As you'll see, you can initiate an SSL VPN session from devices that support the install of a dedicated client (desktops, laptops) and from devices that lack administrative privileges to do so (PDA, smartphone, laptop), as shown in Figure 3-1.
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Figure 3-1 SSL VPN
Deploying a Basic Cisco AnyConnect Full-Tunnel SSL VPN Solution
Basic Cisco AnyConnect full-tunnel SSL VPN uses user authentication by username and password, provides IP address assignment to the client, and uses a basic access control policy. The client also authenticates the ASA with identity certificate-based authentication. Deployment tasks for this scenario are as follows:
- Configure the basic ASA SSL VPN gateway features.
- Configure local user authentication.
- Configure IP address assignment.
- Configure basic access control.
- Install the Cisco AnyConnect VPN Client.
As of this writing, AnyConnect Client officially supports only SSL connections. Starting with version 3.0, which is available for download, AnyConnect is composed of multiple modules and supports additional features (including IPsec IKEv2 VPN terminations on Cisco ASA). The problem here is that this requires ASA 8.4(1) and Adaptive Security Device Manager (ASDM) 6.4(1) at a minimum, which are not available for download at the moment of this writing. For these reasons, this book is limited to configuration scenarios supported by AnyConnect versions earlier than 3.0. You can find more information about AnyConnect Secure Mobility Client 3.0 in the official release notes: www.cisco.com/en/US/docs/security/vpn_client/anyconnect/anyconnect30/release/notes/anyconnect30rn.html#wp1139431.
Configuring Basic Cisco ASA SSL VPN Gateway Features
To initially prepare the ASA for SSL VPN termination, complete the following steps:
Step 1. Provision the ASA with an identity certificate. Your options are as follows:
- Use a self-signed certificate.
- Enroll ASA in Public Key Infrastructure (PKI) with Simple Certificate Enrollment Protocol (SCEP).
- Enroll ASA in PKI with manual cut-and-paste method.
To install a self-signed certificate using the ASDM, navigate to Configuration > Remote Access VPN > Certificate Management > Identity Certificates and click Add. Give the PKI trustpoint a name, choose Add a New Identity Certificate, check Generate Self-Signed Certificate, and then click Add Certificate.
To configure a self-signed certificate by command-line interface (CLI), use the following commands:
ciscoasa(config)# crypto key generate rsa label SELF-SIGNED modulus 2048 ciscoasa(config)# crypto ca trustpoint TEST-CA ciscoasa(config-ca-trustpoint)# id-usage ssl-ipsec ciscoasa(config-ca-trustpoint)# subject-name CN=cisco.com ciscoasa(config-ca-trustpoint)# enrollment self ciscoasa(config-ca-trustpoint)# keypair SELF-SIGNED ciscoasa(config)# crypto ca enroll TEST-CA noconfirm
To enroll with SCEP by using the ASDM, navigate to same the section as for self-signed certificates. Give the PKI trustpoint a name, choose Add a New Identity Certificate (do not check Generate Self-Signed Certificate), and click the Advanced button for enrollment options. From here, you have two options:
- For SCEP enrollment, navigate to Enrollment Mode and choose Request from a CA method, complete the URL (which is in the form http://IP_ADDRESS/certserv/mscep/mscep.dll). Navigate to SCEP Challenge Password and provide the challenge in case the certificate authority (CA) requires it.
- For manual enrollment navigate to Enrollment Mode and choose Request by Manual Enrollment. This requires an additional step: After the certificate is issued, it needs to be imported onto the ASA from a file. For this, select the created trustpoint and click Install. In the new window, choose Install from a File and provide the full path to the base64-encoded certificate.
To configure SCEP enrollment by CLI, use the following commands:
ciscoasa(config)# crypto key generate rsa label SELF-SIGNED modulus 2048 ciscoasa(config)# crypto ca trustpoint TEST-CA ciscoasa(config-ca-trustpoint)# id-usage ssl-ipsec ciscoasa(config-ca-trustpoint)# subject-name CN=cisco.com ciscoasa(config-ca-trustpoint)# enrollment url http://10.10.10.10/certsrv/mscep/mscep.dll ciscoasa(config-ca-trustpoint)# keypair SELF-SIGNED ciscoasa(config)# crypto ca authenticate TEST-CA nointeractive ciscoasa(config)# crypto ca enroll TEST-CA
Step 2. Load the AnyConnect image onto the ASA.
There are different AnyConnect packages for different client operating systems. Choose the one you need, download it from Cisco.com, and load it into ASA flash memory. To make the transfer using the ASDM, navigate to Tools > File Management.
Step 3. Enable SSL VPN termination on desired interfaces.
To enable SSL using the ASDM, navigate to Configuration > Remote Access VPN > Network (Client) Access > AnyConnect Connection Profiles and check the Enable Cisco AnyConnect VPN Client Access on the Interfaces Selected in the Table Below check box. In the pop-up window, select the AnyConnect image. Choose Allow Access and, optionally, Enable DTLS for desired interfaces.
To enable SSL by CLI, use the following commands:
ciscoasa(config)# webvpn ciscoasa(config-webvpn)# enable outside ciscoasa(config-webvpn)# svc enable ciscoasa(config-webvpn)# svc image disk0:/anyconnect-win-2.4.1012-k9.pkg 1
Step 4. Configure and optionally tune SSL Transport Layer Security (TLS) settings.
Here, you can tune SSL VPN by allowing only certain SSL/TLS versions and algorithms and by specifying the identity certificate used (if many exist). To configure it using the ASDM, navigate to Configuration > Remote Access VPN > Network (Client) Access > AnyConnect Connection Profiles and click Click Here to Assign Certificate to Interface (see Figure 3-2).
Figure 3-2 SSL VPN Tuning
To configure it by CLI, use the following commands:
ciscoasa(config)#ssl trustpoint TEST-CA outside ciscoasa(config)# webvpn ciscoasa(config-webvpn)#ssl server-version tlsv1 ciscoasa(config-webvpn)# ssl encryption aes128-sha1 aes256-sha1 3des-sha1 des-sha1
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