Understanding the anomalies | DoS sensors |
Protected addresses:
Each entry in the protected address table includes a source and destination IP address as well as a destination port. The DoS sensor will be applied to traffic matching the three attributes in any table entry.
Note: A new DoS sensor has no protected address table entries. If no addresses are entered, the DoS sensor cannot match any traffic and will not function.
Destination | The IP address of the traffic destination. 0.0.0.0/0 matches all addresses. If |
| the FortiGate unit is running in transparent mode, 0.0.0.0/0 also includes |
| the management IP address. |
Destination | The destination port of the traffic. 0 matches any port. |
Port |
|
Source | The IP address of the traffic source. 0.0.0.0/0 matches all addresses. |
Add | After entering the required destination address, destination port, and |
| source address, select Add to add protected address to the Protected |
| Addresses list. The DoS sensor will be invoked only on traffic matching all |
| three of the entered values. If no addresses appear in the list, the sensor |
| will not be applied to any traffic. |
Understanding the anomalies
Each DoS sensor offers four configurable statistical anomaly types for each of the
TCP, UDP, and ICMP protocols.
Table 10: The four statistical anomaly types.
Flooding
Scan
Source session limit
Destination session limit
If the number of sessions targeting a single destination in one second is over a specified threshold, the destination is experiencing flooding.
If the number of sessions from a single source in one second is over a specified threshold, the source is scanning.
If the number of concurrent sessions from a single source is over a specified threshold, the source session limit is reached.
If the number of concurrent sessions to a single destination is over a specified threshold, the destination session limit is reached.
For each of the TCP, UDP, and ICMP protocols, DoS sensors offer four statistical anomaly types. The result is twelve configurable anomalies.
Figure 14: The twelve individually configurable anomalies
Anomaly | Description |
|
|
tcp_syn_flood | If the SYN packet rate, including retransmission, to one destination |
| IP address exceeds the configured threshold value, the action is |
| executed. The threshold is expressed in packets per second. |
|
|
tcp_port_scan | If the SYN packets rate, including retransmission, from one source |
| IP address exceeds the configured threshold value, the action is |
| executed. The threshold is expressed in packets per second. |
|
|
tcp_src_session | If the number of concurrent TCP connections from one source IP |
| address exceeds the configured threshold value, the action is |
| executed. |
|
|
FortiGate IPS User Guide Version 3.0 MR7
48 |
