Fases del Proyecto

Syntax:--dump-all-html

Description:

Dump all HTML files for benchmarking via iSniff. When there is no file type specified, all HTML files are dumped.

rate

Syntax:--rate <matches_int>,<time_int>;

Description:

Instead of generating log entries every time the signature is detected, use this keyword to generate a log entry only if the signature is detected a specified number of times within a specified time period.

l <matches_int>is the number of times a signature must be detected.

l <time_int>is the length of time in which the signature must be detected, in seconds.

For example, if a custom signature detects a pattern, a log entry will be created every time the signature is detected. If--rate 100,10; is added to the signature, a log entry will be created if the signature is

detected 100 times in the previous 10 seconds. Use this command with--trackto further limit log entries to when the specified number of detections occur within a certain time period involving the same source or destination address rather than all addresses.

rpc_num

Syntax:--rpc_num <app_int>[, <ver_int> | *][, <proc_int> | *>];

Description:

Check for RPC application, version, and procedure numbers in SUNRPC CALL requests. The * wild card can be used for version and procedure numbers.

same_ip

Syntax:--same_ip;

Description:

Check that the source and the destination have the same IP addresses.

track

Syntax:--track {SRC_IP |DST_IP |DHCP_CLIENT |DNS_DOMAIN}[,block_int];

Description:

When used with--rate, this keyword narrows the custom signature rate totals to individual addresses. l SRC_IP:  tracks the packet's source IP.

l DST_IP:  tracks the packet's destination IP.

l DHCP_CLIENT:  tracks the DHCP client's MAC address.

l DNS_DOMAIN:  counts the number of any specific domain name.

l block_inthas the FortiGate unit block connections for the specified number of seconds, from the client or to the server, depending on which is specified.

For example, if--rate 100,10is added to the signature, a log entry will be created if the signature is detected 100 times in the previous 10 seconds. The FortiGate unit maintains a single total, regardless of source and destination address.

If the same custom signature also includes--trackclient; matches are totaled separately for each source address. A log entry is added when the signature is detected 100 times in 10 seconds within traffic from the same source address.

The--trackkeyword can also be used without--rate. If an integer is specified, the client or server will be blocked for the specified number of seconds every time the signature is detected.

Creating a custom signature to block access to example.com

In this first example, you will create a custom signature to block access to the example.com URL.

This example describes the use of the custom signature syntax to block access to a URL. To create the custom signature entry in the FortiGate unit web-based manager, see “Creating a custom IPS signature”.

1. Enter the custom signature basic format.

All custom signatures have a header and at least one keyword/value pair. The header is always the same:

F-SBID( )

The keyword/value pairs appear within the parentheses and each pair is followed by a semicolon.

2. Choose a name for the custom signature

Every custom signature requires a name, so it is a good practice to assign a name before adding any other keywords.Use the--namekeyword to assign the custom signature a name. The name value follows the keyword after a space. Enclose the name value in double-quotes:

F-SBID( --name "Block.example.com"; )

The signature, as it appears here, will not do anything if you try to use it. It has a name, but does not look for any patterns in network traffic. You must specify a pattern that the FortiGate unit will search for.

3. Add a signature pattern

Use the--patternkeyword to specify what the FortiGate unit will search for: F-SBID( --name "Block.example.com"; --pattern "example.com"; ) The signature will now detect the example.com URL appearing in network traffic. The custom signature should only detect the URL in HTTP traffic, however. Any other traffic with the URL should be allowed to pass. For example, an email message to or from example.com should not be stopped.

4. Specify the service

Use the--servicekeyword to limit the effect of the custom signature to only the HTTP protocol. F-SBID( --name "Block.example.com"; --pattern "example.com"; --service HTTP; ) 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 waste of system resources that you can avoid by limiting the search further, as shown below.

5. Specify the traffic type.

Use the --protocol tcp keywordto 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.

6. Ignore case sensitivity

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.

7. Limit pattern scans to only traffic sent from the client

The--flow command 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 do not contact clients until clients first open a communication session. Therefore, using the--flow from_clientcommand will force the FortiGate to ignore all traffic 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.

8. Specify 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 hostkeyword/value pair.

F-SBID( --name "Block.example.com"; --pattern "example.com"; --service HTTP; --no_ case; --flow from_client; --context host; )