
Chapter 11 Firewall
ZyWALL 2WG User’s Guide
261
The following table describes the labels in this screen.
11.11 Firewall Thresholds
For DoS
attacks, the ZyWALL uses thresholds to determine when to start dropping sessions
that do not become fully established (half-open sessions). These thresholds apply globally to
all sessions.
For TCP, half-open means that the session has not reached the established state-the TCP three-
way handshake has not yet been completed. Under normal circumstances, the application that
initiates a session sends a SYN (synchronize) packet to the receiving server. The receiver
sends back an ACK (acknowledgment) packet and its own SYN, and then the initiator
responds with an ACK (acknowledgment). After this handshake, a connection is established.
Figure 161
Three-Way Handshake
For UDP, half-open means that the firewall has detected no return traffic. An unusually high
number (or arrival rate) of half-open sessions could indicate a DOS attack.
Table 72
SECURITY > FIREWALL > Anti-Probing
LABEL
DESCRIPTION
Respond to PING
on
Select the check boxes of the interfaces that you want to reply to incoming Ping
requests.
Clear an interface’s check box to have the ZyWALL not respond to any Ping
requests that come into that interface.
Do not respond to
requests for
unauthorized
services.
Select this option to prevent hackers from finding the ZyWALL by probing for
unused ports. If you select this option, the ZyWALL will not respond to port
request(s) for unused ports, thus leaving the unused ports and the ZyWALL
unseen. If this option is not selected, the ZyWALL will reply with an ICMP port
unreachable packet for a port probe on its unused UDP ports and a TCP reset
packet for a port probe on its unused TCP ports.
Note that the probing packets must first traverse the ZyWALL's firewall rule
checks before reaching this anti-probing mechanism. Therefore if a firewall rule
stops a probing packet, the ZyWALL reacts based on the firewall rule to either
send a TCP reset packet for a blocked TCP packet (or an ICMP port-unreachable
packet for a blocked UDP packets) or just drop the packets without sending a
response packet.
Apply
Click
Apply
to save your changes back to the ZyWALL.
Reset
Click
Reset
to begin configuring this screen afresh.
Содержание ZYWALL 2 WG
Страница 1: ...www zyxel com ZyWALL 2WG Internet Security Appliance User s Guide Version 4 03 12 2007 Edition 1 ...
Страница 2: ......
Страница 8: ...Safety Warnings ZyWALL 2WG User s Guide 8 ...
Страница 42: ...List of Figures ZyWALL 2WG User s Guide 42 ...
Страница 50: ...List of Tables ZyWALL 2WG User s Guide 50 ...
Страница 52: ...52 ...
Страница 80: ...Chapter 2 Introducing the Web Configurator ZyWALL 2WG User s Guide 80 ...
Страница 100: ...Chapter 3 Wizard Setup ZyWALL 2WG User s Guide 100 ...
Страница 140: ...Chapter 4 Tutorial ZyWALL 2WG User s Guide 140 ...
Страница 145: ...145 PART II Network and Wireless LAN Screens 147 Bridge Screens 159 WAN Screens 165 DMZ Screens 201 Wireless LAN 211 ...
Страница 146: ...146 ...
Страница 158: ...Chapter 6 LAN Screens ZyWALL 2WG User s Guide 158 ...
Страница 171: ...Chapter 8 WAN Screens ZyWALL 2WG User s Guide 171 Figure 108 NETWORK WAN General ...
Страница 200: ...Chapter 8 WAN Screens ZyWALL 2WG User s Guide 200 ...
Страница 238: ...238 ...
Страница 258: ...Chapter 11 Firewall ZyWALL 2WG User s Guide 258 Figure 159 SECURITY FIREWALL Rule Summary Edit ...
Страница 270: ...Chapter 11 Firewall ZyWALL 2WG User s Guide 270 Figure 170 My Service Firewall Rule Example Rule Summary Completed ...
Страница 300: ...Chapter 13 Content Filtering Reports ZyWALL 2WG User s Guide 300 ...
Страница 313: ...Chapter 14 IPSec VPN ZyWALL 2WG User s Guide 313 Figure 199 SECURITY VPN VPN Rules IKE Edit Gateway Policy ...
Страница 322: ...Chapter 14 IPSec VPN ZyWALL 2WG User s Guide 322 Figure 202 SECURITY VPN VPN Rules IKE Edit Network Policy ...
Страница 348: ...Chapter 14 IPSec VPN ZyWALL 2WG User s Guide 348 ...
Страница 360: ...Chapter 15 Certificates ZyWALL 2WG User s Guide 360 Figure 229 SECURITY CERTIFICATES My Certificates Create Basic ...
Страница 378: ...Chapter 15 Certificates ZyWALL 2WG User s Guide 378 ...
Страница 380: ...Chapter 16 Authentication Server ZyWALL 2WG User s Guide 380 Figure 239 SECURITY AUTH SERVER Local User Database ...
Страница 384: ...384 ...
Страница 426: ...Chapter 20 Bandwidth Management ZyWALL 2WG User s Guide 426 ...
Страница 479: ...479 PART V Logs and Maintenance Logs Screens 481 Maintenance 511 ...
Страница 480: ...480 ...
Страница 485: ...Chapter 26 Logs Screens ZyWALL 2WG User s Guide 485 Figure 304 LOGS Log Settings ...
Страница 510: ...Chapter 26 Logs Screens ZyWALL 2WG User s Guide 510 ...
Страница 530: ...530 ...
Страница 558: ...Chapter 30 WAN and Dial Backup Setup ZyWALL 2WG User s Guide 558 ...
Страница 564: ...Chapter 31 LAN Setup ZyWALL 2WG User s Guide 564 ...
Страница 570: ...Chapter 32 Internet Access ZyWALL 2WG User s Guide 570 ...
Страница 574: ...Chapter 33 DMZ Setup ZyWALL 2WG User s Guide 574 ...
Страница 578: ...Chapter 34 Route Setup ZyWALL 2WG User s Guide 578 ...
Страница 582: ...Chapter 35 Wireless Setup ZyWALL 2WG User s Guide 582 ...
Страница 594: ...Chapter 37 IP Static Route Setup ZyWALL 2WG User s Guide 594 ...
Страница 614: ...Chapter 38 Network Address Translation NAT ZyWALL 2WG User s Guide 614 ...
Страница 632: ...Chapter 40 Filter Configuration ZyWALL 2WG User s Guide 632 ...
Страница 668: ...Chapter 44 System Maintenance Menus 8 to 10 ZyWALL 2WG User s Guide 668 ...
Страница 672: ...Chapter 45 Remote Management ZyWALL 2WG User s Guide 672 ...
Страница 680: ...Chapter 46 IP Policy Routing ZyWALL 2WG User s Guide 680 ...
Страница 685: ...685 PART VII Troubleshooting and Specifications Troubleshooting 687 Product Specifications 693 ...
Страница 686: ...686 ...
Страница 692: ...Chapter 48 Troubleshooting ZyWALL 2WG User s Guide 692 ...
Страница 702: ...Chapter 49 Product Specifications ZyWALL 2WG User s Guide 702 ...
Страница 704: ...704 ...
Страница 712: ...Appendix A Pop up Windows JavaScripts and Java Permissions ZyWALL 2WG User s Guide 712 ...
Страница 740: ...Appendix D Common Services ZyWALL 2WG User s Guide 740 ...
Страница 768: ...Appendix G Legal Information ZyWALL 2WG User s Guide 768 ...
Страница 774: ...Appendix H Customer Support ZyWALL 2WG User s Guide 774 ...