P-660H/HW/W-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.
Summary of Contents for P-660H - VERSION 3.40
Page 1: ...P 660H HW W T Series ADSL 2 Gateway User s Guide Version 3 40 6 2005...
Page 9: ...P 660H HW W T Series User Guide 9 Customer Support...
Page 31: ...P 660H HW W T Series User Guide 31 List of Figures...
Page 37: ...P 660H HW W T Series User Guide 37 List of Tables...
Page 41: ...P 660H HW W T Series User Guide 41 Introduction to DSL...
Page 61: ...P 660H HW W T Series User Guide 61 Chapter 3 Wizard Setup for Internet Access...
Page 89: ...P 660H HW W T Series User Guide 89 Chapter 5 Wireless LAN...
Page 131: ...P 660H HW W T Series User Guide 131 Chapter 10 Firewalls...
Page 161: ...P 660H HW W T Series User Guide 161 Chapter 13 Remote Management Configuration...
Page 175: ...P 660H HW W T Series User Guide 175 Chapter 14 Universal Plug and Play UPnP...
Page 181: ...P 660H HW W T Series User Guide 181 Chapter 15 Logs Screens...
Page 195: ...P 660H HW W T Series User Guide 195 Chapter 16 Media Bandwidth Management Advanced Setup...
Page 207: ...P 660H HW W T Series User Guide 207 Chapter 17 Maintenance...
Page 217: ...P 660H HW W T Series User Guide 217 Chapter 19 Menu 1 General Setup...
Page 221: ...P 660H HW W T Series User Guide 221 Chapter 20 Menu 2 WAN Backup Setup...
Page 225: ...P 660H HW W T Series User Guide 225 Chapter 21 Menu 3 LAN Setup...
Page 229: ...P 660H HW W T Series User Guide 229 Chapter 22 Wireless LAN Setup...
Page 235: ...P 660H HW W T Series User Guide 235 Chapter 23 Internet Access...
Page 249: ...P 660H HW W T Series User Guide 249 Chapter 25 Static Route Setup...
Page 253: ...P 660H HW W T Series User Guide 253 Chapter 26 Bridging Setup...
Page 269: ...P 660H HW W T Series User Guide 269 Chapter 27 Network Address Translation NAT...
Page 285: ...P 660H HW W T Series User Guide 285 Chapter 29 Filter Configuration...
Page 305: ...P 660H HW W T Series User Guide 305 Chapter 32 System Information and Diagnosis...
Page 317: ...P 660H HW W T Series User Guide 317 Chapter 33 Firmware and Configuration File Maintenance...
Page 323: ...P 660H HW W T Series User Guide 323 Chapter 34 System Maintenance...
Page 327: ...P 660H HW W T Series User Guide 327 Chapter 35 Remote Management...
Page 337: ...P 660H HW W T Series User Guide 337 Chapter 36 IP Policy Routing...
Page 341: ...P 660H HW W T Series User Guide 341 Chapter 37 Call Scheduling...
Page 357: ...P 660H HW W T Series User Guide 357 Appendix A...
Page 359: ...P 660H HW W T Series User Guide 359 Appendix B...
Page 383: ...P 660H HW W T Series User Guide 383 Appendix D...
Page 387: ...P 660H HW W T Series User Guide 387 Appendix F...
Page 393: ...P 660H HW W T Series User Guide 393 Appendix G...
Page 397: ...P 660H HW W T Series User Guide 397 Appendix H...
Page 400: ...P 660H HW W T Series User Guide Appendix I 400...
Page 401: ...P 660H HW W T Series User Guide 401 Appendix I...
Page 455: ...P 660H HW W T Series User Guide 455 Appendix M...
