Navigation Path

Devices > VPN > Site To Site. Then Add VPN > Firepower Threat Defense Device, or edit a listed VPN Topology. Open the Endpoint tab.

Fields

Device

Choose an endpoint node for your deployment:

• A Firepower Threat Defense device managed by this Firepower Management Center.

• A Firepower Threat Defense high availability container managed by this Firepower Management Center.

• An Extranet device, any device (Cisco or third-party) not managed by this Firepower Management Center.

Device Name

For Extranet devices only, provide a name for this device. We recommend naming it such that it is identifiable as an un-managed device.

Interface

If you chose a managed device as your endpoint, choose an interface on that managed device.

For 'Point to Point' deployments, you can also configure an endpoint with dynamic interface. Note that an endpoint with dynamic interface can pair only with an extranet device and cannot pair with an endpoint, which has a managed device.

You can configure device interfaces at Devices > Device Management > Add/Edit device > Interfaces.

IP Address

• If you choose an extranet device, a device not managed by the Firepower Management Center, specify an IP address for the endpoint.

  If you have chosen point-to-point topology and only IKEv1, you can configure backup peer by entering the primary IP address and backup peer IP addresses separated by a comma.

• If you chose a managed device as an endpoint, choose a single IPv4 address or multiple IPv6 addresses from the drop-down list (these are the addresses already assigned to this interface on this managed device).

• All endpoints in a topology must have the same IP addressing scheme. IPv4 tunnels can carry IPv6 traffic and vice-versa. The Protected Networks define which addressing scheme the tunneled traffic will use.

• If the managed device is a high-availability container, choose from a list of interfaces.

This IP is Private

Check the check box if the endpoint resides behind a firewall with network address translation (NAT).

Note	Use this option only when the peer is managed by the same Firepower Management Center and do not use this option if peer is from extranet.

Public IP address

If you checked the This IP is Private check box, specify a public IP address for the firewall. If the endpoint is a responder, specify this value.

Connection Type

Specify the allowed negotiation as bidirectional, answer-only, or originate-only. Supported combinations for the connection type are:

Table 1. Connection Type Supported Combinations

Remote Node	Central Node
Originate-Only	Answer-Only
Bi-Directional	Answer-Only
Bi-Directional	Bi-Directional

Certificate Map

Choose a pre-configured certificate map object, or click Add () to add a certificate map object that defines what information is necessary in the received client certificate for it to be valid for VPN connectivity. See Firepower Threat Defense Certificate Map Objects for details.

Protected Networks

Caution

In the Hub and Spoke topology, for a dynamic crypto map, ensure that you do not select the protected network any for both the endpoints to avoid traffic drop.

Defines the networks that are protected by this VPN Endpoint. The networks may be marked by selecting the list of Subnet/IP Address that define the networks that are protected by this endpoint. Click Add () to select from available Network Objects or add new Network Objects. See Creating Network Objects. Access Control Lists will be generated from the choices made here.

• Subnet/IP Address (Network)—VPN endpoints cannot have the same IP address and protected networks in a VPN endpoint pair cannot overlap. If a list of protected networks for an endpoint contains one or more IPv4 or IPv6 entries, the other endpoint's protected network must have at least one entry of the same type (that is, IPv4 or IPv6). If it does not, then the other endpoint's IP address must be of the same type and must not overlap with the entries in the protected network. (Use /32 CIDR address blocks for IPv4 and /128 CIDR address blocks for IPv6.) If both of these checks fail, the endpoint pair is invalid.

  Note

  Reverse Route Injection is enabled by default in Firepower Management Center. Subnet/IP Address (Network) remains the default selection. When you have selected Protected Networks as Any and observe default route traffic being dropped, disable the Reverse Route Injection under VPN> Site to Site > edit a VPN > IPsec > Enable Reverse Route Injection. Deploy the configuration changes; this will remove set reverse-route (Reverse Route Injection) from the crypto map configuration and remove the VPN-advertised reverse route that causes the reverse tunnel traffic to be dropped.

• Access List (Extended)—An extended access lists provide the capability to control the type of traffic that will be accepted by this endpoint, like GRE or OSPF traffic. Traffic may be restricted either by address or port. Click Add () to add access control list objects.

  Note	Access Control List is supported only in the point to point topology.

For the versions of IKE you have chosen for this topology, specify the IKEv1/IKEv2 Settings.

Note	Settings in this dialog apply to the entire topology, all tunnels, and all managed devices.

Navigation Path

Devices > VPN > Site To Site. Then Add VPN > Firepower Threat Defense Device, or edit a listed VPN Topology. Open the IKE tab.

Fields

Policy

Choose a predefined IKEv1 or IKEv2 policy object or create a new one to use. For details, see Firepower Threat Defense IKE Policies

Authentication Type

Site-to-site VPN supports two authentication methods, pre-shared key and certificate. For an explanation of the two methods, see Deciding Which Authentication Method to Use.

Note	In a VPN topology that supports IKEv1, the Authentication Method specified in the chosen IKEv1 Policy object becomes the default in the IKEv1 Authentication Type setting. These values must match, otherwise, your configuration will error.

• Pre-shared Automatic Key—The Management Center automatically defines the pre-shared key that is used for this VPN. Specify the Pre-shared Key Length, the number of characters in the key, 1-27.

  The character " (double quote) is not supported as part of pre-shared keys. If you have used " in a pre-shared key, ensure that you change the character after you upgrade to Firepower Threat Defense 6.30 or higher.

• Pre-shared Manual Key—Manually assign the pre-shared key that is used for this VPN. Specify the Key and then re-enter it in Confirm Key to confirm.

  When this option is chosen for IKEv2, the Enforce hex-based pre-shared key only check box appears, check if desired. If enforced, you must enter a valid hex value for the key, an even number of 2-256 characters, using numerals 0-9, or A-F.

• Certificate—When you use certificates as the authentication method for VPN connections, peers obtain digital certificates from a CA server in your PKI infrastructure, and trade them to authenticate each other.

  In the Certificate field, select a pre-configured certificate enrollment object. This enrollment object is used to generate a trustpoint with the same name on the managed device. The certificate enrollment object should be associated with and installed on the device, post which the enrollment process is complete, and then a trustpoint is created.

  A trustpoint is a representation of a CA or identity pair. A trustpoint includes the identity of the CA, CA-specific configuration parameters, and an association with one enrolled identity certificate.

  Before you select this option, note the following:

  • Ensure you have enrolled a certificate enrollment object on all the endpoints in the topology—A certificate enrollment object contains the Certification Authority (CA) server information and enrollment parameters that are required for creating Certificate Signing Requests (CSRs) and obtaining Identity Certificates from the specified CA. Certificate Enrollment Objects are used to enroll your managed devices into your PKI infrastructure, and create trustpoints (CA objects) on devices that support VPN connections. For instructions on creating a certificate enrollment object, see Adding Certificate Enrollment Objects, and for instructions on enrolling the object on the endpoints see one of the following as applicable:

    • Installing a Certificate Using Self-Signed Enrollment

    • Installing a Certificate Using SCEP Enrollment

    • Installing a Certificate Using Manual Enrollment

    • Installing a Certificate Using a PKCS12 File

    Note	For a site-to-site VPN topology, ensure that the same certificate enrollment object is enrolled in all the endpoints in the topology. For further details, see the table below.

  • Refer the following table to understand the enrollment requirement for different scenarios. Some of the scenarios require you to override the certificate enrollment object for specific devices. See Managing Object Overrides to understand how to override objects.

    Certificate Enrollment Types	Device identity certificate for all endpoints is from the same CA		Device identity certificate for all endpoints is from different CAs
    	Device-specific parameters are NOT specified in the certificate enrollment object	Device-specific parameters are specified in the certificate enrollment object
    Manual	No override required	Override required	Override required
    SCEP	No override required	Override required	Override required
    PKCS	Override required	Override required	Override required
    Self-signed	Not applicable	Not applicable	Not applicable

  • Understand the VPN certificate limitations mentioned in Firepower Threat Defense VPN Certificate Guidelines and Limitations.

  Note

  If you use a Windows Certificate Authority (CA), the default Application Policies extension is IP security IKE intermediate. If you are using this default setting, you must select the Ignore IPsec Key Usage option in the Advanced Settings section on the Key tab in the PKI Certificate Enrollment dialog box for the object you select. Otherwise, the endpoints cannot complete the site-to-site VPN connection.

Note	Settings in this dialog apply to the entire topology, all tunnels, and all managed devices.

Crypto-Map Type

A crypto map combines all the components required to set up IPsec security associations (SA). When two peers try to establish an SA, they must each have at least one compatible crypto map entry. The proposals defined in the crypto map entry are used in the IPsec security negotiation to protect the data flows specified by that crypto map’s IPsec rules. Choose static or dynamic for this deployment's crypto-map:

• Static—Use a static crypto map in a point-to-point or full mesh VPN topology.

• Dynamic—Dynamic crypto-maps essentially create a crypto map entry without all the parameters configured. The missing parameters are later dynamically configured (as the result of an IPsec negotiation) to match a remote peer’s requirements.

  Dynamic crypto map policies apply only in a hub-and-spoke VPN configuration. In a point-to-point or full mesh VPN topology, you can apply only static crypto map policies. Emulate the use of dynamic crypto-maps in a point-to-point topology by creating a hub-and-spoke topology with two devices. Specify a dynamic IP address for the spoke, and enable dynamic crypto map on this topology.

IKEv2 Mode

For IPsec IKEv2 only, specify the encapsulation mode for applying ESP encryption and authentication to the tunnel. This determines what part of the original IP packet has ESP applied.

• Tunnel mode—(default) Encapsulation mode is set to tunnel mode. Tunnel mode applies ESP encryption and authentication to the entire original IP packet (IP header and data), hiding the ultimate source and destination addresses and becoming the payload in a new IP packet.

  The major advantage of tunnel mode is that the end systems do not need to be modified to receive the benefits of IPsec. This mode allows a network device, such as a router, to act as an IPsec proxy. That is, the router performs encryption on behalf of the hosts. The source router encrypts packets and forwards them along the IPsec tunnel. The destination router decrypts the original IP datagram and forwards it onto the destination system. Tunnel mode also protects against traffic analysis; with tunnel mode, an attacker can only determine the tunnel endpoints and not the true source and destination of the tunneled packets, even if they are the same as the tunnel endpoints.

• Transport preferred— Encapsulation mode is set to transport mode with an option to fallback to tunnel mode if the peer does not support it. In Transport mode only the IP payload is encrypted, and the original IP headers are left intact. Therefore, the admin must select a protected network that matches the VPN interface IP address.

  This mode has the advantages of adding only a few bytes to each packet and allowing devices on the public network to see the final source and destination of the packet. With transport mode, you can enable special processing (for example, QoS) on the intermediate network based on the information in the IP header. However, the Layer 4 header is encrypted, which limits examination of the packet.

• Transport required— Encapsulation mode is set to transport mode only, falling back to tunnel mode is not allowed. If the endpoints cannot successfully negotiate transport mode, due to one endpoint not supporting it, the VPN connection is not made.

Proposals

Click Edit () to specify the proposals for your chosen IKEv1 or IKEv2 method. Select from the available IKEv1 IPsec Proposals or IKEv2 IPsec Proposals objects, or create and then select a new one. See Configure IKEv1 IPsec Proposal Objects and Configure IKEv2 IPsec Proposal Objects for details.

Enable Security Association (SA) Strength Enforcement

Enabling this option ensures that the encryption algorithm used by the child IPsec SA is not stronger (in terms of the number of bits in the key) than the parent IKE SA.

Enable Reverse Route Injection

Reverse Route Injection (RRI) enables static routes to be automatically inserted into the routing process for those networks and hosts protected by a remote tunnel endpoint.

Enable Perfect Forward Secrecy

Whether to use Perfect Forward Secrecy (PFS) to generate and use a unique session key for each encrypted exchange. The unique session key protects the exchange from subsequent decryption, even if the entire exchange was recorded and the attacker has obtained the preshared or private keys used by the endpoint devices. If you select this option, also select the Diffie-Hellman key derivation algorithm to use when generating the PFS session key in the Modulus Group list.

Modulus Group

The Diffie-Hellman group to use for deriving a shared secret between the two IPsec peers without transmitting it to each other. A larger modulus provides higher security but requires more processing time. The two peers must have a matching modulus group. For a full explanation of the options, see Deciding Which Diffie-Hellman Modulus Group to Use.

Lifetime Duration

The number of seconds a security association exists before expiring. The default is 28,800 seconds.

Lifetime Size

The volume of traffic (in kilobytes) that can pass between IPsec peers using a given security association before it expires. The default is 4,608,000 kilobytes. Infinite data is not allowed.

ESPv3 Settings

Validate incoming ICMP error messages

Choose whether to validate ICMP error messages received through an IPsec tunnel and destined for an interior host on the private network.

Enable 'Do Not Fragment' Policy

Define how the IPsec subsystem handles large packets that have the do-not-fragment (DF) bit set in the IP header.

Policy

• Copy DF bit—Maintains the DF bit.

• Clear DF bit—Ignores the DF bit.

• Set DF bit—Sets and uses the DF bit.

Enable Traffic Flow Confidentiality (TFC) Packets

Enable dummy TFC packets that mask the traffic profile which traverses the tunnel. Use the Burst, Payload Size, and Timeout parameters to generate random length packets at random intervals across the specified SA.

The following sections describes the advanced options you can specify in your S2S VPN deployment. These settings apply to the entire topology, all tunnels, and all managed devices.