CLI Book 3: Cisco ASA Series VPN CLI Configuration Guide, 9.2

LAN-to-LAN IPsec VPNs

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A LAN-to-LAN VPN connects networks in different geographic locations.

The ASA supports LAN-to-LAN VPN connections to Cisco or third-party peers when the two peers have IPv4 inside and outside networks (IPv4 addresses on the inside and outside interfaces).

For LAN-to-LAN connections using mixed IPv4 and IPv6 addressing, or all IPv6 addressing, the security appliance supports VPN tunnels if both peers are ASAs and if both inside networks have matching addressing schemes (both IPv4 or both IPv6).

Specifically, the following topologies are supported when both peers are ASAs:

• The ASAs have IPv4 inside networks and the outside network is IPv6 (IPv4 addresses on the inside interfaces and IPv6 addresses on the outside interfaces).
• The ASAs have IPv6 inside networks and the outside network is IPv4 (IPv6 addresses on the inside interface and IPv4 addresses on the outside interfaces).
• The ASAs have IPv6 inside networks and the outside network is IPv6 (IPv6 addresses on the inside and outside interfaces).

Note The ASA supports LAN-to-LAN IPsec connections with Cisco peers, and with third-party peers that comply with all relevant standards.

This chapter describes how to build a LAN-to-LAN VPN connection. It includes the following sections:

• Summary of the Configuration
• Configuring Site-to-Site VPN in Multi-Context Mode
• Configuring Interfaces
• Configuring ISAKMP Policy and Enabling ISAKMP on the Outside Interface
• Creating an IKEv1 Transform Set
• Creating an IKEv2 Proposal
• Configuring an ACL
• Defining a Tunnel Group
• Creating a Crypto Map and Applying It To an Interface

Summary of the Configuration

This section provides a summary of the example LAN-to-LAN configuration this chapter describes. Later sections provide step-by-step instructions.

Configuring Site-to-Site VPN in Multi-Context Mode

Follow these steps to allow site-to-site support in multi-mode for all platforms except the 5505. By performing these steps, you can see how resource allocation breaks down.

Step 1 To configure the VPN in multi-mode, configure a resource class and choose VPN licenses as part of the allowed resource. The "Configuring a Class for Resource Management" provides these configuration steps. The following is an example configuration:

Step 2 Configure a context and make it a member of the configured class that allows VPN licenses. The "Configuring a Security Contextt" provides these configuration steps. The following is an example configuration:

Step 3 Configure connection profiles, policies, crypto maps, and so on, just as would with single context VPN configuration of site-to-site VPN.

Configuring Interfaces

An ASA has at least two interfaces, referred to here as outside and inside. Typically, the outside interface is connected to the public Internet, while the inside interface is connected to a private network and is protected from public access.

To begin, configure and enable two interfaces on the ASA. Then, assign a name, IP address and subnet mask. Optionally, configure its security level, speed, and duplex operation on the security appliance.

Note The ASA’s outside interface address (for both IPv4/IPv6) cannot overlap with the private side address space.

To configure interfaces, perform the following steps, using the command syntax in the examples:

Step 1 To enter Interface configuration mode, in global configuration mode enter the interface command with the default name of the interface to configure. In the following example the interface is ethernet0.

Step 2 To set the IP address and subnet mask for the interface, enter the ip address command. In the following example the IP address is 10.10.4.100 and the subnet mask is 255.255.0.0.

Step 3 To name the interface, enter the nameif command, maximum of 48 characters. You cannot change this name after you set it. In the following example the name of the ethernet0 interface is outside.

Step 4 To enable the interface, enter the no version of the shutdown command. By default, interfaces are disabled.

Step 5 To save your changes, enter the write memory command:

Step 6 To configure a second interface, use the same procedure.

Configuring ISAKMP Policy and Enabling ISAKMP on the Outside Interface

ISAKMP is the negotiation protocol that lets two hosts agree on how to build an IPsec security association (SA). It provides a common framework for agreeing on the format of SA attributes. This includes negotiating with the peer about the SA, and modifying or deleting the SA. ISAKMP separates negotiation into two phases: Phase 1 and Phase 2. Phase 1 creates the first tunnel, which protects later ISAKMP negotiation messages. Phase 2 creates the tunnel that protects data.

IKE uses ISAKMP to setup the SA for IPsec to use. IKE creates the cryptographic keys used to authenticate peers.

The ASA supports IKEv1 for connections from the legacy Cisco VPN client, and IKEv2 for the AnyConnect VPN client.

To set the terms of the ISAKMP negotiations, you create an IKE policy, which includes the following:

• The authentication type required of the IKEv1 peer, either RSA signature using certificates or preshared key (PSK).
• An encryption method, to protect the data and ensure privacy.
• A Hashed Message Authentication Codes (HMAC) method to ensure the identity of the sender, and to ensure that the message has not been modified in transit.
• A Diffie-Hellman group to determine the strength of the encryption-key-determination algorithm. The ASA uses this algorithm to derive the encryption and hash keys.
• For IKEv2, a separate pseudo-random function (PRF) used as the algorithm to derive keying material and hashing operations required for the IKEv2 tunnel encryption.
• A limit to the time the ASA uses an encryption key before replacing it.

With IKEv1 policies, for each parameter, you set one value. For IKEv2, you can configure multiple encryption and authentication types, and multiple integrity algorithms for a single policy. The ASA orders the settings from the most secure to the least secure and negotiates with the peer using that order. This allows you to potentially send a single proposal to convey all the allowed transforms instead of the need to send each allowed combination as with IKEv1.

The following sections provide procedures for creating IKEv1 and IKEv2 policies and enabling them on an interface:

• Configuring ISAKMP Policies for IKEv1 Connections
• Configuring ISAKMP Policies for IKEv2 Connections

Creating an IKEv1 Transform Set

An IKEv1 transform set combines an encryption method and an authentication method. During the IPsec security association negotiation with ISAKMP, the peers agree to use a particular transform set to protect a particular data flow. The transform set must be the same for both peers.

A transform set protects the data flows for the ACL specified in the associated crypto map entry. You can create transform sets in the ASA configuration, and then specify a maximum of 11 of them in a crypto map or dynamic crypto map entry.

Table 10-1 lists valid encryption and authentication methods.

Tunnel Mode is the usual way to implement IPsec between two ASAs that are connected over an untrusted network, such as the public Internet. Tunnel mode is the default and requires no configuration.

To configure a transform set, perform the following site-to-site tasks in either single or multiple context mode:

Step 1 In global configuration mode enter the crypto ipsec ikev1 transform-set command. The following example configures a transform set with the name FirstSet, esp-3des encryption, and esp-md5-hmac authentication. The syntax is as follows:

crypto ipsec ikev1 transform-set transform-set-name encryption-method authentication-method

Step 2 Save your changes.

Creating an IKEv2 Proposal

For IKEv2, you can configure multiple encryption and authentication types, and multiple integrity algorithms for a single policy. The ASA orders the settings from the most secure to the least secure and negotiates with the peer using that order. This allows you to potentially send a single proposal to convey all the allowed transforms instead of the need to send each allowed combination as with IKEv1.

Table 10-1 lists valid IKEv2 encryption and authentication methods.

To configure an IKEv2 proposal, perform the following tasks in either single or multiple context mode:

Step 1 In global configuration mode, use the crypto ipsec ikev2 ipsec-proposal command to enter ipsec proposal configuration mode where you can specify multiple encryption and integrity types for the proposal. In this example, secure is the name of the proposal:

Step 2 Then enter a protocol and encryption types. ESP is the only supported protocol. For example:

Step 3 Enter an integrity type. For example:

Step 4 Save your changes.

Configuring an ACL

The ASA uses access control lists to control network access. By default, the adaptive security appliance denies all traffic. You need to configure an ACL that permits traffic. For more information, see "Information About Access Control Lists" in the general operations configuration guide.

The ACLs that you configure for this LAN-to-LAN VPN control connections are based on the source and translated destination IP addresses. Configure ACLs that mirror each other on both sides of the connection.

An ACL for VPN traffic uses the translated address.

To configure an ACL, perform the following steps:

Step 1 Enter the access-list extended command. The following example configures an ACL named l2l_list that lets traffic from IP addresses in the 192.168.0.0 network travel to the 150.150.0.0 network. The syntax is access-list listname extended permit ip source-ipaddress source-netmask destination-ipaddress destination-netmask.

Step 2 Configure an ACL for the ASA on the other side of the connection that mirrors the ACL. Subnets that are defined in two different crypto ACLs and are attached to the same crypto map should not overlap. In the following example, the prompt for the peer is hostname2.

Note For more information on configuring an ACL with a vpn-filter, see the Specifying a VLAN for Remote Access or Applying a Unified Access Control Rule to the Group Policy.

Defining a Tunnel Group

A tunnel group is a set of records that contain tunnel connection policies. You configure a tunnel group to identify AAA servers, specify connection parameters, and define a default group policy. The ASA stores tunnel groups internally.

There are two default tunnel groups in the ASA: DefaultRAGroup, which is the default IPsec remote-access tunnel group, and DefaultL2Lgroup, which is the default IPsec LAN-to-LAN tunnel group. You can modify them but not delete them.

The main difference between IKE versions 1 and 2 lies in terms of the authentication method they allow. IKEv1 allows only one type of authentication at both VPN ends (that is, either pre-shared key or certificate). However, IKEv2 allows assymetric authentication methods to be configured (that is, pre-shared key authentication for the originator but certificate authentication for the responder) using separate local and remote authentication CLIs. Therefore, with IKEv2 you have assymmetric authentication where one side authenticates with one credential whereas the other side uses another credential (either pre-shared key or certificate).

You can also create one or more new tunnel groups to suit your environment. The ASA uses these groups to configure default tunnel parameters for remote access and LAN-to-LAN tunnel groups when there is no specific tunnel group identified during tunnel negotiation.

To establish a basic LAN-to-LAN connection, you must set two attributes for a tunnel group:

• Set the connection type to IPsec LAN-to-LAN.
• Configure an authentication method for the IP, in the following example, preshared key for IKEv1 and IKEv2.

Note To use VPNs, including tunnel groups, the ASA must be in single-routed mode. The commands to configure tunnel-group parameters do not appear in any other mode.

Step 1 To set the connection type to IPsec LAN-to-LAN, enter the tunnel-group command. The syntax is tunnel-group name type type, where name is the name you assign to the tunnel group, and type is the type of tunnel. The tunnel types as you enter them in the CLI are:

• remote-access (IPsec, SSL, and clientless SSL remote access)
• ipsec-l2l (IPsec LAN to LAN)

In the following example the name of the tunnel group is the IP address of the LAN-to-LAN peer, 10.10.4.108.

Note LAN-to-LAN tunnel groups that have names that are not an IP address can be used only if the tunnel authentication method is Digital Certificates and/or the peer is configured to use Aggressive Mode.

Step 2 To set the authentication method to preshared key, enter the ipsec-attributes mode and then enter the ikev1 pre-shared-key command to create the preshared key. You need to use the same preshared key on both ASAs for this LAN-to-LAN connection.

The key is an alphanumeric string of 1-128 characters.

In the following example the IKEv1 preshared key is 44kkaol59636jnfx:

In the next example, the IKEv2 preshared key is configured also as 44kkaol59636jnfx:

Note You must configure ikev2 remote-authentication pre-shared-key or a certificate to complete the authentication.

Step 3 Save your changes.

To verify that the tunnel is up and running, use the show vpn-sessiondb summary , show vpn-sessiondb detail l2l , or show cry ipsec sa command.

Creating a Crypto Map and Applying It To an Interface

Crypto map entries pull together the various elements of IPsec security associations, including the following:

• Which traffic IPsec should protect, which you define in an ACL.
• Where to send IPsec-protected traffic, by identifying the peer.
• What IPsec security applies to this traffic, which a transform set specifies.
• The local address for IPsec traffic, which you identify by applying the crypto map to an interface.

For IPsec to succeed, both peers must have crypto map entries with compatible configurations. For two crypto map entries to be compatible, they must, at a minimum, meet the following criteria:

• The crypto map entries must contain compatible crypto ACLs (for example, mirror image ACLs). If the responding peer uses dynamic crypto maps, the entries in the ASA crypto ACL must be “permitted” by the peer’s crypto ACL.
• The crypto map entries each must identify the other peer (unless the responding peer is using a dynamic crypto map).
• The crypto map entries must have at least one transform set in common.

If you create more than one crypto map entry for a given interface, use the sequence number (seq-num) of each entry to rank it: the lower the seq-num, the higher the priority. At the interface that has the crypto map set, the ASA evaluates traffic against the entries of higher priority maps first.

Create multiple crypto map entries for a given interface if either of the following conditions exist:

• Different peers handle different data flows.
• You want to apply different IPsec security to different types of traffic (to the same or separate peers), for example, if you want traffic between one set of subnets to be authenticated, and traffic between another set of subnets to be both authenticated and encrypted. In this case, define the different types of traffic in two separate ACLs, and create a separate crypto map entry for each crypto ACL.

To create a crypto map and apply it to the outside interface in global configuration mode, perform the following steps in either single or multiple context mode:

Step 1 To assign an ACL to a crypto map entry, enter the crypto map match address command.

The syntax is crypto map map-name seq-num match address aclname . In the following example the map name is abcmap, the sequence number is 1, and the ACL name is l2l_list .

Step 2 To identify the peer (s) for the IPsec connection, enter the crypto map set peer command.

The syntax is crypto map map-name seq-num set peer { ip_address1 | hostname1 }[... ip_address10 | hostname10 ]. In the following example the peer name is 10.10.4.108.

Step 3 To specify an IKEv1 transform set for a crypto map entry, enter the crypto map ikev1 set transform-set command.

The syntax is crypto map map-name seq-num ikev1 set transform-set transform-set-name .
In the following example the transform set name is FirstSet.

Step 4 To specify an IKEv2 proposal for a crypto map entry, enter the crypto map ikev2 set ipsec-proposal command:

The syntax is crypto map map-name seq-num set ikev2 ipsec-proposal proposal-name .
In the following example the proposal name is secure.

With the crypto map command, you can specify multiple IPsec proposals for a single map index. In that case, multiple proposals are transmitted to the IKEv2 peer as part of the negotiation, and the order of the proposals is determined by the administrator upon the ordering of the crypto map entry.

Note If combined mode (AES-GCM/GMAC) and normal mode (all others) algorithms exist in the IPsec proposal, then you cannot send a single proposal to the peer. You must have at least two proposals in this case, one for combined mode and one for normal mode algorithms.