Packet Data Interworking Function Overview

 

This chapter discusses the features and functions of Packet Data Interworking Function (PDIF) software. It includes the following topics:

•	Product Description

•	Interfaces

•	Sample Deployments

•	Features and Functionality - Base Software

•	Features and Functionality - Licensed Enhanced Feature Support

•	Supported Standards and RFCs

Product Description

The goal of the Fixed Mobile Convergence (FMC) application is to enhance the in-building cellular coverage for FMC subscribers, to reduce the cost of the infrastructure required to carry these calls, and to provide secure access to the carrier’s network from a non-secure network. Designed for use exclusively on the Cisco® ASR 5x00 Chassis, the Packet Data Interworking Function (PDIF) is a network function based on the 3GPP2 X.S0028-200 standard defining CDMA2000 Packet Data Services over an 802.11 WLAN.

A PDIF allows mobile devices to access the Internet over an all-IP WLAN using IKEv2 as the signaling interface. The IKEv2 control path exists between the mobile station (MS) (a dual-mode handset (DMH)) and the PDIF establishing an IPSec tunnel. PDIF also acts as a security gateway protecting CDMA network resources and data. The PDIF is tightly integrated with a collocated Foreign Agent (FA) service, and the PDIF is known throughout this manual as PDIF/FA.

For handsets that do not support mobile IP, PDIF supports proxy mobile IP. If the MS is not suitable for proxy mobile IP registration, it may still be allowed to establish a simple IP session, in which case the traffic is directly routed to the Internet or corporate network from the PDIF. This behavior is controlled through the proxy-mip-required configuration in the domain, local default subscriber, or the corresponding Diameter AVP or RADIUS Access Accept. If this is not present, establishing a simple IP session is permitted. Although not required for Proxy-MIP, this manual documents Proxy-MIP with a custom-designed feature called multiple authentication (Multi-Auth). Instead of the more usual subscriber authentication, Multi-Auth requires both the device and the subscriber be authenticated using EAP/AKA authentication for the first stage (the device authentication) and GTC/MD5 for the second stage (the subscriber authentication). For this installation, neither GTC nor MD5 is supported, which means authentication is done using PAP/CHAP instead.

When the subscriber is mobile, the MS operates as a normal mobile phone, sending voice and data over the CDMA network. When the FMC subscriber returns home, or encounters a WiFi hotspot, the MS detects the presence of the WiFi network, and automatically establishes an IPSec session with the PDIF/FA. When the secure connection has been established and mobile IP registration procedures successfully finished, the PDIF/FA works with other network elements to provide the MS with access to packet data services.

From here, all voice and data communication is carried over the IPSec tunnel and the PDIF/FA functions as a pass-through for the authentication and accounting information on a RADIUS and/or Diameter server. The MS continues operating over the IPSec tunnel until such time as it can no longer access the WiFi Access Point (AP). At this point, the MS switches back to the CDMA network for normal mobile operation.

Platform Requirements

The PDIF service runs on a Cisco® ASR 5x00 chassis running StarOS. The chassis can be configured with a variety of components to meet specific network deployment requirements. For additional information, refer to the installation guide for the chassis and/or contact your Cisco account representative.

Licenses

The PDIF is a licensed Cisco product. Separate session and feature licenses may be required. Contact your Cisco account representative for detailed information on specific licensing requirements. For information on installing and verifying licenses, refer to the “Managing License Keys” section of the “Software Management Operations” chapter in the System Administration Guide.

Interfaces

The figure below shows how the PDIF/FA acts as a security gateway between the Internet and packet data services. All components are located in the home network.

PDIF/FA Mobile IP Interfaces

1.	The IPSec virtual tunnel interface with the MS: The Mode keyword in the IPSec-transform-set configuration mode defaults to Tunnel. In Tunnel mode, the IP datagram is passed to IPSec, where a new IP header is created ahead of the AH and/or ESP IPSec headers. The original IP header is left intact.

2.

The Diameter interface: In a mobile IP network, the IMS Sh interface is used for MAC address validation with the HSS as well as HSS subscriber profile updates. In a Proxy-MIP network using multiple authentication, the HSS server is used to authenticate the device during Stage 1 authentication using the EAP-AKA authentication method.

3.

The RADIUS authentication and accounting interface: In a mobile IP network, this interface is used for subscriber authentication using the EAP-AKA authentication method. For subscriber accounting, the PDIF/FA sends start, stop and interim messages to the accounting server. When used in a Proxy-MIP network using multiple authentication, RADIUS is used with the AAA servers to authenticate the subscriber using the GTC/MD5 authentication methods.

4.	The home agent interface: This interface is used for Proxy mobile IP and mobile IP subscribers. All mobile station packets are tunneled to the HA through this interface. This interface is not used for simple IP subscribers.

5.	The simple IP interface: This interface provides internet access for simple IP users.

Sample Deployments

The following are some sample deployments using a PDIF/FA.

Mobile Station using Mobile IP with PDIF/FA

Overview

As shown in the figure below, the PDIF/FA supports the Fixed Mobile Convergence (FMC) application, which employs a Dual Mode Handset (DMH) to provide a VoIP solution over an IP-based WiFi broadband network. The DMH can access the traditional CDMA voice and data networks over the Radio Access Network (RAN). Over the RAN, the DMH implements circuit-switched voice and standard mobile IP (MIP) data over EVDO Rev. A, using the services of a PDSN and an HA.

PDIF/FA Mobile IP Implementation

Alternately, the DMH can send both voice and data over WiFi when a local AP is available. When the DMH connects to the AP, it establishes an IPSec tunnel over the broadband access network. This tunnel terminates at the PDIF/FA.

The DMH initially gets an IP address, also known as a Tunnel Inner Address (TIA), from the PDIF/FA when the DMH establishes the first IPSec tunnel. The PDIF/FA assigns the TIA from its IP address pool. The DMH then starts mobile IP through this initial TIA-based IPSec tunnel.

When the DMH successfully sets up mobile IP, it receives the home address from the HA. The DMH then establishes a second IPSec tunnel using this HA. Once the DMH successfully establishes the second IPSec tunnel with the PDIF/FA, the PDIF/FA tears down the first TIA-based IPSec tunnel to free the TIA, which then returns to the IP address pool. If required, use the no release-tia command in config-subscriber mode to prevent the TIA from returning to the pool. The DMH sends packetized voice and data through the PDIF/FA to the HA through the second IPSec tunnel.

In this scenario, the PDIF/FA forwards all the packets between the DMH and the HA. From there, voice packets are delivered to the Session Initiation Protocol (SIP) infrastructure, while data is delivered to the Internet or other appropriate destinations.

Mobile IP / Native Simple IP Call Minimum Requirements

The following provides the minimum requirements for each call type:

Mobile IP Calls

The PDIF/FA assumes MIP tunnel establishment over IPSec tunnel as part of the PDIF call flow as soon as any one of the following three possible conditions is met:

1.	The default subscriber profile has configured, or:

2.	The Radius VSA SN1-PDIF-MIP-Required is returned by AAA during user authentication, or,

3.	The MS requests the MIP session type by injecting the IKEv2 configuration attribute 3GPP2_MIP4_MODE.

Native Simple IP Calls

The PDIF/FA assumes a native simple IP session over an IPSec tunnel if:

1.	The MS (DMH) does not request 3GPP2_MIP4_MODE in IKEv2 exchange, and:

2.	If a subscriber profile is defined, it does not have the pdif mobile-ip required parameter, and:

3.	The AAA server does not return the VSA SN1-PDIF-MIP-Required during MS user authentication.

Mobile IP Session Setup over IPSec

The following diagram and table describe the mobile IP session setup over IPSec.

Mobile IP Session Setup over IPSec

Mobile IP over IPSec Call Flow Description

Step	Description
1	After the MS learns the IP address of the PDIF, the MS and the PDIF/FA exchange IKE_SA_INIT messages to negotiate an acceptable cryptographic suite.
2	The MS initiates IKE_AUTH exchange messages with the PDIF/FA. The MS omits the AUTH parameter to the PDIF/FA, indicating that it wants to use EAP over IKEv2. The MS includes its identity in the IDi payload of the IKE_AUTH request. The IDi is set to be the same as the NAI and the NAI realm is chosen appropriately for M-NAI devices.The MS embeds the MAC address of the WiFi access point (AP) in the NAI and includes the IKEv2 configuration payload. Attributes included in the CFG_REQUEST are at least the INTERNAL_IP4_ADDRESS (with the length set to zero), the INTERNAL_IP4_DNS, and the 3GPP2_MIP_MODE.
3	When the PDIF/FA receives the IKE_AUTH request, it checks if MAC address authorization is enabled. If so, the PDIF/FA uses the ims-sh-service interface to the HSS and requests the list of authorized APs for this user via a User Data Request (UDR).
4	The HSS answers with the list of authorized WiFi APs for the user.
5	After checking that the AP MAC address in the realm portion of the NAI matches with one of the authorized MAC addresses received from the HSS, the PDIF/FA strips the AP MAC address from the realm portion of the NAI and sends the resulting NAI as an EAP response identity to the H-AAA using a RADIUS Access-Request message. This message includes at least the user-name set as the NAI being sent in the EAP response identity, the 3GPP2 correlation ID, the EAP-Message attribute, and the message-authenticator attribute.
6	The H-AAA verifies the identity and checks that WiFi service is allowed for the subscriber. The H-AAA generates a random value RAND and AUTN based on the shared DMU CHAP-key and a sequence number.The H-AAA sends the EAP-Request/AKA Challenge to the PDIF/FA via a RADIUS access-challenge. The EAP-Request/AKA Challenge contains the AT_RAND, AT_AUTN, and the AT_MAC attribute to protect the integrity of the EAP message.
7	The PDIF/FA sends an IKE_AUTH response to the MS with the EAP-Request/AKA-Challenge message received from the H-AAA.
8	The MS verifies the authentication parameters in the EAP-Request/AKA-Challenge message and if the verification is successful, it responds to the challenge with an IKE_AUTH Request message to the PDIF/FA. The main payload of this message is the EAP-Response/AKA-Challenge message.
9	The PDIF/FA forwards the EAP-Response/AKA-Challenge message to the H-AAA via a RADIUS access-request message (RRQ).
10	If authentication succeeds, the H-AAA sends a RADIUS access-accept message with the EAP-message attribute containing EAP Success. The H-AAA sends the EAP-Success and the MSK generated during the EAP-AKA authentication process to the PDIF/FA. The 64-byte MSK is split into two 32-byte parts, with the first 32 bytes sent in the MS-MPPE-REC-KEY and the second 32 bytes sent in the MS-MPEE-SEND-KEY.Both of these attributes (the values of which are encrypted) are needed to construct the 64-byte MSK at the PDIF/FA. If either are missing, the PDIF/FA rejects the session. In addition, the H-AAA sends other attributes equivalent to what it normally sends to the PDSN for a simple IP session. The attributes include at least the following: The Framed-Pool (if required) so that the PDIF/FA can assign a TIA from the right IP address pool, the Session-Timeout, and The Idle-Timeout.
11	The PDIF/FA forwards the EAP Success message to the MS in an IKE_AUTH Response message.
12	The MS calculates the MSK (RFC 4187) and uses it to generate the AUTH payload to authenticate the first IKE_SA_INIT message. The MS sends the AUTH payload in an IKE_AUTH Request message to the PDIF/FA.
13	The PDIF/FA uses the MSK to check the correctness of the AUTH payload received from the MS and calculates its own AUTH payload for the MS to verify [RFC 4306]. The PDIF/FA sends the AUTH payload to the MS together with the Configuration Payload (CP) containing security associations and the rest of the IKEv2 parameters in the IKE_AUTH Response message, and the IKEv2 negotiation terminates.The CP contains the TIA and IP address of the DNS servers that the device had requested earlier. Although the MS requested a DNS address by including only a single payload option for INTERNAL_IP4_DNS, the PDIF/FA may include both a primary DNS address and a secondary DNS address if one is available.
14	After a CHILD_SA is created using the TIA, if the PDIF/FA received 3GPP2_MIP_MODE during the IKEv2 negotiation, or if MIP_Required subscriber configuration is present in the subscriber profiles, the PDIF/FA sends agent advertisements to the MS.
15	The MS sends a MIP RRQ (including the NAI extension), an MN-AAA authentication extension, etc., to the FA. The HA IP address is set to 0 (zero) because the H-AAA assigns the HA. This is the usual NAI without the MAC address of the WiFi AP in the realm.
16	The PDIF/FA sends a RADIUS access-request to the H-AAA to authenticate the MS credential conveyed in the MN-AAA authentication extension and requests the assignment of an HA.
17	The H-AAA authenticates the MS successfully and sends the RADIUS access-accept message with the HA IP address.
18	The PDIF/FA forwards the RRQ to the HA.
19	The HA sends an access-request to the H-AAA to retrieve the MN-HA key in order to authenticate the MN-HA extension.
20	The HA receives the MN-HA key and authenticates the extension.
21	The HA assigns the IP address (HoA) for the MS and sends the RRP back to the PDIF/FA.
22	The PDIF/FA sends the HoA IP address to the MS.
23	After the MS obtains the HoA in the RRP, the MS sends the CREATE_CHILD_SA message with the Traffic Selector payload for Initiator (TSi) set to the HoA. This IKEv2 exchange creates a new IPSec SA.
24	The PDIF/FA sends a RADIUS accounting start message to the H-AAA.
25	The PDIF/FA then updates the subscriber's HSS profile with the indication that the IPSec session is active and the appropriate IP address.In this case, since it is MIP, it is the HoA assigned by the HA. In the case of simple IP Fallback, it would be the TIA assigned by the PDIF/FA. The HSS profile is updated using the Profile Update-Request (PUR) command.
26	PDIF/FA sends Delete payload in the informational message to delete the old IPSec SA associated with the previously assigned TIA.

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Simple IP and Simple IP Fallback

For some simple IP deployments, the PDIF/FA authenticates the MS and provides an IP address for packet data services. In addition, the PDIF/FA supports Simple IP fallback if the MS abandons mobile IP operations due to not being able to successfully finish mobile IP registration after the first TIA-based IPSec tunnel is established. These scenarios are described below.

PDIF Simple IP Implementation

As described for mobile IP, during the initial IPSec tunnel establishment the MS gets a publicly routable TIA from a pool specified in the Framed Pool RADIUS attribute. When the IKEv2 negotiation finishes, an IPSec SA with a TIA is established as shown above.

Under normal situations, the MS successfully finishes mobile IP and establishes a new IPSec tunnel. However, if mobile IP fails, and simple IP fallback mode is enabled, the MS can revert to simple IP fallback mode and start using the TIA as the source IP address for all communication.

Important: Simple IP fallback is disabled by default. Use the pdif mobile-ip simple-ip-fallback command in config-subscriber mode to enable simple IP fallback.

Under these circumstances, the PDIF/FA opens the IPSec tunnel to data traffic and forwards any packets from the MS to the Internet directly. Any received packets from the Internet will be forwarded to the MS. A summary of this process from the point the TIA is assigned is given below:

Simple IP Fallback Message Sequence

Simple IP Fallback Message Sequence

Step	Description
1	With the IPSec Child SA (Security Association) and TIA already in place, the PDIF sends advertisements to the MS.
2	The MS sends a Registration Request (RRQ) message to the PDIF. The PDIF sends an authentication request to the AAA server over the RADIUS interface.
3	The AAA server authenticates successfully and sends the IP address of the HA.
4	The PDIF forwards the RRQ message to the HA.
5	The HA denies the request. The PDIF forwards the denial code to the MS.
6	The session setup timer expires and the PDIF goes into fallback mode. The PDIF sends a RADIUS Accounting Start message.
7	The AAA server sends a RADIUS Accounting Response message.
8	The PDIF updates the HSS with the TIA address of the subscriber.
9	The HSS sends an acknowledgement to the PDIF.

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Simple IP Fallback Minimum Requirements

There are certain minimum requirements for simple IP fallback, as follows:

•	There must be a context defined in the CLI configuration.

•	The default subscriber must be defined in the CLI configuration.

•	Mobile IP Simple IP Fallback must be defined in the CLI configuration. For example:

configuration

  context <pdif-in>

     subscriber default

     pdif mobile-ip simple-ip-fallback

     exit

•	The MS has to request MIP by sending an RRQ message to the PDIF/FA. If the MS indicated an intent to use mobile IP (or was configured with the MIP_Required parameter) but failed to send an RRQ message, the IPSec session would be disconnected rather than completing a simple IP fallback call.

•	On supported networks, the PDIF/FA only assumes simple IP fallback mode if mobile IP is attempted but fails when the MS tries to use mobile IP as the first choice but encounters a problem such as the HA not responding.

Features and Functionality - Base Software

This section describes the features and functions supported by default in the base PDIF software and the benefits they provide.

Important: All known restrictions are shown in Appendix B.

The following is a list of the features in this section:

•	PSC2 Support

•	Duplicate Session Detection

•	Unsupported Critical Payload Handling

•	Registration Revocation

•	CHILD SA Rekey Support

•	Denial of Service (DoS) Protection: Cookie Challenge

•	MAC Address Validation

•	RADIUS Accounting

•	Special RADIUS Attribute Handling

•	IPv6 Support

•	IPv6 Neighbor Discovery

•	IPv6 Static Routing

•	Port-Switch-On-L3-Fail for IPv6

•	IKEv2 Keep-Alive (Dead Peer Detection (DPD))

•	Congestion Control and Overload Disconnect

•	SCTP (Stream Control Transmission Protocol) Support

•	X.509 Digital Trusted Certificate Support

•	2048-bit Certificate Key Functionality

•	Custom DNS Handling

PSC2 Support

The PDIF supports the Packet Services Card 2 (PSC2). The PSC2 is the next-generation packet forwarding card for the ASR 5000. The PSC2 provides increased aggregate throughput and performance, and a higher number of subscriber sessions.

The PSC2 has been enhanced with a faster network processor unit, featuring two quad-core x86 2.5Ghz CPUs, 32 GB of RAM. These processors run a single copy of the operating system. The operating system running on the PSC2 treats the two dual-core processors as a 4-way multi-processor.

The PSC2 has a 2.5 G/bps-based security processor that provides the highest performance for cryptographic acceleration of next-generation IP Security (IPSec), Secure Sockets Layer (SSL), and wireless LAN/WAN security applications with the latest security algorithms.

For more information about PSC2s, see the Product Overview Guide.

Duplicate Session Detection

When an MS sets up a new session, the PDIF automatically checks for any remnants of abandoned calls and if found, clears them.

During a call, the processes of clearing the old session and establishing the new session run in parallel, optimizing processing functions.

With every new session setup, the PDIF supports a mechanism to verify whether there is any old session that is bound with the same International Mobile Subscriber Identity (IMSI) number. This is derived from the Callback-Id AVP in the last DEA message from the HSS after it has verified the subscriber.

For example, if an MS accesses the PDIF and subsequently moves out of the Wi-Fi coverage area, when the MS comes back on line, it could initiate a new session. After authentication, if an old session with the same IMSI is detected, the PDIF starts clearing it by sending a proxy-MIP Deregistration request to the HA. Once a Deregistration request is sent and a Deregistration response is received, the PDIF resumes the new session setup by sending a proxy-MIP Registration request. This setup procedure continues after the PDIF receives a proxy-MIP Deregistration response from the HA.

IMSI-based duplicate session detection is supported per source PDIF context. The PDIF requires only one source context to be configured per PDIF, therefore duplicate session detection across the entire chassis is possible. The feature is designed with the assumption that no more than one call with duplicate identifies are in the setup stage at any time. There is no limit to the number of duplicate session handling iterations.

When an old session is cleared, the PDIF sends Diameter STR messages and Radius Accounting STOP messages to corresponding AAA servers.

The PDIF allows duplicate session detection based on the NAI or IMSI. Note that when detecting based on the NAI, it is the first-phase (Multi-Authentication device authentication phase) NAI that is used.

If NAI-based duplication session handling is enabled, the PDIF sends an INFORMATIONAL (Delete) message to the MS.

Duplicate Session Detection is configured in PDIF-Service mode. The default is NAI-based.

Note that this configuration applies only to calls established after the configuration is made. It is therefore suggested that this selection be made in the boot-time configuration before any calls are established. For example, if NAI-based is used initially and an X number of calls is established, and then the configuration changes to IMSI-based, IMSI-based duplicate session handling does not apply to the calls established before the configuration change.

Unsupported Critical Payload Handling

This feature provides a mechanism whereby the PDIF ignores all unsupported critical payloads and continues processing as if those payloads were never received.

For MOBIKE IKEv2 messages, the PDIF returns UNSUPPORTED_CRITICAL_PAYLOAD in the IKEv2 response messages. The PDIF also drops all NAT-T keep-alive messages.

Registration Revocation

Registration Revocation is a general mechanism whereby the HA providing mobile IP or proxy mobile IP functionality to a mobile node notifies the PDIF/FA of the termination of a binding. This functionality provides the following benefits:

•	Timely release of mobile IP resources at the FA and/or HA

•	Accurate accounting

•	Timely notification to mobile node of change in service

Important: Mobile IP registration revocation is also supported for proxy mobile IP. However, in this implementation, only the HA can initiate the revocation.

Important: For more information, see Mobile-IP Registration Revocation chapter in this guide.

CHILD SA Rekey Support

During Child SA (Security Association) rekeying, there exists momentarily (500ms or less) two Child SAs. This is to make sure that transient packets for the old Child SA are still processed and not dropped.

PDIF-initiated rekeying is disabled by default. This is the recommended setting, although rekeying can be enabled through the Crypto Configuration Payload mode commands. By default, rekey request messages from the MS are ignored.

Denial of Service (DoS) Protection: “Cookie Challenge”

There are several known Denial of Service (DoS) attacks associated with IKEv2. Through a configurable option in the Config Crypto-Template mode, the PDIF can implement the IKEv2 “cookie challenge” payload method as described in [RFC 4306]. This is intended to protect against the PDIF creating too many half-opened sessions or other similar mechanisms. The default is not enabled. If the IKEv2 cookie feature is enabled, when the number of half-opened IPSec sessions exceeds the reasonable limit (or the trigger point with other detection mechanisms), the PDIF invokes the cookie challenge payload mechanism to insure that only legitimate subscribers are initiating the IKEv2 tunnel request, and not a spoofed attack.

If the IKEv2 cookie feature is enabled, and the number of half-opened IPSec sessions exceeds the configured limit of any integer between 0 and 100,000, the call setup is as shown in the figure below.

DoS Cookie-Challenge-Enabled IKEv2 Message Exchange

DoS Cookie Challenge Enabled IKEv2 Message Exchange

Step	Description
1	The MS places a call to the WiFi AP.
2	The WiFi AP returns the IP address of the PDIF.
3	The MS sends an IKE_SA_INIT request. message.
4	The PDIF sends the Notify (cookie) payload to the MS to request retransmission of the IKE_SA_INIT request message to include the Notify (cookie) payload in the message.
5	Upon receipt of the retransmitted message, the PDIF verifies the cookie payload and ensures it is the same cookie as the one it had sent.
6	If the cookie challenge is met, setup continues as normal with an IKE_SA_INIT response message.

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Cookie Challenge Statistics

Cookie challenge statistics appear in the outputs for the following commands:

•	show crypto managers summary ikev2-stats: Shows the total number of invalid cookies per manager instance.

•	show crypto managers summary npu-stats: Shows NPU statistics on each IPSec manager.

•	show crypto statistics: Shows the combined data statistics for the given context name. Includes the number of cookie flows, the number of cookie flow packets, and the total number of cookie errors.

•	show crypto statistics ikev2: Shows the control statistics for a given context name. Includes the output for show crypto statistics, plus Total IKEv2 Cookie Statistics, Cookie Notify Sent, Cookie Notify Received, Cookie Notify Match, Cookie Notify NOT Match, and Invalid Notify Payload Cookie.

MAC Address Validation

The MS embeds the MAC address from the WiFi AP in the NAI when it sends an IKEv2 AUTH request. If MAC address validation is enabled on the PDIF, it sends a Diameter User-Data-Request (UDR) message to the HSS with the NAI from the MS. The HSS returns a User-Data-Answer (UDA) message to the PDIF containing a list of authorized MAC addresses.

If the PDIF finds the MAC address in this list, the MAC address validation succeeds, and the PDIF continues with the IKEv2 call. The MS starts EAP authentication through IKEv2 AUTH procedures. If configured to do so, the PDIF removes the MAC address from the NAI when sending authentication requests to external RADIUS servers. If the embedded MAC address is not removed, the authentication check fails, because the AAA server cannot accommodate embedded MAC addresses.

If the MAC address is not in the list, the MAC address authorization fails, and the IKEv2 session is terminated with a Notify Message Type 16382 - Private User Errors message.

If the HSS interface is not reachable, it is possible that the IKEv2 session setup could continue as if the MAC authorization had succeeded. However, such error behaviors, including various Diameter error codes from the HSS, are configuration options. That means if an HSS returns an error, the action could be either to continue or to terminate the session. This is discussed in Diameter Failure Handling.

Important: See also Diameter Authentication Failure-Handling in the Command Line Interface Reference.

RADIUS Accounting

RADIUS Accounting messages are not generated while mobile IP setup is in progress.

•	A RADIUS accounting START message is generated when the session is established.

•	RADIUS INTERIM accounting messages are generated at configured intervals in a call.

•	A RADIUS STOP accounting message is sent to the AAA server when the call ends.

There is no session dormancy in the PDIF. Once the session is active, the session never goes to a dormant state.

Important: RADIUS attributes and customizable dictionary types are described in the AAA and GTPP Interface Administration and Reference. For the impact of attributes in Request and Reply messages, see also Mobile IP Native Simple IP Call Minimum Requirements. There is additional attribute information in the Session Termination section in Troubleshooting.

Special RADIUS Attribute Handling

Certain attributes require special handling on the PDIF with the attribute values either controlled by a RADIUS dictionary entry or a PDIF-service configurable. No configuration has no behavioral effect.

•

3GPP2-Serving-PCF. The generation of each new custom dictionary requires a new PDIF image. Configured in the pdif-service mode, the command aaa attribute 3gpp2-serving-pcf <ip-address> specifies the required values for the attribute without building a new software image. If configured, this attribute is sent in RADIUS accounting messages.

The following attributes are in custom dictionaries but have a customer-requested component.

•

Calling-Station-ID. Required for PDIF RADIUS messages, there is a “dummy” value of 000000000000000 (fifteen zeros) set in this attribute. For non-PDIF product lines, the configured value may be taken only if no attributes are received through the corresponding access protocols. Configurable in the PDIF-service.

•	NAS-Port-Type. The 3GPP2 X.P0028-200 standard requires this value to be set as “5 (= Virtual).” Controlled through the RADIUS dictionary.

•	Service-Type. Cisco specifies a Service Type of “framed” for PDIF messages. Controlled through the RADIUS dictionary.

•	Framed-Protocol. There is no attribute value defined for IPSec. Cisco specifies a value of “PPP” for PDIF messages. Controlled through the RADIUS dictionary.

•	BSID. Base Station ID is used in billing for calculating time-zone offsets. There is a dummy value set in this attribute for RADIUS messages from the PDIF. Configured in the PDIF-service.

•

3GPP2-MEID and 3GPP2-ESN. Since the customer billing system expects these attributes, a null value is set in these attributes for RADIUS messages from the PDIF. Mobile Equipment Identifier (MEID) uniquely identifies the mobile equipment and is the future replacement for Electronic Serial Number (ESN) of the Mobile Station. Controlled through the RADIUS dictionary.

•	3GPP2-Last-Activity. The event timestamp is set in this attribute where applicable in RADIUS messages from PDIF. This attribute is the same as the 3GPP2-Last-User-Activity-Time standard attribute.

•	3GPP2-Service-Option. Set with a default value of 4095. Configurable in the PDIF-service.

•	SN-Disconnect-Reason.This is a Cisco VSA that specifies a more detailed reason for session disconnection.

•	3GPP2-Active-Time If required for billing purposes, this VSA could be populated with the session length by generating a new RADIUS dictionary with this attribute. Unless specifically requested, a custom RADIUS dictionary does not include the 3GPP2-Active-Time VSA.

Mobile IP and Proxy Mobile IP Attributes

Important: The SN-Proxy-MIP attribute is required when PDIF supports proxy mobile IP. The PDIF-Mobile-IP-Required attribute is SN1-PDIF-MIP-Required. These attributes need to be returned in a AAA response message or the mobile IP call fails, although there might be an option for simple IP call setup. See the Sample Deployments section for more information on attribute messaging.

IPv6 Support

This section describes the level of IPv6 support. All known restrictions are shown in Engineering Restrictions. Configuration examples are shown in Configuration.

Native IPv6 supports configuration of interfaces and routes with IPv6 (128-bit) addressing. PDIF supports IPv6 for communication with Diameter servers over SCTP. Using the Diameter proxy mechanism, each PSC needs a unique IPv6 address. Multiple IPv6 interfaces per context are supported.

Native IPv6 interfaces communicate with the Diameter servers. PDIF supports the configuration of 32 IPv6 Ethernet interfaces and 32 IPv6 loopback interfaces per context:

•	One configured (CIDR global or site-local) IPv6 address per interface.

•

Support for auto-configuration of link-local address based on an assigned MAC address. If the MAC address changes, the link-local addresses are updated accordingly. If a virtual MAC address is configured, it uses that MAC address for the link-local IFID. Note that this is distinct from the manual configuration of IPv6 addresses described below.

IPv6 Neighbor Discovery

IPv6 Neighbor Discovery protocol is used to dynamically discover the directly attached devices on IPv6 interfaces. It facilitates the mapping of MAC addresses to IPv6 Addresses. PDIF supports a subset of IPv6 Neighbor Discovery as defined by [RFC 2461] as follows:

•	Uses IPv6 Neighbor Discovery to learn the Ethernet link-layer addresses of the directly connected next-hop gateway.

•	Supports configuration of static IPv6 neighbors.

•	Adds link-local addresses to Ethernet type interfaces automatically.

•	Performs Unsolicited Neighbor Advertisement on line card switchover.

•	Responds to neighbor discovery requests for the PDIF IPv6 addresses.

IPv6 Static Routing

Native IPv6 routing allows the forwarding of IPv6 packets between IPv6 networks. The forwarding lookup is based on destination IPv6 address longest prefix match.

PDIF supports configuration of static routes including a default route. If a default route is configured, all IPv6 traffic is forwarded to the configured next-hop defined by the default route.

Port-Switch-On-L3-Fail for IPv6

IPv4 port failover redundancy if L3 connectivity is lost is extended to support IPv6 addresses.

For more information on configuring port-switch-on-l3-fail, see Ethernet Interface Configuration Commands in the Command Line Interface Reference and Creating and Configuring Ethernet Interfaces and Ports in the System Element Configuration Procedures section of the System Administration Guide.

IKEv2 Keep-Alive (Dead Peer Detection (DPD))

PDIF supports DPD protocol messages originating from both the MS and the PDIF/FA. DPD is configured on a per-PDIF-service basis. The administrator can also disable DPD and the PDIF/FA does not initiate DPD exchanges with the MS when disabled. However, the PDIF/FA always responds to DPD availability checks initiated by the MS regardless of the PDIF/FA idle timer configuration.

Important: For a number of failure scenarios involving Dead Peer Detection, refer to the Troubleshooting chapter.

Congestion Control and Overload Disconnect

Congestion control is an operator-configurable facility. When the PDIF chassis reaches certain limits (based on CPU utilization, port utilization, and other controls) the system enters a congested state. When in a congested state, existing calls are not impacted but new calls are potentially restricted.There is a separate subscriber-level configuration to enable/disable the feature on a per-subscriber basis. There is also a subscriber-level configurable for inactivity-time and connect-time thresholds to remove some old and abandoned calls from the system.

The disconnection scenario is as follows:

•	If only idle-time-threshold is configured, sessions exceeding this threshold would be selected for disconnection.

•	If only connect-time-threshold is configured, sessions exceeding this threshold would be selected for disconnection.

•	If both idle-time-threshold and connect-time-threshold are configured, sessions with an idle-time greater than the idle-time threshold and a connect-time greater than the connect-time-threshold would be selected for disconnection.

•	If neither idle-time-threshold nor connect-time-threshold is configured, sessions are sorted based on the idle-timer, and sessions with a longer idle-timer are deleted first.

SCTP (Stream Control Transmission Protocol) Support

PDIF provides support for SCTP (Stream Control Transmission Protocol) for use in communicating with Diameter peers over IPv6.

Diameter/SCTP connections are set up for administratively enabled Diameter peers whenever the system configuration is loaded. In the event of certain card or task-level failures, SCTP connections are torn down and re-established (but note that the Diameter state will still be maintained).

SCTP complies with the description in [RFC 2960 Section 5.1.1] for how to handle the case where the peer is incapable of supporting all of the outbound streams that the endpoint wants to configure. Specifically, PDIF does not abort the session but instead adjusts the association's number of outbound streams to match the number of inbound streams advertised by the peer (in the event that the number sent is less).

X.509 Digital Trusted Certificate Support

A digital certificate is an electronic credit card that establishes one's credentials when doing business or other transactions on the Web. Some digital certificates conform to ITU-T standard X.509 for a Public Key Infrastructure (PKI) and Privilege Management Infrastructure (PMI). X.509 specifies, among other things, standard formats for public key certificates, certificate revocation lists, attribute certificates, and a certification path validation algorithm.

The PDIF generates an SNMP notification when the certificate is within 30 days of expiration and approximately once a day until a new certificate is provided. The operator needs to generate a new certificate and then configure the new certificate using the CLI. The certificate is then used for all new sessions.

Important: For more configuration information, refer to Global Configuration in the Command Line Interface Reference.

2048-bit Certificate Key Functionality

This enhancement supports PDIF session setup when a PDIF certificate includes an RSA key size of 2048 bits. This includes:

•	2048-bit private key configuration in Global Configuration mode

•	Certificate configuration that includes 2048-bit public keys

•	The calculation of the AUTH payload in the first IKE_AUTH response from the PDIF using the 2048-bit private key

•	Transporting the PDIF certificates with 2048-bit RSA public key length from the PDIF to the MS

•	The validation of the AUTH payload using the 2048-bit RSA public key

•	Dynamically applying a new 2048-bit certificate to 1024-bit or 2048-bit certificates with no service interruption to in-process calls

•	The PDIF forwarding the first IKE_AUTH response with the CERT payload to the IPMS server (as it currently does), and the IPMS server decoding the message (if the proper IKE SA key is available)

•	Collocation of certificates with 1024-bit keys and 2049-bit keys

•	Fragmented packets are visible in external system output

Collocation of Certificate with 1024-bit Key and 2048-bit Key

Currently available dual-mode Wi-Fi handsets can only process certificates with 1024-bit key length. Future handsets will support 2048-bit key length only. During the transition period, it is possible that two different types of certificates must be configured in the same PDIF chassis:

•	1024-bit key only handset (abbreviated as 1024-bit MS)

•	2048-bit key only handset (abbreviated as 2048-bit MS)

PDIF is informed as to which certificate the MS will receive.

Distinguishing Between 1024-bit and 2048-bit Key Certificates

Certificates are configured in Global Configuration mode and bound to a crypto template. The crypto template is mapped to each PDIF service. The MS uses different PDIF services depending on which key length it can support.

The MS first resolves the IP address of the PDIF service with a pre-configured FQDN. As shown in the following figure, two different FQDNs may be configured to initiate session setup with two different PDIF services.

Distinguishing Between 1024-bit and 2048-bit Key Certificates

Custom DNS Handling

By default, the PDIF always returns a DNS address in the CP payload if one is received from the configuration or the HA. A new CLI has been added defining an alternate series of supported behaviors depending on the number of INTERNAL_IP4_DNS. These include, but are not limited to, the following:

•	Provides a mechanism whereby the DNS address present in configurations will be sent to the MS in the CP payload only if the MS requests one.

•	The address 0.0.0.0 is treated as invalid and not included.

Important: For more information including full definitions for each of the trigger behaviors, see Configuring Crypto Template in Configuration, and also see the Command Line Interface Reference.

Features and Functionality - Licensed Enhanced Feature Support

This section covers any feature not covered by the base PDIF software and is licensed either separately or in a customized bundle of feature licenses.

Important: Contact your local Sales or Support representative for information on how to obtain a license.

This section describes the following features:

•	PDIF Service

•	Multiple PDIF Services

•	Lawful Intercept

•	Diameter Authentication Failure Handling

•	Online Upgrade

•	Operation Over a Common IPv4 Network

•	Operation Over a Common IPv6 Network

•	Session Recovery Support

•	IPSec/IKEv2

•	Simple IP Fallback

•

Simple IP

•	Proxy Mobile IP

•	Multiple Authentication in a Proxy Mobile IP Network

•	RADIUS Authentication

•	Termination

•	Session Recovery

•	Intelligent Packet Monitoring System (IPMS)

•	Multiple Traffic Selectors

•	Selective Diameter Profile Update Request Control

•	Support of SHA2 Algorithms

PDIF Service

The PDIF service and the processes associated with it define the PDIF itself. The PDIF service enables mobile stations to interface with the PDIF.

The PDIF service configuration includes the following:

•	The IPv4 address for the service: This is the PDIF IP address to which the MS tries to connect. The MS sends IKEv2 messages to this IP address and this address must be a valid address in the context. PDIF service will not be up and running if this IP address is not configured.

•

The name of the crypto template for IKEv2: A crypto template is used to configure an IKEv2 PDIF IPSec policy. It includes most of the IPSec parameters and IKEv2 parameters for keep-alive, lifetime, NAT-T and cryptographic and authentication algorithms. There must be one crypto template per PDIF service. The PDIF service will not be up and running without a crypto-template configuration.

•	The EAP profile name: This profile defines the EAP authentication methods.

•	Multiple authentication support: The multiple authentication configuration is a part of the crypto template.

•	IKEv2 and IPSec transform sets: These define the negotiable algorithms for IKE SA and CHILD SA setup to connect calls to the PDIF/FA.

•	Configure the setup timeout value: The MS connection attempt is terminated if the MS does not establish a successful connection within the configured value.

•	Mobile IP foreign agent context and foreign agent service: This defines the system context where mobile IP foreign agent functionalities are configured.

•	Max-sessions: The maximum number of subscriber sessions allowed by this PDIF service.

•	PDIF supports a domain template for storing domain related configuration: The domain name is taken from the received NAI and searched in the domain template database.

•	3GPP2 serving PCF address: This configurable specifies what value in the RADIUS attribute when sending authentication and accounting messages.

•	Duplicate session detection parameters: PDIF supports either NAI (first phase authentication) or IMSI to be used for duplicate session detection. This configuration specifies whether duplicate session detection is based on IMSI or NAI. The default is NAI.

When the PDIF service is configured in the system with the IP address, crypto template, etc., the PDIF is ready to accept IKEv2 control packets for establishing IKEv2 PDIF sessions.

There is a limit to the number of CHILD SAs supported by each PDIF service. Traditionally, other Cisco services limit this to the number of subscriber sessions. The PDIF treats this as the number of CHILD SAs. This means that if each subscriber establishes only a single CHILD SA, the limit will be equal to the number of subscriber sessions. During CHILD SA rekeying, for a small duration of time, there are two CHILD SAs in the system. This is to make sure that transient packets for the old CHILD SA are still processed (not dropped).

Multiple PDIF Services

The PDIF supports multiple PDIF services running simultaneously on the same chassis. This feature enables operators to configure PDIF services with different crypto templates to support multiple subscriber handsets and to set per-service maximum session limits. The total number of sessions for all PDIF services running simultaneously on the same chassis must fall under the PDIF session counting license limit.

Lawful Intercept

The Cisco Lawful Intercept feature is supported on the PDIF. Lawful Intercept is a license-enabled, standards-based feature that provides telecommunications service providers with a mechanism to assist law enforcement agencies in monitoring suspicious individuals for potential illegal activity. For additional information and documentation on the Lawful Intercept feature, contact your Cisco account representative.

Diameter Authentication Failure Handling

Diameter EAP failure handling defines error handling for both Session Termination Requests and for EAP Requests.

Specific actions (continue, retry-and-terminate, or terminate) can be associated with each possible result-code. EAP failure handling is flexible enough that wide ranges of result codes can be defined with the same action, or actions can be bound on a per-result-code basis.

A failure does not necessarily mean a summary termination of a call.

diameter authentication <failure-handling> session-termination-request

diameter result-code 5001-5005 action continue

configures result codes 5001, 5002, 5004 and 5005 to mean the session could continue regardless of the error,

and

diameter authentication <failure-handling> session-termination-request

diameter result-code 5003 action terminate

configures result code 5003 to mean terminate the session immediately.

In this scenario, the PDIF receives the DEA from an HSS with the failure code 5003 to terminate the IKE setup for the session. The PDIF sends the IKE_AUTH Response containing a Notify Payload with the type as AUTH_FAILED plus the EAP payload if one was received in the DEA.

When the PDIF received the last DEA message with AVPs that are not in the dictionary, and with the M-bit set to 1, the PDIF disconnects the session.

Important: Refer to Configuring Diameter Authentication Failure Handling in the AAA and GTPP Interface Administration and Reference and the Command Line Interface Reference for more information.

Online Upgrade

The customer has the benefits of upgrading software from a fully redundant device without the expense of maintaining a fully loaded, fully redundant ASR 5000 in a permanent state of standby.

The PDIF supports online software upgrades with a single software version difference between two chassis. For example, upgrading from Release 8.1 to 8.2 is supported. Support for a chassis running greater differences in software versions would be qualified by Cisco on an as-needed basis.

Important: Refer to the Maintenance chapter in this guide for information on how to perform the upgrade.

The online upgrade process calls for a spare ASR 5000 to temporarily perform the services currently being provided by a live networked chassis and upgrade the software with minimal service interruption. This model is called Active-Standby, as one chassis is designated as active and the other as standby. The standby chassis does not handle any new, incoming sessions because the DNS allocating new sessions does not know about the backup chassis. The backup is only required to handle sessions that were already on the primary chassis when it was administratively disconnected from the DNS server. Except for the data loss during the brief chassis switch-over, the session information (accounting and timers) are synchronized so that they are accurate when the backup becomes the active PDIF.

Important: Online upgrade requires miscellaneous internal processing that may result in intensive CPU utilization. Up to 50% CPU utilization overhead should be expected during the upgrade.

The Active-Standby Upgrade Model

The Active-Standby model is shown below:

Active-Standby Online Upgrade Model

The active and standby chassis are connected by an SRP redundancy link to monitor and control the chassis state. Both active and standby chassis have SRP-activated resources defined. Resources could mean loopback interfaces, broadcast interfaces, or IP pools, depending on the installation. For this example, use loopback interfaces.

These resources are the same between the active and standby PDIF. Loopback IP addresses in ingress and egress contexts, and IP pools in egress contexts, are usually SRP-activated resources. The result is that only the currently active chassis enables the SRP-activated resources. The activate command is srp-activate.

Important: Ingress and egress contexts could be the same context. The SRP context must be a separate context.

In the network diagram below, each ingress context has loopback interface A defined, which is SRP-activated. PDIF service A is bound to this interface. The standby chassis has the same interface and PDIF service defined. Both interface and service can only be enabled on the active chassis. Similarly, interface B is defined in the egress context, which can be activated only in the active chassis.

When the active chassis switches over, the standby chassis becomes active and enables all SRP-activated IP interfaces and IP pools so that it can function as a mirror image of the former primary PDIF.

Loopback Interface Configuration

Operation Over a Common IPv4 Network

The PDIF supports L2 switching to enable carriers not using dynamic routing between the core nodes to perform an online upgrade.

In the example below, the SRP virtual MAC address is configured for the SRP-activated loopback address for the subnet. This allows the standby chassis to seamlessly assume the active role in the network after a switchover. Attached devices continue to send to the same SRP virtual MAC address and the currently active chassis responds to ARP requests for the shared loopback IP address. This scheme allows fast standby-to-active transitions, since the SRP virtual MAC address does not change during the switchover.

When the ASR 5000 transitions from backup to primary, the PDIF sends Gratuitous ARPs to update the port-MAC table of the adjacent switch.

Switchover Example for Common IPv4 Subnet

Operation Over a Common IPv6 Network

For AAA context with Diameter/SCTP/IPv6 configuration, multiple loopback IPv6 addresses are configured as Diameter endpoints. The customer can SRP-activate these loopback addresses and, upon SRP switchover, the HSS/SLF still sees the same Diameter peer endpoint. No new Diameter peer configuration to the HSS/SLF is required.

With SRP switchover operation in effect, the PDIF shuts down all the SCTP connections to the HSS/SLF. Then the former backup PDIF immediately creates new SCTP connections with the HSS/SLF. In this reestablishment process, the backup chassis sends an Unsolicited Neighbor Advertisement message to the adjacent switch, which is then used to overwrite its port MAC address table as shown in the diagram below.

Switchover Example for a Common IPv6 Subnet

Other Devices

The following table summarizes how other network devices see two ASR 5000s chassis during online upgrade. The table below assumes that a SRP-activated loopback address is configured in the source (toward the MS), the destination (toward the HA), and the AAA contexts (Diameter and RADIUS).

The Chassis as seen from Other Network Devices During Upgrade

Network Entity	Consideration in Two-Chassis Configuration
L3 switch (MS ~ PDIF)	This L3 switch sees two chassis as a single entity. Only the physical port in the switch changes due to the switchover operation by G-ARP. The rest of the ASR 5000 information (IP address and MAC address) remain the same.
L3 switch (PDIF ~ HA)	This L3 switch sees two chassis as a single entity. Only the physical port in the switch changes due to the switchover operation by G-ARP. The rest of the ASR 5000 information (IP address and MAC address) remains the same.
Diameter Server	The MS sees two PDIFs as the same entity. However, upon switchover the SCTP connection is disconnected and then a new SCTP connection with ASR 5000 is established immediately.If an L3 switch exists between the PDIF and Diameter server, it sees two chassis as a single entity. Only the physical port in the switch changes due to the switchover operation by IPv6 Unsolicited Neighbor Advertisement. The rest of the ASR 5000 information (IP address and MAC address) remains the same.
RADIUS Server	This L3 switch sees these two chassis as a single entity. Only the physical port in the switch changes due to the switchover operation by G-ARP. The rest of the chassis information (IP address and MAC address) remains the same.If there should be an L3 switch between the PDIF and a RADIUS server, it sees two chassis as a single entity. Only the physical port in the switch changes due to the switchover operation by G-ARP, and the rest of the ASR 5000 information (IP address and MAC address) remains the same.
IPMS Server	Each chassis is connected to an independent IPMS Server. When a switchover takes place, the new IPMS Server continues to capture and store the call logs (signaling messages and events).
O&M Device	Each chassis is connected to an independent O&M Device. When a switchover takes place, the new O&M Device continues to perform the function as the original device was configured.

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Session Recovery Support

The session recovery feature provides seamless failover and almost instantaneous reconstruction of subscriber session information in the event of a hardware or software fault within the same chassis, preventing a fully connected user session from being dropped.

Session recovery is performed by mirroring key software processes (the session manager and the AAA manager, for example) within a single PDIF. These mirrored processes remain in an idle state (in standby mode), wherein they perform no processing, until they may be needed in the case of a software failure (a session manager task aborts, for example). The system spawns new instances of standby mode sessions and AAA managers for each active Control Processor (CP) being used.

Additionally, other key system-level software tasks such as VPN manager are performed on a physically separate Packet Services Card (PSC/PSC2) to ensure that a double software fault (the session manager and the VPN manager fail at same time on same card, for example) cannot occur. The PSC used to host the VPN manager process is in active mode and is reserved by the operating system for this sole use when session recovery is enabled.

The additional hardware resources required for session recovery include a standby System Management Card (SMC) and a standby PSC.

There are two modes for session recovery.

•

Task recovery mode: Wherein one or more session manager failures occur and are recovered without the need to use resources on a standby PSC. In this mode, recovery is performed by using the mirrored standby-mode session manager tasks running on active PSCs. The standby-mode task is renamed, made active, and is then populated using information from other tasks such as AAA manager.

•	Full PSC recovery mode: Used when a PSC hardware failure occurs, or when a PSC migration failure happens. In this mode, the standby PSC is made active and the standby-mode session manager and AAA manager tasks on the newly-activated PSC perform session recovery.

Session/call state information is saved in the peer AAA manager task because each AAA manager and session manager task is paired together. To ensure task recovery, these pairs are started on physically different PSCs.

Important: For more information on session recovery support, refer to Session Recovery in this guide.

IPSec/IKEv2

IKEv2 and IPSec transform sets configured in the crypto template define the negotiable algorithms for IKE SA and CHILD SA setup to connect calls to the PDIF/FA by creating two secure tunnels. The first, called the Tunnel Inner Address (TIA) is for signaling traffic, but in some cases it can be used for user traffic which can then use the TIA IP address. The second IPSec SA connects the MS to an HA for a mobile IP call.

Refer to Sample Deployments for a full description of how a variety of calls are successfullyset up (and torn down) in a variety of network scenarios.

At the beginning of IKEv2 session setup, the PDIF and MS exchange capability for multiple authentication. Multiple authentication is configured in the crypto template of the PDIF service. When multiple authentication is enabled in the PDIF service, the PDIF will include MULTIPLE_AUTH_SUPPORTED Notify payload in the initial IKEv2 setup response.

The MS first sends an NAI for the device authentication, in which EAP-AKA is used. After the successful EAP-AKA transaction between the MS and the HSS, the HSS is expected to return the IMSI number for this subscriber. The PDIF uses the authorized IMSI number for session management.

Once the device authentication is successful, the MS notifies the PDIF of its intention to continue subscriber authentication only if the PDIF indicates it has multiple authentication support during the initial IKEv2 exchanges. The MS sends the second NAI that may be different from the first one used during the device authentication. The subscriber authentication is completed either using EAP-MD5 or EAP-GTC. Upon successful authentication, the PDIF continues proxy MIP registration before granting its access to the network.

Even if the PDIF sends the MULTIPLE_AUTH_SUPPORTED capability in the initial IKEv2 setup response, the MS may not support multiple authentication and hence may not include MULTIPLE_AUTH_SUPPORTED Notify payload in the subsequent IKEv2 AUTH exchange. In this case, the MS may only go through the first authentication (which is EAP-AKA authentication). After EAP-AKA authentication, if proxy-mip-required is configured for the session (either through the domain or the default subscriber or the corresponding Diameter AVP), the PDIF will establish a proxy mobile IP session with the HA. The assigned IP address is normally done by the HA and the PDIF receives this address through proxy mobile IP RRP. The PDIF will pass this address back to the MS through the final IKE_AUTH exchange. On the other hand, if proxy-mip-required configuration is not present or disabled, then the PDIF will continue the simple IP session setup by allocating the IP address for the MS from the locally configured pool.

When the MS sends MULTI_AUTH_SUPPORTED Notify payload in subsequent IKE_ AUTH exchanges, the PDIF knows the MS wants to do the second authentication. After the first successful EAP-AKA authentication, the MS will indicate to the PDIF regarding the second authentication (through ANOTHER_AUTH_FOLLOWS Notify payload in the final IKEv2 AUTH request). Please note that the IP address of the MS will not be assigned during the first authentication if the second authentication is to happen. The MS will then initiate the second authentication IKEv2 exchanges. In some networks, this second authentication uses the RADIUS AAA interface. The proxy-mip-required attribute will normally be present in the subscriber profile (or in the domain or default subscriber template) through a RADIUS attribute in the Access Accept message. After successful authentication, if proxy-mip-required is enabled, the PDIF will setup a proxy mobile IP session with the HA, and the HA assigns an IP address to the MS. If proxy-mip-required is disabled (or not present in the subscriber/domain profile), the PDIF establishes a simple IP session and routes traffic using the direct IP interface.

Simple IP Fallback

Network operators with handsets that are mobile IP capable may want the MS to be connected to the network and capable of doing data transfer even though the mobile IP registration process might fail under certain situations. If the mobile IP registration failures are due to HA reachability issues or any authentication problems, the MS should still be able to connect to the network using a simple IP connection, assuming that simple IP fallback is enabled in the PDIF configuration. See Simple IP and Simple IP Fallback in this chapter for a full description of this type of network configuration.

Simple IP

Simple IP is a solution for network providers whose subscribers fall primarily within a limited set of requirements. It provides the following:

•	A mobility solution for subscribers who do not typically roam outside their immediate coverage area.

•	An appropriate level of service for users who do not use the network in such as way as to need constant service between coverage areas. For example, subscribers who do not perform large file downloads.

•	A mechanism to complete a call even if the proxy-mip-required or mip-required attributes are not configured in the subscriber or domain profile.

Proxy Mobile IP

Proxy mobile IP has the following benefits:

•	Allows an MS that does not support mobile IP to have the same roaming benefits of one that does.

•	The PDIF communicates with the HA and acts as if the PDIF itself were the handset.

•	Proxy mobile IP is configured through the proxy-mip-required configuration, or the corresponding Diameter AVP or RADIUS Access Accept messages. If neither are present, the PDIF establishes a simple IP session and the PDIF routes the call to the Internet or corporate network.

Proxy mobile IP provides a mobility solution for subscribers whose mobile nodes do not support mobile IP protocol. The PDIF sets up the mobile IP tunnel with the HA and the PDIF proxies or acts on behalf of the handset as if it were the handset. The subscriber receives an IP address from either the service provider or from their home network. As the subscriber roams through the network as if it were using a full mobile IP connection, the IP address is maintained providing the subscriber with the opportunity to use IP applications that require seamless mobility such as transferring files.

Important: Refer to Proxy Mobile-IP in the System Administration Guide for more information.

Multiple Authentication in a Proxy Mobile IP Network

Multiple authentication requires authenticating both the device and the subscriber.

At the beginning of the IKEv2 session setup, the PDIF and the MS exchange capability for multiple authentication. Multiple authentication is configured in the PDIF service as part of the crypto template where it is associated with an EAP profile. The EAP profile defines the authentication mode and method. If multiple authentication is enabled in the crypto template, the PDIF includes a MULTIPLE_AUTH_SUPPORTED Notify payload in the initial IKEv2 setup response.

Important: Even if the PDIF confirms MULTIPLE_AUTH_SUPPORTED capability in the initial IKEv2 setup response, the MS may not support multiple authentication and hence may not include a MULTIPLE_AUTH_SUPPORTED Notify payload in the subsequent IKEv2 AUTH exchange. In this case, the MS may only go through the first-phase (EAP-AKA) of device authentication.

During initial IKEv2/IPSec security setup exchanges, the MS undergoes both device authentication and subscriber authentication. This is because even if the device is fully authenticated, a PDIF may not be able to tell which service profile is applicable for the MS, nor the correct IP address to assign.

Important: First-phase authentication refers to device authentication, and second-phase authentication refers to subscriber authentication.

AAA Group Selection

A maximum of 64 AAA groups is allowed on the ASR 5000. This could be spread across multiple contexts or all groups can be configured within a single VPN context.

A maximum of 320 RADIUS servers is allowed on the chassis.

When the aaa-large-configuration command is issued, this number becomes 800 AAA groups and 1600 RADIUS servers configured within the chassis.

The PDIF service allows you to specify a different AAA group for each authentication phase. A given AAA group supports either Diameter or RADIUS authentication, but not both. In deployments where the NAI used in the first-phase authentication is different from the NAI used in the second-phase authentication, each NAI can point to different domain profiles in the PDIF.

RADIUS Authentication

Please see the document AAA and GTPP Interface Administration and Reference for information on AAA, RADIUS, and Diameter groups.

The second authentication uses RADIUS for subscriber authentication. The PDIF supports EAP termination mode during the second half of multiple authentication. In this mode, EAP exchange takes place between the MS and the PDIF, and the PDIF takes the information exchanged in the EAP payload over IKEv2 into RADIUS attributes to support CHAP/PAP authentication with the RADIUS server, and vice versa.

By default, the PDIF initiates EAP-MD5 authentication and sends an EAP payload with an MD5-Challenge to the MS. The MS returns an MD5-Challenge response in the EAP payload. Upon receipt, the PDIF sends an RADIUS Access Request message which includes an NAI, a CHAP-Password, a CHAP-challenge (derived from the EAP payload), and an IMSI number (which is the calling station ID). Once the AAA server returns an Access-Accept message, optional attributes such as Framed-IP-Address and HA address are expected for the subsequent session setup processing. The PDIF translates this Access-Accept message into an EAP Success message, and returns this in an IKE_AUTH Response message.

It is possible that some MSs may not support CHAP authentication. In this case, the MS is expected to return the EAP payload with a legacy-Nak message when the PDIF sends an MD5-Challenge message. Upon receipt of the legacy-Nak message, the PDIF initiates an EAP-GTC procedure. When the MS returns EAP-GTC including its own password, the PDIF sends a RADIUS Access Request message which includes an NAI, a password, and an IMSI number. Once the AAA server returns an Access-Accept message, attributes such as Framed-IP-Address and HA address are expected for the subsequent session setup processing. The PDIF translates the Access-Accept message as EAP success, and returns this in an IKE_AUTH Response message.

If EAP-GTC is configured, then the EAP-GTC method is used instead of the EAP-MD5 method.

The PDIF does the following for IKEv2 and RADIUS authentication:

The PDIF terminates EAP-MD5/GTC authentication. The PDIF understands the values in the EAP payload, and maps them as RADIUS attributes for CHAP/PAP authentication.

Upon request from the MS, the PDIF performs EAP-GTC authentication instead of EAP-MD5.

Each domain profile may be configured with two AAA groups, one for Diameter and the other for RADIUS.

In deployments where both NAI happen to be the same for both authentications, it will point to the same AAA group and thereafter only one protocol (either RADIUS or Diameter) is used.

There are cases where the domain template may not be associated with a given NAI. In such cases, the default AAA groups are used for authentication. Since authentication happens in two phases, and each using Diameter and RADIUS AAA groups respectively, there needs to be two default AAA groups (one for Diameter authentication and one for RADIUS authentication) for multiple authentication. The default AAA groups are configured in the PDIF service.

First-Phase Authentication

During first-phase authentication, the HSS authenticates the device. The MS first sends an NAI for device authentication. After the successful EAP-AKA transaction between the MS and the HSS, the HSS is expected to return an IMSI number for this subscriber. The PDIF takes this authorized IMSI number for session management.

This authentication method uses EAP between the MS and the AAA server, and the PDIF acts as a pass-through agent.

Important: First-phase authentication must use the EAP-AKA method.

Depending on the number of HSSs in the network, it is possible that a Subscription Locator Function (SLF) would be introduced into the network as a Diameter proxy or relay agent. If deployed, the SLF would be the first point of contact for the PDIF.

The protocol stack between the PDIF and the HSS/SLF is Diameter over SCTP over IPv6.

Second-Phase Authentication

Second-phase authentication uses EAP-MD5 or EAP-GTC authentication with IKEv2 using a legacy RADIUS server, which does not understand or implement EAP. This could be the same AAA server as those deployed in any existing EV-DO network. In this case, EAP authentication happens between the MS and the PDIF.

The protocol stack between the PDIF and the AAA server is RADIUS over UDP over IPv4.

The two algorithms for second-phase authentication are EAP-MD5 (which is the same as CHAP authentication) and EAP-GTC (which is the same as PAP authentication). When the MS sends the NAI to identify the subscriber, the PDIF initiates the EAP-Request with a challenge. Once the MS returns the challenge response, the PDIF maps it to a RADIUS ACCESS_REQUEST message to complete CHAP authentication. There is an internal mechanism to inform each peer if one method is not supported and to renegotiate to use the other supported method.

In general, session attributes during first-phase authentication are overwritten by those from second-phase authentication, unless specified separately. Exceptions to this include session-timeout and idle-timeout, when the lower values are taken.

Termination

During session setup, if there are any configuration mismatches or the PDIF cannot get the required information, the session setup process is terminated and appropriate log messages are generated.

If multiple-auth-supported is not enabled on the PDIF, and the MS still sends a MULTIPLE_AUTH_SUPPORTED Notify payload marked with the critical bit set, the PDIF returns UNSUPPORTED_PAYLOAD. Otherwise, the PDIF ignores it and processes the IKE packet as if the payload was never received. This is non-standard MS behavior.

Important: The multiple authentication process in a proxy mobile IP network is described in the Proxy-MIP chapter in this guide.

Session Recovery

The session recovery feature provides reconstruction of subscriber session information in the event of a hardware or software fault within the system, providing seamless failover andpreventing a fully connected user session from being dropped.

In addition to maintaining call state information, information is retained in order to:

•	Recover IPSec manager policies, all template maps, and all subscriber maps.

•	Use the policies (including templates) to recover CHILD SA tunnels, flow IDs, andstatistics.

•	Recover or reconfigure NPU flow IDs and data path handles.

•	Recover and restore the IKEv2 stack state for all tunnels.

•	Supply the IKEv2 stack with needed data statistics to determine rekey and DPD states.

•	Recover Diameter session information.

Recovery requires a complex interaction between IPSec and session subsystems. The IPSec subsystem also interacts with a Datapath that includes daughter cards, daughter card managers, and the NPU. The session recovery feature is disabled by default on the system, even when the feature use key is present.

The IPSec controller does not send an IPSec manager death notification to any subsystem. This allows the daughter card to continue to receive and decrypt IPSec tunnel data. It also allows both the session manager and daughter card to continue carrying subscriber traffic using NPU flows and IPSec SAs to transmit the data.

A session manager is created on a PSC and a corresponding AAA manager is created on a different PSC but is created with the same instance number. A session manager saves (check-points) its Call Recovery Record (CRR) on the AAA manager with an instance ID the same as its own. This pairs up the session manager and the AAA manager and at the same time guarantees session recovery in the event of a single PSC failure.

IPSec manager is also created on a PSC. When a PDIF call request arrives, the IPSec manager picks a session manager for this particular call using a demux library on the same PSC. This means the IPSec manager is associated with the session managers on the PSC.

The session subsystem continues to use the AAA manager as its storage system for the PDIF because AAA needs to provide other subscriber-related information to the session manager. Now that the session manager and the IPSec manager are paired on the same PSC, the IPSec manager is assured of data recovery in case of PSC failure. This is because the session manager saves its data on the AAA manager on a backup PSC.

Important: For more information, refer to the PDIF Session Recovery chapter in this guide.

Intelligent Packet Monitoring System (IPMS)

The IPMS provides a control-packet capture, database, and query facility. It provides the functions to assist operators to analyze and investigate call-related events at a later time.

Important: IPMS is described in the IPMS System Administration Guide.

Multiple Traffic Selectors

The PDIF can be configured with multiple IPSec traffic classes, each containing up to 128 traffic selectors, which are used during traffic selector negotiation with UEs. Multiple traffic selectors allow the PDIF to direct outbound traffic to selected IP addresses based on the following protocols: IP, TCP, UDP, and ICMP. The PDIF can also direct TCP and UDP traffic to selected IP addresses and port ranges.

Important: In this software release, the PDIF supports IPv4 traffic selectors only.

Per RFC 4306, when a packet arrives at an IPSec subsystem and matches a 'protect' selector in its Security Policy Database (SPD), the subsystem must protect the packet via IPSec tunneling. Traffic selectors enable an IPSec subsystem to accomplish this by allowing two endpoints to share information from their SPDs. Traffic selectors can be used to assure that both endpoint SPDs are consistent and can aid in the dynamic update of an SPD. Traffic selector payloads contain the selection criteria for packets being sent over IPSec security associations (SAs).

During traffic selector negotiation, each endpoint sends two traffic selector payloads in the messages exchanged during the creation of an IPSec SA. The first traffic selector payload is known as the TSi (Traffic Selector-initiator) and the second is known as the TSr (Traffic Selector-responder). Each traffic selector payload contains one or more traffic selectors, and each traffic selector can contain an IP address range, a port range, and an IP protocol ID. During traffic selector negotiation between the UE and the PDIF, the UE assumes the role of the initiator as it initiates an IPSec SA for its traffic, and the PDIF assumes the role of the responder. The PDIF can use multiple traffic selectors in its role as the responder.

Traffic selectors are applied to calls via an AAA attribute. During call setup, the PDIF's AAA manager selects the traffic class to use for a call based on the Radius vendor-specific attribute (VSA) TrafficSelector-class, which is received from the AAA server. The PDIF's Session Manager passes the selected traffic class configuration from its AAA Manager to its IPSec Manager, which then sends the traffic selectors to the UE in the TSr for all CHILD SAs in the call. If no matching traffic selector classes or traffic selectors have been configured on the PDIF, or if the PDIF does not receive the TrafficSelector-class attribute from the AAA server, or if the value of the received TrafficSelector-class attribute is 0, the PDIF returns the default traffic selector to the UE in the TSr, which allows all inbound traffic.

The PDIF saves the traffic class configuration in each call during call setup. Configuration changes made to the existing traffic class configuration will apply to new calls only. There is no hard limit to the maximum number of allowed traffic classes, but the recommended limit is 50.

When incoming traffic from a UE does not match any of the configured traffic selectors, the PDIF does not reject the traffic. Instead, the PDIF keeps a per-call counter to record the number of packets that do not match the configured traffic selectors. Outgoing traffic from the PDIF to the UE is not subject to traffic selection or checking.

Selective Diameter Profile Update Request Control

For mobile IP calls, the Selective Diameter Profile Update Request Control feature allows WiFi data-only sessions to co-exist with VoIP sessions on the PDIF platform.

When the PDIF is accessed by voice-enabled devices, it needs to interact with the HSS in order for a subscriber session to access the IP core network. When the PDIF is accessed by data-only devices, there is no need to interact with the HSS.

This feature is used to identify which subscriber sessions need to have the PDIF and the HSS exchange Diameter Profile Update Request (PUR) and Profile Update Answer (PUA) messages, and allows the PDIF to handle the call setup for a data-only client without having to interact with the HSS.

Selective PUR profiles on the AAA server are mapped to subscribers during AAA authentication via the Radius vendor-specific attribute (VSA) FMC-Type. FMC-Type has these possible values: voice or data. When the AAA server sets the FMC-Type value to voice, the PDIF and the HSS exchange PUR and PUA messages. When the AAA server sets the FMC-Type value to data, the PDIF and the HSS do not exchange PUR and PUA messages.

This feature is enabled by default and requires no configuration.

Support of SHA2 Algorithms

In addition to SHA1, the following algorithm variations, collectively known as SHA2, are now supported in the Cisco ASR5000 IKEv2 stack: SHA-256, SHA-384, and SHA-512. These algorthims provide an additional level of security as authentication mechanisms for IKE and IKEv2 protocols.

The truncated variants, known as Hash-based Message Authentication Mode (HMAC), are used in conjunction with the with SHA-256, SHA-384, and SHA-512 algorithms in IKE and IKEv2. The untruncated variants are known as Pseudo-Random Functions (PRFs), also used with IKE and IKEv2.

The authentication variants ensure that packets are authentic and cannot be modified in transit. PRF variants provide secure pseudo-random functions for generating keyed material and protocol-specific numeric quantities.

The following table summarizes the sizes associated with the algorithms.

Sizes Associated with SHA2 Algorithms

Algorithm ID	Block Size	Output Length	Truncated Length	Key Length	Algorithm Type
For Authentication (with truncated output
HMAC-SHA-256-128	512	256	128	256	Auth/integ
HMAC-SHA-384-192	1024	384	192	384	Auth/inte
HMAC-SHA-512-256	1024	512	256	512	Auth/inte
For PRFs (with untruncated output
PRF-HMAC-SHA-256	512	256	None	Variable	PRF
PRF-HMAC-SHA-384	1024	384	None	Variable	PRF
PRF-HMAC-SHA-512	1024	512	None	Variable	PRF

‌

Supported Standards and RFCs

3GPP2 References

•	P.S0001-B Version 2.0 cdma2000 Wireless IP Network Standard

•	X.S0011-001-C v3.0 cdma2000 Wireless IP Network Standard; Introduction

•	X.S0011-002-C v3.0 cdma2000 Wireless IP Network Standard: Simple IP and Mobile IP Services

•	X-S0013-000-A v1.0 All-IP Core Network Multimedia Domain - Overview

•	X.S0013-010-0 v2.0 All-IP Core Network Multimedia Domain - IP Multimedia Subsystem Sh Interface; Signaling Flows and Message Contents – Stage 2

•	X.S0013-010-A v1.0 All-IP Core Network Multimedia Domain - IP Multimedia Subsystem Sh Interface; Signaling Flows and Message Contents – Stage 2

•	X.S0013-011-A v1.0 All-IP Core Network Multimedia Domain - Sh Interface Based on Diameter Protocol; Protocol Details – Stage 3

•	X.S0016-000-B v1.0 3GPP2 MMS Specification Overview Multimedia Messaging System Specification

•	X.S0016-000-C v1.0 Multimedia Messaging Service - Overview

•	X.S0028-000-0 v1.0 cdma2000 Packet Data Services: Wireless Local Area Network (WLAN) Interworking - List of Parts

•	X.S0028-100-0 v1.0 cdma2000 Packet Data Services: Wireless Local Area Network (WLAN) Interworking - Access to Internet

•	X.S0028-200-0 v1.0 cdma2000 Packet Data Services: Wireless Local Area Network (WLAN) Interworking - Access to Operator Service and Mobility

IETF References

•	RFC 1594 (March 1994): “FYI on Questions and Answers to Commonly asked “New Internet User” Questions”

•	RFC 2104 (February 1997): “HMAC: Keyed-Hashing for Message Authentication”

•	RFC 2401 (November 1998): “Security Architecture for the Internet Protocol”

•	RFC 2403 (November 1998): “The Use of HMAC-MD5-96 within ESP and AH”

•	RFC 2404 (November 1998): “The Use of HMAC-SHA-1-96 within ESP and AH”

•	RFC 2405 (November 1998): “The ESP DES-CBC Cipher Algorithm With Explicit IV”

•	RFC 2451 (November 1998): “The ESP CBC-Mode Cipher Algorithms”

•	RFC 3526 (May 2003): “More Modular Exponential (MODP) Diffie-Hellman groups for Internet Key Exchange (IKE)”

•	RFC 3539: (June 2003): “Authentication, Authorization and Accounting (AAA) Transport Profile”

•	RFC 3588 (September 2003): “Diameter Base Protocol”

•	RFC 3602 (September 2003): “The AES-CBC Cipher Algorithm and Its Use with IPSec”

•	RFC 3706 (February 2004): “A Traffic-Based Method of Detecting Dead Internet Key Exchange (IKE) Peers”

•	RFC 3775 (June 2004): “Mobility Support in IPv6”

•	RFC 4187 (January 2006): “Extensible Authentication Protocol Method for 3rd Generation Authentication and Key Agreement”

•	RFC 4301 (December 2005): “Security Architecture for the Internet Protocol”

•	RFC 4302 (December 2005): “IP Authentication Header”

•	RFC 4303 (December 2005): “IP Encapsulating Security Payload (ESP)”

•	RFC 4305 (December 2005): “Cryptographic Algorithm Implementation Requirements for Encapsulating Security Payload (ESP) and Authentication Header (AH)”

•	RFC 4306 (December 2005): “Internet Key Exchange (IKEv2) Protocol”

•	RFC 4307 (December 2005): “Cryptographic Algorithms for Use in the Internet Key Exchange Version 2 (IKEv2)”

•	RFC 4308 (December 2005): “Cryptographic Suites for IPSec”

•	RFC 4718 (October 2006): “IKEv2 Clarifications and Implementation Guidelines”

•	RFC 4835 (April 2007): “Cryptographic Algorithm Implementation RFC Requirements for Encapsulating Security Payload (ESP) and Authentication Header (AH)”

Object Management Group (OMG) Standards

•	CORBA 2.6 Specification 01-09-35, Object Management Group

 

 

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