Prestige 662HW Series User’s Guide
151
Chapter 13 Firewalls
Figure 57
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.
13.5.1 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
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Страница 7: ...Prestige 662HW Series User s Guide 7 Customer Support...
Страница 43: ...Prestige 662HW Series User s Guide 43 Introduction to DSL...
Страница 53: ...Prestige 662HW Series User s Guide 53 Chapter 1 Getting To Know Your Prestige...
Страница 59: ...Prestige 662HW Series User s Guide 59 Chapter 2 Introducing the Web Configurator...
Страница 77: ...Prestige 662HW Series User s Guide 77 Chapter 5 Password Setup...
Страница 89: ...Prestige 662HW Series User s Guide 89 Chapter 7 DMZ...
Страница 111: ...Prestige 662HW Series User s Guide 111 Chapter 8 Wireless LAN Setup...
Страница 127: ...Prestige 662HW Series User s Guide 127 Chapter 9 WAN Setup...
Страница 139: ...Prestige 662HW Series User s Guide 139 Chapter 10 Network Address Translation NAT Screens...
Страница 157: ...Prestige 662HW Series User s Guide 157 Chapter 13 Firewalls...
Страница 203: ...Prestige 662HW Series User s Guide 203 Chapter 16 Content Access Control...
Страница 211: ...Prestige 662HW Series User s Guide 211 Chapter 17 Anti Virus Packet Scan...
Страница 217: ...Prestige 662HW Series User s Guide 217 Chapter 18 Introduction to IPSec...
Страница 249: ...Prestige 662HW Series User s Guide 249 Chapter 20 Remote Management Configuration...
Страница 263: ...Prestige 662HW Series User s Guide 263 Chapter 21 Universal Plug and Play UPnP...
Страница 269: ...Prestige 662HW Series User s Guide 269 Chapter 22 Logs Screens...
Страница 295: ...Prestige 662HW Series User s Guide 295 Chapter 24 Maintenance...
Страница 301: ...Prestige 662HW Series User s Guide 301 Chapter 25 Introducing the SMT...
Страница 305: ...Prestige 662HW Series User s Guide 305 Chapter 26 Menu 1 General Setup...
Страница 319: ...Prestige 662HW Series User s Guide 319 Chapter 29 Wireless LAN Setup...
Страница 325: ...Prestige 662HW Series User s Guide 325 Chapter 30 Internet Access...
Страница 339: ...Prestige 662HW Series User s Guide 339 Chapter 32 Static Route Setup...
Страница 343: ...Prestige 662HW Series User s Guide 343 Chapter 33 Bridging Setup...
Страница 375: ...Prestige 662HW Series User s Guide 375 Chapter 36 Filter Configuration...
Страница 395: ...Prestige 662HW Series User s Guide 395 Chapter 39 System Information and Diagnosis...
Страница 411: ...Prestige 662HW Series User s Guide 411 Chapter 40 Firmware and Configuration File Maintenance...
Страница 417: ...Prestige 662HW Series User s Guide 417 Chapter 41 System Maintenance...
Страница 421: ...Prestige 662HW Series User s Guide 421 Chapter 42 Remote Management...
Страница 433: ...Prestige 662HW Series User s Guide 433 Chapter 44 Call Scheduling...
Страница 449: ...Prestige 662HW Series User s Guide 449 Chapter 46 SA Monitor...
Страница 453: ...Prestige 662HW Series User s Guide 453 Chapter 47 Internal SPTGEN...
Страница 459: ...Prestige 662HW Series User s Guide 459 Appendix A Pin Assignments Figure 290 Ethernet Cable Pin Assignments...
Страница 479: ...Prestige 662HW Series User s Guide 479 Appendix C IP Subnetting...
Страница 485: ...Prestige 662HW Series User s Guide 485 Appendix E Wireless LAN and IEEE 802 11...
Страница 492: ...Prestige 662HW Series User s Guide Appendix H Triangle Route 492...
Страница 493: ...Prestige 662HW Series User s Guide 493 Appendix H Triangle Route...
Страница 525: ...Prestige 662HW Series User s Guide 525 Appendix K Example Internal SPTGEN Screens...
Страница 527: ...Prestige 662HW Series User s Guide 527 Appendix L Command Interpreter...
Страница 529: ...Prestige 662HW Series User s Guide 529 Appendix M Firewall Commands...
Страница 533: ...Prestige 662HW Series User s Guide 533 Appendix N NetBIOS Filter Commands...
Страница 535: ...Prestige 662HW Series User s Guide 535 Appendix O Brute Force Password Guessing Protection...