FortiOS 6 – IPSEC Phase 1 parameters

Phase 1 parameters

This chapter provides detailed step-by-step procedures for configuring a FortiGate unit to accept a connection from a remote peer or dialup client. The Phase 1 parameters identify the remote peer or clients and supports authentication through preshared keys or digital certificates. You can increase access security further using peer identifiers, certificate distinguished names, group names, or the FortiGate extended authentication (XAuth) option for authentication purposes.

The information and procedures in this section do not apply to VPN peers that perform negotiations using manual keys.

The following topics are included in this section:

Overview

Defining the tunnel ends

Choosing Main mode or Aggressive mode

Choosing the IKE version

Authenticating the FortiGate unit

Authenticating remote peers and clients

Defining IKE negotiation parameters

Using XAuth authentication

Dynamic IPsec route control

Overview

To configure IPsec Phase 1 settings, go to VPN > IPsec Tunnels and edit the Phase 1 Proposal (if it is not available, you may need to click the Convert to Custom Tunnel button).

IPsec Phase 1 settings define:

  • The remote and local ends of the IPsec tunnel l If Phase 1 parameters are exchanged in multiple rounds with encrypted authentication information (main mode) or in a single message with authentication information that is not encrypted (aggressive mode)
  • If a preshared key or digital certificates will be used to authenticate the FortiGate unit to the VPN peer or dialup client
  • If the VPN peer or dialup client is required to authenticate to the FortiGate unit. A remote peer or dialup client can authenticate by peer ID or, if the FortiGate unit authenticates by certificate, it can authenticate by peer certificate. l The IKE negotiation proposals for encryption and authentication
  • Optional XAuth authentication, which requires the remote user to enter a user name and password. A FortiGate VPN server can act as an XAuth server to authenticate dialup users. A FortiGate unit that is a dialup client can also be configured as an XAuth client to authenticate itself to the VPN server.

For all the Phase 1 web-based manager fields, see IPsec VPN in the web-based manager on page 32.

 

Defining the tunnel ends

To begin defining the Phase 1 configuration, go to VPN > IPsec Tunnels and select Create New. Enter a unique descriptive name for the VPN tunnel and follow the instructions in the VPN Creation Wizard.

The Phase 1 configuration mainly defines the ends of the IPsec tunnel. The remote end is the remote gateway with which the FortiGate unit exchanges IPsec packets. The local end is the FortiGate interface that sends and receives IPsec packets.

The remote gateway can be:

l A static IP address l A domain name with a dynamic IP address l A dialup client

A statically addressed remote gateway is the simplest to configure. You specify the IP address. Unless restricted in the security policy, either the remote peer or a peer on the network behind the FortiGate unit can bring up the tunnel.

If the remote peer has a domain name and subscribes to a dynamic DNS service, you need to specify only the domain name. The FortiGate unit performs a DNS query to determine the appropriate IP address. Unless restricted in the security policy, either the remote peer or a peer on the network behind the FortiGate unit can bring up the tunnel.

If the remote peer is a dialup client, only the dialup client can bring up the tunnel. The IP address of the client is not known until it connects to the FortiGate unit. This configuration is a typical way to provide a VPN for client PCs running VPN client software such as the FortiClient Endpoint Security application.

The local end of the VPN tunnel, the Local Interface, is the FortiGate interface that sends and receives the IPsec packets. This is usually the public interface of the FortiGate unit that is connected to the Internet (typically the WAN1 port). Packets from this interface pass to the private network through a security policy.

By default, the local VPN gateway is the IP address of the selected Local Interface. If you are configuring an interface mode VPN, you can optionally use a secondary IP address of the Local Interface as the local gateway.

Choosing Main mode or Aggressive mode

The FortiGate unit and the remote peer or dialup client exchange Phase 1 parameters in either Main mode or Aggressive mode. This choice does not apply if you use IKE version 2, which is available only for route-based configurations.

l In Main mode, the Phase 1 parameters are exchanged in multiple rounds with encrypted authentication information l In Aggressive mode, the Phase 1 parameters are exchanged in a single message with unencrypted authentication information.

Although Main mode is more secure, you must select Aggressive mode if there is more than one dialup Phase 1 configuration for the interface IP address, and the remote VPN peer or client is authenticated using an identifier local ID. Aggressive mode might not be as secure as Main mode, but the advantage to Aggressive mode is that it Choosing the IKE version

is faster than Main mode (since fewer packets are exchanged). Aggressive mode is typically used for remote access VPNs. But you would also use aggressive mode if one or both peers have dynamic external IP addresses. Descriptions of the peer options in this guide indicate whether Main or Aggressive mode is required.


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