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P-660H/HW-T Series User’ Guide
125
Chapter 10 Firewalls
Figure 51
Stateful Inspection
The previous figure shows the Prestige’s default firewall rules in action as well as
demonstrates how stateful inspection works. User A can initiate a Telnet session from within
the LAN and responses to this request are allowed. However other Telnet traffic initiated from
the WAN is blocked.
10.5.1 Stateful Inspection Process
In this example, the following sequence of events occurs when a TCP packet leaves the LAN
network through the firewall's WAN interface. The TCP packet is the first in a session, and the
packet's application layer protocol is configured for a firewall rule inspection:
1
The packet travels from the firewall's LAN to the WAN.
2
The packet is evaluated against the interface's existing outbound access list, and the
packet is permitted (a denied packet would simply be dropped at this point).
3
The packet is inspected by a firewall rule to determine and record information about the
state of the packet's connection. This information is recorded in a new state table entry
created for the new connection. If there is not a firewall rule for this packet and it is not an
attack, then the settings in the
Default Policy
screen determine the action for this packet.
4
Based on the obtained state information, a firewall rule creates a temporary access list
entry that is inserted at the beginning of the WAN interface's inbound extended access
list. This temporary access list entry is designed to permit inbound packets of the same
connection as the outbound packet just inspected.
5
The outbound packet is forwarded out through the interface.
6
Later, an inbound packet reaches the interface. This packet is part of the connection
previously established with the outbound packet. The inbound packet is evaluated against
the inbound access list, and is permitted because of the temporary access list entry
previously created.
7
The packet is inspected by a firewall rule, and the connection's state table entry is updated
as necessary. Based on the updated state information, the inbound extended access list
Содержание P-660H Series
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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 ...