Chapter 11 Firewall
ZyWALL 2 Plus User’s Guide
212
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 140
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 52
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 ADSL 2+ Security Gateway
Страница 1: ...www zyxel com ZyWALL 2 Plus Internet Security Appliance User s Guide Version 4 03 12 2007 Edition 1 ...
Страница 2: ......
Страница 25: ...Table of Contents ZyWALL 2 Plus User s Guide 25 Index 679 ...
Страница 26: ...Table of Contents ZyWALL 2 Plus User s Guide 26 ...
Страница 46: ...46 ...
Страница 88: ...Chapter 3 Wizard Setup ZyWALL 2 Plus User s Guide 88 ...
Страница 131: ...131 PART II Network LAN Screens 133 Bridge Screens 145 WAN Screens 151 DMZ Screens 171 Wireless LAN 181 ...
Страница 132: ...132 ...
Страница 144: ...Chapter 6 LAN Screens ZyWALL 2 Plus User s Guide 144 ...
Страница 180: ...Chapter 9 DMZ Screens ZyWALL 2 Plus User s Guide 180 ...
Страница 190: ...190 ...
Страница 209: ...Chapter 11 Firewall ZyWALL 2 Plus User s Guide 209 Figure 138 SECURITY FIREWALL Rule Summary Edit ...
Страница 221: ...Chapter 11 Firewall ZyWALL 2 Plus User s Guide 221 Figure 149 My Service Firewall Rule Example Rule Summary Completed ...
Страница 222: ...Chapter 11 Firewall ZyWALL 2 Plus User s Guide 222 ...
Страница 252: ...Chapter 13 Content Filtering Reports ZyWALL 2 Plus User s Guide 252 ...
Страница 265: ...Chapter 14 IPSec VPN ZyWALL 2 Plus User s Guide 265 Figure 178 SECURITY VPN VPN Rules IKE Edit Gateway Policy ...
Страница 274: ...Chapter 14 IPSec VPN ZyWALL 2 Plus User s Guide 274 Figure 181 SECURITY VPN VPN Rules IKE Edit Network Policy ...
Страница 306: ...Chapter 15 Certificates ZyWALL 2 Plus User s Guide 306 Figure 203 SECURITY CERTIFICATES My Certificates Create Basic ...
Страница 328: ...Chapter 16 Authentication Server ZyWALL 2 Plus User s Guide 328 ...
Страница 330: ...330 ...
Страница 346: ...Chapter 17 Network Address Translation NAT ZyWALL 2 Plus User s Guide 346 ...
Страница 350: ...Chapter 18 Static Route ZyWALL 2 Plus User s Guide 350 ...
Страница 398: ...Chapter 21 Remote Management ZyWALL 2 Plus User s Guide 398 ...
Страница 416: ...Chapter 24 ALG Screen ZyWALL 2 Plus User s Guide 416 ...
Страница 417: ...417 PART V Logs and Maintenance Logs Screens 419 Maintenance 447 ...
Страница 418: ...418 ...
Страница 423: ...Chapter 25 Logs Screens ZyWALL 2 Plus User s Guide 423 Figure 274 LOGS Log Settings ...
Страница 466: ...466 ...
Страница 474: ...Chapter 27 Introducing the SMT ZyWALL 2 Plus User s Guide 474 ...
Страница 496: ...Chapter 30 LAN Setup ZyWALL 2 Plus User s Guide 496 ...
Страница 504: ...Chapter 32 DMZ Setup ZyWALL 2 Plus User s Guide 504 ...
Страница 508: ...Chapter 33 Wireless Setup ZyWALL 2 Plus User s Guide 508 ...
Страница 556: ...Chapter 38 Filter Configuration ZyWALL 2 Plus User s Guide 556 ...
Страница 570: ...Chapter 40 System Information Diagnosis ZyWALL 2 Plus User s Guide 570 ...
Страница 586: ...Chapter 41 Firmware and Configuration File Maintenance ZyWALL 2 Plus User s Guide 586 ...
Страница 594: ...Chapter 42 System Maintenance Menus 8 to 10 ZyWALL 2 Plus User s Guide 594 ...
Страница 598: ...Chapter 43 Remote Management ZyWALL 2 Plus User s Guide 598 ...
Страница 603: ...603 PART VII Troubleshooting and Specifications Troubleshooting 605 Product Specifications 613 ...
Страница 604: ...604 ...
Страница 612: ...Chapter 45 Troubleshooting ZyWALL 2 Plus User s Guide 612 ...
Страница 620: ...620 ...
Страница 644: ...Appendix B Pop up Windows JavaScripts and Java Permissions ZyWALL 2 Plus User s Guide 644 ...
Страница 668: ...Appendix E Importing Certificates ZyWALL 2 Plus User s Guide 668 ...
Страница 672: ...Appendix F Legal Information ZyWALL 2 Plus User s Guide 672 ...
Страница 678: ...Appendix G Customer Support ZyWALL 2 Plus User s Guide 678 ...