Defining VPN security policies

This section explains how to specify the source and destination IP addresses of traffic transmitted through an IPsec VPN, and how to define appropriate security policies.

The following topics are included in this section:

Defining policy addresses

Defining security policies for policy-based and route-based VPNs

Defining policy addresses

A VPN tunnel has two end points. These end points may be VPN peers such as two FortiGate gateways. Encrypted packets are transmitted between the end points. At each end of the VPN tunnel, a VPN peer intercepts encrypted packets, decrypts the packets, and forwards the decrypted IP packets to the intended destination.

You need to define firewall addresses for the private networks behind each peer. You will use these addresses as the source or destination address depending on the security policy.

policy addresses

Example topology for the following policies

In general:

• In a gateway-to-gateway, hub-and-spoke, dynamic DNS, redundant-tunnel, or transparent configuration, you need to define a policy address for the private IP address of the network behind the remote VPN peer (for example, 168.10.0/255.255.255.0 or 192.168.10.0/24).
• In a peer-to-peer configuration, you need to define a policy address for the private IP address of a server or host behind the remote VPN peer (for example, 16.5.1/255.255.255.255 or 172.16.5.1/32 or 172.16.5.1).

For a FortiGate dialup server in a dialup-client or Internet-browsing configuration:

• If you are not using VIP addresses, or if the FortiGate dialup server assigns VIP addresses to FortiClient dialup clients through FortiGate DHCP relay, select the predefined destination address “all” in the security policy to refer to the dialup clients.
• If you assign VIP addresses to FortiClient dialup clients manually, you need to define a policy address for the VIP address assigned to the dialup client (for example, 254.254.1/32), or a subnet address from which the VIP addresses are assigned (for example, 10.254.254.0/24 or 10.254.254.0/255.255.255.0).
• For a FortiGate dialup client in a dialup-client or Internet-browsing configuration, you need to define a policy address for the private IP address of a host, server, or network behind the FortiGate dialup server.

Defining a security IP address

1. Go to Policy & Objects > Addresses and select Create New.
2. In the Name field, type a descriptive name that represents the network, server(s), or host(s).
3. In Type, select Subnet.
4. In the Subnet/IP Range field, type the corresponding IP address and subnet mask.

For a subnet you could use the format 172.16.5.0/24 or its equivalent 172.16.5.0/255.255.255.0. For a server or host it would likely be 172.16.5.1/32. Alternately you can use an IP address range such as 192.168.10.[80-100] or 192.168.10.80-192.168.10.100.

5. Select OK.

Defining security policies for policy-based and route-based VPNs

Security policies allow IP traffic to pass between interfaces on a FortiGate unit. You can limit communication to particular traffic by specifying source address and destination addresses. Then only traffic from those addresses will be allowed.

Policy-based and route-based VPNs require different security policies.

• A policy-based VPN requires an IPsec security policy. You specify the interface to the private network, the interface to the remote peer and the VPN tunnel. A single policy can enable traffic inbound, outbound, or in both directions.
• A route-based VPN requires an Accept security policy for each direction. As source and destination interfaces, you specify the interface to the private network and the virtual IPsec interface (Phase 1 configuration) of the VPN. The IPsec interface is the destination interface for the outbound policy and the source interface for the inbound policy. One security policy must be configured for each direction of each VPN interface.

There are examples of security policies for both policy-based and route-based VPNs throughout this guide. See Route-based or policy-based VPN on page 117.

If the security policy, which grants the VPN Connection is limited to certain services,

DHCP must be included, otherwise the client won’t be able to retrieve a lease from the FortiGate’s (IPsec) DHCP server, because the DHCP Request (coming out of the tunnel) will be blocked.

Policy-based VPN

An IPsec security policy enables the transmission and reception of encrypted packets, specifies the permitted direction of VPN traffic, and selects the VPN tunnel. In most cases, a single policy is needed to control both inbound and outbound IP traffic through a VPN tunnel. Be aware of the following considerations below before creating an IPsec security policy.

Allow traffic to be initiated from the remote site

Security policies specify which IP addresses can initiate a tunnel. By default, traffic from the local private network initiates the tunnel. When the Allow traffic to be initiated form the remote site option is selected, traffic from a dialup client, or a computer on a remote network, initiates the tunnel. Both can be enabled at the same time for bi-directional initiation of the tunnel.

Outbound and inbound NAT

When a FortiGate unit operates in NAT mode, you can also enable inbound or outbound NAT. Outbound NAT may be performed on outbound encrypted packets or IP packets in order to change their source address before they are sent through the tunnel. Inbound NAT is performed to intercept and decrypt emerging IP packets from the tunnel.

By default, these options are not selected in security policies and can only be set through the CLI. For more information on this, see the “config firewall” chapter of the FortiGate CLI Reference.

Source and destination addresses

Most security policies control outbound IP traffic. A VPN outbound policy usually has a source address originating on the private network behind the local FortiGate unit, and a destination address belonging to a dialup VPN client or a network behind the remote VPN peer. The source address that you choose for the security policy identifies from where outbound cleartext IP packets may originate, and also defines the local IP address or addresses that a remote server or client will be allowed to access through the VPN tunnel. The destination address that you choose identifies where IP packets must be forwarded after they are decrypted at the far end of the tunnel, and determines the IP address or addresses that the local network will be able to access at the far end of the tunnel.

Enabling other policy features

You can fine-tune a policy for services such as HTTP, FTP, and POP3, enable logging, traffic shaping, antivirus protection, web filtering, email filtering, file transfer, email services, and optionally allow connections according to a predefined schedule.

As an option, differentiated services (diffserv or DSCP) for the security policy can be enabled through the CLI. For more information on this feature, see the Traffic Shaping handbook chapter, or the “firewall” chapter of the FortiGate CLI Reference.

Before you begin

Before you define the IPsec policy, you must:

l Define the IP source and destination addresses. See Defining policy addresses on page 72. l Specify the Phase 1 authentication parameters. See Phase 1 parameters on page 46. l Specify the Phase 2 parameters. See Phase 2 parameters on page 66.

Defining an IPsec security policy

1. Go to Policy & Objects > IPv4 Policy.
2. Select Create New and set the following options:

3. You may enable UTM features, and/or event logging, or select advanced settings to authenticate a user group, or shape traffic. For more information, see the Firewall handbook chapter.
4. Select OK.
5. Place the policy in the policy list above any other policies having similar source and destination addresses.

Defining multiple IPsec policies for the same tunnel

You must define at least one IPsec policy for each VPN tunnel. If the same remote server or client requires access to more than one network behind a local FortiGate unit, the FortiGate unit must be configured with an IPsec policy for each network. Multiple policies may be required to configure redundant connections to a remote destination or control access to different services at different times.

To ensure a secure connection, the FortiGate unit must evaluate policies with Action set to IPsec before

ACCEPT and DENY. Because the FortiGate unit reads policies starting at the top of the list, you must move all IPsec policies to the top of the list, and be sure to reorder your multiple IPsec policies that apply to the tunnel so that specific constraints can be evaluated before general constraints.

Adding multiple IPsec policies for the same VPN tunnel can cause conflicts if the policies specify similar source and destination addresses, but have different settings for the same service. When policies overlap in this manner, the system may apply the wrong IPsec policy or the tunnel may fail.

For example, if you create two equivalent IPsec policies for two different tunnels, it does not matter which one comes first in the list of IPsec policies — the system will select the correct policy based on the specified source and destination addresses. If you create two different IPsec policies for the same tunnel (that is, the two policies treat traffic differently depending on the nature of the connection request), you might have to reorder the IPsec policies to ensure that the system selects the correct IPsec policy.

Route-based VPN

When you define a route-based VPN, you create a virtual IPsec interface on the physical interface that connects to the remote peer. You create ordinary Accept security policies to enable traffic between the IPsec interface and the interface that connects to the private network. This makes configuration simpler than for policy-based VPNs, which require IPsec security policies.

security policies for policy-based and route-based VPNs

Defining security policies for a route-based VPN

1. Go to Policy & Objects > IPv4 Policy.
2. Select Create New and define an ACCEPT security policy to permit communication between the local private network and the private network behind the remote peer. Enter these settings in particular:

To permit the remote client to initiate communication, you need to define a security policy for communication in that direction.

3. Select Create New and enter these settings in particular: