface in XML format.

8. Upon receiving the user profile, Prime Access Registrar parses the User-Data AVP, extracts the location information, and copies it to the E-UTRANCellGlobalId environment variable. Prime Access Registrar can be configured to run the following script at 3GPP authorization service outgoing script to check the E-UTRANCellGlobalId variable and reject/accept the UE based on the location information.

Following are sample CLI configurations for 3GPP authorization service with RADIUS and Diameter:

Mobile Equipment Identity Check Support in Cisco Prime Access Registrar

The Mobile Equipment Identity is used between the 3GPP AAA Server and the Equipment Identity Registrar (EIR) to check the identity status of a Mobile Equipment (ME) for e.g. to ensure the ME is not stolen or verify that the ME has no faults. This procedure is mapped to the commands ME-Identity-Check-Request/Answer (ECR/ECA).

In SWm interface, the IMEI number is retrieved by ePDG from the client and is sent in the Terminal-Information AVP of the DER packet.

In STa interface, Prime Access Registrar retrieves the IMEI information using additional AVPs in the EAP call flows as shown in the sample configuration below.

Table 6-1 lists the attributes added to support the EIR check feature in EAP-SIM, EAP-AKA, and EAP-AKA-PRIME services.