P-660H/HW-T Series User’ Guide
Chapter 10 Firewalls
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temporary entries might be modified, in order to permit only packets that are valid for the
current state of the connection.
8
Any additional inbound or outbound packets that belong to the connection are inspected
to update the state table entry and to modify the temporary inbound access list entries as
required, and are forwarded through the interface.
9
When the connection terminates or times out, the connection's state table entry is deleted
and the connection's temporary inbound access list entries are deleted.
10.5.2 Stateful Inspection and the Prestige
Additional rules may be defined to extend or override the default rules. For example, a rule
may be created which will:
• Block all traffic of a certain type, such as IRC (Internet Relay Chat), from the LAN to the
Internet.
• Allow certain types of traffic from the Internet to specific hosts on the LAN.
• Allow access to a Web server to everyone but competitors.
• Restrict use of certain protocols, such as Telnet, to authorized users on the LAN.
These custom rules work by evaluating the network traffic’s Source IP address, Destination IP
address, IP protocol type, and comparing these to rules set by the administrator.
Note:
The ability to define firewall rules is a very powerful tool. Using custom rules, it
is possible to disable all firewall protection or block all access to the Internet.
Use extreme caution when creating or deleting firewall rules. Test changes
after creating them to make sure they work correctly.
Below is a brief technical description of how these connections are tracked. Connections may
either be defined by the upper protocols (for instance, TCP), or by the Prestige itself (as with
the "virtual connections" created for UDP and ICMP).
10.5.3 TCP Security
The Prestige uses state information embedded in TCP packets. The first packet of any new
connection has its SYN flag set and its ACK flag cleared; these are "initiation" packets. All
packets that do not have this flag structure are called "subsequent" packets, since they
represent data that occurs later in the TCP stream.
If an initiation packet originates on the WAN, this means that someone is trying to make a
connection from the Internet into the LAN. Except in a few special cases (see "Upper Layer
Protocols" shown next), these packets are dropped and logged.
If an initiation packet originates on the LAN, this means that someone is trying to make a
connection from the LAN to the Internet. Assuming that this is an acceptable part of the
security policy (as is the case with the default policy), the connection will be allowed. A cache
entry is added which includes connection information such as IP addresses, TCP ports,
sequence numbers, etc.
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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 ...
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Страница 402: ...P 660H HW T Series User Guide 401 Appendix I ...
Страница 456: ...P 660H HW T Series User Guide 455 Appendix M ...
