Authenticating PPTP and L2TP VPN users

PPTP and L2TP are older VPN tunneling protocols that do not provide authentication themselves. FortiGate units restrict PPTP and L2TP access to users who belong to one specified user group. Users authenticate themselves to the FortiGate unit by username/password. You can configure PPTP and L2TP VPNs only in the CLI. Before you configure the VPN, create a firewall user group and add to it the users who are permitted to use the VPN. Users are authenticated when they attempt to connect to the VPN. For more information about configuring PPTP or L2TP VPNs, see the FortiGate CLI Reference.

 

Single Sign-On authentication for users

“Single Sign-On” means that users logged on to a computer network are authenticated for access to network resources through the FortiGate unit without having to enter their username and password again. FortiGate units directly provide Single Sign On capability for:

• Microsoft Windows networks using either Active Directory or NTLM authentication
• Novell networks, using eDirectory

In combination with a FortiAuthenticator unit, the FortiGate unit can provide Single Sign-On capability that integrates multiple external network authentication systems such as Windows Active Directory, Novell e- Directory, RADIUS and LDAP. The FortiAuthenticator unit gathers user logon information from all of these sources and sends it to the FortiGate unit.

Through the SSO feature, the FortiGate unit knows the username, IP address, and external user groups to which the user belongs. When the user tries to access network resources, the FortiGate unit selects the appropriate security policy for the destination. If the user belongs to one of the permitted user groups, the connection is allowed.

For detailed information about SSO, see

• Single Sign-On using a FortiAuthenticator unit on page 541
• Agent-based FSSO on page 553

 

User’s view of authentication

From the user’s point of view, they see a request for authentication when they try to access a protected resource, such as an FTP repository of intellectual property or simply access a website on the Internet. The way the request is presented to the user depends on the method of access to that resource.

VPN authentication usually controls remote access to a private network.

 

Web–based user authentication

Security policies usually control browsing access to an external network that provides connection to the Internet. In this case, the FortiGate unit requests authentication through the web browser.

The user types a username and password and then selects Continue or Login. If the credentials are incorrect, the authentication screen is redisplayed with blank fields so that the user can try again. When the user enters valid credentials, access is granted to the required resource. In some cases, if a user tries to authenticate several times without success, a message appears, such as: “Too many bad login attempts. Please try again in a few minutes.” This indicates the user is locked out for a period of time. This prevents automated brute force password hacking attempts. The administrator can customize these settings if required.

After a defined period of user inactivity (the authentication timeout, defined by the FortiGate administrator), the user’s access expires. The default is 5 minutes. To access the resource, the user will have to authenticate again.

 

VPN client-based authentication

A VPN provides remote clients with access to a private network for a variety of services that include web browsing, email, and file sharing. A client program such as FortiClient negotiates the connection to the VPN and manages the user authentication challenge from the FortiGate unit.

FortiClient can store the username and password for a VPN as part of the configuration for the VPN connection and pass them to the FortiGate unit as needed. Or, FortiClient can request the username and password from the user when the FortiGate unit requests them.

SSL VPN is a form of VPN that can be used with a standard Web browser. There are two modes of SSL VPN operation (supported in NAT/Route mode only):

• web-only mode, for remote clients equipped with a web-browser only
• tunnel mode, for remote computers that run a variety of client and server applications.

After a defined period of user inactivity on the VPN connection (the idle timeout, defined by the FortiGate administrator), the user’s access expires. The default is 30 minutes. To access the resource, the user will have to authenticate again.

 

FortiGate administrator’s view of authentication

Authentication is based on user groups. The FortiGate administrator configures authentication for security policies and VPN tunnels by specifying the user groups whose members can use the resource. Some planning is required to determine how many different user groups need to be created. Individual user accounts can belong to multiple groups, making allocation of user privileges very flexible.

A member of a user group can be:

• a user whose username and password are stored on the FortiGate unit
• a user whose name is stored on the FortiGate unit and whose password is stored on a remote or external authentication server
• a remote or external authentication server with a database that contains the username and password of each person who is permitted access

The general process of setting up authentication is as follows:

1. If remote or external authentication is needed, configure the required servers.

2. Configure local and peer (PKI) user identities. For each local user, you can choose whether the FortiGate unit or a remote authentication server verifies the password. Peer members can be included in user groups for use in security policies.

3. Create user groups.

4. Add local/peer user members to each user group as appropriate. You can also add an authentication server to a user group. In this case, all users in the server’s database can authenticate. You can only configure peer user groups through the CLI.

5. Configure security policies and VPN tunnels that require authenticated access.

For authentication troubleshooting, see the specific chapter for the topic or for general issues see Troubleshooting on page 622.