Fortinet IPS manual DoS sensors

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DoS sensors

DoS sensors

The FortiGate IPS uses a traffic anomaly detection feature to identify network traffic that does not fit known or common traffic patterns and behavior. For example, one type of flooding is the denial of service (DoS) attack that occurs when an attacking system starts an abnormally high number of sessions with a target system. The high number of sessions slows down or disables the target system so legitimate users can no longer use it. This type of attack gives the DoS sensor its name, although it is capable of detecting and protecting against a number of anomaly attacks.

You can enable or disable logging for each traffic anomaly, and configure the detection threshold and action to take when the detection threshold is exceeded.

You can create multiple DoS sensors. Each sensor consists of 12 anomaly types that you can configure. Each sensor examines the network traffic in sequence, from top to bottom. When a sensor detects an anomaly, it applies the configured action. Multiple sensors allow great granularity in detecting anomalies because each sensor can be configured to examine traffic from a specific address, to a specific address, on a specific port, in any combination.

When arranging the DoS sensors, place the most specific sensors at the top and the most general at the bottom. For example, a sensor with one protected address table entry that includes all source addresses, all destination addresses, and all ports will match all traffic. If this sensor is at the top of the list, no subsequent sensors will ever execute.

The traffic anomaly detection list can be updated only when the FortiGate firmware image is upgraded.

Note: If virtual domains are enabled on the FortiGate unit, the Intrusion Protection settings must be configured separately in each VDOM. All sensors and custom signatures will appear only in the VDOM in which they were created.

This section describes:

•Viewing the DoS sensor list

•Configuring DoS sensors

•Understanding the anomalies

FortiGate IPS User Guide Version 3.0 MR7
01-30007-0080-20080916	45

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Contents E R G U I D E Trademarks Contents IPS sensors Protocol decodersDoS sensors SYN flood attacksFortiGate IPS IntroductionFortinet documentation About this documentDocument conventions Typographic conventionsFortiGate Pptp VPN User Guide Customer service and technical support Fortinet Knowledge CenterComments on Fortinet technical documentation IPS overview and general configuration IPS settings and controlsThis section contains the following topics Default signature and anomaly settings When to use IPSDefault fail open setting Config ips global Set fail-open enable disable endConfiguring logging and alert email Setting the buffer sizeMonitoring the network and dealing with attacks Controlling sessionsAttack log messages Signature FortiGuard Center AnomalyCreating a protection profile that uses IPS sensors Using IPS sensors in a protection profileAdding protection profiles to firewall policies Select Create NewAdding protection profiles to user groups Using IPS sensors in a protection profile Predefined signatures IPS predefined signaturesViewing the predefined signature list Enable SettingsColumn Clear All FiltersCreate a sensor and add IPS filters to it Viewing the predefined signature list Custom signatures IPS custom signaturesViewing the custom signature list Adding custom signatures using the web-based manager Custom signature configurationAdding custom signatures using the CLI Command syntax patternCreating custom signatures Custom signature fieldsShows the valid characters for custom signature fields Attackid Custom signature syntaxName BufferOverflow SrcportContent keywords Keyword and value Description Deprecated, see pattern and context keywords Context uri Pattern GETPattern yahoo.com Context hostRegex/mdelim PcreRegexdelimismxAEGRU Uri !uristrIP header keywords Keyword and Value Description Protocol tcpTCP header keywords Keyword and Value Description Tcpflags S,12 Tcpflags APUDP header keywords Keyword and Value Description Icmp keywords Keyword and Value UsageOther keywords Keyword and Value Description Example 1 signature to block access to example.com Example custom signaturesSbid --name Block.example.com Sbid --name Block.example.com Example 2 signature to block the Smtp ‘vrfy’ command Sbid --name Block.SMTP.VRFY.CMDSbid --name Block.SMTP.VRFY.CMD --pattern vrfy Creating custom signatures Protocol decoders Protocol decodersUpgrading the IPS protocol decoder list Protocol decoder list Protocols Protocol decoder names Port Viewing the protocol decoder listAlldefaultpass AlldefaultIPS sensors Viewing the IPS sensor listAdding an IPS sensor Configuring IPS sensorsProtectclient ProtectemailserverIPS sensor filters IPS sensor attributesReset Configuring filtersIPS sensor overrides Delete and Edit Delete or edit the filter IconsApplication Configuring pre-defined and custom overridesSource Exempt IPDoS sensors Viewing the DoS sensor list Configuring DoS sensorsSequence in which the sensors examine network traffic Appears, and select OKDoS sensor attributes Anomaly configurationName Enter or change the DoS sensor name Comments Will appear in the DoS sensor listUnderstanding the anomalies Udpflood Anomaly Description TcpdstsessionUdpscan UdpsrcsessionUnderstanding the anomalies What is a SYN flood attack? SYN flood attacksHow SYN floods work What is SYN proxy? What is SYN threshold?FortiGate IPS Response to SYN flood attacks How IPS works to prevent SYN floodsIPS operation before synflood threshold is reached Configuring SYN flood protection Suggested settings for different network conditionsConfigure the options for tcpsynflood Select OK Icmp sweep attacks What is an Icmp sweep?How Icmp sweep attacks work FortiGate IPS response to Icmp sweep attacksPredefined Icmp signatures Icmp sweep anomalies Configuring Icmp sweep protection FortiGate Version 3.0 MR7 IPS User Guide IndexTechnical support