Protocol tcp | Fortinet IPS guide


Custom signatures	Creating custom signatures

Table 5: IP header keywords

Keyword and Value	Description

--dst_addr [!]<ipv4>;	The destination IP address.
	To have the FortiGate search for a packet that does
	not contain the specified address, add an
	exclamation mark (!) before the IP address.
	You can define up to 28 IP addresses or CIDR
	blocks. Enclose the comma separated list in square
	brackets.
	Example:
	•	dst_addr [172.20.0.0/16,10.1.0.0/16,
		192.168.0.0/16]

--ip_id <field_int>;	Check the IP ID field for the specified value.
--ip_option {rr eol nop	Use the ip_option keyword to check various IP
ts sec lsrr ssrr	option settings. The available options include:
satid any};	• rr: Check if IP RR (record route) option is
		present.
	• eol: Check if IP EOL (end of list) option is
		present.
	• nop: Check if IP NOP (no op) option is present.
	• ts: Check if IP TS (time stamp) option is
		present.
	• sec: Check if IP SEC (IP security) option is
		present.
	• lsrr: Check if IP LSRR (loose source routing)
		option is present.
	• ssrr: Check if IP SSRR (strict source routing)
		option is present.
	• satid: Check if IP SATID (stream identifier)
		option is present.
	• any: Check if IP any option is present.
--ip_tos <field_int>;	Check the IP TOS field for the specified value.
--ip_ttl [< >] <ttl_int>;	Check the IP time-to-live value against the
	specified value. Optionally, you can check for an IP
	time-to-live greater-than (>) or less-than (<) the
	specified value with the appropriate symbol.

--protocol	Check the IP protocol header.
{<protocol_int> tcp	Example:
udp icmp};		--protocol tcp;
--src_addr [!]<ipv4>;	The source IP address.
	To have the FortiGate search for a packet that does
	not contain the specified address, add an
	exclamation mark (!) before the IP address.
	You can define up to 28 IP addresses or CIDR
	blocks. Enclose the comma separated list in square
	brackets.
	Example:
	•	src_addr 192.168.13.0/24

FortiGate IPS User Guide Version 3.0 MR7
01-30007-0080-20080916	29

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Fortinet IPS manual Protocol tcp, IP header keywords Keyword and Value Description

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 Comments on Fortinet technical documentation Customer service and technical supportFortinet Knowledge Center This section contains the following topics IPS overview and general configurationIPS settings and controls 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 Viewing the predefined signature list Predefined signaturesIPS predefined signatures Enable SettingsColumn Clear All Filters Create a sensor and add IPS filters to it Viewing the predefined signature list Viewing the custom signature list Custom signaturesIPS custom signatures Adding custom signatures using the web-based manager Custom signature configurationAdding custom signatures using the CLI Command syntax pattern Shows the valid characters for custom signature fields Creating custom signaturesCustom 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 Other keywords Keyword and Value Description UDP header keywords Keyword and Value DescriptionIcmp keywords Keyword and Value Usage Sbid --name Block.example.com Example 1 signature to block access to example.comExample custom signatures Sbid --name Block.example.com Sbid --name Block.SMTP.VRFY.CMD --pattern vrfy Example 2 signature to block the Smtp ‘vrfy’ commandSbid --name Block.SMTP.VRFY.CMD Creating custom signatures Upgrading the IPS protocol decoder list Protocol decodersProtocol decoders 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 How SYN floods work What is a SYN flood attack?SYN flood attacks 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 Configure the options for tcpsynflood Select OK Configuring SYN flood protectionSuggested settings for different network conditions 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