DoS sensors | Fortinet IPS manual

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

Image 45

Fortinet IPS manual DoS sensors

Contents

E R G U I D E Trademarks Contents IPS sensors Protocol decodersDoS sensors SYN flood attacks FortiGate IPS Introduction Fortinet documentation About this documentDocument conventions Typographic conventions FortiGate 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 end Configuring logging and alert email Setting the buffer sizeMonitoring the network and dealing with attacks Controlling sessions Attack log messages Signature FortiGuard Center Anomaly Creating a protection profile that uses IPS sensors Using IPS sensors in a protection profileAdding protection profiles to firewall policies Select Create New Adding 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 Filters Create 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 pattern Creating custom signatures Custom signature fieldsShows the valid characters for custom signature fields Attackid Custom signature syntaxName BufferOverflow Srcport Content keywords Keyword and value Description Deprecated, see pattern and context keywords Context uri Pattern GETPattern yahoo.com Context host Regex/mdelim PcreRegexdelimismxAEGRU Uri !uristr IP header keywords Keyword and Value Description Protocol tcp TCP header keywords Keyword and Value Description Tcpflags S,12 Tcpflags AP UDP 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 list Alldefaultpass AlldefaultIPS sensors Viewing the IPS sensor list Adding an IPS sensor Configuring IPS sensorsProtectclient Protectemailserver IPS sensor filters IPS sensor attributes Reset Configuring filtersIPS sensor overrides Delete and Edit Delete or edit the filter Icons Application Configuring pre-defined and custom overrides Source Exempt IP DoS sensors Viewing the DoS sensor list Configuring DoS sensorsSequence in which the sensors examine network traffic Appears, and select OK DoS sensor attributes Anomaly configurationName Enter or change the DoS sensor name Comments Will appear in the DoS sensor list Understanding the anomalies Udpflood Anomaly Description TcpdstsessionUdpscan Udpsrcsession Understanding 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 floods IPS 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 attacks Predefined Icmp signatures Icmp sweep anomalies Configuring Icmp sweep protection FortiGate Version 3.0 MR7 IPS User Guide Index Technical support