Networking

When configuring your network, ensure that there is no ‘back door’ access to the protected network. For example, if there is a wireless access point, it must be appropriately protected with password and encryption.

Be sure to also maintain an up-to-date network diagram which includes IP addressing, cabling, and network elements.

Routing configuration

• Always configure a default route.
• Add blackhole routes for subnets reachable using VPN tunnels. This ensures that if a VPN tunnel goes down, traffic is not mistakingly routed to the Internet unencrypted.

Policy routing

Keep the number of policy routes to a minimum to optimize performance in route lookup and to simplify troubleshooting.

Dynamic routing

• Select a Router ID that matches an IP assigned to an interface. This avoids the likelihood of having two devices with the same router ID.
• For routing over an IPsec tunnel, assign IP addresses to both ends of the tunnel.

Advanced routing

Use the following best practices for advanced routing when dealing with Border Gateway Protocol (BGP) and Open Shortest Path First (OSPF).

Border Gateway Protocol (BGP)

If you are using BGP, it is recommended that you enable soft-reconfiguration. This has two benefits:

• It allows you to perform ‘soft clear’ of peers after a change is made to a BGP policy.
• It provides greater visibility into the specific prefixes learned from each neighbor.

Leave soft-reconfiguration disabled if your FortiGate does not have much unused memory. Soft-reconfiguration requires keeping separate copies of prefixes received and advertised, in addition to the local BGP database.

Networking

Open Shortest Path First (OSPF)

l Avoid use of passive interfaces wherever possible. l Avoid use of virtual links to connect areas. All areas should be designed to connect directly to the backbone area. l Ensure that all backbone routers have a minimum of two peering connections to other backbone neighbors. l An entire OSPF domain should be under common administration.

Network Address Translation (NAT)

• Beware of misconfiguring the IP Pool range. Double-check the start and end IP addresses of each IP pool. The IP pool should not overlap with addresses assigned to FortiGate interfaces or to any hosts on directly connected networks.
• If you have internal and external users accessing the same servers, use split DNS to offer an internal IP to internal users so that they don’t have to use the external-facing VIP.

Configuring NAT

Do not enable NAT for inbound traffic unless it is required by an application. If, for example, NAT is enabled for inbound SMTP traffic, the SMTP server might act as an open relay.

Transparent Mode

• Do not connect two ports to the same VLAN on a switch or to the same hub. Some Layer 2 switches become unstable when they detect the same MAC address originating on more than one switch interface or from more than one VLAN.
• If you operate multiple VLANs on your FortiGate unit, assign each VLAN id to its own forwarding domain to ensure that the scope of the broadcast does not extend beyond the VLAN it originated in.

To protect against Layer 2 loops:

• Enable stpforward on all interfaces. l Use separate VDOMs for production traffic (TP mode VDOM) and management traffic (NAT mode VDOM).
• Only place those interfaces used for production in the TP mode VDOM. Place all other interfaces in the NAT mode VDOM. This protects against potential Layer 2 loops.

Using virtual IPs (VIPs)

• Use the external IP of 0.0.0.0 when creating a VIP for a FortiGate unit where the external interface IP address is dynamically assigned.
• Be sure to select the correct external interface when creating a new virtual IP (VIP). The external interface should be set to the interface at which the FortiGate unit receives connection requests from external networks.

Policy configuration

Configuring the FortiGate unit with an ‘allow all’ traffic policy is very undesirable. While this does greatly simplify the configuration, it is less secure. As a security measure, it is best practice for the policy rulebase to ‘deny’ by default, and not the other way around.

Policy configuration changes

On a heavy-loaded system, plan configuration changes during low usage periods in order to minimize impact on CPU usage and established sessions. In this scenario, it is considered a best practice to de-accelerate the hardwareaccelerated sessions.

You can configure de-accelerated behaviour on hardware-accelerated sessions using CLI commands to control how the processor manages policy configuration changes. The following CLI commands are to be used:

config system settings set firewall-session-dirty { check-all | check-new | check-policy-option }

end where you want the following to be true:

Policy whitelisting

• Allow only the necessary inbound and outbound traffic.
• If possible, limit traffic to specific addresses or subnets. This allows the FortiGate unit to drop traffic to and from unexpected addresses.

IPS and DoS policies

• Because it is critical to guard against attacks on services that you make available to the public, configure IPS signatures to block matching signatures. For example, if you have a web server, configure the action of web server signatures to Block.
• Your FortiGate unit includes IPS signatures written to protect specific software titles from DoS attacks. Enable the signatures for the software you have installed and set the signature action to Block.
• DoS attacks are launched against vulnerabilities. Maintain a FortiGuard IPS subscription to ensure your FortiGate unit automatically receives new and updated IPS signatures as they are released.

Policy configuration

• Use and configure DoS policies to appropriate levels based on your network traffic and topology. This will help drop traffic if an abnormal amount is received. The key is to set a good threshold. The threshold defines the maximum number of sessions/packets per second of normal traffic. If the threshold is exceeded, the action is triggered. Threshold defaults are general recommendations, but your network may require very different values. One way to find the correct values for your environment is to set the action to Pass and enable logging. Observe the logs and adjust the threshold values until you can determine the value at which normal traffic begins to generate attack reports. Set the threshold above this value with the margin you want. Note that the smaller the margin, the more protected your system will be from DoS attacks, but your system will also be more likely to generate false alarms.

Patch management

When vulnerabilities are discovered in software, the software vendors release updates that fix these problems. Keeping your software and operating system up-to-date is a vital step to prevent infection and defend against attacks.

• Follow the latest advisories and reports on the FortiGuard webpage. l Apply updates to all software as the updates become available.
• FortiGuard Vulnerability Management can help identify security weaknesses in your network. This subscription service is available through FortiScan and FortiAnalyzer units.
• Apply firmware updates to your FortiGate unit as they are released.
• Subscribe to FortiGuard AntiVirus and IPS services, so that AntiVirus and IPS scanning engines are automatically updated when new version are released.

Web filtering

FortiGuard Web Filtering can help stop infections from malware sites and help prevent communication if an infection occurs.

• Enable FortiGuard Web Filtering at the network edge. l Install the FortiClient application and use FortiGuard Web Filtering on any systems that bypass your FortiGate unit.
• Block categories such as Pornography, Malware, Spyware, and Phishing. These categories are more likely to be dangerous

Email filter

Spam is a common means by which attacks are delivered. Users often open email attachments they should not, and infect their own machine.

l Enable email filtering at the network edge for all types of email traffic. l Use FortiClient endpoint IPS scanning for protection against threats that get into your network. l Subscribe to the FortiGuard AntiSpam Service.

URL filtering

Best practices for URL filtering can be divided into four categories: flow-based versus proxy based filtering; local category/rating feature; URL filter ‘Exempt’ action; and Deep Scan.

Flow-based versus proxy-based

Try to avoid mixing flow-based and proxy-based features in the same profile if you are not using IPS or Application Control.

Local category/rating feature

Local categories and local rating features consume a large amount of CPU resources, so use these features as little as possible. It is better to use Local categories instead of using the ‘override’ feature, since the ‘override’ feature is more complicated and more difficult to troubleshoot.

URL filter ‘Exempt’ action

When using the URL filter ‘Exempt’ option,webfilter, antivirus and dlp scans are bypassed by default, so use this option only for trusted sites.

Configuration notes: You need to configure ‘Exempt’ actions in the URL filter if you want to bypass the FortiGuard

Web Filter.You can configure which particular inspection(s) you want to bypass using the set exempt command in config webfilter urlfilter.

Deep Scan

The ‘Deep Scan’ feature is much heavier on resources than ‘HTTPS URL Scan Only’. Deep Scan is much more accurate, since many sites (such as various Google applications) cannot be scanned separately without deep scanning enabled.

Intrusion Prevention System (IPS)

Your FortiGate’s IPS system can detect traffic attempting to exploit this vulnerability. IPS may also detect when infected systems communicate with servers to receive instructions. Refer to the following list of best practices regarding IPS.

• Enable IPS scanning at the network edge for all services. l Use FortiClient endpoint IPS scanning for protection against threats that get into your network.
• Subscribe to FortiGuard IPS Updates and configure your FortiGate unit to receive push updates. This will ensure you receive IPS signature updates as soon as they are available.
• Because it is critical to guard against attacks on services that you make available to the public, configure IPS signatures to block matching signatures. For example, if you have a web server, configure the action of web server signatures to Block.
• Create and use security profiles with specific signatures and anomalies you need per-interface and per-rule.
• Do not use predefined or generic profiles. While these profiles are convenient to supply immediate protection, you should create profiles to suit your network environment.
• If you do use the default profiles, reduce the IPS signatures/anomalies enabled in the profile to conserve processing time and memory.
• If you are going to enable anomalies, make sure you tune thresholds according to your environment. l If you need protection, but not audit information, disable the logging option. l Tune the IP-protocol parameter accordingly.

Antivirus

• Enable antivirus scanning at the network edge for all services. l Use FortiClient endpoint antivirus scanning for protection against threats that get into your network.
• Subscribe to FortiGuard AntiVirus Updates and configure your FortiGate unit to receive push updates. This will ensure you receive antivirus signature updates as soon as they are available.
• To ensure that all AV push updates occur, ensure you have an AV profile enabled in a security policy.
• Enable only the protocols you need to scan. If you have antivirus scans occurring on the SMTP server, or use FortiMail, it is redundant to have scanning occur on the FortiGate unit as well.
• Reduce the maximum file size to be scanned. Viruses usually travel in small files of around 1 to 2 megabytes.
• Do not quarantine files unless you regularly monitor and review them. This is otherwise a waste of space and impacts performance.
• Examine antivirus reports and log messages periodically. Take particular notice of repeated detections. For example, repeated virus detection in SMTP traffic could indicate a system on your network is infected and is attempting to contact other systems to spread the infection using a mass mailer.