Fortinet IPS manual Sbid --name Block.example.com

Creating custom signatures Custom signatures

The FortiGate unit will limit its search for the pattern to the HTTP protocol. Even though the HTTP protocol uses only TCP traffic, the FortiGate will search for HTTP protocol communication in TCP, UDP, and ICMP traffic. This is a needless waste of system resources.

5Specifying the traffic type.

Use the --protocol tcp keyword to limit the effect of the custom signature to only TCP traffic. This will save system resources by not unnecessarily scanning UDP and ICMP traffic.

F-SBID( --name "Block.example.com"; --pattern "example.com"; --service HTTP; --protocol tcp; )

The FortiGate unit will limit its search for the pattern to TCP traffic and ignore UDP and ICMP network traffic.

6Ignoring case sensitivity

By default, patterns are case sensitive. If a user directed his or her browser to Example.com, the custom signature would not recognize the URL as a match.

Use the --no_casekeyword to make the pattern matching case insensitive.

F-SBID( --name "Block.example.com"; --pattern "example.com"; --service HTTP; --no_case; )

Unlike all of the other keywords in this example, the --no_casekeyword has no value. Only the keyword is required.

7Limiting pattern scans to only traffic sent from the client

The --flowcommand can be used to further limit the network traffic being scanned to only that send by the client or by the server.

F-SBID( --name "Block.example.com";

--pattern "example.com"; --service HTTP; --no_case; --flow from_client; )

Web servers don’t contact clients until clients first open a communication session. Therefore, using the --flow from_client command will force the FortiGate until to ignore all traffic originating from the server. Since the majority of HTTP traffic flows from the server to the client, this will save considerable system resources and still maintain protection.

8Specifying the context

When the client browser tries to contact example.com, a DNS is first consulted to get the example.com server IP address. The IP address is then specified in the URL field of the HTTP communication. The domain name will still appear in the host field so this custom signature will not function without the --context host keyword/value pair.

F-SBID( --name "Block.example.com";

--pattern "example.com"; --service HTTP; --no_case; --flow from_client; --context host; )

	FortiGate IPS User Guide Version 3.0 MR7
34	01-30007-0080-20080916