Category Archives: FortiOS

Phase 2 parameters

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Phase 2 parameters

This section describes the Phase 2 parameters that are required to establish communication through a VPN. The following topics are included in this section:

Phase 2 settings

Configuring the Phase 2 parameters

 

Phase 2 settings

After IPsec VPN Phase 1 negotiations complete successfully, Phase 2 negotiation begins. Phase 2 parameters define the algorithms that the FortiGate unit can use to encrypt and transfer data for the remainder of the session. The basic Phase 2 settings associate IPsec Phase 2 parameters with a Phase 1 configuration.

When defining Phase 2 parameters, you can choose any set of Phase 1 parameters to set up a secure connection and authenticate the remote peer.

For more information on Phase 2 settings in the web-based manager, see IPsec VPN in the web-based manager on page 1611.

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

 

Phase 2 Proposals

In Phase 2, the VPN peer or client and the FortiGate unit exchange keys again to establish a secure communication channel. The Phase 2 Proposal parameters select the encryption and authentication algorithms needed to generate keys for protecting the implementation details of Security Associations (SAs). The keys are generated automatically using a Diffie-Hellman algorithm.

 

Replay Detection

IPsec tunnels can be vulnerable to replay attacks. Replay Detection enables the FortiGate unit to check all IPsec packets to see if they have been received before. If any encrypted packets arrive out of order, the FortiGate unit discards them.

 

IKE/IPsec Extended Sequence Number (ESN) support

64-bit Extended Sequence numbers (as described in RFC 4303, RFC 4304 as an addition to IKEv1, and RFC 5996 for IKEv2.) are supported for IPsec when Replay Detection is enabled.

 

Perfect Forward Secrecy (PFS)

By default, Phase 2 keys are derived from the session key created in Phase 1. Perfect Forward Secrecy (PFS) forces a new Diffie-Hellman exchange when the tunnel starts and whenever the Phase 2 keylife expires, causing a new key to be generated each time. This exchange ensures that the keys created in Phase 2 are unrelated to the Phase 1 keys or any other keys generated automatically in Phase 2.

 

Keylife

The Keylife setting sets a limit on the length of time that a Phase 2 key can be used. The default units are seconds. Alternatively, you can set a limit on the number of kilobytes (KB) of processed data, or both. If you select both, the key expires when either the time has passed or the number of KB have been processed. When the Phase 2 key expires, a new key is generated without interrupting service.

 

Quick mode selectors

Quick mode selectors determine which IP addresses can perform IKE negotiations to establish a tunnel. By only allowing authorized IP addresses access to the VPN tunnel, the network is more secure.

The default settings are as broad as possible: any IP address or configured address object, using any protocol, on any port.

While the drop down menus for specifying an address also show address groups, the use of address groups is not supported.

The two types of objects have been broken into sections with the address groups at the bottom of the list to make it easy to determine if one of the choices in the drop down menu is an address or an address group.

When configuring Quick Mode selector Source address and Destination address, valid options include IPv4 and IPv6 single addresses, IPv4 subnet, or IPv6 subnet. For more information on IPv6 IPsec VPN, see IPv6 IPsec VPNs on page 1764.

 

There are some configurations that require specific selectors:

  • The VPN peer is a third-party device that uses specific phase2 selectors.
  • The FortiGate unit connects as a dialup client to another FortiGate unit, in which case (usually) you must specify a source IP address, IP address range, or subnet. However, this is not required if you are using dynamic routing and mode-cfg.

 

With FortiOS VPNs, your network has multiple layers of security, with quick mode selectors being an important line of defence.

  • Routes guide traffic from one IP address to another.
  • Phase 1 and Phase 2 connection settings ensure there is a valid remote end point for the VPN tunnel that agrees on the encryption and parameters.
  • Quick mode selectors allow IKE negotiations only for allowed peers.
  • Security policies control which IP addresses can connect to the VPN.
  • Security policies also control what protocols are allowed over the VPN along with any bandwidth limiting.

FortiOS is limited with IKEv2 selector matching. When using IKEv2 with a named traffic selector, no more than 32 subnets per traffic selector are added, since FortiOS doesn’t fully implement the IKEv2 selector matching rules.

The workaround is to use multiple Phase 2s. If the configuration is FGT <-> FGT, then the better alternative is to just use 0.0.0.0 <-> 0.0.0.0 and use the firewall policy for enforcement.

 

Using the add-route option

Consider using the add-route option to add a route to a peer destination selector. Phase 2 includes the option of allowing the add-route to automatically match the settings in Phase 1. For more information, refer to Phase 1 parameters on page 1624.

 

Syntax

Phase 2

config vpn ipsec {phase2 | phase2-interface}

edit <name>

set add-route {phase1 | enable | disable}

end end

 

Configuring the Phase 2 parameters

If you are creating a hub-and-spoke configuration or an Internet-browsing configuration, you may have already started defining some of the required Phase 2 parameters. If so, edit the existing definition to complete the configuration.

 

Specifying the Phase 2 parameters

1. Go to VPN > IPsec Tunnels and create the new custom tunnel or edit an existing tunnel.

2. Open the Phase 2 Selectors panel (if it is not available, you may need to click the Convert to Custom Tunnel button).

3. Enter a Name for the Phase 2 configuration, and select a Phase 1 configuration from the drop-down list.

4. Select Advanced.

5. Include the appropriate entries as follows:

 

Phase 2 Proposal                      Select the encryption and authentication algorithms that will be used to change data into encrypted code.

or delete encryption and authentication algorithms as required. Select a minimum of one and a maximum of three combinations. The remote peer must be configured to use at least one of the proposals that you define.

It is invalid to set both Encryption and Authentication to null.

Encryption                                         Select a symmetric-key algorithms:

NULL — Do not use an encryption algorithm.

DES — Digital Encryption Standard, a 64-bit block algorithm that uses a 56-bit key.

3DES — Triple-DES; plain text is encrypted three times by three keys.

AES128 — A 128-bit block algorithm that uses a 128-bit key.

AES192 — A 128-bit block algorithm that uses a 192-bit key.

AES256 — A 128-bit block algorithm that uses a 256-bit key.

Authentication                           You can select either of the following message digests to check the authen- ticity of messages during an encrypted session:

NULL — Do not use a message digest.

MD5 — Message Digest 5.

SHA1 — Secure Hash Algorithm 1 – a 160-bit message digest.

To specify one combination only, set the Encryption and Authentication options of the second combination to NULL. To specify a third com- bination, use the Add button beside the fields for the second combination.

For information regarding NP accelerated offloading of IPsec VPN authen- tication algorithms, please refer to the Hardware Acceleration handbook chapter.

Enable replay detection           Optionally enable or disable replay detection. Replay attacks occur when an unauthorized party intercepts a series of IPsec packets and replays them back into the tunnel.

Enable perfect forward secrecy (PFS)

Enable or disable PFS. Perfect forward secrecy (PFS) improves security by forcing a new Diffie-Hellman exchange whenever keylife expires.

Diffie–Hellman Group                Select one Diffie-Hellman group (1, 2, 5, or 14 through 21). The remote peer or dialup client must be configured to use the same group.

Keylife                                        Select the method for determining when the Phase 2 key expires: Seconds, KBytes, or Both. If you select Both, the key expires when either the time has passed or the number of KB have been processed. The range is from 120 to 172800 seconds, or from 5120 to 2147483648 KB.

Autokey Keep Alive                  Enable the option if you want the tunnel to remain active when no data is being processed.

Auto–negotiate                           Enable the option if you want the tunnel to be automatically renegotiated when the tunnel expires.

DHCP–IPsec                                Select Enable if the FortiGate unit acts as a dialup server and FortiGate DHCP server or relay will be used to assign VIP addresses to FortiClient dia- lup clients. The DHCP server or relay parameters must be configured sep- arately.

If the FortiGate unit acts as a dialup server and the FortiClient dialup client VIP addresses match the network behind the dialup server, select Enable to cause the FortiGate unit to act as a proxy for the dialup clients.

This is available only for Phase 2 configurations associated with a dialup Phase 1 configuration. It works only on policy-based VPNs.

 

Autokey Keep Alive

The Phase 2 SA has a fixed duration. If there is traffic on the VPN as the SA nears expiry, a new SA is negotiated and the VPN switches to the new SA without interruption. If there is no traffic, however, the SA expires (by default) and the VPN tunnel goes down. A new SA will not be generated until there is traffic.

The Autokey Keep Alive option ensures that a new Phase 2 SA is negotiated, even if there is no traffic, so that the VPN tunnel stays up.

 

Auto–negotiate

By default, the Phase 2 security association (SA) is not negotiated until a peer attempts to send data. The triggering packet and some subsequent packets are dropped until the SA is established. Applications normally resend this data, so there is no loss, but there might be a noticeable delay in response to the user.

If the tunnel goes down, the auto-negotiate feature (when enabled) attempts to re-establish the tunnel. Auto- negotiate initiates the Phase 2 SA negotiation automatically, repeating every five seconds until the SA is established.

Automatically establishing the SA can be important for a dialup peer. It ensures that the VPN tunnel is available for peers at the server end to initiate traffic to the dialup peer. Otherwise, the VPN tunnel does not exist until the dialup peer initiates traffic.

The auto-negotiate feature is available through the Command Line Interface (CLI) via the following commands:

config vpn ipsec phase2 edit <phase2_name>

set auto-negotiate enable end

 

Installing dynamic selectors via auto-negotiate

The IPsec SA connect message generated is used to install dynamic selectors. These selectors can now be installed via the auto-negotiate mechanism. When phase 2 has auto-negotiate enabled, and phase 1 has mesh- selector-type set to subnet, a new dynamic selector will be installed for each combination of source and destination subnets. Each dynamic selector will inherit the auto-negotiate option from the template selector and begin SA negotiation. Phase 2 selector sources from dial-up clients will all establish SAs without traffic being initiated from the client subnets to the hub.

 

DHCP–IPsec

Select this option if the FortiGate unit assigns VIP addresses to FortiClient dialup clients through a DHCP server or relay. This option is available only if the Remote Gateway in the Phase 1 configuration is set to Dialup User and it works only on policy-based VPNs.

With the DHCP-IPsec option, the FortiGate dialup server acts as a proxy for FortiClient dialup clients that have VIP addresses on the subnet of the private network behind the FortiGate unit. In this case, the FortiGate dialup server acts as a proxy on the local private network for the FortiClient dialup client. When a host on the network behind the dialup server issues an ARP request that corresponds to the device MAC address of the FortiClient host (when a remote server sends an ARP to the local FortiClient dialup client), the FortiGate unit answers the ARP request on behalf of the FortiClient host and forwards the associated traffic to the FortiClient host through the tunnel.

This feature prevents the VIP address assigned to the FortiClient dialup client from causing possible arp broadcast problems — the normal and VIP addresses can confuse some network switches by two addresses having the same MAC address.

 


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FortiGate IPSec Phase 1 parameters

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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.

For more information on Phase 1 parameters in the web-based manager, see IPsec VPN in the web-based manager on page 1611.

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
  • 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.
  • 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 1611.

If you want to control how IKE is negotiated when there is no traffic, as well as the length of time the unit waits for negotiations to occur, use the negotiation-timeout and auto-negotiate commands in the CLI.

 

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:

  • A static IP address
  • A domain name with a dynamic IP address
  • 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.

  • In Main mode, the Phase 1 parameters are exchanged in multiple rounds with encrypted authentication information
  • 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 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.

 

Choosing the IKE version

If you create a route-based VPN, you have the option of selecting IKE version 2. Otherwise, IKE version 1 is used. IKEv2, defined in RFC 4306, simplifies the negotiation process that creates the security association (SA).

If you select IKEv2:

  • There is no choice in Phase 1 of Aggressive or Main mode.
  • FortiOS does not support Peer Options or Local ID.
  • Extended Authentication (XAUTH) is not available.
  • You can select only one Diffie-Hellman Group.
  • You can utilize EAP and MOBIKE.

 

IKEv2 cookie notification for IKE_SA_INIT

IKEv2 offers an optional exchange within IKE_SA_INIT (the initial exchange between peers when establishing a secure tunnel) as a reuslt of an inherent vulnerability in IPsec implementations, as described in RFC 5996.

Two expected attacks against IKE are state and CPU exhaustion, where the target is flooded with session initiation requests from forged IP addresses. These attacks can be made less effective if a responder uses minimal CPU and commits no state to an SA until it knows the initiator can receive packets at the address from which it claims to be sending them.

If the IKE_SA_INIT response includes the cookie notification, the initiator MUST then retry the IKE_SA_INIT request, and include the cookie notification containing the received data as the first payload, and all other payloads unchanged.

Upon detecting that the number of half-open IKEv2 SAs is above the threshold value, the VPN dialup server requires all future SA_INIT requests to include a valid cookie notification payload that the server sends back, in order to preserve CPU and memory resources.

For most devices, the threshold value is set to 500, half of the maximum 1,000 connections. This feature is enabled by default in FortiOS 5.4.

IKEv2 Quick Crash Detection

There is support for IKEv2 Quick Crash Detection as described in RFC 6290.

RFC 6290 describes a method in which an IKE peer can quickly detect that the gateway peer that it has and established an IKE session with has rebooted, crashed, or otherwise lost IKE state. When the gateway receives IKE messages or ESP packets with unknown IKE or IPsec SPIs, the IKEv2 protocol allows the gateway to send the peer an unprotected IKE message containing INVALID_IKE_SPI or INVALID_SPI notification payloads.

RFC 6290 introduces the concept of a QCD token, which is generated from the IKE SPIs and a private QCD secret, and exchanged between peers during the protected IKE AUTH exchange.

 

To add Quick Crash Detection – CLI Syntax

config system settings

set ike-quick-crash-detect [enable | disable]

end

 

Authenticating the FortiGate unit

The FortiGate unit can authenticate itself to remote peers or dialup clients using either a pre-shared key or an RSA Signature (certificate).

 

Authenticating the FortiGate unit with digital certificates

To authenticate the FortiGate unit using digital certificates, you must have the required certificates installed on the remote peer and on the FortiGate unit. The signed server certificate on one peer is validated by the presence of the root certificate installed on the other peer. If you use certificates to authenticate the FortiGate unit, you can also require the remote peers or dialup clients to authenticate using certificates.

For more information about obtaining and installing certificates, see the FortiOS User Authentication guide.

 

To authenticate the FortiGate unit using digital certificates

1. Go to VPN > IPsec Tunnels and create the new custom tunnel or edit an existing tunnel.

2. Edit the Phase 1 Proposal (if it is not available, you may need to click the Convert to Custom Tunnel button):

Name                                           Enter a name that reflects the origination of the remote connection. For interface mode, the name can be up to 15 characters long.

Remote Gateway                       Select the nature of the remote connection.

Each option changes the available fields you must configure. For more information, see Authenticating the FortiGate unit on page 1627.

Local Interface                          Select the interface that is the local end of the IPsec tunnel. For more information, see Authenticating the FortiGate unit on page 1627. The local interface is typically the WAN1 port.

Mode                                           Select a mode. It is easier to use Aggressive mode.

In Main mode, parameters are exchanged in multiple encrypted rounds. In Aggressive mode, parameters are exchanged in a single unencrypted message.

Aggressive mode must be used when the remote VPN peer or client has a dynamic IP address, or the remote VPN peer or client will be authenticated using an identifier (local ID).

For more information, see Authenticating the FortiGate unit on page 1627.

Authentication Method            Select Signature.

Certificate Name                        Select the name of the server certificate that the FortiGate unit will use to authenticate itself to the remote peer or dialup client during Phase 1 nego- tiations.

You must obtain and load the required server certificate before this selec- tion. See the FortiOS User Authentication guide. If you have not loaded any certificates, use the certificate named Fortinet_Factory.

Peer Options                             Peer options define the authentication requirements for remote peers or dialup clients. They are not for your FortiGate unit itself.

See Authenticating the FortiGate unit on page 1627.

Advanced                                   You can use the default settings for most Phase 1 configurations. Changes are required only if your network requires them. These settings includes IKE version, DNS server, P1 proposal encryption and authentication set- tings, and XAuth settings. See Authenticating the FortiGate unit on page 1627.

3. If you are configuring authentication parameters for a dialup user group, optionally define extended authentication

(XAuth) parameters in the Advanced section. See Authenticating the FortiGate unit on page 1627.

4. Select OK.

 

Authenticating the FortiGate unit with a pre-shared key

The simplest way to authenticate a FortiGate unit to its remote peers or dialup clients is by means of a pre-shared key. This is less secure than using certificates, especially if it is used alone, without requiring peer IDs or extended authentication (XAuth). Also, you need to have a secure way to distribute the pre-shared key to the peers.

If you use pre-shared key authentication alone, all remote peers and dialup clients must be configured with the same pre-shared key. Optionally, you can configure remote peers and dialup clients with unique pre-shared keys. On the FortiGate unit, these are configured in user accounts, not in the phase_1 settings. For more information, see Authenticating the FortiGate unit on page 1627.

The pre-shared key must contain at least 6 printable characters and best practices dictate that it be known only to network administrators. For optimum protection against currently known attacks, the key must consist of a minimum of 16 randomly chosen alphanumeric characters.

If you authenticate the FortiGate unit using a pre-shared key, you can require remote peers or dialup clients to authenticate using peer IDs, but not client certificates.

 

To authenticate the FortiGate unit with a pre-shared key

1. Go to VPN > IPsec Tunnels and create the new custom tunnel or edit an existing tunnel.

2. Edit the Phase 1 Proposal (if it is not available, you may need to click the Convert to Custom Tunnel button):

Name                                           Enter a name that reflects the origination of the remote connection.

Remote Gateway                       Select the nature of the remote connection. For more information, see Authenticating the FortiGate unit on page 1627.

Local Interface                          Select the interface that is the local end of the IPsec tunnel. For more information, see Authenticating the FortiGate unit on page 1627. The local interface is typically the WAN1 port.

Mode                                           Select Main or Aggressive mode.

In Main mode, the Phase 1 parameters are exchanged in multiple rounds with encrypted authentication information.

In Aggressive mode, the Phase 1 parameters are exchanged in single message with authentication information that is not encrypted.

When the remote VPN peer or client has a dynamic IP address, or the remote VPN peer or client will be authenticated using an identifier (local ID), you must select Aggressive mode if there is more than one dialup Phase 1 configuration for the interface IP address.

For more information, see Authenticating the FortiGate unit on page 1627.

 

Authentication Method            Select Pre–shared Key.

Pre–shared Key                          Enter the preshared key that the FortiGate unit will use to authenticate itself to the remote peer or dialup client during Phase 1 negotiations. You must define the same value at the remote peer or client. The key must con- tain at least 6 printable characters and best practices dictate that it only be known by network administrators. For optimum protection against currently known attacks, the key must consist of a minimum of 16 randomly chosen alphanumeric characters.

Peer options                              Peer options define the authentication requirements for remote peers or dialup clients, not for the FortiGate unit itself. You can require the use of peer IDs, but not client certificates. For more information, see Authentic- ating the FortiGate unit on page 1627.

Advanced                                   You can retain the default settings unless changes are needed to meet your specific requirements. See Authenticating the FortiGate unit on page 1627.

3. If you are configuring authentication parameters for a dialup user group, optionally define extended authentication

(XAuth) parameters. See Authenticating the FortiGate unit on page 1627.

4. Select OK.

 

Authenticating remote peers and clients

Certificates or pre-shared keys restrict who can access the VPN tunnel, but they do not identify or authenticate the remote peers or dialup clients. You have the following options for authentication:

 

Methods of authenticating remote VPN peers

Certificates or Pre-shared key        Local ID  User account pre- shared keys

Reference

Certificates                                                                                                       See Enabling VPN access for specific certificate holders on page 1630.

Either                                                        X                                                  See Enabling VPN access by peer identifier on page 1632.

Pre–shared key                                                                       X                     See Enabling VPN access with user accounts and pre-shared keys on page 1633.

Pre–shared key                                        X                          X

See Enabling VPN access with user accounts and pre-shared keys on page 1633.

Repeated Authentication in Internet Key Exchange (IKEv2) Protocol

This feature provides the option to control whether a device requires its peer to re-authenticate or whether re-key is sufficient. It does not influence the re-authentication or re-key behavior of the device itself, which is controlled by the peer (with the default being to re-key).

This solution is in response to RFC 4478. This solution is intended to limit the time that security associations (SAs) can be used by a third party who has gained control of the IPsec peer.

 

CLI Syntax:

config vpn ipsec phase1-interface edit p1

set reauth [enable | disable]

next end

disable: Disable IKE SA re-authentication.

enable: Enable IKE SA re-authentication.

 

Enabling VPN access for specific certificate holders

When a VPN peer or dialup client is configured to authenticate using digital certificates, it sends the Distinguished Name (DN) of its certificate to the FortiGate unit. This DN can be used to allow VPN access for the certificate holder. That is, a FortiGate unit can be configured to deny connections to all remote peers and dialup clients except the one having the specified DN.

 

Before you begin

The following procedures assume that you already have an existing Phase 1 configuration (see Authenticating remote peers and clients on page 1629). Follow the procedures below to add certificate-based authentication parameters to the existing configuration.

Before you begin, you must obtain the certificate DN of the remote peer or dialup client. If you are using the FortiClient application as a dialup client, refer to FortiClient online help for information about how to view the certificate DN. To view the certificate DN of a FortiGate unit, see To view server certificate information and obtain the local DN on page 1631.

Use the config user peer CLI command to load the DN value into the FortiGate configuration. For example, if a remote VPN peer uses server certificates issued by your own organization, you would enter information similar to the following:

config user peer edit DN_FG1000

set cn 192.168.2.160 set cn-type ipv4

end

The value that you specify to identify the entry (for example, DN_FG1000) is displayed in the Accept this peer certificate only list in the IPsec Phase 1 configuration when you return to the web-based manager.

If the remote VPN peer has a CA-issued certificate to support a higher level of credibility, you would enter information similar to the following in the CLI:

config user peer edit CA_FG1000

set ca CA_Cert_1

set subject FG1000_at_site1

end

 

The value that you specify to identify the entry (for example, CA_FG1000) is displayed in the Accept this peer certificate only list in the IPsec Phase 1 configuration when you return to the web-based manager. For more information about these CLI commands, see the “user” chapter of the FortiGate CLI Reference.

A group of certificate holders can be created based on existing user accounts for dialup clients. To create the user accounts for dialup clients, see the “User” chapter of the FortiGate Administration Guide. To create the certificate group afterward, use the config user peergrp CLI command. See the “user” chapter of the FortiGate CLI Reference.

 

To view server certificate information and obtain the local DN

1. Go to System > Certificates.

2. Note the CN value in the Subject field (for example, CN = 16.10.125, CN = info@fortinet.com, or CN = www.example.com).

 

To view CA root certificate information and obtain the CA certificate name

1. Go to System > Certificates > CA Certificates.

2. Note the value in the Name column (for example, CA_Cert_1).

 

Configuring certificate authentication for a VPN

With peer certificates loaded, peer users and peer groups defined, you can configure your VPN to authenticate users by certificate.

 

To enable access for a specific certificate holder or a group of certificate holders

1. At the FortiGate VPN server, go to VPN > IPsec Tunnels and create the new custom tunnel or edit an existing tunnel.

2. Edit the Phase 1 Proposal (if it is not available, you may need to click the Convert to Custom Tunnel button).

3. From the Authentication Method list, select RSA Signature.

4. From the Certificate Name list, select the name of the server certificate that the FortiGate unit will use to authenticate itself to the remote peer or dialup client

5. Under Peer Options, select one of these options:

  • To accept a specific certificate holder, select Accept this peer certificate only and select the name of the certificate that belongs to the remote peer or dialup client. The certificate DN must be added to the FortiGate configuration through CLI commands before it can be selected here. See Before you begin on page 1630.
  • To accept dialup clients who are members of a certificate group, select Accept this peer certificate group only and select the name of the group. The group must be added to the FortiGate configuration through CLI commands before it can be selected here. See Before you begin on page 1630.

6. If you want the FortiGate VPN server to supply the DN of a local server certificate for authentication purposes, select Advanced and then from the Local ID list, select the DN of the certificate that the FortiGate VPN server is to use.

7. Select OK.

 

Enabling VPN access by peer identifier

Whether you use certificates or pre-shared keys to authenticate the FortiGate unit, you can require that remote peers or clients have a particular peer ID. This adds another piece of information that is required to gain access to the VPN. More than one FortiGate/FortiClient dialup client may connect through the same VPN tunnel when the dialup clients share a preshared key and assume the same identifier.

A peer ID, also called local ID, can be up to 63 characters long containing standard regular expression characters. Local ID is set in phase1 Aggressive Mode configuration.

You cannot require a peer ID for a remote peer or client that uses a pre-shared key and has a static IP address.

To authenticate remote peers or dialup clients using one peer ID

1. At the FortiGate VPN server, go to VPN > IPsec Tunnels and create the new custom tunnel or edit an existing tunnel.

2. Edit the Phase 1 Proposal (if it is not available, you may need to click the Convert to Custom Tunnel button).

3. Select Aggressive mode in any of the following cases:

  • The FortiGate VPN server authenticates a FortiGate dialup client that uses a dedicated tunnel
  • A FortiGate unit has a dynamic IP address and subscribes to a dynamic DNS service
  • FortiGate/FortiClient dialup clients sharing the same preshared key and local ID connect through the same VPN tunnel

4. For the Peer Options, select This peer ID and type the identifier into the corresponding field.

5. Select OK.

To assign an identifier (local ID) to a FortiGate unit

Use this procedure to assign a peer ID to a FortiGate unit that acts as a remote peer or dialup client.

1. Go to VPN > IPsec Tunnels and create the new custom tunnel or edit an existing tunnel.

2. Edit the Phase 1 Proposal (if it is not available, you may need to click the Convert to Custom Tunnel button).

3. Select Advanced.

4. In the Local ID field, type the identifier that the FortiGate unit will use to identify itself.

5. Set Mode to Aggressive if any of the following conditions apply:

  • The FortiGate unit is a dialup client that will use a unique ID to connect to a FortiGate dialup server through a dedicated tunnel.
  • The FortiGate unit has a dynamic IP address, subscribes to a dynamic DNS service, and will use a unique ID to connect to the remote VPN peer through a dedicated tunnel.
  • The FortiGate unit is a dialup client that shares the specified ID with multiple dialup clients to connect to a FortiGate dialup server through the same tunnel.

6. Select OK.

 

To configure the FortiClient application

Follow this procedure to add a peer ID to an existing FortiClient configuration:

1. Start the FortiClient application.

2. Go to VPN > Connections, select the existing configuration.

3. Select Advanced > Edit > Advanced.

4. Under Policy, select Config.

5. In the Local ID field, type the identifier that will be shared by all dialup clients. This value must match the This peer ID value that you specified previously in the Phase 1 gateway configuration on the FortiGate unit.

6. Select OK to close all dialog boxes.

7. Configure all dialup clients the same way using the same preshared key and local ID.

 

Enabling VPN access with user accounts and pre-shared keys

You can permit access only to remote peers or dialup clients that have pre-shared keys and/or peer IDs configured in user accounts on the FortiGate unit.

If you want two VPN peers (or a FortiGate unit and a dialup client) to accept reciprocal connections based on peer IDs, you must enable the exchange of their identifiers when you define the Phase 1 parameters.

The following procedures assume that you already have an existing Phase 1 configuration (see Authenticating remote peers and clients on page 1629). Follow the procedures below to add ID checking to the existing configuration.

Before you begin, you must obtain the identifier (local ID) of the remote peer or dialup client. If you are using the FortiClient Endpoint Security application as a dialup client, refer to the Authenticating FortiClient Dialup Clients Technical Note to view or assign an identifier. To assign an identifier to a FortiGate dialup client or a FortiGate unit that has a dynamic IP address and subscribes to a dynamic DNS service, see To assign an identifier (local ID) to a FortiGate unit on page 1632.

If required, a dialup user group can be created from existing user accounts for dialup clients. To create the user accounts and user groups, see the User Authentication handbook chapter.

The following procedure supports FortiGate/FortiClient dialup clients that use unique preshared keys and/or peer IDs. The client must have an account on the FortiGate unit and be a member of the dialup user group.

The dialup user group must be added to the FortiGate configuration before it can be selected. For more information, see the User Authentication handbook chapter.

The FortiGate dialup server compares the local ID that you specify at each dialup client to the FortiGate user- account user name. The dialup-client preshared key is compared to a FortiGate user-account password.

 

To authenticate dialup clients using unique preshared keys and/or peer IDs

1. At the FortiGate VPN server, go to VPN > IPsec Tunnels and create the new custom tunnel or edit an existing tunnel.

2. Edit the Phase 1 Proposal (if it is not available, you may need to click the Convert to Custom Tunnel button).

3. If the clients have unique peer IDs, set Mode to Aggressive.

4. Clear the Pre–shared Key field.

The user account password will be used as the preshared key.

5. Select Peer ID from dialup group and then select the group name from the list of user groups.

6. Select OK.

Follow this procedure to add a unique pre-shared key and unique peer ID to an existing FortiClient configuration.

 

To configure FortiClient – pre-shared key and peer ID

1. Start the FortiClient Endpoint Security application.

2. Go to VPN > Connections, select the existing configuration.

3. Select Advanced > Edit.

4. In the Preshared Key field, type the FortiGate password that belongs to the dialup client (for example, 1234546).

The user account password will be used as the preshared key.

5. Select Advanced.

6. Under Policy, select Config.

7. In the Local ID field, type the FortiGate user name that you assigned previously to the dialup client (for example, FortiClient).

8. Select OK to close all dialog boxes.

Configure all FortiClient dialup clients this way using unique preshared keys and local IDs. Follow this procedure to add a unique pre-shared key to an existing FortiClient configuration.

 

To configure FortiClient – preshared key only

1. Start the FortiClient Endpoint Security application.

2. Go to VPN > Connections, select the existing configuration

3. Select Advanced > Edit.

4. In the Preshared Key field, type the user name, followed by a “+” sign, followed by the password that you specified previously in the user account settings on the FortiGate unit (for example, FC2+1FG6LK)

5. Select OK to close all dialog boxes.

Configure all the FortiClient dialup clients this way using their unique peer ID and pre-shared key values.

 

 

Defining IKE negotiation parameters

In Phase 1, the two peers exchange keys to establish a secure communication channel between them. As part of the Phase 1 process, the two peers authenticate each other and negotiate a way to encrypt further communications for the duration of the session. For more information see Defining IKE negotiation parameters on page 1635. The Phase 1 Proposal parameters select the encryption and authentication algorithms that are used to generate keys for protecting negotiations.

 

The IKE negotiation parameters determine:

  • Which encryption algorithms may be applied for converting messages into a form that only the intended recipient can read
  • Which authentication hash may be used for creating a keyed hash from a preshared or private key
  • Which Diffie-Hellman group (DH Group) will be used to generate a secret session key

Phase 1 negotiations (in main mode or aggressive mode) begin as soon as a remote VPN peer or client attempts to establish a connection with the FortiGate unit. Initially, the remote peer or dialup client sends the FortiGate unit a list of potential cryptographic parameters along with a session ID. The FortiGate unit compares those parameters to its own list of advanced Phase 1 parameters and responds with its choice of matching parameters to use for authenticating and encrypting packets. The two peers handle the exchange of encryption keys between them, and authenticate the exchange through a preshared key or a digital signature.

 

Generating keys to authenticate an exchange

The FortiGate unit supports the generation of secret session keys automatically using a Diffie-Hellman algorithm. These algorithms are defined in RFC 2409. The Keylife setting in the Phase 1 Proposal area determines the amount of time before the Phase 1 key expires. Phase 1 negotiations are re-keyed automatically when there is an active security association. See Dead peer detection on page 1638.

You can enable or disable automatic re-keying between IKE peers through the phase1-rekey attribute of the config system global CLI command. For more information, see the “System” chapter of the FortiGate CLI Reference.

When in FIPS-CC mode, the FortiGate unit requires DH key exchange to use values at least 3072 bits long. However most browsers need the key size set to 1024. You can set the minimum size of the DH keys in the CLI.

config system global set dh-params 3072

end

When you use a preshared key (shared secret) to set up two-party authentication, the remote VPN peer or client and the FortiGate unit must both be configured with the same preshared key. Each party uses a session key derived from the Diffie-Hellman exchange to create an authentication key, which is used to sign a known combination of inputs using an authentication algorithm (such as HMAC-MD5, HMAC-SHA-1, or HMAC-SHA-256). Hash-based Message Authentication Code (HMAC) is a method for calculating an authentication code using a hash function plus a secret key, and is defined in RFC 2104. Each party signs a different combination of inputs and the other party verifies that the same result can be computed.

For information regarding NP accelerated offloading of IPsec VPN authentication algorithms, please refer to the Hardware Acceleration handbook chapter.

When you use preshared keys to authenticate VPN peers or clients, you must distribute matching information to all VPN peers and/or clients whenever the preshared key changes.

As an alternative, the remote peer or dialup client and FortiGate unit can exchange digital signatures to validate each other’s identity with respect to their public keys. In this case, the required digital certificates must be installed on the remote peer and on the FortiGate unit. By exchanging certificate DNs, the signed server certificate on one peer is validated by the presence of the root certificate installed on the other peer.

The following procedure assumes that you already have a Phase 1 definition that describes how remote VPN peers and clients will be authenticated when they attempt to connect to a local FortiGate unit. For information about the Local ID and XAuth options, see Defining IKE negotiation parameters on page 1635 and Defining IKE negotiation parameters on page 1635. Follow this procedure to add IKE negotiation parameters to the existing definition.

 

Defining IKE negotiation parameters

1. Go to VPN > IPsec Tunnels and create the new custom tunnel or edit an existing tunnel.

2. Edit the Phase 1 Proposal (if it is not available, you may need to click the Convert to Custom Tunnel button).

3. Select Phase 1 Proposal and include the appropriate entries as follows:

Phase 1 Proposal                      Select the encryption and authentication algorithms that will be used to generate keys for protecting negotiations.

Add or delete encryption and authentication algorithms as required. Select a minimum of one and a maximum of three combinations. The remote peer must be configured to use at least one of the proposals that you define.

It is invalid to set both Encryption and Authentication to null.

Encryption                                 Select a symmetric-key algorithms:

NULL — Do not use an encryption algorithm.

DES — Digital Encryption Standard, a 64-bit block algorithm that uses a

56-bit key.

3DES — Triple-DES; plain text is encrypted three times by three keys.

AES128 — A 128-bit block algorithm that uses a 128-bit key. AES192 — A 128-bit block algorithm that uses a 192-bit key. AES256 — A 128-bit block algorithm that uses a 256-bit key.

Authentication                           You can select either of the following message digests to check the authen- ticity of messages during an encrypted session:

NULL — Do not use a message digest.

MD5 — Message Digest 5.

SHA1 — Secure Hash Algorithm 1 – a 160-bit message digest.

To specify one combination only, set the Encryption and Authentication options of the second combination to NULL. To specify a third com- bination, use the Add button beside the fields for the second combination.

For information regarding NP accelerated offloading of IPsec VPN authen- tication algorithms, please refer to the Hardware Acceleration handbook chapter.

Diffie–Hellman Group                Select one or more Diffie-Hellman groups from DH groups 1, 2, 5, and 14 through 21. When using aggressive mode, DH groups cannot be nego- tiated. By default, DH group 14 is selected, to provide sufficient protection for stronger cipher suites that include AES and SHA2. If you select multiple DH groups, the order they appear in the configuration is the order in which they are negotiates.

If both VPN peers (or a VPN server and its client) have static IP addresses and use aggressive mode, select a single DH group. The setting on the FortiGate unit must be identical to the setting on the remote peer or dialup client.

When the remote VPN peer or client has a dynamic IP address and uses aggressive mode, select up to three DH groups on the FortiGate unit and one DH group on the remote peer or dialup client. The setting on the remote peer or dialup client must be identical to one of the selections on the FortiGate unit.

If the VPN peer or client employs main mode, you can select multiple DH groups. At least one of the settings on the remote peer or dialup client must be identical to the selections on the FortiGate unit.

Keylife                                        Type the amount of time (in seconds) that will be allowed to pass before the IKE encryption key expires. When the key expires, a new key is gen- erated without interrupting service. The keylife can be from 120 to 172800 seconds.

Nat-traversal                              Enable this option if a NAT device exists between the local FortiGate unit and the VPN peer or client. The local FortiGate unit and the VPN peer or cli- ent must have the same NAT traversal setting (both selected or both cleared). When in doubt, enable NAT-traversal. See NAT traversal on page 1638.

Keepalive Frequency               If you enabled NAT traversal, enter a keepalive frequency setting. The value represents an interval from 0 to 900 seconds where the connection will be maintained with no activity. For additional security this value must be as low as possible. See NAT keepalive frequency on page 1638.

Dead Peer Detection                 Enable this option to reestablish VPN tunnels on idle connections and clean up dead IKE peers if required. This feature minimizes the traffic required to check if a VPN peer is available or unavailable (dead). See Dead peer detection on page 1638.

 

NAT traversal

Network Address Translation (NAT) is a way to convert private IP addresses to publicly routable Internet addresses and vise versa. When an IP packet passes through a NAT device, the source or destination address in the IP header is modified. FortiGate units support NAT version 1 (encapsulate on port 500 with non-IKE marker), version 3 (encapsulate on port 4500 with non-ESP marker), and compatible versions.

NAT cannot be performed on IPsec packets in ESP tunnel mode because the packets do not contain a port number. As a result, the packets cannot be demultiplexed. To work around this, the FortiGate unit provides a way to protect IPsec packet headers from NAT modifications. When the Nat-traversal option is enabled, outbound encrypted packets are wrapped inside a UDP IP header that contains a port number. This extra encapsulation allows NAT devices to change the port number without modifying the IPsec packet directly.

To provide the extra layer of encapsulation on IPsec packets, the Nat-traversal option must be enabled whenever a NAT device exists between two FortiGate VPN peers or a FortiGate unit and a dialup client such as FortiClient. On the receiving end, the FortiGate unit or FortiClient removes the extra layer of encapsulation before decrypting the packet.

Additionally, you can force IPsec to use NAT traversal. If NAT is set to Forced, the FortiGate will use a port value of zero when constructing the NAT discovery hash for the peer. This causes the peer to think it is behind a NAT device, and it will use UDP encapsulation for IPsec, even if no NAT is present. This approach maintains interoperability with any IPsec implementation that supports the NAT-T RFC.

 

NAT keepalive frequency

When a NAT device performs network address translation on a flow of packets, the NAT device determines how long the new address will remain valid if the flow of traffic stops (for example, the connected VPN peer may be idle). The device may reclaim and reuse a NAT address when a connection remains idle for too long.

To work around this, when you enable NAT traversal specify how often the FortiGate unit sends periodic keepalive packets through the NAT device in order to ensure that the NAT address mapping does not change during the lifetime of a session. To be effective, the keepalive interval must be smaller than the session lifetime value used by the NAT device.

The keepalive packet is a 138-byte ISAKMP exchange.

 

Dead peer detection

Sometimes, due to routing issues or other difficulties, the communication link between a FortiGate unit and a VPN peer or client may go down. Packets could be lost if the connection is left to time out on its own. The FortiGate unit provides a mechanism called Dead Peer Detection, sometimes referred to as gateway detection or ping server, to prevent this situation and reestablish IKE negotiations automatically before a connection times out: the active Phase 1 security associations are caught and renegotiated (rekeyed) before the Phase 1 encryption key expires.

By default, Dead Peer Detection sends probe messages every five seconds by default (see dpd- retryinterval in the FortiGate CLI Reference). If you are experiencing high network traffic, you can experiment with increasing the ping interval. However longer intervals will require more traffic to detect dead peers which will result in more traffic.

In the web-based manager, the Dead Peer Detection option can be enabled when you define advanced Phase 1 options. The config vpn ipsec phase1 CLI command supports additional options for specifying a retry count and a retry interval.

For more information about these commands and the related config router gwdetect CLI command, see the FortiGate CLI Reference.

For example, enter the following CLI commands to configure dead peer detection on the existing IPsec Phase 1 configuration called test to use 15 second intervals and to wait for 3 missed attempts before declaring the peer dead and taking action.

config vpn ipsec phase1 edit test

set dpd [disable | on-idle | on-demand]

set dpd-retryinveral 15 set dpd-retrycount 3

next end

 

Using XAuth authentication

Extended authentication (XAuth) increases security by requiring the remote dialup client user to authenticate in a separate exchange at the end of Phase 1. XAuth draws on existing FortiGate user group definitions and uses established authentication mechanisms such as PAP, CHAP, RADIUS, and LDAP to authenticate dialup clients. You can configure a FortiGate unit to function either as an XAuth server or an XAuth client.If the server or client is attempting a connection using XAuth and the other end is not using XAuth, the failed connection attempts that are logged will not specify XAuth as the reason.

Using the FortiGate unit as an XAuth server

A FortiGate unit can act as an XAuth server for dialup clients. When the Phase 1 negotiation completes, the FortiGate unit challenges the user for a user name and password. It then forwards the user’s credentials to an external RADIUS or LDAP server for verification.

If the user records on the RADIUS server have suitably configured Framed-IP-Address fields, you can assign client virtual IP addresses by XAuth instead of from a DHCP address range. See FortiClient dialup-client configurations on page 1702.

The authentication protocol to use for XAuth depends on the capabilities of the authentication server and the XAuth client:

  • Select PAP Server whenever possible.
  • You must select PAP Server for all implementations of LDAP and some implementations of Microsoft RADIUS.
  • Select Auto Server when the authentication server supports CHAP Server but the XAuth client does not. The FortiGate unit will use PAP to communicate with the XAuth client and CHAP to communicate with the authentication server. You can also use Auto Server to allows multiple source interfaces to be defined in an IPsec/IKE policy

Before you begin, create user accounts and user groups to identify the dialup clients that need to access the network behind the FortiGate dialup server. If password protection will be provided through an external RADIUS or LDAP server, you must configure the FortiGate dialup server to forward authentication requests to the authentication server. For information about these topics, see the FortiGate User Authentication Guide.

 

To authenticate a dialup user group using XAuth settings

1. At the FortiGate dialup server, go to VPN > IPsec Tunnels and create the new custom tunnel or edit an existing tunnel.

2. Edit the Phase 1 Proposal (if it is not available, you may need to click the Convert to Custom Tunnel button).

3. Under XAuth, select the Server Type setting, which determines the type of encryption method to use between the XAuth client, the FortiGate unit and the authentication server. Select one of the following options:

  • PAP Server —Password Authentication Protocol.
  • CHAP Server — Challenge-Handshake Authentication Protocol.
  • Auto Server —Use PAP between the XAuth client and the FortiGate unit, and CHAP between the FortiGate unit and the authentication server. This option allows multiple source interfaces to be defined in an IPsec/IKE policy.

4. From the User Group list, select the user group that needs to access the private network behind the FortiGate unit. The group must be added to the FortiGate configuration before it can be selected here. For multiple source interfaces to be defined in the IPsec/IKE policy, select Inherit Groups from Policy.

5. Select OK.

 

Using the FortiGate unit as an XAuth client

If the FortiGate unit acts as a dialup client, the remote peer, acting as an XAuth server, might require a username and password. You can configure the FortiGate unit as an XAuth client, with its own username and password, which it provides when challenged.

 

To configure the FortiGate dialup client as an XAuth client

1. At the FortiGate dialup client, go to VPN > IPsec Tunnels and create the new custom tunnel or edit an existing tunnel.

2. Edit the Phase 1 Proposal (if it is not available, you may need to click the Convert to Custom Tunnel button).

3. Under XAuth, select Enable as Client.

4. In the Username field, type the FortiGate PAP, CHAP, RADIUS, or LDAP user name that the FortiGate XAuth server will compare to its records when the FortiGate XAuth client attempts to connect.

5. In the Password field, type the password to associate with the user name.

6. Select OK.

 

Dynamic IPsec route control

You can add a route to a peer destination selector by using the add-route option, which is available for all dynamic IPsec Phases 1 and 2, for both policy-based and route-based IPsec VPNs. This option was previously only available when mode-cfg was enabled in Phase 1.

The add-route option adds a route to the FortiGate unit’s routing information base when the dynamic tunnel is negotiated. You can use the distance and priority options to set the distance and priority of this route. If this results in a route with the lowest distance, it is added to the FortiGate unit’s forwarding information base.

You can also enable add-route in any policy-based or route-based Phase 2 configuration that is associated with a dynamic (dialup) Phase 1. In Phase 2, add-route can be enabled, disabled, or set to use the same route as Phase 1.

The add-route feature is enabled by default and is configured in the CLI.

 

Syntax

Phase 1

config vpn ipsec edit <name>

set type dynamic

set add-route {enable | disable}

end end

 

Phase 2

 

config vpn ipsec {phase2 | phase2-interface}

edit <name>

set add-route {phase1 | enable | disable}

end end

 

Blocking IPsec SA Negotiation

For interface-based IPsec, IPsec SA negotiation blocking can only be removed if the peer offers a wildcard selector. If a wildcard selector is offered then the wildcard route will be added to the routing table with the distance/priority value configured in Phase 1 and, if that is the route with the lowest distance, it is installed into the forwarding information base.

In cases where this occurs, it is important to ensure that the distance value configured on Phase 1 is set appropriately.

 


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IPsec Monitor

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IPsec Monitor

You can use the IPsec Monitor to view activity on IPsec VPN tunnels and start or stop those tunnels. The display provides a list of addresses, proxy IDs, and timeout information for all active tunnels, including tunnel mode and route-based (interface mode) tunnels.

To view the IPsec monitor, go to Monitor > IPsec Monitor.

For dialup VPNs, the list provides status information about the VPN tunnels established by dialup clients, and their IP addresses.

For static IP or dynamic DNS VPNs, the list provides status and IP addressing information about VPN tunnels, active or not, to remote peers that have static IP addresses or domain names. You can also start and stop individual tunnels from the list.

 


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Concentrator

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Concentrator

In a hub-and-spoke configuration, policy-based VPN connections to a number of remote peers radiate from a single, central FortiGate unit. Site-to-site connections between the remote peers do not exist; however, you can establish VPN tunnels between any two of the remote peers through the FortiGate unit’s “hub”.

In a hub-and-spoke network, all VPN tunnels terminate at the hub. The peers that connect to the hub are known as “spokes”. The hub functions as a concentrator on the network, managing all VPN connections between the spokes. VPN traffic passes from one tunnel to the other through the hub.

You define a concentrator to include spokes in the hub-and-spoke configuration. You create the concentrator in

VPN > IPsec Concentrator and select Create New. A concentrator configuration specifies which spokes to include in an IPsec hub-and-spoke configuration.

Concentrator Name                   Type a name for the concentrator.

Available Tunnels                     A list of defined IPsec VPN tunnels. Select a tunnel from the list and then select the right arrow.

Members                                    A list of tunnels that are members of the concentrator. To remove a tunnel from the concentrator, select the tunnel and select the left arrow.


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FortiClient VPN

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FortiClient VPN

Use the FortiClient VPN for OS X, Windows, and Android VPN Wizard option when configuring an IPsec VPN for remote users to connect to the VPN tunnel using FortiClient.

 

When configuring a FortiClient VPN connection, the settings for Phase 1 and Phase 2 settings are automatically configured by the FortiGate unit. They are set to:

  • Remote Gateway — Dialup User
  • Mode — Aggressive
  • Default settings for Phase 1 and 2 Proposals
  • XAUTH Enable as Server (Auto)
  • IKE mode-config will be enabled
  • Peer Option — “Any peer ID”

The remainder of the settings use the current FortiGate defaults. Note that FortiClient settings need to match these FortiGate defaults. If you need to configure advanced settings for the FortiClient VPN, you must do so using the CLI.

Name                                           Enter a name for the FortiClient VPN.

Local Outgoing Interface         Select the local outgoing interface for the VPN.

Authentication Method            Select the type of authentication used when logging in to the VPN.

Preshared Key                           If Pre–shared Key was selected in Authentication Method, enter the pre-shared key in the field provided.

User Group                                Select a user group. You can also create a user group from the drop-down list by selecting Create New.

Address Range Start IP            Enter the start IP address for the DHCP address range for the client.

Address Range End IP             Enter the end IP address for the address range.

Subnet Mask                              Enter the subnet mask.

Enable IPv4 Split Tunnel         Enabled by default, this option enables the FortiClient user to use the VPN to access internal resources while other Internet access is not sent over the VPN, alleviating potential traffic bottlenecks in the VPN connection. Dis- able this option to have all traffic sent through the VPN tunnel.

Accessible Networks                Select from a list of internal networks that the FortiClient user can access.

Client Options                           These options affect how the FortiClient application behaves when con- nected to the FortiGate VPN tunnel. When enabled, a check box for the cor- responding option appears on the VPN login screen in FortiClient, and is not enabled by default.

Save Password – When enabled, if the user selects this option, their pass- word is stored on the user’s computer and will automatically populate each time they connect to the VPN.

Auto Connect – When enabled, if the user selects this option, when the FortiClient application is launched, for example after a reboot or system startup, FortiClient will automatically attempt to connect to the VPN tunnel.

Always Up (Keep Alive) – When enabled, if the user selects this option, the FortiClient connection will not shut down. When not selected, during periods of inactivity, FortiClient will attempt to stay connected every three minutes for a maximum of 10 minutes.

Endpoint Registration              When selected, the FortiGate unit requests a registration key from FortiCli- ent before a connection can be established. A registration key is defined by going to System > Advanced.

For more information on FortiClient VPN connections to a FortiGate unit, see the FortiClient Administration Guide.

DNS Server                                 Select which DNS server to use for this VPN:

Use System DNS — Use the same DNS servers as the FortiGate unit. These are configured at Network > DNS. This is the default option. Specify — Specify the IP address of a different DNS server.


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Phase 2 configuration

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Phase 2 configuration

After IPsec Phase 1 negotiations end successfully, you begin Phase 2. You can configure the Phase 2 parameters to define the algorithms that the FortiGate unit may use to encrypt and transfer data for the remainder of the session. During Phase 2, you select specific IPsec security associations needed to implement security services and establish a tunnel.

The basic Phase 2 settings associate IPsec Phase 2 parameters with the Phase 1 configuration that specifies the remote end point of the VPN tunnel. In most cases, you need to configure only basic Phase 2 settings.

These settings are mainly configured in the CLI, although some options are available after the tunnel is created using the VPN Creation Wizard (using the Convert to Custom Tunnel option).

Name                                           Type a name to identify the Phase 2 configuration.

Phase 1                                       Select the Phase 1 tunnel configuration. For more information on con- figuring Phase 1, see Phase 1 configuration on page 1611. The Phase 1 configuration describes how remote VPN peers or clients will be authen- ticated on this tunnel, and how the connection to the remote peer or client will be secured.

Advanced                                   Define advanced Phase 2 parameters. For more information, see Phase 2 advanced configuration settings below.

 

Phase 2 advanced configuration settings

In Phase 2, the FortiGate unit and the VPN peer or client exchange keys again to establish a secure communication channel between them. You select the encryption and authentication algorithms needed to generate keys for protecting the implementation details of Security Associations (SAs). These are called Phase 2 Proposal parameters. The keys are generated automatically using a Diffie-Hellman algorithm.

You can use a number of additional advanced Phase 2 settings to enhance the operation of the tunnel.

Phase 2 Proposal                      Select the encryption and authentication algorithms that will be proposed to the remote VPN peer. You can specify up to three proposals. To estab- lish a VPN connection, at least one of the proposals that you specify must match configuration on the remote peer.

Initially there are two proposals. Add and Delete icons are next to the second Authentication field.

It is invalid to set both Encryption and Authentication to NULL.

Encryption                                 Select a symmetric-key algorithms:

NULL — Do not use an encryption algorithm.

DES — Digital Encryption Standard, a 64-bit block algorithm that uses a

56-bit key.

3DES — Triple-DES; plain text is encrypted three times by three keys.

AES128 — A 128-bit block algorithm that uses a 128-bit key. AES192 — A 128-bit block algorithm that uses a 192-bit key. AES256 — A 128-bit block algorithm that uses a 256-bit key.

Authentication                           You can select either of the following message digests to check the authen- ticity of messages during an encrypted session:

NULL — Do not use a message digest.

MD5 — Message Digest 5.

SHA1 — Secure Hash Algorithm 1 – a 160-bit message digest.

 

To specify one combination only, set the Encryption and Authentication options of the second combination to NULL. To specify a third com- bination, use the Add button beside the fields for the second combination.

 

Enable replay detection           Replay attacks occur when an unauthorized party intercepts a series of IPsec packets and replays them back into the tunnel.

 

Enable perfect forward secrecy (PFS)

Perfect forward secrecy (PFS) improves security by forcing a new Diffie-Hellman exchange whenever keylife expires.

 

Diffie–Hellman Group                Select one Diffie-Hellman group (1, 2, 5, or 14 through 21). This must match the DH Group that the remote peer or dialup client uses.

 

Keylife                                        Select the method for determining when the Phase 2 key expires: Seconds, KBytes, or Both. If you select Both, the key expires when either the time has passed or the number of KB have been processed.

 

Autokey Keep Alive                  Select the check box if you want the tunnel to remain active when no data is being processed.

 

Auto–negotiate                           Enable the option if you want the tunnel to be automatically renegotiated when the tunnel expires.

 

DHCP–IPsec                                Provide IP addresses dynamically to VPN clients. This is available for Phase 2 configurations associated with a dialup Phase 1 configuration.

You also need configure a DHCP server or relay on the private network interface. You must configure the DHCP parameters separately.

If you configure the DHCP server to assign IP addresses based on RADIUS user group attributes, you must also set the Phase 1 Peer Options to Peer ID from dialup group and select the appropriate user group. See Phase 1 configuration on page 1611.

If the FortiGate unit acts as a dialup server and you manually assigned FortiClient dialup clients VIP addresses that match the network behind the dialup server, selecting the check box will cause the FortiGate unit to act as a proxy for the dialup clients.

Quick Mode Selector                Specify the source and destination IP addresses to be used as selectors for IKE negotiations. If the FortiGate unit is a dialup server, keep the default value of 0.0.0.0/0 unless you need to circumvent problems caused by ambiguous IP addresses between one or more of the private networks mak- ing up the VPN. You can specify a single host IP address, an IP address range, or a network address. You may optionally specify source and des- tination port numbers and a protocol number.

If you are editing an existing Phase 2 configuration, the Source address and Destination address fields are unavailable if the tunnel has been con- figured to use firewall addresses as selectors. This option exists only in the CLI.

Source address                         If the FortiGate unit is a dialup server, enter the source IP address that cor- responds to the local senders or network behind the local VPN peer (for example, 172.16.5.0/24 or 172.16.5.0/255.255.255.0 for a subnet, or 172.16.5.1/32 or 172.16.5.1/255.255.255.255 for a server or host, or 192.168.10.[80-100] or 192.168.10.80-192.168.10.100 for an address range). A value of 0.0.0.0/0 means all IP addresses behind the local VPN peer.

If the FortiGate unit is a dialup client, source address must refer to the private network behind the Fortinet dialup client.

Source port                                Enter the port number that the local VPN peer uses to transport traffic related to the specified service (protocol number). The range is from 0 to 65535. To specify all ports, type 0.

Destination address                 Enter the destination IP address that corresponds to the recipients or net- work behind the remote VPN peer (for example, 192.168.20.0/24 for a subnet, or 172.16.5.1/32 for a server or host, or 192.168.10.[80-100] for an address range). A value of 0.0.0.0/0 means all IP addresses behind the remote VPN peer.

 

Destination port                        Enter the port number that the remote VPN peer uses to transport traffic related to the specified service (protocol number). To specify all ports, enter 0.

 

Protocol                                      Enter the IP protocol number of the service. To specify all services, enter 0.


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IPsec VPN in the web-based manager

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IPsec VPN in the web-based manager

To configure an IPsec VPN, use the general procedure below. With these steps, your FortiGate unit will automatically generate unique IPsec encryption and authentication keys. If a remote VPN peer or client requires a specific IPsec encryption or authentication key, you must configure your FortiGate unit to use manual keys instead.

1. Define Phase 1 parameters to authenticate remote peers and clients for a secure connection. See IPsec VPN in the web-based manager on page 1611.

2. Define Phase 2 parameters to create a VPN tunnel with a remote peer or dialup client. See IPsec VPN in the web- based manager on page 1611.

3. Create a security policy to permit communication between your private network and the VPN. Policy-based VPNs have an action of IPSEC, where for interface-based VPNs the security policy action is ACCEPT. See Defining VPN security policies on page 1648.

The FortiGate unit implements the Encapsulated Security Payload (ESP) protocol. Internet Key Exchange (IKE) is performed automatically based on pre-shared keys or X.509 digital certificates. Interface mode, supported in NAT mode only, creates a virtual interface for the local end of a VPN tunnel.

This chapter contains the following sections: Phase 1 configuration

Phase 2 configuration

Concentrator

IPsec Monitor

 

Phase 1 configuration

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.

If you want to control how the IKE negotiation is processed when there is no traffic, as well as the length of time the FortiGate unit waits for negotiations to occur, you can use the negotiation-timeout and auto- negotiate commands in the CLI.

For more information, refer to Phase 2 parameters on page 1642 and Phase 2 parameters on page 1642.

Name                                           Type a name for the Phase 1 definition. The maximum name length is 15 characters for an interface mode VPN, 35 characters for a policy-based VPN. If Remote Gateway is Dialup User, the maximum name length is further reduced depending on the number of dialup tunnels that can be established: by 2 for up to 9 tunnels, by 3 for up to 99 tunnels, 4 for up to 999 tunnels, and so on.

For a tunnel mode VPN, the name normally reflects where the remote con- nection originates. For a route-based tunnel, the FortiGate unit also uses the name for the virtual IPsec interface that it creates automatically.

Select the category of the remote connection:

Remote Gateway

Static IP Address — If the remote peer has a static IP address.

Dialup User — If one or more FortiClient or FortiGate dialup clients with dynamic IP addresses will connect to the FortiGate unit.

Dynamic DNS — If a remote peer that has a domain name and sub-scribes to a dynamic DNS service will connect to the FortiGate unit.

IP Address                                 If you selected Static IP Address, enter the IP address of the remote peer.

Dynamic DNS                            If you selected Dynamic DNS, enter the domain name of the remote peer.

Local Interface                          This option is available in NAT mode only. Select the name of the interface through which remote peers or dialup clients connect to the FortiGate unit.

By default, the local VPN gateway IP address is the IP address of the inter- face that you selected.

Main mode — the Phase 1 parameters are exchanged in multiple rounds with encrypted authentication information.

Aggressive mode — the Phase 1 parameters are exchanged in single message with authentication information that is not encrypted.

Mode

When the remote VPN peer has a dynamic IP address and is authenticated by a pre-shared key, you must select Aggressive mode if there is more than one dialup phase1 configuration for the interface IP address.

When the remote VPN peer has a dynamic IP address and is authenticated by a certificate, you must select Aggressive mode if there is more than one Phase 1 configuration for the interface IP address and these Phase 1 con- figurations use different proposals.

Authentication Method            Select Preshared Key or RSA Signature.

Pre–shared Key

If you selected Pre–shared Key, enter the pre-shared key that the FortiGate unit will use to authenticate itself to the remote peer or dialup cli- ent during Phase 1 negotiations. You must define the same key at the remote peer or client. The key must contain at least 6 printable characters. For optimum protection against currently known attacks, the key must con- sist of a minimum of 16 randomly chosen alphanumeric characters.

Certificate Name                        If you selected RSA Signature, select the name of the server certificate that the FortiGate unit will use to authenticate itself to the remote peer or dialup client during Phase 1 negotiations. For information about obtaining and loading the required server certificate, see the FortiOS User Authentic- ation guide.

Peer Options

Peer options are available to authenticate VPN peers or clients, depending on the Remote Gateway and Authentication Method settings.

Any peer ID                                Accept the local ID of any remote VPN peer or client. The FortiGate unit does not check identifiers (local IDs). You can set Mode to Aggressive or Main.

You can use this option with RSA Signature authentication. But, for highest security, configure a PKI user/group for the peer and set Peer Options to Accept this peer certificate only.

This option is available when Aggressive Mode is enabled. Enter the iden- tifier that is used to authenticate the remote peer. This identifier must match the Local ID that the remote peer’s administrator has configured.

 

This peer ID

If the remote peer is a FortiGate unit, the identifier is specified in the Local ID field of the Advanced Phase 1 configuration.

If the remote peer is a FortiClient user, the identifier is specified in the Local ID field, accessed by selecting Config in the Policy section of the VPN connection’s Advanced Settings.

Peer ID from dialup group       Authenticate multiple FortiGate or FortiClient dialup clients that use unique identifiers and unique pre-shared keys (or unique pre-shared keys only) through the same VPN tunnel.

You must create a dialup user group for authentication purposes. Select the group from the list next to the Peer ID from dialup group option.

You must set Mode to Aggressive when the dialup clients use unique identifiers and unique pre-shared keys. If the dialup clients use unique pre- shared keys only, you can set Mode to Main if there is only one dialup Phase 1 configuration for this interface IP address.

Phase 1 advanced configuration settings

You can use the following advanced parameters to select the encryption and authentication algorithms that the FortiGate unit uses to generate keys for the IKE exchange. You can also use the following advanced parameters to ensure the smooth operation of Phase 1 negotiations.

These settings are mainly configured in the CLI, although some options are available after the tunnel is created using the VPN Creation Wizard (using the Convert to Custom Tunnel option).

VXLAN over IPsec                  Packets with VXLAN header are encapsulated within IPsec tunnel mode.

New attributes in IPsec phase1 settings have been added.

To configure VXLAN over IPsec – CLI:

config vpn ipsec phase1-interface/phase1 edit ipsec

set interface <name>

set encapsulation vxlan/gre (new)

set encapsulation-address ike/ipv4/ipv6 (New)

set encap-local-gw4 xxx.xxx.xxx.xxx (New)

set encap-remote-gw xxx.xxx.xxx.xxx (New)

next end

You can define an idle timer for IPsec tunnels. When no traffic has passed through the tunnel for the configured idle-timeout value, the IPsec tunnel will be flushed.

 

IPsec tunnel idle timer

To configure IPsec tunnel idle timeout – CLI:

config vpn ipsec phase1-interface edit p1

set idle-timeout [enable | disable]

set idle-timeoutinterval <integer> //IPsec tunnel idle timeout in minutes (10 – 43200).

end end

 

IPv6 Version                              Select if you want to use IPv6 addresses for the remote gateway and inter- face IP addresses.

Specify an IP address for the local end of the VPN tunnel. Select one of the following:

Local Gateway IP

Main Interface IP — The FortiGate unit obtains the IP address of the interface from the network interface settings.

Specify — Enter a secondary address of the interface selected in the

Phase 1 Local Interface field.

You cannot configure Interface mode in a transparent mode VDOM.

Phase 1 Proposal                      Select the encryption and authentication algorithms used to generate keys for protecting negotiations and add encryption and authentication algorithms as required.

You need to select a minimum of one and a maximum of three com- binations. The remote peer or client must be configured to use at least one of the proposals that you define.

Select one of the following symmetric-key encryption algorithms:

DES — Digital Encryption Standard, a 64-bit block algorithm that uses a 56-bit key.

3DES — Triple-DES; plain text is encrypted three times by three keys.

AES128 — A 128-bit block algorithm that uses a 128-bit key. AES192 — A 128-bit block algorithm that uses a 192-bit key. AES256 — A 128-bit block algorithm that uses a 256-bit key.

You can select either of the following message digests to check the authen- ticity of messages during an encrypted session:

MD5 — Message Digest 5.

SHA1 — Secure Hash Algorithm 1 – a 160-bit message digest.

To specify one combination only, set the Encryption and Authentication options of the second combination to NULL. To specify a third com- bination, use the Add button beside the fields for the second combination.

Diffie–Hellman Group                Select one or more Diffie-Hellman groups from DH groups 1, 2, 5, and 14 through 21. At least one of the Diffie-Hellman Group settings on the remote peer or client must match one the selections on the FortiGate unit. Failure to match one or more DH groups will result in failed negotiations.

Keylife Enter the time (in seconds) that must pass before the IKE encryption key expires. When the key expires, a new key is generated without interrupting service. The keylife can be from 120 to 172 800 seconds.

Local ID                                      If the FortiGate unit will act as a VPN client and you are using peer IDs for authentication purposes, enter the identifier that the FortiGate unit will sup- ply to the VPN server during the Phase 1 exchange.

If the FortiGate unit will act as a VPN client, and you are using security cer- tificates for authentication, select the distinguished name (DN) of the local server certificate that the FortiGate unit will use for authentication pur- poses.

If the FortiGate unit is a dialup client and will not be sharing a tunnel with other dialup clients (that is, the tunnel will be dedicated to this Fortinet dia- lup client), set Mode to Aggressive.

Note that this Local ID value must match the peer ID value given for the remote VPN peer’s Peer Options.

This option supports the authentication of dialup clients. It is available for IKE v1 only.

XAuth Disable — Select if you do not use XAuth.

Enable as Client — If the FortiGate unit is a dialup client, enter the user name and password that the FortiGate unit will need to authenticate itself to the remote XAuth server.

Enable as Server — This is available only if Remote Gateway is set to

Dialup User. Dialup clients authenticate as members of a dialup user group. You must first create a user group for the dialup clients that need access to the network behind the FortiGate unit.

You must also configure the FortiGate unit to forward authentication requests to an external RADIUS or LDAP authentication server.

Select a Server Type setting to determine the type of encryption method to use between the FortiGate unit, the XAuth client and the external authentication server, and then select the user group from the User Group list.

Username                                   Enter the user name that is used for authentication.

Password                                   Enter the password that is used for authentication.

NAT Traversal                            Select the check box if a NAT device exists between the local FortiGate unit and the VPN peer or client. The local FortiGate unit and the VPN peer or client must have the same NAT traversal setting (both selected or both cleared) to connect reliably.

Additionally, you can force IPsec to use NAT traversal. If NAT is set to Forced, the FortiGate will use a port value of zero when constructing the NAT discovery hash for the peer. This causes the peer to think it is behind a NAT device, and it will use UDP encapsulation for IPsec, even if no NAT is present. This approach maintains interoperability with any IPsec imple- mentation that supports the NAT-T RFC.

Keepalive Frequency               If you enabled NAT–traversal, enter a keepalive frequency setting.

Dead Peer Detection                 Select this check box to reestablish VPN tunnels on idle connections and clean up dead IKE peers if required. You can use this option to receive noti- fication whenever a tunnel goes up or down, or to keep the tunnel con- nection open when no traffic is being generated inside the tunnel. For example, in scenarios where a dialup client or dynamic DNS peer connects from an IP address that changes periodically, traffic may be suspended while the IP address changes.

With Dead Peer Detection selected, you can use the config vpn ipsec phase1 (tunnel mode) or config vpn ipsec phase1- interface (interface mode) CLI command to optionally specify a retry count and a retry interval.

 

IKE fragmentation

UDP fragmentation can cause issues in IPsec when either the ISP or perimeter firewall(s) cannot pass or fragment the oversized UDP packets that occur when using a very large public security key (PSK). The result is that IPsec tunnels do not come up. The solution is IKE fragmentation.

For most configurations, enabling IKE fragmentation allows connections to automatically establish when they otherwise might have failed due to intermediate nodes dropping IKE messages containing large certificates, which typically push the packet size over 1500 bytes.

FortiOS will fragment a packet on sending if, and only if, all the following are true:

  • Phase 1 contains “set fragmentation enable”.
  • The packet is larger than the minimum MTU (576 for IPv4, 1280 for IPv6).
  • The packet is being re-transmitted.

By default, IKE fragmentation is enabled, but upon upgrading, any existing phase1-interface may have have “set fragmentation disable” added in order to preserve the existing behaviour of not supporting fragmentation.

 

To enable or disable IKE fragmentation – CLI

config vpn ipsec phase1-interface edit 1

set fragmentation [enable | disable]

next end

 


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IPsec VPN overview

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IPsec VPN overview

This section provides a brief overview of IPsec technology and includes general information about how to configure IPsec VPNs using this guide.

The following topics are included in this section: Types of VPNs

Planning your VPN General preparation steps

How to use this guide to configure an IPsec VPN

VPN configurations interact with the firewall component of the FortiGate unit. There must be a security policy in place to permit traffic to pass between the private network and the VPN tunnel.

Security policies for VPNs specify:

  • The FortiGate interface that provides the physical connection to the remote VPN gateway, usually an interface connected to the Internet
  • The FortiGate interface that connects to the private network
  • IP addresses associated with data that has to be encrypted and decrypted
  • Optionally, a schedule that restricts when the VPN can operate
  • Optionally, the services (types of data) that can be sent

When the first packet of data that meets all of the conditions of the security policy arrives at the FortiGate unit, a VPN tunnel may be initiated and the encryption or decryption of data is performed automatically afterward. For more information, see Defining VPN security policies on page 1648.

Where possible, you should create route-based VPNs. Generally, route-based VPNs are more flexible and easier to configure than policy-based VPNs — by default they are treated as interfaces. However, these two VPN types have different requirements that limit where they can be used.

 

Types of VPNs

FortiGate unit VPNs can be policy-based or route-based. There is little difference between the two types. In both cases, you specify Phase 1 and Phase 2 settings. However there is a difference in implementation. A route-based VPN creates a virtual IPsec network interface that applies encryption or decryption as needed to any traffic that it carries. That is why route-based VPNs are also known as interface-based VPNs. A policy-based VPN is implemented through a special security policy that applies the encryption you specified in the Phase 1 and Phase 2 settings.

 

Route–based VPNs

For a route-based VPN, you create two security policies between the virtual IPsec interface and the interface that connects to the private network. In one policy, the virtual interface is the source. In the other policy, the virtual interface is the destination. This creates bidirectional policies that ensure traffic will flow in both directions over the VPN.

A route-based VPN is also known as an interface-based VPN.

Each route-based IPsec VPN tunnel requires a virtual IPsec interface. As such, the amount of possible route-based IPsec VPNs is limited by the system.interface table size. The system.interface table size for most devices is 8192.

For a complete list of table sizes for all devices, refer to the Maximum Values table.

 

Policy–based VPNs

For a policy-based VPN, one security policy enables communication in both directions. You enable inbound and outbound traffic as needed within that policy, or create multiple policies of this type to handle different types of traffic differently. For example HTTPS traffic may not require the same level of scanning as FTP traffic.

A policy-based VPN is also known as a tunnel-mode VPN.

 

Comparing policy-based or route-based VPNs

For both VPN types you create Phase 1 and Phase 2 configurations. Both types are handled in the stateful inspection security layer, assuming there is no IPS or AV. For more information on the three security layers, see the FortiOS Troubleshooting guide.

The main difference is in the security policy.

You create a policy-based VPN by defining an IPSEC security policy between two network interfaces and associating it with the VPN tunnel (Phase 1) configuration.

You create a route-based VPN by creating a virtual IPsec interface. You then define a regular ACCEPT security policy to permit traffic to flow between the virtual IPsec interface and another network interface. And lastly, configure a static route to allow traffic over the VPN.

Where possible, you should create route-based VPNs. Generally, route-based VPNs are more flexible and easier to configure than policy-based VPNs — by default they are treated as interfaces. However, these two VPN types have different requirements that limit where they can be used.

 

Comparison of policy-based and route-based VPNs

 

Features Policy-based Route-based
 

Both NAT and transparent modes available

  

Yes

  

NAT mode only
 

L2TP–over–IPsec supported

  

Yes

  

No
 

GRE–over–IPsec supported

  

No

  

Yes
 

 

security policy requirements

  

Requires a security policy with IPSEC action that specifies the VPN tunnel

  

Requires only a simple security policy with ACCEPT action
 

Number of policies per VPN

  

One policy controls connections in both directions

  

A separate policy is required for connections in each direction

 

 

Planning your VPN

It is a good idea to plan the VPN configuration ahead of time. This will save time later and help you configure your VPN correctly.

All VPN configurations are comprised of numerous required and optional parameters. Before you begin, you need to determine:

  • Where the IP traffic originates and where it needs to be delivered
  • Which hosts, servers, or networks to include in the VPN
  • Which VPN devices to include in the configuration
  • Through which interfaces the VPN devices communicate
  • Through which interfaces do private networks access the VPN gateways

Once you have this information, you can select a VPN topology that suits the network environment.

 

Network topologies

The topology of your network will determine how remote peers and clients connect to the VPN and how VPN traffic is routed.

 

VPN network topologies and brief descriptions

Topology                                 Description

Gateway-to-gateway con- figurations

Standard one-to-one VPN between two FortiGate units. See Gateway-to- gateway configurations on page 1655.

Hub-and-spoke configurations     One central FortiGate unit has multiple VPNs to other remote FortiGate units. See Hub-and-spoke configurations on page 1671.

Dynamic DNS configuration        One end of the VPN tunnel has a changing IP address and the other end must go to a dynamic DNS server for the current IP address before estab- lishing a tunnel. See Dynamic DNS configuration on page 1688.

Typically remote FortiClient dialup-clients use dynamic IP addresses through NAT devices. The FortiGate unit acts as a dialup server allowing dialup VPN connections from multiple sources. See FortiClient dialup-client configurations on page 1702.

Similar to FortiClient dialup-client configurations but with more gateway-to- gateway settings such as unique user authentication for multiple users on a single VPN tunnel. See FortiGate dialup-client configurations on page 1716.

Secure web browsing performed by dialup VPN clients, and/or hosts behind a remote VPN peer. See Internet-browsing configuration on page 1729.

 

Topology                                 Description

Redundant VPN con- figurations

Options for supporting redundant and partially redundant IPsec VPNs, using route-based approaches. See Redundant VPN configurations on page 1734.

Transparent mode VPNs

In transparent mode, the FortiGate acts as a bridge with all incoming traffic being broadcast back out on all other interfaces. Routing and NAT must be performed on external routers. See Transparent mode VPNs on page 1759.

L2TP and IPsec (Microsoft VPN)

Configure VPN for Microsoft Windows dialup clients using the built in L2TP software. Users do not have to install any See L2TP and IPsec (Microsoft VPN) on page 1778.

These sections contain high-level configuration guidelines with cross-references to detailed configuration procedures. If you need more detail to complete a step, select the cross-reference in the step to drill-down to more detail. Return to the original procedure to complete the procedure. For a general overview of how to configure a VPN, see Planning your VPN .

 

General preparation steps

A VPN configuration defines relationships between the VPN devices and the private hosts, servers, or networks making up the VPN. Configuring a VPN involves gathering and recording the following information. You will need this information to configure the VPN.

  • The private IP addresses of participating hosts, servers, and/or networks. These IP addresses represent the source addresses of traffic that is permitted to pass through the VPN. A IP source address can be an individual IP address, an address range, or a subnet address.
  • The public IP addresses of the VPN end-point interfaces. The VPN devices establish tunnels with each other through these interfaces.
  • The private IP addresses associated with the VPN-device interfaces to the private networks. Computers on the private networks behind the VPN gateways will connect to their VPN gateways through these interfaces.

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