VPN authentication

VPN authentication

Authentication involves authenticating the user. In IPsec VPNs authenticating the user is optional, but authentication of the peer device is required. This section includes:

l Authenticating IPsec VPN peers (devices) l Authenticating IPsec VPN users l Authenticating SSL VPN users l Authenticating PPTP and L2TP VPN users

Authenticating IPsec VPN peers (devices)

A VPN tunnel has one end on a local trusted network, and the other end is at a remote location. The remote peer (device) must be authenticated to be able to trust the VPN tunnel. Without that authentication, it is possible for a malicious hacker to masquerade as a valid VPN tunnel device and gain access to the trusted local network.

The three ways to authenticate VPN peers are with a preshared key, RSA X.509 certificate, or a specific peer ID value.

The simplest way for IPsec VPN peers to authenticate each other is through the use of a preshared key, also called a shared secret. The preshared key is a text string used to encrypt the data exchanges that establish the VPN tunnel. The preshared key must be six or more characters. The VPN tunnel cannot be established if the two peers do not use the same key. The disadvantage of preshared key authentication is that it can be difficult to securely distribute and update the preshared keys.

RSA X.509 certificates are a better way for VPN peers to authenticate each other. Each peer offers a certificate signed by a Certificate Authority (CA) which the other peer can validate with the appropriate CA root certificate.

For more information about certificates, see Certificate-based authentication on page 107.

 

You can supplement either preshared key or certificate authentication by requiring the other peer to provide a specific peer ID value. The peer ID is a text string configured on the peer device. On a FortiGate peer or FortiClient Endpoint Security peer, the peer ID provided to the remote peer is called the Local ID.

Authenticating IPsec VPN users

An IPsec VPN can be configured to accept connections from multiple dynamically addressed peers. You would do this to enable employees to connect to the corporate network while traveling or from home. On a FortiGate unit, you create this configuration by setting the Remote Gateway to Dialup User.

It is possible to have an IPsec VPN in which remote peer devices authenticate using a common preshared key or a certificate, but there is no attempt to identify the user at the remote peer. To add user authentication, you can do one of the following:

l require a unique preshared key for each peer l require a unique peer ID for each peer l require a unique peer certificate for each peer l require additional user authentication (XAuth)

The peer ID is a text string configured on the peer device. On a FortiGate peer or FortiClient Endpoint Security peer, the peer ID provided to the remote peer is called the Local ID.

Authenticating SSL VPN users

SSL VPN users can be l user accounts with passwords stored on the FortiGate unit l user accounts authenticated by an external RADIUS, LDAP or TACACS+ server l PKI users authenticated by certificate

You need to create a user group for your SSL VPN. Simply create a firewall user group, enable SSL VPN access for the group, and select the web portal the users will access.

SSL VPN access requires an SSL VPN security policy that permits access to members of your user group.

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.


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