Chapter 10 Firewalls
P-79X Series User’s Guide
108
Figure 63 Three-Way Handshake
For UDP, half-open means that the firewall has detected no return traffic. An unusually high number
(or arrival rate) of half-open sessions could indicate a DOS attack.
10.4.1 Threshold Values
If everything is working properly, you probably do not need to change the threshold settings as the
default threshold values should work for most small offices. Tune these parameters when you
believe the P-79X has been receiving DoS attacks that are not recorded in the logs or the logs show
that the P-79X is classifying normal traffic as DoS attacks. Factors influencing choices for threshold
values are:
1 The maximum number of opened sessions.
2 The minimum capacity of server backlog in your LAN network.
3 The CPU power of servers in your LAN network.
4 Network bandwidth.
5 Type of traffic for certain servers.
Reduce the threshold values if your network is slower than average for any of these factors
(especially if you have servers that are slow or handle many tasks and are often busy).
• If you often use P2P applications such as file sharing with eMule or eDonkey, it’s recommended
that you increase the threshold values since lots of sessions will be established during a small
period of time and the P-79X may classify them as DoS attacks.
10.4.2 Configuring Firewall Thresholds
The P-79X also sends alerts whenever TCP Maximum Incomplete is exceeded. The global values
specified for the threshold and timeout apply to all TCP connections.
Click Firewall > Threshold to bring up the next screen.
To Next Page
Loading...
