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P-660H/HW-T Series User’ Guide
Chapter 11 Firewall Configuration
150
11.12.1 Threshold Values
Tune these parameters when something is not working and after you have checked the firewall
counters. These default values should work fine for most small offices. Factors influencing
choices for threshold values are:
• The maximum number of opened sessions.
• The minimum capacity of server backlog in your LAN network.
• The CPU power of servers in your LAN network.
• Network bandwidth.
• Type of traffic for certain servers.
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), then the default values should be
reduced.
You should make any changes to the threshold values before you continue configuring
firewall rules.
11.12.2 Half-Open Sessions
An unusually high number of half-open sessions (either an absolute number or measured as
the arrival rate) could indicate that a Denial of Service attack is occurring. For TCP, "half-
open" means that the session has not reached the established state-the TCP three-way
handshake has not yet been completed (see
). For UDP, "half-open"
means that the firewall has detected no return traffic.
The Prestige measures both the total number of existing half-open sessions and the rate of
session establishment attempts. Both TCP and UDP half-open sessions are counted in the total
number and rate measurements. Measurements are made once a minute.
When the number of existing half-open sessions rises above a threshold (
max-incomplete
high
), the Prestige starts deleting half-open sessions as required to accommodate new
connection requests. The Prestige continues to delete half-open requests as necessary, until the
number of existing half-open sessions drops below another threshold (
max-incomplete low
).
When the rate of new connection attempts rises above a threshold (
one-minute high
), the
Prestige starts deleting half-open sessions as required to accommodate new connection
requests. The Prestige continues to delete half-open sessions as necessary, until the rate of new
connection attempts drops below another threshold (
one-minute low
). The rate is the number
of new attempts detected in the last one-minute sample period.
11.12.2.1 TCP Maximum Incomplete and Blocking Time
An unusually high number of half-open sessions with the same destination host address could
indicate that a Denial of Service attack is being launched against the host.
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Страница 10: ...P 660H HW T Series User Guide 9 Customer Support ...
Страница 32: ...P 660H HW T Series User Guide 31 List of Figures ...
Страница 38: ...P 660H HW T Series User Guide 37 List of Tables ...
Страница 42: ...P 660H HW T Series User Guide 41 Introduction to DSL ...
Страница 62: ...P 660H HW T Series User Guide 61 Chapter 3 Wizard Setup for Internet Access ...
Страница 90: ...P 660H HW T Series User Guide 89 Chapter 5 Wireless LAN ...
Страница 132: ...P 660H HW T Series User Guide 131 Chapter 10 Firewalls ...
Страница 162: ...P 660H HW T Series User Guide 161 Chapter 13 Remote Management Configuration ...
Страница 176: ...P 660H HW T Series User Guide 175 Chapter 14 Universal Plug and Play UPnP ...
Страница 182: ...P 660H HW T Series User Guide 181 Chapter 15 Logs Screens ...
Страница 196: ...P 660H HW T Series User Guide 195 Chapter 16 Media Bandwidth Management Advanced Setup ...
Страница 208: ...P 660H HW T Series User Guide 207 Chapter 17 Maintenance ...
Страница 218: ...P 660H HW T Series User Guide 217 Chapter 19 Menu 1 General Setup ...
Страница 222: ...P 660H HW T Series User Guide 221 Chapter 20 Menu 2 WAN Backup Setup ...
Страница 226: ...P 660H HW T Series User Guide 225 Chapter 21 Menu 3 LAN Setup ...
Страница 230: ...P 660H HW T Series User Guide 229 Chapter 22 Wireless LAN Setup ...
Страница 236: ...P 660H HW T Series User Guide 235 Chapter 23 Internet Access ...
Страница 250: ...P 660H HW T Series User Guide 249 Chapter 25 Static Route Setup ...
Страница 254: ...P 660H HW T Series User Guide 253 Chapter 26 Bridging Setup ...
Страница 270: ...P 660H HW T Series User Guide 269 Chapter 27 Network Address Translation NAT ...
Страница 286: ...P 660H HW T Series User Guide 285 Chapter 29 Filter Configuration ...
Страница 306: ...P 660H HW T Series User Guide 305 Chapter 32 System Information and Diagnosis ...
Страница 318: ...P 660H HW T Series User Guide 317 Chapter 33 Firmware and Configuration File Maintenance ...
Страница 324: ...P 660H HW T Series User Guide 323 Chapter 34 System Maintenance ...
Страница 328: ...P 660H HW T Series User Guide 327 Chapter 35 Remote Management ...
Страница 338: ...P 660H HW T Series User Guide 337 Chapter 36 IP Policy Routing ...
Страница 342: ...P 660H HW T Series User Guide 341 Chapter 37 Call Scheduling ...
Страница 354: ...P 660H HW T Series User Guide 353 Chapter 38 Troubleshooting Figure 233 Security Setting ActiveX Controls ...
Страница 358: ...P 660H HW T Series User Guide 357 Appendix A ...
Страница 360: ...P 660H HW T Series User Guide 359 Appendix B ...
Страница 384: ...P 660H HW T Series User Guide 383 Appendix D ...
Страница 388: ...P 660H HW T Series User Guide 387 Appendix F ...
Страница 394: ...P 660H HW T Series User Guide 393 Appendix G ...
Страница 398: ...P 660H HW T Series User Guide 397 Appendix H ...
Страница 401: ...P 660H HW T Series User Guide Appendix I 400 ...
Страница 402: ...P 660H HW T Series User Guide 401 Appendix I ...
Страница 456: ...P 660H HW T Series User Guide 455 Appendix M ...