A security policy is a template of security settings that can be applied to specific traffic at specific times. The policy can be applied:

The policy can be configured:

The security policies can also limit the number of user sessions.

The Zyxel Device uses stateful inspection in its security policies. The Zyxel Device restricts access by screening data packets against defined access rules. It also inspects sessions. For example, traffic from one zone is not allowed unless it is initiated by a computer in another zone first.

A zone is a group of interfaces. Group the Zyxel Device’s interfaces into different zones based on your needs. You can configure security policies for data passing between zones or even between interfaces.

Security Policies can be grouped based on the direction of travel of packets to which they apply. Here is the The Zyxel Device has default Security Policy behavior for traffic going through the Zyxel Device in various directions.

Policies with Device as the To Zone apply to traffic going to the Zyxel Device itself. By default:

When you configure a Security Policy rule for packets destined for the Zyxel Device itself, make sure it does not conflict with your service control rule. The Zyxel Device checks the security policy before the service control rules for traffic destined for the Zyxel Device.

A From Any To Device direction policy applies to traffic from an interface which is not in a zone.

Security Policies with from any and/or to any as the packet direction are called global Security Policies. The global Security Policies are the only Security Policies that apply to an interface that is not included in a zone. The from any policies apply to traffic coming from the interface and the to any policies apply to traffic going to the interface.

The Zyxel Device checks the schedule, user name (user’s login name on the Zyxel Device), source IP address and object, destination IP address and object, IP protocol type of network traffic (service) and Security Service profile criteria against the Security Policies (in the order you list them). When the traffic matches a policy, the Zyxel Device takes the action specified in the policy.

You can specify users or user groups in Security Policies. For example, to allow a specific user from any computer to access a zone by logging in to the Zyxel Device, you can set up a policy based on the user name only. If you also apply a schedule to the Security Policy, the user can only access the network at the scheduled time. A user-aware Security Policy is activated whenever the user logs in to the Zyxel Device and will be disabled after the user logs out of the Zyxel Device.

Accessing the Zyxel Device or network resources through the Zyxel Device requires a NAT session and corresponding Security Policy session. Peer to peer applications, such as file sharing applications, may use a large number of NAT sessions. A single client could use all of the available NAT sessions and prevent others from connecting to or through the Zyxel Device. The Zyxel Device lets you limit the number of concurrent NAT/Security Policy sessions a client can use.

If an alternate gateway on the LAN has an IP address in the same subnet as the Zyxel Device’s LAN IP address, return traffic may not go through the Zyxel Device. This is called an asymmetrical or “triangle” route. This causes the Zyxel Device to reset the connection, as the connection has not been acknowledged.

You can have the Zyxel Device permit the use of asymmetrical route topology on the network (not reset the connection). However, allowing asymmetrical routes may let traffic from the WAN go directly to the LAN without passing through the Zyxel Device. A better solution is to use virtual interfaces to put the Zyxel Device and the backup gateway on separate subnets. Virtual interfaces allow you to partition your network into logical sections over the same interface. See the chapter about interfaces for more information.

By putting LAN 1 and the alternate gateway in different subnets, all returning network traffic must pass through the Zyxel Device to the LAN. The following steps describe such a scenario.

Use this screen to enable or disable the Security Policy and asymmetrical routes, set a maximum number of sessions per host, and display the configured Security Policies. Specify from which zone packets come and to which zone packets travel to display only the policies specific to the selected direction. Note the following.

The following table describes the labels in this screen.

Anomaly Detection and Prevention (ADP) protects against anomalies based on violations of protocol standards (RFCs – Requests for Comments) and abnormal flows such as port scans. This section introduces ADP, anomaly profiles and applying an ADP profile to a traffic direction.

Traffic anomaly policies look for abnormal behavior or events such as port scanning, sweeping or network flooding. They operate at OSI layer-2 and layer-3. Traffic anomaly policies may be updated when you upload new firmware.

Protocol anomalies are packets that do not comply with the relevant RFC (Request For Comments). Protocol anomaly detection includes:

Protocol anomaly policies may be updated when you upload new firmware.

 

When creating ADP profiles. you may find that certain policies are triggering too many false positives or false negatives. A false positive is when valid traffic is flagged as an attack. A false negative is when invalid traffic is wrongly allowed to pass through the Zyxel Device. As each network is different, false positives and false negatives are common on initial ADP deployment.

To counter this, you could create a ‘monitor profile’ that creates logs, but all actions are disabled. Observe the logs over time and try to eliminate the causes of the false alarms. When you’re satisfied that they have been reduced to an acceptable level, you could then create an ‘in-line profile’ whereby you configure appropriate actions to be taken when a packet matches a policy.

ADP profiles consist of traffic anomaly profiles and protocol anomaly profiles. To create a new profile, select a base profile and then click OK to go to the profile details screen. Type a new profile name, enable or disable individual policies and then edit the default log options and actions.

 

Traffic anomaly detection looks for abnormal behavior such as scan or flooding attempts.

Protocol anomalies are packets that do not comply with the relevant RFC (Request For Comments). Protocol anomaly detection includes:

When an IP packet is larger than the Maximum Transmission Unit (MTU) configured in the Zyxel Device, it is fragmented using the TCP or ICMP protocol.

A Teardrop attack falsifies the offset which defines the size of the fragment and the original packet. A series of IP fragments with overlapping offset fields can cause some systems to crash, hang, or reboot when fragment reassembling is attempted at the destination.

IP Spoofing is used to gain unauthorized access to network devices by modifying packet headers so that it appears that the packets originate from a host within a trusted network.

In an IP Spoof from a LAN interface, the source address appears to be in a different subnet from that Zyxel Device LAN interface.

Use this screen to limit the number of concurrent NAT/Security Policy sessions a client can use. You can apply a default limit for all users and individual limits for specific users, addresses, or both. The individual limit takes priority if you apply both.

Use this screen to configure rules that define a session limit for specific users or addresses.