Chapter 14 Firewall
VMG1312-T10C User’s Guide
163
The following table describes the labels in this screen.
14.5.1 The DoS Advanced Screen
For DoS
attacks, the Device uses thresholds to determine when to start dropping sessions that do
not become fully established (half-open sessions). These thresholds apply globally to all sessions.
For TCP, half-open means that the session has not reached the established state-the TCP three-way
handshake has not yet been completed. Under normal circumstances, the application that initiates
a session sends a SYN (synchronize) packet to the receiving server. The receiver sends back an ACK
(acknowledgment) packet and its own SYN, and then the initiator responds with an ACK
(acknowledgment). After this handshake, a connection is established.
Figure 111
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.
14.5.1.1 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 Device has been receiving DoS attacks that are not recorded in the logs or the logs
show that the Device 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.
Table 66
Security > Firewall > Dos
LABEL
DESCRIPTION
Denial of Services Enable this to protect against DoS attacks. The Device will drop sessions that surpass
maximum thresholds.
Apply
Click this to save your changes.
Cancel
Click this to restore your previously saved settings.
Advanced
Click this to go to a screen to specify maximum thresholds at which the Device will start
dropping sessions.
Содержание VMG1312-T10C
Страница 4: ...Contents Overview VMG1312 T10C User s Guide 4 ...
Страница 12: ...Table of Contents VMG1312 T10C User s Guide 12 ...
Страница 13: ...13 PART I User s Guide ...
Страница 14: ...14 ...
Страница 20: ...Chapter 1 Introduction VMG1312 T10C User s Guide 20 ...
Страница 28: ...28 ...
Страница 34: ...Chapter 4 Connection Status and System Info VMG1312 T10C User s Guide 34 ...
Страница 39: ...Chapter 5 WAN Setup VMG1312 T10C User s Guide 39 Figure 19 Network Setting Broadband Internet Connection ...
Страница 106: ...Chapter 7 Home Networking VMG1312 T10C User s Guide 112 ...
Страница 144: ...Chapter 13 Filter VMG1312 T10C User s Guide 152 ...
Страница 164: ...Chapter 15 Parental Control VMG1312 T10C User s Guide 172 ...
Страница 172: ...Chapter 16 Certificates VMG1312 T10C User s Guide 180 ...
Страница 178: ...Chapter 17 System Monitor VMG1312 T10C User s Guide 186 ...
Страница 180: ...Chapter 18 User Account VMG1312 T10C User s Guide 188 ...
Страница 184: ...Chapter 20 System VMG1312 T10C User s Guide 192 ...
Страница 190: ...Chapter 22 Log Setting VMG1312 T10C User s Guide 198 ...
Страница 196: ...Chapter 24 Backup Restore VMG1312 T10C User s Guide 204 ...
Страница 208: ...Chapter 25 Remote Management VMG1312 T10C User s Guide 216 4 The command line interface displays ...
Страница 214: ...Chapter 26 Diagnostic VMG1312 T10C User s Guide 222 ...
Страница 232: ...Appendix B Legal Information VMG1312 T10C User s Guide 240 ...