# IP Security

This chapter provides information on configuring an enhanced or extended service. The product Administration Guides provide examples and procedures for configuration of basic services on the system. It is recommended that you select the configuration example that best meets your service model, and configure the required elements for that model, as described in the respective product Administration Guide, before using the procedures in this chapter.

IMPORTANT:

The IP Security is a licensed Cisco feature. A separate feature license 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.

CAUTION:

IPSec parameter configurations saved using this release may not function properly with older software releases.

This chapter contains the following sections:

- Overview
- IPSec Terminology
- Implementing IPSec for PDN Access Applications
- Implementing IPSec for Mobile IP Applications
- Implementing IPSec for L2TP Applications
- Transform Set Configuration
- ISAKMP Policy Configuration
- ISAKMP Crypto Map Configuration
- Dynamic Crypto Map Configuration
- Manual Crypto Map Configuration
- Crypto Map and Interface Association
- FA Services Configuration to Support IPSec
- HA Service Configuration to Support IPSec
- RADIUS Attributes for IPSec-based Mobile IP Applications
- LAC Service Configuration to Support IPSec
- Subscriber Attributes for L2TP Application IPSec Support
- PDSN Service Configuration for L2TP Support
- Redundant IPSec Tunnel Fail-Over
- Redundant IPSec Tunnel Fail-over Configuration
- Dead Peer Detection (DPD) Configuration
- APN Template Configuration to Support L2TP
- IPSec for LTE/SAE Networks

Overview

IP Security (IPSec) is a suite of protocols that interact with one another to provide secure private communications across IP networks. These protocols allow the system to establish and maintain secure tunnels with peer security gateways. IPSec can be implemented on the system for the following applications:

- PDN Access: Subscriber IP traffic is routed over an IPSec tunnel from the system to a secure gateway on the packet data network (PDN) as determined by access control list (ACL) criteria. This application can be implemented for both core network service and HA-based systems. The following figure shows IPSec configurations.

Figure 1. IPSec Applications

- Mobile IP: Mobile IP control signals and subscriber data is encapsulated in IPSec tunnels that are established between foreign agents (FAs) and home agents (HAs) over the Pi interfaces.

  IMPORTANT:

  Once an IPSec tunnel is established between an FA and HA for a particular subscriber, all new Mobile IP sessions using the same FA and HA are passed over the tunnel regardless of whether or not IPSec is supported for the new subscriber sessions. Data for existing Mobile IP sessions is unaffected.
- L2TP: L2TP-encapsulated packets are routed from the system to an LNS/secure gateway over an IPSec tunnel.

Note that: IPSec can be implemented for both attribute-based and compulsory tunneling applications for 3GPP2 services.

Applicable Products and Relevant Sections

The IPSec feature is supported for various products. The following table indicates the products on which the feature is supported and the relevant sections within the chapter that pertain to that product.

Applicable Product(s) | Refer to Sections
--- | ---
PDSN/FA/HA | Implementing IPSec for PDN Access Applications Implementing IPSec for Mobile IP Applications Transform Set Configuration ISAKMP Policy Configuration ISAKMP Crypto Map Configuration Dynamic Crypto Map Configuration Manual Crypto Map Configuration Crypto Map and Interface Association FA Services Configuration to Support IPSec HA Service Configuration to Support IPSec RADIUS Attributes for IPSec-based Mobile IP Applications LAC Service Configuration to Support IPSec Subscriber Attributes for L2TP Application IPSec Support PDSN Service Configuration for L2TP Support Redundant IPSec Tunnel Fail-Over Dead Peer Detection (DPD) Configuration
GGSN/FA/HA | Implementing IPSec for PDN Access Applications Implementing IPSec for Mobile IP Applications Implementing IPSec for L2TP Applications Transform Set Configuration ISAKMP Policy Configuration ISAKMP Crypto Map Configuration Dynamic Crypto Map Configuration Manual Crypto Map Configuration Crypto Map and Interface Association FA Services Configuration to Support IPSec HA Service Configuration to Support IPSec RADIUS Attributes for IPSec-based Mobile IP Applications LAC Service Configuration to Support IPSec Redundant IPSec Tunnel Fail-Over Dead Peer Detection (DPD) Configuration TAPN Template Configuration to Support L2TP
ASN GW | Implementing IPSec for PDN Access Applications Implementing IPSec for Mobile IP Applications Implementing IPSec for L2TP Applications Transform Set Configuration ISAKMP Policy Configuration ISAKMP Crypto Map Configuration Dynamic Crypto Map Configuration Manual Crypto Map Configuration Crypto Map and Interface Association FA Services Configuration to Support IPSec HA Service Configuration to Support IPSec RADIUS Attributes for IPSec-based Mobile IP Applications LAC Service Configuration to Support IPSec Subscriber Attributes for L2TP Application IPSec Support Redundant IPSec Tunnel Fail-Over Dead Peer Detection (DPD) Configuration

IPSec Terminology

There are four items related to IPSec support on the system that must be understood prior to beginning configuration. They are:

- Crypto Access Control List (ACL)
- Transform Set
- ISAKMP Policy
- Crypto Map

Crypto Access Control List (ACL)

As described in the IP Access Control Lists chapter of this guide, ACLs on the system define rules, usually permissions, for handling subscriber data packets that meet certain criteria. Crypto ACLs, however, define the criteria that must be met in order for a subscriber data packet to be routed over an IPSec tunnel.

Unlike other ACLs that are applied to interfaces, contexts, or one or more subscribers, crypto ACLs are matched with crypto maps. In addition, crypto ACLs contain only a single rule while other ACL types can consist of multiple rules.

Prior to routing, the system examines the properties of each subscriber data packet. If the packet properties match the criteria specified in the crypto ACL, the system will initiate the IPSec policy dictated by the crypto map.

Transform Set

Transform Sets are used to define IPSec security associations (SAs). IPSec SAs specify the IPSec protocols to use to protect packets.

Transform sets are used during Phase 2 of IPSec establishment. In this phase, the system and a peer security gateway negotiate one or more transform sets (IPSec SAs) containing the rules for protecting packets. This negotiation ensures that both peers can properly protect and process the packets.

ISAKMP Policy

Internet Security Association Key Management Protocol (ISAKMP) policies are used to define Internet Key Exchange (IKE) SAs. The IKE SAs dictate the shared security parameters (i.e. which encryption parameters to use, how to authenticate the remote peer, etc.) between the system and a peer security gateway.

During Phase 1 of IPSec establishment, the system and a peer security gateway negotiate IKE SAs. These SAs are used to protect subsequent communications between the peers including the IPSec SA negotiation process.

Crypto Map

Crypto Maps define the tunnel policies that determine how IPSec is implemented for subscriber data packets.
There are three types of crypto maps supported by the system. They are:

- Manual crypto maps
- ISAKMP crypto maps
- Dynamic crypto maps

Manual Crypto Maps

These are static tunnels that use pre-configured information (including security keys) for establishment. Because they rely on statically configured information, once created, the tunnels never expire; they exist until their configuration is deleted.

Manual crypto maps define the peer security gateway to establish a tunnel with, the security keys to use to establish the tunnel, and the IPSec SA to be used to protect data sent/received over the tunnel. Additionally, manual crypto maps are applied to specific system interfaces.

IMPORTANT:

Because manual crypto map configurations require the use of static security keys (associations), they are not as secure as crypto maps that rely on dynamically configured keys. Therefore, it is recommended that they only be configured and used for testing purposes.

ISAKMP Crypto Maps

These tunnels are similar to manual crypto maps in that they require some statically configured information such as the IP address of a peer security gateway and that they are applied to specific system interfaces.

However, ISAKMP crypto maps offer greater security because they rely on dynamically generated security associations through the use of the Internet Key Exchange (IKE) protocol.

When ISAKMP crypto maps are used, the system uses the pre-shared key configured for map as part of the Diffie-Hellman (D-H) exchange with the peer security gateway to initiate Phase 1 of the establishment process. Once the exchange is complete, the system and the security gateway dynamically negotiate IKE SAs to complete Phase 1. In Phase 2, the two peers dynamically negotiate the IPSec SAs used to determine how data traversing the tunnel will be protected.

Dynamic Crypto Maps

These tunnels are used for protecting L2TP-encapsulated data between the system and an LNS/security gateway or Mobile IP data between an FA service configured on one system and an HA service configured on another.

The system determines when to implement IPSec for L2TP-encapsulated data either through attributes returned upon successful authentication for attribute based tunneling, or through the configuration of the LAC service used for compulsory tunneling.

The system determines when to implement IPSec for Mobile IP based on RADIUS attribute values as well as the configurations of the FA and HA service(s).

Implementing IPSec for PDN Access Applications

This section provides information on the following topics:

- How the IPSec-based PDN Access Configuration Works
- Configuring IPSec Support for PDN Access

In covering these topics, this section assumes that ISAKMP crypto maps are configured/used as opposed to manual crypto maps.

How the IPSec-based PDN Access Configuration Works

The following figure and the text that follows describe how sessions accessing a PDN using IPSec are processed by the system.
Figure 2. IPSec PDN Access Processing
Table 1. IPSec PDN Access Processing

Step | Description
--- | ---
1. | A subscriber session or PDP context Request, in GGSN service, arrives at the system.
2. | The system processes the subscriber session or request as it would typically.
3. | Prior to routing the session packets, the system compares them against configured Access Control Lists (ACLs).
4. | The system determines that the packet matches the criteria of an ACL that is associated with a configured crypto map.
5. | From the crypto map, the system determines the following: The map type, in this case ISAKMP The pre-shared key used to initiate the Internet Key Exchange (IKE) and the IKE negotiation mode The IP address of the security gateway Whether perfect forward secrecy (PFS) should be enabled for the IPSec SA and if so, what group should be used IPSec SA lifetime parameters The name of a configured transform set defining the IPSec SA
6. | To initiate the IKE SA negotiation, the system performs a Diffie-Hellman exchange of the pre-shared key specified in the crypto map with the specified peer security gateway.
7. | The system and the security gateway negotiate an ISAKMP policy (IKE SA) to use to protect further communications.
8. | Once the IKE SA has been negotiated, the system negotiates an IPSec SA with the security gateway using the transform method specified in the transform sets.
9. | Once the IPSec SA has been negotiated, the system protects the data according to the IPSec SAs established during step 8 and sends it over the IPSec tunnel.

### Configuring IPSec Support for PDN Access

This section provides a list of the steps required to configure IPSec functionality on the system in support of PDN access. Each step listed refers to a different section containing the specific instructions for completing the required procedure.

IMPORTANT:

These instructions assume that the system was previously configured to support subscriber data sessions either as a core service or an HA. In addition, parameters configured using this procedure must be configured in the same destination context on the system.

1. Configure one or more IP access control lists (ACLs) according to the information and instructions located in IP Access Control Lists chapter of this guide.
2. Configure one or more transform sets according to the instructions located in the Transform Set Configuration section of this chapter.
3. Configure one or more ISAKMP policies according to the instructions located in the ISAKMP Policy Configuration section of this chapter.
4. Configure an ipsec-isakmp crypto map according to the instructions located in the ISAKMP Crypto Map Configuration section of this chapter.
5. Apply the crypto map to an interface on the system according to the instructions located in the Crypto Map and Interface Association section of this chapter.
6. Save your configuration to flash memory, an external memory device, and/or a network location using the Exec mode command save configuration. For additional information on how to verify and save configuration files, refer to the System Administration Guide and the Command Line Interface Reference.

Implementing IPSec for Mobile IP Applications

This section provides information on the following topics:

- How the IPSec-based Mobile IP Configuration Works
- Configuring IPSec Support for Mobile IP

How the IPSec-based Mobile IP Configuration Works

The following figure and the text that follows describe how Mobile IP sessions using IPSec are processed by the system.
Figure 3. IPSec-based Mobile IP Session Processing
Table 2. IPSec-based Mobile IP Session Processing

Step | Description
--- | ---
1. | FA service receives a Mobile IP registration request from the mobile node.
2. | FA sends an Access-Request to the FAAA server with the 3GPP2-IKE-Secret-Request attribute equal to yes.
3. | The FAAA proxies the request to the HAAA.
4. | The HAAA returns an Access-Accept message including the following attributes: 3GPP2-Security-Level set to 3 for IPSec tunnels and registration messages 3GPP2-MIP-HA-Address indicating the IP address of the HA that the FA is to communicate with. 3GPP2-KeyId providing an identification number for the IKE secret (alternatively, the keys may be statically configured for the FA and/or HA) 3GPP2-IKE-Secret indicating the pre-shared secret to use to negotiate the IKE SA
5. | The FAAA passes the accept message to the FA with all of the attributes.
6. | The FA determines if an IPSec SA already exists based on the HA address supplied. If so, that SA will be used. If not, a new IPSec SA will be negotiated.
7. | The FA determines the appropriate crypto map to use for IPSec protection based on the HA address attribute. It does this by comparing the address received to those configured using the isakmp peer-ha command. From the crypto map, the system determines the following: The map type, in this case dynamic Whether perfect forward secrecy (PFS) should be enabled for the IPSec SA and if so, what group should be used IPSec SA lifetime parameters The name of one or more configured transform set defining the IPSec SA
8. | To initiate the IKE SA negotiation, the FA performs a Diffie-Hellman (D-H) exchange of the ISAKMP secret specified in the IKE secret attribute with the peer HA dictated by the HA address attribute. Included in the exchange is the Key ID received from the HAAA.
9. | Upon receiving the exchange, the HA sends an access request to the HAAA with the following attributes: 3GPP2-S-Request (note that this attribute is not used if the IPSec keys are statically configured) 3GPP2-User-name (the username specified is the IP addresses of the FA and HA). The password used in the access request is the RADIUS shared secret.
10. | The HAAA returns an Access-Accept message to the HA with the following attributes: 3GPP2-S indicating the “S” secret used to generate the HA’s response to the D-H exchange 3GPP2-S-Lifetime indicating the length of time that the “S” secret is valid 3GPP2-Security-Level set to 3 for IPSec tunnels and registration messages (optional)
11. | The HA determines the appropriate crypto map to use for IPSec protection based on the FA’s address. It does this by comparing the address received to those configured using the isakmp peer-fa command. From the crypto map, the system determines the following: The map type, in this case dynamic Whether perfect forward secrecy (PFS) should be enabled for the IPSec SA and if so, what group should be used IPSec SA lifetime parameters The name of one or more configured transform set defining the IPSec SA
12. | The HA creates a response to the D-H exchange using the “S” secret and the Key ID sent by the FA.
13. | The HA sends IKE SA negotiation D-H exchange response to the FA.
14. | The FA and the HA negotiate an ISAKMP (IKE) policy to use to protect further communications.
15. | Once the IKE SA has been negotiated, the system negotiates an IPSec SA with the security gateway using the transform method specified in the transform sets.
16. | Once the IPSec SA has been negotiated, the system protects the data according to the IPSec SAs established during step 15 and sends it over the IPSec tunnel.

IMPORTANT:

Once an IPSec tunnel is established between an FA and HA for a particular subscriber, all new Mobile IP sessions using the same FA and HA are passed over the tunnel regardless of whether or not IPSec is supported for the new subscriber sessions. Data for existing Mobile IP sessions is unaffected.

### Configuring IPSec Support for Mobile IP

This section provides a list of the steps required to configure IPSec functionality on the system in support of Mobile IP. Each step listed refers to a different section containing the specific instructions for completing the required procedure.

IMPORTANT:

These instructions assume that the systems were previously configured to support subscriber data sessions either as an FA or an HA.

1. Configure one or more transform sets for the FA system according to the instructions located in the Transform Set Configuration section of this chapter. The transform set(s) must be configured in the same context as the FA service.
2. Configure one or more ISAKMP policies or the FA system according to the instructions located in the ISAKMP Policy Configuration section of this chapter. The ISAKMP policy(ies) must be configured in the same context as the FA service.
3. Configure an ipsec-isakmp crypto map or the FA system according to the instructions located in the Dynamic Crypto Map Configuration section of this chapter. The crypto map(s) must be configured in the same context as the FA service.
4. Optional. Configure DPD for the FA to help prevent IPSec tunnel state mismatches between the FA and HA according to the instructions located in the Dead Peer Detection (DPD) Configuration section of this chapter.

   IMPORTANT:

   Though the use of DPD is optional, it is recommended in order to ensure service availability.
5. Configure the FA Service or the FA system according to the instructions located in the FA Services Configuration to Support IPSec section of this chapter.
6. Configure one or more transform sets for the HA system according to the instructions located in the Transform Set Configuration section of this chapter. The transform set(s) must be configured in the same context as the HA service.
7. Configure one or more ISAKMP policies or the HA system according to the instructions located in the ISAKMP Policy Configuration section of this chapter. The ISAKMP policy(ies) must be configured in the same context as the HA service.
8. Configure an ipsec-isakmp crypto map or the HA system according to the instructions located in the Dynamic Crypto Map Configuration section of this chapter. The crypto map(s) must be configured in the same context as the HA service.
9. Optional. Configure DPD for the HA to help prevent IPSec tunnel state mismatches between the FA and HA according to the instructions located in the Dead Peer Detection (DPD) Configuration section of this chapter.

   IMPORTANT:

   Though the use of DPD is optional, it is recommended in order to ensure service availability.
10. Configure the HA Service or the HA system according to the instructions located in the section of this chapter.
11. Configure the required attributes for RADIUS-based subscribers according to the information located in the RADIUS Attributes for IPSec-based Mobile IP Applications section of this chapter.
12. Save your configuration to flash memory, an external memory device, and/or a network location using the Exec mode command save configuration. For additional information on how to verify and save configuration files, refer to the System Administration Guide and the Command Line Interface Reference.

Implementing IPSec for L2TP Applications

This section provides information on the following topics:

- How IPSec is Used for Attribute-based L2TP Configurations
- Configuring Support for L2TP Attribute-based Tunneling with IPSec
- How IPSec is Used for PDSN Compulsory L2TP Configurations
- Configuring Support for L2TP PDSN Compulsory Tunneling with IPSec
- How IPSec is Used for L2TP Configurations on the GGSN
- Configuring GGSN Support for L2TP Tunneling with IPSec

How IPSec is Used for Attribute-based L2TP Configurations

The following figure and the text that follows describe how IPSec-encrypted attribute-based L2TP sessions are processed by the system.
Figure 4. Attribute-based L2TP, IPSec-Encrypted Session Processing
Table 3. Attribute-based L2TP, IPSec-Encrypted Session Processing

Step | Description
--- | ---
1. | A subscriber session arrives at the system.
2. | The system attempts to authenticate the subscriber with the AAA server.
3. | The profile attributes returned upon successful authentication by the AAA server indicate that session data is to be tunneled using L2TP. In addition, attributes specifying a crypto map name and ISAKMP secret are also supplied indicating that IP security is also required.
4. | The system determines that the crypto map name supplied matches a configured crypto map.
5. | From the crypto map, the system determines the following: The map type, in this case dynamic Whether perfect forward secrecy (PFS) should be enabled for the IPSec SA and if so, what group should be used IPSec SA lifetime parameters The name of one or more configured transform set defining the IPSec SA
6. | To initiate the IKE SA negotiation, the system performs a Diffie-Hellman exchange of the ISAKMP secret specified in the profile attribute with the specified peer LNS/security gateway.
7. | The system and the LNS/security gateway negotiate an ISAKMP (IKE) policy to use to protect further communications.
8. | Once the IKE SA has been negotiated, the system negotiates an IPSec SA with the LNS/security gateway using the transform method specified in the transform sets.
9. | Once the IPSec SA has been negotiated, the system protects the L2TP encapsulated data according to the IPSec SAs established during step 9 and sends it over the IPSec tunnel.

### Configuring Support for L2TP Attribute-based Tunneling with IPSec

This section provides a list of the steps required to configure IPSec functionality on the system in support of attribute-based L2TP tunneling. Each step listed refers to a different section containing the specific instructions for completing the required procedure.

IMPORTANT:

These instructions assume that the system was previously configured to support subscriber data sessions and L2TP tunneling either as a PDSN or an HA. In addition, with the exception of subscriber attributes, all other parameters configured using this procedure must be configured in the same destination context on the system as the LAC service.

1. Configure one or more transform sets according to the instructions located in the Transform Set Configuration section of this chapter.
2. Configure one or more ISAKMP policies according to the instructions located in the ISAKMP Policy Configuration section of this chapter.
3. Configure an ipsec-isakmp crypto map according to the instructions located in the Dynamic Crypto Map Configuration section of this chapter.
4. Configure the subscriber profile attributes according to the instructions located in the Subscriber Attributes for L2TP Application IPSec Support section of this chapter.
5. Save your configuration to flash memory, an external memory device, and/or a network location using the Exec mode command save configuration. For additional information on how to verify and save configuration files, refer to the System Administration Guide and the Command Line Interface Reference.

How IPSec is Used for PDSN Compulsory L2TP Configurations

The following figure and the text that follows describe how IPSec-encrypted PDSN compulsory L2TP sessions are processed by the system.
Figure 5. PDSN Compulsory L2TP, IPSec-Encrypted Session Processing
Table 4. PDSN Compulsory L2TP, IPSec-Encrypted Session Processing

Step | Description
--- | ---
1. | A subscriber session arrives at a PDSN service on the system that is configured to perform compulsory tunneling. The system uses the LAC service specified in the PDSN service’s configuration.
2. | The LAC service dictates the peer LNS to use and also specifies the following parameters indicating that IP security is also required: Crypto map name ISAKMP secret
3. | The system determines that the crypto map name supplied matches a configured crypto map.
4. | From the crypto map, the system determines the following: The map type, in this case dynamic Whether perfect forward secrecy (PFS) should be enabled for the IPSec SA and if so, what group should be used IPSec SA lifetime parameters The name of one or more configured transform set defining the IPSec SA
5. | To initiate the IKE SA negotiation, the system performs a Diffie-Hellman exchange of the ISAKMP secret specified by the attribute with the specified peer LNS/security gateway.
6. | The system and the LNS/security gateway negotiate an ISAKMP policy (IKE SA) to use to protect further communications.
7. | Once the IKE SA has been negotiated, the system negotiates an IPSec SA with the LNS/security gateway.
8. | Once the IPSec SA has been negotiated, the system protects the L2TP encapsulated data according to the rules specified in the transform set and sends it over the IPSec tunnel.

### Configuring Support for L2TP PDSN Compulsory Tunneling with IPSec

This section provides a list of the steps required to configure IPSec functionality on the system in support of PDSN compulsory L2TP tunneling. Each step listed refers to a different section containing the specific instructions for completing the required procedure.

IMPORTANT:

These instructions assume that the system was previously configured to support PDSN compulsory tunneling subscriber data sessions. In addition, all parameters configured using this procedure must be configured in the same destination context on the system as the LAC service.

1. Configure one or more transform sets according to the instructions located in the Transform Set Configuration section of this chapter.
2. Configure one or more ISAKMP policies according to the instructions located in the ISAKMP Policy Configuration section of this chapter.
3. Configure an ipsec-isakmp crypto map according to the instructions located in the Dynamic Crypto Map Configuration section of this chapter.
4. Configure the subscriber profile attributes according to the instructions located in the Subscriber Attributes for L2TP Application IPSec Support section of this chapter.
5. Save your configuration to flash memory, an external memory device, and/or a network location using the Exec mode command save configuration. For additional information on how to verify and save configuration files, refer to the System Administration Guide and the Command Line Interface Reference.

How IPSec is Used for L2TP Configurations on the GGSN

The following figure and the text that follows describe how IPSec-encrypted attribute-based L2TP sessions are processed by the system.
Figure 6. GGSN PDP Context Processing with IPSec-Encrypted L2TP
Table 5. GGSN PDP Context Processing with IPSec-Encrypted L2TP

Step | Description
--- | ---
1. | A subscriber session/PDP Context Request arrives at the system.
2. | The configuration of the APN accessed by the subscriber indicates that session data is to be tunneled using L2TP. In addition, attributes specifying a crypto map name and ISAKMP secret are also supplied indicating that IP security is also required.
3. | The system determines that the crypto map name supplied matches a configured crypto map.
4. | From the crypto map, the system determines the following: The map type, in this case dynamic Whether perfect forward secrecy (PFS) should be enabled for the IPSec SA and if so, what group should be used IPSec SA lifetime parameters The name of one or more configured transform set defining the IPSec SA
5. | To initiate the IKE SA negotiation, the system performs a Diffie-Hellman exchange of the ISAKMP secret specified in the profile attribute with the specified peer LNS/security gateway.
6. | The system and the LNS/security gateway negotiate an ISAKMP (IKE) policy to use to protect further communications.
7. | Once the IKE SA has been negotiated, the system negotiates an IPSec SA with the LNS/security gateway using the transform method specified in the transform sets.
8. | Once the IPSec SA has been negotiated, the system protects the L2TP encapsulated data according to the IPSec SAs established during step 9 and sends it over the IPSec tunnel.

### Configuring GGSN Support for L2TP Tunneling with IPSec

This section provides a list of the steps required to configure the GGSN to encrypt L2TP tunnels using IPSEC. Each step listed refers to a different section containing the specific instructions for completing the required procedure.

IMPORTANT:

These instructions assume that the system was previously configured to support subscriber PDP contexts and L2TP tunneling either as a GGSN. In addition, all parameters configured using this procedure must be configured in the same destination context on the system as the LAC service.

1. Configure one or more transform sets according to the instructions located in the Transform Set Configuration section of this chapter.
2. Configure one or more ISAKMP policies according to the instructions located in the ISAKMP Policy Configuration section of this chapter.
3. Configure an ipsec-isakmp crypto map according to the instructions located in the Dynamic Crypto Map Configuration section of this chapter.
4. Configure APN support for encrypting L2TP tunnels using IPSec according to the instructions located in the APN Template Configuration to Support L2TP section of this chapter.
5. Save your configuration to flash memory, an external memory device, and/or a network location using the Exec mode command save configuration. For additional information on how to verify and save configuration files, refer to the System Administration Guide and the Command Line Interface Reference.

## Transform Set Configuration

This section provides instructions for configuring transform sets on the system.

IMPORTANT:

This section provides the minimum instruction set for configuring transform set on your system. For more information on commands that configure additional parameters and options, refer to the Context Configuration Mode Commands and Crypto Transform Configuration Mode chapters in the Command Line Interface Reference.

To configure the crypto transform set for IPSec:

1. Configure crypto transform set by applying the example configuration in the Configuring Transform Set section.
2. Verify your Crypto Transform Set configuration by following the steps in the Verifying the Crypto Transform Set Configuration section.
3. Save your configuration to flash memory, an external memory device, and/or a network location using the Exec mode command save configuration. For additional information on how to verify and save configuration files, refer to the System Administration Guide and the Command Line Interface Reference.

Configuring Transform Set

Use the following example to create the crypto transform set on your system:

    configure

       context <ctxt_name>

          crypto ipsec transform-set <transform_name> ah hmac { md5-96 | none |sha1-96 } esp hmac { { md5-96 | none | sha1-96 } { cipher {des-cbc | 3des-cbc | aes-cbc } | none }

             mode { transport | tunnel }

             end

Notes:

- <ctxt_name> is the system context in which you wish to create and configure the crypto transform set(s).
- <transform_name> is the name of the crypto transform set in the current context that you want to configure for IPSec configuration.
- For more information on parameters, refer to the IPSec Transform Configuration Mode Commands chapter in the Command Line Interface Reference.

### Verifying the Crypto Transform Set Configuration

These instructions are used to verify the crypto transform set(s) was/were configured.

1. Verify that your header crypto transform set configurations by entering the following command in Exec Mode in specific context:

       show crypto transform-set transform_name

   This command produces an output similar to that displayed below using the configuration of a transform set named test1.

       Transform-Set test1
       :

       AH : none

       ESP :hmac md5-96,
       3des-cbc

       Encaps Mode: TUNNEL

## ISAKMP Policy Configuration

This section provides instructions for configuring ISAKMP policies on the system. ISAKMP policy configuration is only required if the crypto map type is either ISAKMP or Dynamic.

IMPORTANT:

This section provides the minimum instruction set for configuring ISAKMP policies on the system. For more information on commands that configure additional parameters and options, refer to the Context Configuration Mode Commands and ISAKMP Configuration Mode Commands chapters in the Command Line Interface Reference.

To configure the ISAKMP policy for IPSec:

1. Configure crypto transform set by applying the example configuration in the Configuring ISAKMP Policy section.
2. Verify your ISAKMP policy configuration by following the steps in the Verifying the ISAKMP Policy Configuration section.
3. Save your configuration to flash memory, an external memory device, and/or a network location using the Exec mode command save configuration. For additional information on how to verify and save configuration files, refer to the System Administration Guide and the Command Line Interface Reference.

Configuring ISAKMP Policy

Use the following example to create the ISAKMP policy on your system:

    configure

       context <ctxt_name>

          ikev1 policy <priority>

             encryption { 3des-cbc | des-cbc }

             hash { md5 | sha1 }

             group { 1 | 2 | 3 | 4 | 5 }

             lifetime <time>

             end

Notes:

- <ctxt_name> is the system context in which you wish to create and configure the ISAKMP policy.
- <priority> dictates the order in which the ISAKMP policies are proposed when negotiating IKE SAs.
- For more information on parameters, refer to the ISAKMP Configuration Mode Commands chapter in the Command Line Interface Reference.

### Verifying the ISAKMP Policy Configuration

These instructions are used to verify the ISAKMP policy configuration.

1. Verify that your ISAKMP policy configuration by entering the following command in Exec Mode in specific context:

       show crypto isakmp policy priority

   This command produces an output similar to that displayed below that displays the configuration of an ISAKMP policy with priority 1.

       1 ISAKMP Policies
       are configured

       Priority : 1

       Authentication Method
       : preshared-key

       Lifetime : 120 seconds

       IKE group : 5

       hash : md5

       encryption : 3des-cbc

   CAUTION:

   Modification(s) to an existing ISAKMP policy configuration will not take effect until the related security association has been cleared. Refer to the clear crypto security-association command located in the Exec Mode Commands chapter of the Command Line Interface Reference for more information.

## ISAKMP Crypto Map Configuration

This section provides instructions for configuring ISAKMP crypto maps.

IMPORTANT:

This section provides the minimum instruction set for configuring ISAKMP crypto maps on the system. For more information on commands that configure additional parameters and options, refer to the Context Configuration Mode Commands and Crypto Map ISAKMP Configuration Mode chapters in the Command Line Interface Reference.

To configure the ISAKMP crypto maps for IPSec:

1. Configure ISAKMP crypto map by applying the example configuration in the Configuring ISAKMP Crypto Maps section.
2. Verify your ISAKMP crypto map configuration by following the steps in the Verifying the ISAKMP Crypto Map Configuration section.
3. Save your configuration to flash memory, an external memory device, and/or a network location using the Exec mode command save configuration. For additional information on how to verify and save configuration files, refer to the System Administration Guide and the Command Line Interface Reference.

Configuring ISAKMP Crypto Maps

Use the following example to create the ISAKMP crypto map on your system:

    configure

       context <ctxt_name>

          crypto map <map_name> ipsec-isakmp

             set peer <agw_address>

             set isakmp preshared-key <isakmp_key>

             set mode { aggressive | main }

             set pfs { group1 | group2 | group5 }

             set transform-set <transform_name>

             match address <acl_name> [ preference ]

             match crypto-group <group_name> { primary | secondary }

             end

Notes:

- <ctxt_name> is the system context in which you wish to create and configure the ISAKMP crypto maps.
- <map_name> is name by which the ISAKMP crypto map will be recognized by the system.
- <acl_name> is name of the pre-configured ACL. It is used for configurations not implementing the IPSec Tunnel Failover feature and match the crypto map to a previously defined crypto ACL. This is an optional parameter.
- <group_name> is name of the Crypto group configured in the same context. It is used for configurations using the IPSec Tunnel Failover feature. This is an optional parameter. For more information, refer to the Redundant IPSec Tunnel Fail-Over section of this chapter.
- For more information on parameters, refer to the Crypto Map ISAKMP Configuration Mode Commands chapter in the Command Line Interface Reference.

### Verifying the ISAKMP Crypto Map Configuration

These instructions are used to verify the ISAKMP crypto map configuration.

1. Verify that your ISAKMP crypto map configurations by entering the following command in Exec Mode in specific context:

       show crypto map [ tag map_name | type
       ipsec-isakmp ]

   This command produces an output similar to that displayed below that displays the configuration of a crypto map named test_map2.

       Map Name : test_map2

       ========================================

         Payload :

               crypto_acl2:
       permit tcp host 10.10.2.12 neq 35 any

         Crypto map Type
       : ISAKMP

         IKE Mode : MAIN

         IKE pre-shared key
       : 3fd32rf09svc

         Perfect Forward
       Secrecy : Group2

         Hard Lifetime :

               28800 seconds

               4608000 kilobytes

         Number of Transforms:
       1

         Transform : test1

               AH : none

               ESP: md5 3des-cbc

               Encaps mode:
       TUNNEL

         Local Gateway: Not
       Set

         Remote Gateway:
       192.168.1.1

   CAUTION:

   Modification(s) to an existing ISAKMP crypto map configuration will not take effect until the related security association has been cleared. Refer to the clear crypto security-association command located in the Exec Mode Commands chapter of the Command Line Interface Reference for more information.

## Dynamic Crypto Map Configuration

This section provides instructions for configuring dynamic crypto maps. Dynamic crypto maps should only be configured in support of L2TP or Mobile IP applications.

IMPORTANT:

This section provides the minimum instruction set for configuring dynamic crypto maps on the system. For more information on commands that configure additional parameters and options, refer to the Context Configuration Mode Commands and Crypto Map Dynamic Configuration Mode chapters in the Command Line Interface Reference.

To configure the dynamic crypto maps for IPSec:

1. Configure dynamic crypto maps by applying the example configuration in the Configuring Dynamic Crypto Maps section.
2. Verify your dynamic crypto map configuration by following the steps in the Verifying the Dynamic Crypto Map Configuration section.
3. Save your configuration to flash memory, an external memory device, and/or a network location using the Exec mode command save configuration. For additional information on how to verify and save configuration files, refer to the System Administration Guide and the Command Line Interface Reference.

Configuring Dynamic Crypto Maps

Use the following example to create the crypto transform set on your system:

    configure

       context <ctxt_name>

          crypto map <map_name> ipsec-dynamic

             set pfs { group1 | group2 | group5 }

             set transform-set <transform_name>

             end

Notes:

- <ctxt_name> is the system context in which you wish to create and configure the dynamic crypto maps.
- <map_name> is name by which the dynamic crypto map will be recognized by the system.
- For more information on parameters, refer to the Crypto Map Dynamic Configuration Mode Commands chapter in the Command Line Interface Reference.

### Verifying the Dynamic Crypto Map Configuration

These instructions are used to verify the dynamic crypto map configuration.

1. Verify that your dynamic crypto map configurations by entering the following command in Exec Mode in specific context:

       show crypto map [ tag map_name | type
       ipsec-dynamic ]

   This command produces an output similar to that displayed below using the configuration of a dynamic crypto map named test_map3.

       Map Name : test_map3

       ========================================

         Crypto map Type
       : ISAKMP (Dynamic)

         IKE Mode : MAIN

         IKE pre-shared key
       :

         Perfect Forward
       Secrecy : Group2

         Hard Lifetime :

               28800 seconds

               4608000 kilobytes

         Number of Transforms:
       1

         Transform : test1

               AH : none

               ESP: md5 3des-cbc

               Encaps mode:
       TUNNEL

         Local Gateway: Not
       Set

         Remote Gateway:
       Not Set

   CAUTION:

   Modification(s) to an existing dynamic crypto map configuration will not take effect until the related security association has been cleared. Refer to the clear crypto security-association command located in the Exec Mode Commands chapter of the Command Line Interface Reference for more information.

## Manual Crypto Map Configuration

This section provides instructions for configuring manual crypto maps on the system.

IMPORTANT:

Because manual crypto map configurations require the use of static security keys (associations), they are not as secure as crypto maps that rely on dynamically configured keys. Therefore, it is recommended that they only be configured and used for testing purposes.

IMPORTANT:

This section provides the minimum instruction set for configuring manual crypto maps on the system. For more information on commands that configure additional parameters and options, refer to the Context Configuration Mode Commands and Crypto Map Manual Configuration Mode chapters in the Command Line Interface Reference.

To configure the manual crypto maps for IPSec:

1. Configure manual crypto map by applying the example configuration in the Configuring Manual Crypto Maps section.
2. Verify your manual crypto map configuration by following the steps in the Verifying the Manual Crypto Map Configuration section.
3. Save your configuration to flash memory, an external memory device, and/or a network location using the Exec mode command save configuration. For additional information on how to verify and save configuration files, refer to the System Administration Guide and the Command Line Interface Reference.

Configuring Manual Crypto Maps

Use the following example to create the manual crypto map on your system:

    configure

       context <ctxt_name>

          crypto map <map_name> ipsec-manual

             set peer <agw_address>

             match address <acl_name> [ preference ]

             set transform-set <transform_name>

             set session-key { inbound | outbound } { ah <ah_spi> [ encrypted ] key <ah_key> | esp <esp_spi> [ encrypted ] cipher <encryption_key> [ encrypted ] authenticator <auth_key> }

             end

Notes:

- <ctxt_name> is the system context in which you wish to create and configure the manual crypto maps.
- <map_name> is name by which the manual crypto map will be recognized by the system.
- <acl_name> is name of the pre-configured ACL. It is used for configurations not implementing the IPSec Tunnel Failover feature and match the crypto map to a previously defined crypto ACL. This is an optional parameter.
- The length of the configured key must match the configured algorithm.
- <group_name> is name of the Crypto group configured in the same context. It is used for configurations using the IPSec Tunnel Failover feature. This is an optional parameter.
- For more information on parameters, refer to the Crypto Map Manual Configuration Mode Commands chapter in the Command Line Interface Reference.

### Verifying the Manual Crypto Map Configuration

These instructions are used to verify the manual crypto map configuration.

1. Verify that your manual crypto map configurations by entering the following command in Exec Mode in specific context:

       show crypto map [ tag map_name | type
       ipsec-manual ]

   This command produces an output similar to that displayed below that displays the configuration of a crypto map named test_map.

       Map Name : test_map

       ========================================

         Payload :

               crypto_acl1:
       permit tcp host 1.2.3.4 gt 30 any

         Crypto map Type
       : manual(static)

         Transform : test1

               Encaps mode:
       TUNNEL

         Transmit Flow

               Protocol :
       ESP

               SPI : 0x102
       (258)

               Hmac : md5,
       key: 23d32d23cs89

               Cipher : 3des-cbc,
       key: 1234asd3c3d

         Receive Flow

               Protocol :
       ESP

               SPI : 0x101
       (257)
             Hmac : md5, key: 008j90u3rjp

               Cipher : 3des-cbc,
       key: sdfsdfasdf342d32

         Local Gateway: Not
       Set

         Remote Gateway:
       192.168.1.40

   CAUTION:

   Modification(s) to an existing manual crypto map configuration will not take effect until the related security association has been cleared. Refer to the clear crypto security-association command located in the Exec Mode Commands chapter of the Command Line Interface Reference for more information.

## Crypto Map and Interface Association

This section provides instructions for applying manual or ISAKMP crypto maps to interfaces configured on the system. Dynamic crypto maps should not be applied to interfaces.

IMPORTANT:

This section provides the minimum instruction set for applying manual or ISAKMP crypto maps to an interface on the system. For more information on commands that configure additional parameters and options, refer to the Command Line Interface Reference.

To apply the crypto maps to an interface:

1. Configure a manual or ISAKMP crypto map by applying the example configuration in any of the following sections:
2. Apply desired crypto map to system interface by following the steps in the Applying Crypto Map to an Interface section
3. Verify your manual crypto map configuration by following the steps in the Verifying the Interface Configuration with Crypto Map section.
4. Save your configuration to flash memory, an external memory device, and/or a network location using the Exec mode command save configuration. For additional information on how to verify and save configuration files, refer to the System Administration Guide and the Command Line Interface Reference.

Applying Crypto Map to an Interface

Use the following example to apply an existing crypto map to an interface on your system:

    configure

       context <ctxt_name>

          interface <interface_name>

          crypto-map <map_name>

          end

Notes:

- <ctxt_name> is the system context in which the interface is configured to apply crypto map.
- <interface_name> is the name of a specific interface configured in the context to which the crypto map will be applied.
- <map_name> is name of the preconfigured ISAKMP or a manual crypto map.

### Verifying the Interface Configuration with Crypto Map

These instructions are used to verify the interface configuration with crypto map.

1. Verify that your interface is configured properly with crypto map by entering the following command in Exec Mode in specific context:

       show configuration context ctxt_name | grep interface

   The interface configuration aspect of the display should look similar to that shown below. In this example an interface named 20/6 was configured with a crypto map called isakmp_map1.

       interface 20/6

       ip address 192.168.4.10 255.255.255.0

              crypto-map isakmp_map1

## FA Services Configuration to Support IPSec

This section provides instructions for configuring FA services to support IPSec.

These instructions assume that the FA service was previously configured and system is ready to serve as an FA.

IMPORTANT:

This section provides the minimum instruction set for configuring an FA service to support IPSec on the system. For more information on commands that configure additional parameters and options, refer to the Command Line Interface Reference.

To configure the FA service to support IPSec:

1. Modify FA service configuration by following the steps in the Modifying FA service to Support IPSec section
2. Verify your FA service configuration by following the steps in the Verifying the FA Service Configuration with IPSec section.
3. Save your configuration to flash memory, an external memory device, and/or a network location using the Exec mode command save configuration. For additional information on how to verify and save configuration files, refer to the System Administration Guide and the Command Line Interface Reference.

Modifying FA service to Support IPSec

Use the following example to modify FA service to support IPSec on your system:

    configure

       context <ctxt_name>

          fa-service <fa_svc_name>

             isakmp peer-ha <ha_address> crypto-map <map_name> [ secret <preshared_secret> ]

             isakmp default crypto-map <map_name> [ secret <preshared_secret> ]

             end

Notes:

- <ctxt_name> is the system context in which the FA service is configured to support IPSec.
- <fa_svc_name> is name of the FA service for which you are configuring IPSec.
- <ha_address> is IP address of the HA service to which FA service will communicate on IPSec.
- <map_name> is name of the preconfigured ISAKMP or a manual crypto map.
- A default crypto map for the FA service to be used in the event that the AAA server returns an HA address that is not configured as an ISAKMP peer HA.
- For maximum security, the default crypto map should be configured in addition to peer-ha crypto maps instead of being used to provide IPSec SAs to all HAs. Note that once an IPSec tunnel is established between the FA and HA for a particular subscriber, all new Mobile IP sessions using the same FA and HA are passed over the tunnel regardless of whether or not IPSec is supported for the new subscriber sessions. Data for existing Mobile IP sessions is unaffected.

### Verifying the FA Service Configuration with IPSec

These instructions are used to verify the FA service to support IPSec.

1. Verify that your FA service is configured properly with IPSec by entering the following command in Exec Mode in specific context:

       show fa-service { name service_name | all }

   The output of this command is a concise listing of FA service parameter settings configured on the system.

## HA Service Configuration to Support IPSec

This section provides instructions for configuring HA services to support IPSec.

These instructions assume that the HA service was previously configured and system is ready to serve as an HA.

IMPORTANT:

This section provides the minimum instruction set for configuring an HA service to support IPSec on the system. For more information on commands that configure additional parameters and options, refer to the Command Line Interface Reference.

To configure the HA service to support IPSec:

1. Modify HA service configuration by following the steps in the Modifying HA service to Support IPSec section
2. Verify your HA service configuration by following the steps in the Verifying the HA Service Configuration with IPSec section.
3. Save your configuration to flash memory, an external memory device, and/or a network location using the Exec mode command save configuration. For additional information on how to verify and save configuration files, refer to the System Administration Guide and the Command Line Interface Reference.

Modifying HA service to Support IPSec

Use the following example to modify an existing HA service to support IPSec on your system:

    configure

       context <ctxt_name>

          ha-service <ha_svc_name>

             isakmp aaa-context <aaa_ctxt_name>

             isakmp peer-fa <fa_address>
    crypto-map <map_name> [ secret <preshared_secret> ]

             end

Notes:

- <ctxt_name> is the system context in which the FA service is configured to support IPSec.
- <ha_svc_name> is name of the HA service for which you are configuring IPSec.
- <fa_address> is IP address of the FA service to which HA service will communicate on IPSec.
- <aaa_ctxt_name> name of the context through which the HA service accesses the HAAA server to fetch the IKE S Key and S Lifetime parameters.
- <map_name> is name of the preconfigured ISAKMP or a manual crypot map.

### Verifying the HA Service Configuration with IPSec

These instructions are used to verify the HA service to support IPSec.

1. Verify that your HA service is configured properly with IPSec by entering the following command in Exec Mode in specific context:

       show ha-service { name service_name | all }

   The output of this command is a concise listing of HA service parameter settings configured on the system.

RADIUS Attributes for IPSec-based Mobile IP Applications

As described in the How the IPSec-based Mobile IP Configuration Works section of this chapter, the system uses attributes stored in a subscriber’s RADIUS profile to determine how IPSec should be implemented.
The table below lists the attributes that must be configured in the subscriber’s RADIUS attributes to support IPSec for Mobile IP. These attributes are contained in the following dictionaries:

- 3GPP2
- 3GPP2-835
- Starent
- Starent-835
- Starent-VSA1
- Starent-VSA1-835

Table 6. Attributes Used for Mobile IP IPSec Support

Attribute | Description | Variable
--- | --- | ---
3GPP2-Security-Level | This attribute indicates the type of security that the home network mandates on the visited network. | Integer value: 3 : Enables IPSec for tunnels and registration messages 4 : Disables IPSec
3GPP2 -KeyId | This attribute contains the opaque IKE Key Identifier for the FA/HA shared IKE secret. | Supported value for the first eight bytes is the network-order FA IP address in hexadecimal characters. Supported value for the next eight bytes is the network-order HA IP address in hexadecimal characters. Supported value for the final four bytes is a timestamp in network order, indicating when the key was created, and is the number of seconds since January 1, 1970, UTC.
3GPP2-IKE-Secret | This attribute contains the FA/HA shared secret for the IKE protocol. This attribute is salt-encrypted. | A binary string of 1 to 127 bytes.
3GPP2-S | This attribute contains the 'S' secret parameter used to make the IKE pre-shared secret. | A binary string of the value of 'S' consisting of 1 to 127 characters.
3GPP2- S-Lifetime | This attribute contains the lifetime of the 'S' secret parameter used to make the IKE pre-shared secret. | An integer in network order, indicating the time in seconds since January 1, 1970 00:00 UTC. Note that this is equivalent to the Unix operating system expression of time.

## LAC Service Configuration to Support IPSec

This section provides instructions for configuring LAC services to support IPSec.

IMPORTANT:

These instructions are required for compulsory tunneling. They should only be performed for attribute-based tunneling if the Tunnel-Service-Endpoint, the SN1-Tunnel-ISAKMP-Crypto-Map, or the SN1 -Tunnel-ISAKMP-Secret are not configured in the subscriber profile.

These instructions assume that the LAC service was previously configured and system is ready to serve as an LAC server.

IMPORTANT:

This section provides the minimum instruction set for configuring an LAC service to support IPSec on the system. For more information on commands that configure additional parameters and options, refer to the Command Line Interface Reference.

To configure the LAC service to support IPSec:

1. Modify LAC service configuration by following the steps in the Modifying LAC service to Support IPSec section.
2. Verify your LAC service configuration by following the steps in the Verifying the LAC Service Configuration with IPSec section.
3. Save your configuration to flash memory, an external memory device, and/or a network location using the Exec mode command save configuration. For additional information on how to verify and save configuration files, refer to the System Administration Guide and the Command Line Interface Reference.

Modifying LAC service to Support IPSec

Use the following example to modify an existing LAC service to support IPSec on your system:

    configure

       context <ctxt_name>

          lac-service <lac_svc_name>

             peer-lns <ip_address> [encrypted] secret <secret> [crypto-map <map_name> { [encrypted] isakmp-secret <secret> } ] [ description <text> ] [ preference <integer>]

             isakmp aaa-context <aaa_ctxt_name>

             isakmp
    peer-fa <fa_address> crypto-map
    <map_name> [ secret <preshared_secret> ]

             end

Notes:

- <ctxt_name> is the destination context where the LAC service is configured to support IPSec.
- <lac_svc_name> is name of the LAC service for which you are configuring IPSec.
- <lns_address> is IP address of the LNS node to which LAC service will communicate on IPSec.
- <aaa_ctxt_name> name of the context through which the HA service accesses the HAAA server to fetch the IKE S Key and S Lifetime parameters.
- <map_name> is name of the preconfigured ISAKMP or a manual crypot map.

### Verifying the LAC Service Configuration with IPSec

These instructions are used to verify the LAC service to support IPSec.

1. Verify that your LAC service is configured properly with IPSec by entering the following command in Exec Mode in specific context:

       show lac-service nameservice_name

   The output of this command is a concise listing of LAC service parameter settings configured on the system.

Subscriber Attributes for L2TP Application IPSec Support

In addition to the subscriber profile attributes listed in the RADIUS and Subscriber Profile Attributes Used section of the L2TP Access Concentrator chapter in this guide, the table below lists the attributes required to support IPSec for use with attribute-based L2TP tunneling.
These attributes are contained in the following dictionaries:

- Starent
- Starent-835

Table 7. Subscriber Attributes for IPSec encrypted L2TP Support

RADIUS Attribute | Local SubscriberAttribute | Description | Variable
--- | --- | --- | ---
SN1-Tunnel-ISAKMP- Crypto-Map | tunnel l2tp crypto-map | The name of a crypto map configured on the system. | A salt-encrypted ascii string specifying the crypto-map to use for this subscriber. It can be tagged, in which case it is treated as part of a tunnel group.
SN1 -Tunnel-ISAKMP- Secret | tunnel l2tp crypto-map isakmp-secret | The pre-shared secret that will be used as part of the D-H exchange to negotiate an IKE SA. | A salt-encrypted string specifying the IKE secret. It can be tagged, in which case it is treated as part of a tunnel group.

## PDSN Service Configuration for L2TP Support

PDSN service configuration is required for compulsory tunneling and optional for attribute-based tunneling.

For attribute-based tunneling, a configuration error could occur such that upon successful authentication, the system determines that the subscriber session requires L2TP but can not determine the name of the context in which the appropriate LAC service is configured from the attributes supplied. As a precautionary, a parameter has been added to the PDSN service configuration options that will dictate the name of the context to use. It is strongly recommended that this parameter be configured.

This section contains instructions for modifying the PDSN service configuration for either compulsory or attribute-based tunneling.

These instructions assume that the PDSN service was previously configured and system is ready to serve as a PDSN.

This section provides the minimum instruction set for configuring an L2TP service on the PDSN system. For more information on commands that configure additional parameters and options, refer to the Command Line Interface Reference.

To configure the PDSN service to support L2TP:

1. Modify PDSN service to configure compulsory tunneling or attribute-based tunneling by applying the example configuration in any of the following sections:
   - Modifying PDSN service to Support Attribute-based L2TP Tunneling
   - Modifying PDSN service to Support Compulsory L2TP Tunneling
2. Verify your LAC service configuration by following the steps in the Verifying the PDSN Service Configuration for L2TP section.
3. Save your configuration to flash memory, an external memory device, and/or a network location using the Exec mode command save configuration. For additional information on how to verify and save configuration files, refer to the System Administration Guide and the Command Line Interface Reference.

Modifying PDSN service to Support Attribute-based L2TP Tunneling

Use the following example to modify an existing PDSN service to support attribute-based L2TP tunneling on your system:

    configure

       context <ctxt_name>

          pdsn-service <pdsn_svc_name>

             ppp
    tunnel-context <lac_ctxt_name>

             end

Notes:

- <ctxt_name> is the destination context where the PDSN service is configured.
- <pdsn_svc_name> is name of the PDSN service for which you are configuring attribute-based L2TP tunneling.
- <lac_ctxt_name> is the name of the destination context where the LAC service is located.

Modifying PDSN service to Support Compulsory L2TP Tunneling

Use the following example to modify an existing PDSN service to support compulsory L2TP tunneling on your system:

    configure

       context <ctxt_name>

          pdsn-service <pdsn_svc_name>

             ppp tunnel-context <lac_ctxt_name>

             ppp tunnel-type l2tp

             end

Notes:

- <ctxt_name> is the destination context where the PDSN service is configured.
- <pdsn_svc_name> is name of the PDSN service for which you are configuring attribute-based L2TP tunneling.
- <lac_ctxt_name> is name of the destination context where the LAC service is located.

### Verifying the PDSN Service Configuration for L2TP

These instructions are used to verify the PDSN service to support L2TP.

1. Verify that your PDSN service is configured properly with L2TP by entering the following command in Exec Mode in specific context:

       show pdsn-service name service_name

   The output of this command is a concise listing of PDSN service parameter settings configured on the system.

Redundant IPSec Tunnel Fail-Over

The Redundant IPSec Tunnel Fail-Over functionality is included with the IPSec feature license and allows the configuration of a secondary ISAKMP crypto map-based IPSec tunnel over which traffic is routed in the event that the primary ISAKMP crypto map-based tunnel cannot be used.

This feature introduces the concept of crypto (tunnel) groups when using IPSec tunnels for access to packet data networks (PDNs). A crypto group consists of two configured ISAKMP crypto maps. Each crypto map defines the IPSec policy for a tunnel. In the crypto group, one tunnel serves as the primary, the other as the secondary (redundant). Note that the method in which the system determines to encrypt user data in an IPSec tunnel remains unchanged.

Group tunnels are perpetually maintained with IPSec Dead Peer Detection (DPD) packets exchanged with the peer security gateway.

IMPORTANT:

The peer security gateway must support RFC 3706 in order for this functionality to function properly.

When the system determines that incoming user data traffic must be routed over one of the tunnels in a group, the system automatically uses the primary tunnel until either the peer is unreachable (the IPSec DPD packets cease), or the IPSec tunnel fails to re-key. If the primary peer becomes unreachable, the system automatically begins to switch user traffic to the secondary tunnel. The system can be configured to either automatically switch user traffic back to the primary tunnel once the corresponding peer security gateway is reachable and the tunnel is configured, or require manual intervention to do so.
This functionality also supports the generation of Simple network Management Protocol (SNMP) notifications indicating the following conditions:

- Primary Tunnel is down: A primary tunnel that was previously "up" is now "down" representing an error condition.
- Primary Tunnel is up: A primary tunnel that was previously "down" is now "up".
- Secondary tunnel is down: A secondary tunnel that was previously "up" is now "down" representing an error condition.
- Secondary Tunnel is up: A secondary tunnel that was previously "down" is now "up".
- Fail-over successful: The switchover of user traffic was successful. This is generated for both primary-to-secondary and secondary-to-primary switchovers.
- Unsuccessful fail-over: An error occurred when switching user traffic from either the primary to secondary tunnel or the secondary to primary tunnel.

Supported Standards

Support for the following standards and requests for comments (RFCs) has been added with the Redundant IPSec Tunnel Fail-over functionality:

- RFC 3706, A Traffic-Based Method of Detecting Dead Internet Key Exchange (IKE) Peers, February 2004

## Redundant IPSec Tunnel Fail-over Configuration

This section provides information and instructions for configuring the Redundant IPSec Tunnel Fail-over feature. These instructions assume that the system was previously configured to support subscriber data sessions either as a core service or an HA.

IMPORTANT:

Parameters configured using this procedure must be configured in the same context on the system.

IMPORTANT:

The system supports a maximum of 32 crypto groups per context. However, configuring crypto groups to use the same loopback interface for secondary IPSec tunnels is not recommended and may compromise redundancy on the chassis.

IMPORTANT:

This section provides the minimum instruction set for configuring crypto groups on the system. For more information on commands that configure additional parameters and options, refer Command Line Interface Reference.

To configure the Crypto group to support IPSec:

1. Configure a crypto group by following the steps in the Configuring Crypto Group section
2. Configure one or more ISAKMP policies according to the instructions provided in the ISAKMP Policy Configuration section of this chapter.
3. Configure IPSec DPD settings using the instructions provided in the Dead Peer Detection (DPD) Configuration section of this chapter.
4. Configure an ISAKMP crypto map for the primary and secondary tunnel according to the instructions provided in the ISAKMP Crypto Map Configuration section of this chapter.
5. Match the existing ISAKMP crypto map to Crypto group by following the steps in the Modify ISAKMP Crypto Map Configuration to Match Crypto Group section
6. Verify your Crypto Group configuration by following the steps in the Verifying the Crypto Group Configuration section.
7. Save your configuration to flash memory, an external memory device, and/or a network location using the Exec mode command save configuration. For additional information on how to verify and save configuration files, refer to the System Administration Guide and the Command Line Interface Reference.

Configuring Crypto Group

Use the following example to configure a crypto group on your system for redundant IPSec tunnel fail-over support:

    configure

       context <ctxt_name>

          ikev1 keepalive dpd interval <dur> timeout
    <dur> num-retry <retries>

          crypto-group <group_name>

             match address <acl_name> [ <preference> ]

             switchover auto [ do-not-revert ]

             end

Notes:

- <ctxt_name> is the destination context where the Crypto Group is to be configured.
- <group_name> is name of the Crypto group you want to configure for IPSec tunnel failover support.
- <acl_name> is name of the pre-configured crypto ACL. It is used for configurations not implementing the IPSec Tunnel Failover feature and match the crypto map to a previously defined crypto ACL. For more information on crypto ACL, refer Crypto Access Control List (ACL) section of this chapter.

Modify ISAKMP Crypto Map Configuration to Match Crypto Group

Use the following example to match the crypto group with ISAKMP crypto map on your system:

    configure

       context <ctxt_name>

          crypto map <map_name1> ipsec-isakmp

             match crypto-group <group_name> primary

             end

    configure

       context <ctxt_name>

          crypto map <map_name> ipsec-isakmp

             match crypto-group <group_name> secondary

             end

Notes:

- <ctxt_name> is the system context in which you wish to create and configure the ISAKMP crypto maps.
- <group_name> is name of the Crypto group configured in the same context for IPSec Tunnel Failover feature.
- <map_name1> is name of the preconfigured ISAKMP crypto map to match with crypto group as primary.
- <map_name2> is name of the preconfigured ISAKMP crypto map to match with crypto group as secondary.

### Verifying the Crypto Group Configuration

These instructions are used to verify the crypto group configuration.

1. Verify that your system is configured properly with crypto group by entering the following command in Exec Mode in specific context:

       show crypto group [ summary | name group_name ]

   The output of this command is a concise listing of crypto group parameter settings configured on the system.

## Dead Peer Detection (DPD) Configuration

This section provides instructions for configuring the Dead Peer Detection (DPD).

Defined by RFC 3706, Dead Peer Detection (DPD) is used to simplify the messaging required to verify communication between peers and tunnel availability.

DPD is configured at the context level and is used in support of the IPSec Tunnel Failover feature (refer to the Redundant IPSec Tunnel Fail-Over section) and/or to help prevent tunnel state mismatches between an FA and HA when IPSec is used for Mobile IP applications. When used with Mobile IP applications, DPD ensures the availability of tunnels between the FA and HA. (Note that the starIPSECDynTunUp and starIPSECDynTunDown SNMP traps are triggered to indicate tunnel state for the Mobile IP scenario.)

Regardless of the application, DPD must be supported/configured on both security peers. If the system is configured with DPD but it is communicating with a peer that does not have DPD configured, IPSec tunnels still come up. However, the only indication that the remote peer does not support DPD exists in the output of the show crypto isakmp security-associations summary command.

IMPORTANT:

If DPD is enabled while IPSec tunnels are up, it will not take affect until all of the tunnels are cleared.

IMPORTANT:

DPD must be configured in the same context on the system as other IPSec Parameters.

To configure the Crypto group to support IPSec:

1. Enable dead peer detection on system in support of the IPSec Tunnel Failover feature by following the steps in the Configuring Crypto Group section
2. Verify your Crypto Group configuration by following the steps in the Verifying the DPD Configuration section.
3. Save your configuration to flash memory, an external memory device, and/or a network location using the Exec mode command save configuration. For additional information on how to verify and save configuration files, refer to the System Administration Guide and the Command Line Interface Reference.

Configuring Crypto Group

Use the following example to configure a crypto group on your system for redundant IPSec tunnel fail-over support:

    configure

       context <ctxt_name>

          ikev1 keepalive dpd
    interval <dur> timeout <dur> num-retry <retries>

          end

Notes:

- <ctxt_name> is the destination context where the Crypto Group is to be configured.

### Verifying the DPD Configuration

These instructions are used to verify the dead peer detection configuration.

1. Verify that your system is configured properly with crypto group with DPD by entering the following command in Exec Mode in specific context:

       show crypto group [ summary | name
       group_name ]

   The output of this command is a concise listing of crypto group parameter settings configured on the system.

## APN Template Configuration to Support L2TP

This section provides instructions for adding L2TP support for APN templates configured on the system.

These instructions assume that the APN template was previously configured on this system.

IMPORTANT:

This section provides the minimum instruction set for configuring an APN template to support L2TP for APN. For more information on commands that configure additional parameters and options, refer to the Command Line Interface Reference.

To configure the APN to support L2TP:

1. Modify preconfigured APN template by following the steps in the Modifying APN Template to Support L2TP section
2. Verify your APN configuration by following the steps in the Verifying the APN Configuration for L2TP section.
3. Save your configuration to flash memory, an external memory device, and/or a network location using the Exec mode command save configuration. For additional information on how to verify and save configuration files, refer to the System Administration Guide and the Command Line Interface Reference.

Modifying APN Template to Support L2TP

Use the following example to modify APN template to support L2TP:

    configure

       context <ctxt_name>

          apn <apn_name>

             tunnel l2tp [ peer-address <lns_address> [ [ encrypted ] secret <l2tp_secret> ] [ preference <num> ] [ tunnel-context <tunnel_ctxt_name> ] [ local-address <agw_ip_address> ] [ crypto-map <map_name> { [ encrypted ] isakmp-secret <crypto_secret> } ]

             end

Notes:

- <ctxt_name> is the system context in which the APN template is configured.
- <apn_name> is name of the preconfigured APN template in which you want to configure L2TP support.
- <lns_address> is IP address of the LNS node to which this APN will communicate.
- <tunnel_ctxt_name> is the L2TP context in which the L2TP tunnel is configured.
- <agw_ip_address> is the local IP address of the GGSN in which this APN template is configured.
- <map_name> is the preconfigured crypto map (ISAKMP or manual) which is to use for L2TP.

### Verifying the APN Configuration for L2TP

These instructions are used to verify the APN template configuration for L2TP.

1. Verify that your APN is configured properly with L2TP by entering the following command in Exec Mode in specific context:

       show apn { all | name apn_name }

   The output of this command is a concise listing of FA service parameter settings configured on the system.

IPSec for LTE/SAE Networks

The Cisco MME (Mobility Management Entity), S-GW (Serving Gateway), and P-GW (Packet Data Network Gateway) support IPSec and IKEv2 encryption using IPv4 and IPv6 addressing in LTE/SAE (Long Term Evolution/System Architecture Evolution) networks. IPSec and IKEv2 encryption enables network domain security for all IP packet-switched networks, providing confidentiality, integrity, authentication, and anti-replay protection via secure IPSec tunnels.

Encryption Algorithms

IPSec for LTE/SAE supports the following control and data path encryption algorithms:

- AES-CBC-128 (Advanced Encryption Standard-Cipher Block Chaining-128)
- AES-CBC-256 (Advanced Encryption Standard-Cipher Block Chaining-256)
- DES-CBC (Data Encryption Standard-Cipher Block Chaining)
- 3DES-CBC (Triple Data Encryption Standard-Cipher Bock Chaining)

HMAC Functions

IPSec for LTE/SAE supports the following data path HMAC (Hash-based Message Authentication Code) functions:

- AES-XCBC-MAC-96 (Advanced Encryption Standard-X Cipher Block Chaining-Message Authentication Code-96)
- MD5-96 (Message Digest 5-96)
- SHA1-96 (Secure Hash Algorithm 1-96)

IPSec for LTE/SAE supports the following control path HMAC (Hash-based Message Authentication Code) functions:

- AES-XCBC-MAC-96 (Advanced Encryption Standard-X Cipher Block Chaining-Message Authentication Code-96)
- MD5-96 (Message Digest 5-96)
- SHA1-96 (Secure Hash Algorithm 1-96)
- SHA2-256-128 (Secure Hash Algorithm 2-256-128)
- SHA2-384-192 (Secure Hash Algorithm 2-384-192)
- SHA2-512-256 (Secure Hash Algorithm 2-512-256)

Diffie-Hellman Groups

IPSec for LTE/SAE supports the following Diffie-Hellman groups for IKE and Child SAs (Security Associations):

- Diffie-Hellman Group 1: 768-bit MODP (Modular Exponential) Group
- Diffie-Hellman Group 2: 1024-bit MODP Group
- Diffie-Hellman Group 5: 1536-bit MODP Group
- Diffie-Hellman Group 14: 2048-bit MODP Group
- None: No Diffie-Hellman Group (no perfect forward secrecy)

Dynamic Node-to-Node IPSec Tunnels

IPSec for LTE/SAE enables network nodes to initiate an IPSec tunnel with another node for secure signaling and data traffic between the nodes, enabling up to 64K dynamic, service-integrated IPSec tunnels per chassis. Once established, a dynamic node-to-node IPSec tunnel continues to carry all of the signaling and/or bearer traffic between the nodes. Dynamic node-to-node IPSec for LTE/SAE is supported on the S1-MME interface for signaling traffic between the eNodeB and the MME, on the S1-U interface for data traffic between the eNodeB and the S-GW, and on the S5 interface for data traffic between the S-GW and the P-GW.

Dynamic node-to-node IPSec gets configured using dynamic IKEv2 crypto templates, which are used to specify common cryptographic parameters for the IPSec tunnels such as the encryption algorithm, HMAC function, and Diffie-Hellman group. Additional information necessary for creating node-to-node IPSec tunnels such as revocation lists are fetched dynamically from the IPSec tunnel requests.

For configuration instructions for dynamic node-to-node IPSec, see the configuration chapter in the administration guides for the MME, S-GW, and P-GW.

ACL-based Node-to-Node IPSec Tunnels

Node-to-node IPSec for LTE/SAE can also be configured using crypto ACLs (Access Control Lists), which define the matching criteria used for routing subscriber data packets over an IPSec tunnel. ACL-based node-to-node IPSec tunnels are supported on the S1-MME interface for signaling traffic between the eNodeB and the MME, on the S1-U interface for data traffic between the eNodeB and the S-GW, and on the S5 interface for data traffic between the S-GW and the P-GW.

Unlike other ACLs that are applied to interfaces, contexts, or to one or more subscribers, crypto ACLs are applied via matching criteria to crypto maps, which define tunnel policies that determine how IPSec is implemented for subscriber data packets. Prior to routing, the system examines the properties of each subscriber data packet. If the packet properties match the criteria specified in the crypto ACL, the system initiates the IPSec policy dictated by the crypto map. ACL-based node-to-node IPSec tunnels are configured using either IKEv2-IPv4 or IKEv2-IPv6 crypto maps for IPv4 or IPv6 addressing.

Up to 150 ACL-based node-to-node IPSec tunnels are supported on the system, each with one SA bundle that includes one Tx and one Rx endpoint. However, to avoid significant performance degradation, dynamic node-to-node IPSec tunnels are recommended. If ACL-based node-to-node IPSec tunnels are used, a limit of about ten ACL-based node-to-node IPSec tunnels per system is recommended.

For configuration instructions for ACL-based node-to-node IPSec, see the configuration chapter in the administration guides for the MME, S-GW, and P-GW.

For more information on ACLs, see the System Administration Guide.

Traffic Selectors

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 selector payloads contain the selection criteria for packets being sent over IPSec security associations (SAs). Traffic selectors can be created on the P-GW, S-GW, and MME for dynamic node-to-node IPSec tunnels during crypto template configuration by specifying a range of peer IPv4 or IPV6 addresses from which to carry traffic over IPSec tunnels.

For example, consider an eNodeB with an IP address of 1.1.1.1 and an S-GW with a service address of 2.2.2.2. The S-GW is registered to listen for IKE requests from the eNodeBs in the network using the following information:

- Local Address: 2.2.2.2
- Peer Address Network: 1.1.0.0 Mask: 255.255.0.0
- Payload ACL (Access Control List): udp host 2.2.2.2 eq 2123 1.1.0.0 0.0.255.255

When an IKE request arrives the S-GW from eNodeB address 1.1.1.1, the IPSec subsystem converts the payload ACL to: udp host 2.2.2.2 eq 2123 host 1.1.1.1, and this payload becomes the traffic selector for the IPSec tunnel being negotiated.

To properly accommodate control traffic between IPSec nodes, each child SA must include at least two traffic selectors: one with a well-known port in the source address, and one with a well-known port in the destination address. Continuing the example above, the final traffic selectors would be:

- Destination port as well-known port: udp host 2.2.2.2 1.1.0.0 0.0.255.255 eq 2123
- Source port as well-known port: udp host 2.2.2.2 eq 2123 1.1.0.0 0.0.255.255

Note that for ACL-based node-to-node IPSec tunnels, the configured crypto ACL becomes the traffic selector with no modification.

Authentication Methods

IPSec for LTE/SAE includes the following authentication methods:

- PSK (Pre-Shared Key) Authentication: A pre-shared key is a shared secret that was previously shared between two network nodes. IPSec for LTE/SAE supports PSK such that both IPSec nodes must be configured to use the same shared secret.
- X.509 Certificate-based Peer Authentication: IPSec for LTE/SAE supports X.509 certificate-based peer authentication and CA (Certificate Authority) certificate authentication as described below.

X.509 Certificate-based Peer Authentication

X.509 specifies standard formats for public key certificates, certificate revocation lists, attribute certificates, and a certification path validation algorithm. X.509 certificates are configured on each IPSec node so that it can send the certificate as part of its IKE_AUTH_REQ for the remote node to authenticate it. These certificates can be in PEM (Privacy Enhanced Mail) or DER (Distinguished Encoding Rules) format, and can be fetched from a repository via HTTP or FTP.

CA certificate authentication is used to validate the certificate that the local node receives from a remote node during an IKE_AUTH exchange.

A maximum of sixteen certificates and sixteen CA certificates are supported per system. One certificate is supported per service, and a maximum of four CA certificates can be bound to one crypto template.

For configuration instructions for X.509 certificate-based peer authentication, see the configuration chapter in the administration guides for the MME, S-GW, and P-GW.
The figure below shows the message flow during X.509 certificate-based peer authentication. The table that follows the figure describes each step in the message flow.
Figure 7. X.509 Certificate-based Peer Authentication
Table 8. X.509 Certificate-based Peer Authentication

Step | Description
--- | ---
1. | The peer node initiates an IKEv2 exchange with the local node, known as the IKE_SA_INIT exchange, by issuing an IKE_SA_INIT Request to negotiate cryptographic algorithms, exchange nonces, and perform a Diffie-Hellman exchange with the local node.
2. | The local node responds with an IKE_SA_INIT Response by choosing a cryptographic suite from the initiator’s offered choices, completing the Diffie-Hellman and nonce exchanges with the peer node. In addition, the local node includes the list of CA certificates that it will accept in its CERTREQ payload. For successful peer authentication, the CERTREQ payload must contain at least one CA certificate that is in the trust chain of the peer certificate. At this point in the negotiation, the IKE_SA_INIT exchange is complete and all but the headers of all the messages that follow are encrypted and integrity-protected.
3. | The peer node initiates an IKE_AUTH exchange with the local node by including the IDi payload, setting the CERT payload to the peer certificate, and including the AUTH payload containing the signature of the previous IKE_SA_INIT Request message (in step 1) generated using the private key of the peer certificate. The authentication algorithm used to generate the AUTH payload is also included in the AUTH payload. The peer node also includes the CERTREQ payload containing the list of SHA-1 hash algorithms for local node authentication. For successful server authentication, the CERTREQ payload must contain at least one CA certificate that is in the trust chain of the peer certificate.
4. | Using the CA certificate corresponding to the peer certificate, the local node first verifies that the peer certificate in the CERT payload has not been modified and the identity included in the IDi corresponds to the identity in the peer certificate. If the verification is successful, using the public key of the peer certificate, the local node generates the expected AUTH payload and compares it with the received AUTH payload. If they match, the authentication of the peer node is successful. Otherwise, the local node sends an IKEv2 Notification message indicating authentication failure.
5. | The local node responds with the IKE_AUTH Response, including the IDr payload, setting the CERT payload to the local node certificate, and including the AUTH payload containing the signature of the IKE_SA_INIT Response message (in step 2) generated using the private key of the local node certificate. The authentication algorithm used to generate the AUTH payload is also included in the AUTH payload.
6. | Using the CA certificate corresponding to the local node certificate, the peer node first verifies that the local node certificate in the CERT payload has not been modified. If the verification is successful, using the public key of the local node certificate, the peer generates the expected AUTH payload and compares it with the received AUTH payload. If they match, the local node authentication is successful. This completes the IKE_AUTH exchange.
7. | An IPSec SA gets established between the peer node and the local node. If more IPSec SAs are needed, either the peer or local node can initiate the creation of additional Child SAs using a CREATE_CHILD_SA exchange.

Certificate Revocation Lists

Certificate revocation lists track certificates that have been revoked by the CA (Certificate Authority) and are no longer valid. Per RFC 3280, during certificate validation, IPSec for LTE/SAE checks the certificate revocation list to verify that the certificate the local node receives from the remote node has not expired and hence is still valid.

During configuration via the system CLI, one certificate revocation list is bound to each crypto template and can be fetched from its repository via HTTP or FTP.

Child SA Rekey Support

Rekeying of an IKEv2 Child Security Association (SA) occurs for an already established Child SA whose lifetime (either time-based or data-based) is about to exceed a maximum limit. The IPSec subsystem initiates rekeying to replace the existing Child SA. During rekeying, two Child SAs exist momentarily (500ms or less) to ensure that transient packets from the original Child SA are processed by the IPSec node and not dropped.

Child SA rekeying is disabled by default, and rekey requests are ignored. This feature gets enabled in the Crypto Configuration Payload Mode of the system’s CLI.

IKEv2 Keep-Alive Messages (Dead Peer Detection)

IPSec for LTE/SAE supports IKEv2 keep-alive messages, also known as Dead Peer Detection (DPD), originating from both ends of an IPSec tunnel. Per RFC 3706, DPD is used to simplify the messaging required to verify communication between peers and tunnel availability. You configure DPD on each IPSec node. You can also disable DPD, and the node will not initiate DPD exchanges with other nodes. However, the node always responds to DPD availability checks initiated by another node regardless of its DPD configuration.

E-UTRAN/EPC Logical Network Interfaces Supporting IPSec Tunnels

The figure below shows the logical network interfaces over which secure IPSec tunnels can be created in an E-UTRAN/EPC (Evolved UMTS Terrestrial Radio Access Network/Evolved Packet Core) network. The table that follows the figure provides a description of each logical network interface.
Figure 8. E-UTRAN/EPC Logical Network Interfaces Supporting IPSec Tunnels
Table 9. E-UTRAN/EPC Logical Network Interfaces Supporting IPSec Tunnels

Interface | Description
--- | ---
S1-MME Interface | This interface is the reference point for the control plane protocol between the eNodeB and the MME. The S1-MME interface uses S1-AP (S1- Application Protocol) over SCTP (Stream Control Transmission Protocol) as the transport layer protocol for guaranteed delivery of signaling messages between the MME and the eNodeB (S1). When configured, the S1-AP over SCTP signaling traffic gets carried over an IPSec tunnel. When a subscriber UE initiates a connection with the eNodeB, the eNodeB initiates an IPSec tunnel with the MME, and SCTP signaling for all subsequent subscriber UEs served by this MME gets carried over the same IPSec tunnel. The MME can also initiate an IPSec tunnel with the eNodeB when the following conditions exist: The first tunnel setup is always triggered by the eNodeB. This is the tunnel over which initial SCTP exchanges occur. The MME initiates additional tunnels to the eNodeB after an SCTP connection is set up if the MME is multi-homed: a tunnel is initiated from MME's second address to the eNodeB. The eNodeB is multi-homed: tunnels are initiated from the MME's primary address to each secondary address of the eNodeB. Both of the prior two conditions: a tunnel is initiated from each of MME's addresses to each address of the eNodeB.
S1-U Interface | This interface is the reference point for bearer channel tunneling between the eNodeB and the S-GW. Typically, the eNodeB initiates an IPSec tunnel with the S-GW over this interface for subscriber data traffic. But the S-GW may also initiate an IPSec tunnel with the eNodeB, if required.
S5 Interface | This interface is the reference point for tunneling between the S-GW and the P-GW. Based on the requested APN from a subscriber UE, the MME selects both the S-GW and the P-GW that the S-GW connects to. GTP-U data traffic is carried over the IPSec tunnel between the S-GW and P-GW for the current and all subsequent subscriber UEs.

IPSec Tunnel Termination

IPSec tunnel termination occurs during the following scenarios:

- Idle Tunnel Termination: When a session manager for a service detects that all subscriber sessions using a given IPSec tunnel have terminated, the IPSec tunnel also gets terminated after a timeout period.
- Service Termination: When a service running on a network node is brought down for any reason, all corresponding IPSec tunnels get terminated. This may be caused by the interface for a service going down, a service being stopped manually, or a task handling an IPSec tunnel restarting.
- Unreachable Peer: If a network node detects an unreachable peer via Dead Peer Detection (DPD), the IPSec tunnel between the nodes gets terminated. DPD can be enabled per P-GW, S-GW, and MME service via the system CLI during crypto template configuration.
- E-UTRAN Handover Handling: Any IPSec tunnel that becomes unusable due to an E-UTRAN network handover gets terminated, while the network node to which the session is handed initiates a new IPSec tunnel for the session.