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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.
Summary of Contents for ZYWALL 2 WG
Page 2: ......
Page 8: ...Safety Warnings ZyWALL 2WG User s Guide 8 ...
Page 42: ...List of Figures ZyWALL 2WG User s Guide 42 ...
Page 50: ...List of Tables ZyWALL 2WG User s Guide 50 ...
Page 52: ...52 ...
Page 80: ...Chapter 2 Introducing the Web Configurator ZyWALL 2WG User s Guide 80 ...
Page 100: ...Chapter 3 Wizard Setup ZyWALL 2WG User s Guide 100 ...
Page 140: ...Chapter 4 Tutorial ZyWALL 2WG User s Guide 140 ...
Page 146: ...146 ...
Page 158: ...Chapter 6 LAN Screens ZyWALL 2WG User s Guide 158 ...
Page 171: ...Chapter 8 WAN Screens ZyWALL 2WG User s Guide 171 Figure 108 NETWORK WAN General ...
Page 200: ...Chapter 8 WAN Screens ZyWALL 2WG User s Guide 200 ...
Page 238: ...238 ...
Page 300: ...Chapter 13 Content Filtering Reports ZyWALL 2WG User s Guide 300 ...
Page 348: ...Chapter 14 IPSec VPN ZyWALL 2WG User s Guide 348 ...
Page 378: ...Chapter 15 Certificates ZyWALL 2WG User s Guide 378 ...
Page 384: ...384 ...
Page 426: ...Chapter 20 Bandwidth Management ZyWALL 2WG User s Guide 426 ...
Page 479: ...479 PART V Logs and Maintenance Logs Screens 481 Maintenance 511 ...
Page 480: ...480 ...
Page 485: ...Chapter 26 Logs Screens ZyWALL 2WG User s Guide 485 Figure 304 LOGS Log Settings ...
Page 510: ...Chapter 26 Logs Screens ZyWALL 2WG User s Guide 510 ...
Page 530: ...530 ...
Page 558: ...Chapter 30 WAN and Dial Backup Setup ZyWALL 2WG User s Guide 558 ...
Page 564: ...Chapter 31 LAN Setup ZyWALL 2WG User s Guide 564 ...
Page 570: ...Chapter 32 Internet Access ZyWALL 2WG User s Guide 570 ...
Page 574: ...Chapter 33 DMZ Setup ZyWALL 2WG User s Guide 574 ...
Page 578: ...Chapter 34 Route Setup ZyWALL 2WG User s Guide 578 ...
Page 582: ...Chapter 35 Wireless Setup ZyWALL 2WG User s Guide 582 ...
Page 594: ...Chapter 37 IP Static Route Setup ZyWALL 2WG User s Guide 594 ...
Page 614: ...Chapter 38 Network Address Translation NAT ZyWALL 2WG User s Guide 614 ...
Page 632: ...Chapter 40 Filter Configuration ZyWALL 2WG User s Guide 632 ...
Page 668: ...Chapter 44 System Maintenance Menus 8 to 10 ZyWALL 2WG User s Guide 668 ...
Page 672: ...Chapter 45 Remote Management ZyWALL 2WG User s Guide 672 ...
Page 680: ...Chapter 46 IP Policy Routing ZyWALL 2WG User s Guide 680 ...
Page 686: ...686 ...
Page 692: ...Chapter 48 Troubleshooting ZyWALL 2WG User s Guide 692 ...
Page 702: ...Chapter 49 Product Specifications ZyWALL 2WG User s Guide 702 ...
Page 704: ...704 ...
Page 712: ...Appendix A Pop up Windows JavaScripts and Java Permissions ZyWALL 2WG User s Guide 712 ...
Page 740: ...Appendix D Common Services ZyWALL 2WG User s Guide 740 ...
Page 768: ...Appendix G Legal Information ZyWALL 2WG User s Guide 768 ...
Page 774: ...Appendix H Customer Support ZyWALL 2WG User s Guide 774 ...