P-662H/HW-D Series User’s Guide
Chapter 10 Firewalls
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• 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 ZyXEL Device itself (as
with the "virtual connections" created for UDP and ICMP).
10.5.3 TCP Security
The ZyXEL Device 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.
When the ZyXEL Device receives any subsequent packet (from the Internet or from the LAN),
its connection information is extracted and checked against the cache. A packet is only
allowed to pass through if it corresponds to a valid connection (that is, if it is a response to a
connection which originated on the LAN).
10.5.4 UDP/ICMP Security
UDP and ICMP do not themselves contain any connection information (such as sequence
numbers). However, at the very minimum, they contain an IP address pair (source and
destination). UDP also contains port pairs, and ICMP has type and code information. All of
this data can be analyzed in order to build "virtual connections" in the cache.
For instance, any UDP packet that originates on the LAN will create a cache entry. Its IP
address and port pairs will be stored. For a short period of time, UDP packets from the WAN
that have matching IP and UDP information will be allowed back in through the firewall.
Содержание 802.11g ADSL 2+ 4-Port Security Gateway HW-D Series
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Страница 10: ...P 662H HW D Series User s Guide 10 Customer Support ...
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Страница 64: ...P 662H HW D Series User s Guide 64 Chapter 2 Introducing the Web Configurator ...
Страница 84: ...P 662H HW D Series User s Guide 84 Chapter 4 Bandwidth Management Wizard ...
Страница 108: ...P 662H HW D Series User s Guide 108 Chapter 5 WAN Setup ...
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Страница 155: ...P 662H HW D Series User s Guide Chapter 8 DMZ 155 Figure 81 DMZ Private and Public Address Example ...
Страница 156: ...P 662H HW D Series User s Guide 156 Chapter 8 DMZ ...
Страница 188: ...P 662H HW D Series User s Guide 188 Chapter 11 Firewall Configuration Figure 97 Firewall Edit Rule ...
Страница 202: ...P 662H HW D Series User s Guide 202 Chapter 11 Firewall Configuration ...
Страница 210: ...P 662H HW D Series User s Guide 210 Chapter 12 Anti Virus Packet Scan ...
Страница 214: ...P 662H HW D Series User s Guide 214 Chapter 13 Content Filtering ...
Страница 232: ...P 662H HW D Series User s Guide 232 Chapter 14 Content Access Control ...
Страница 238: ...P 662H HW D Series User s Guide 238 Chapter 15 Introduction to IPSec ...
Страница 273: ...P 662H HW D Series User s Guide Chapter 17 Certificates 273 Figure 144 My Certificate Details ...
Страница 284: ...P 662H HW D Series User s Guide 284 Chapter 17 Certificates Figure 152 Trusted Remote Host Details ...
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Страница 303: ...P 662H HW D Series User s Guide Chapter 19 Bandwidth Management 303 Figure 162 Bandwidth Management Monitor ...
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Страница 308: ...P 662H HW D Series User s Guide 308 Chapter 20 Dynamic DNS Setup ...
Страница 332: ...P 662H HW D Series User s Guide 332 Chapter 22 Universal Plug and Play UPnP ...
Страница 338: ...P 662H HW D Series User s Guide 338 Chapter 23 System ...
Страница 344: ...P 662H HW D Series User s Guide 344 Chapter 24 Logs ...
Страница 350: ...P 662H HW D Series User s Guide 350 Chapter 25 Tools ...
Страница 363: ...P 662H HW D Series User s Guide Chapter 27 Troubleshooting 363 Figure 213 Security Setting ActiveX Controls ...
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Страница 368: ...P 662H HW D Series User s Guide 368 Product Specifications ...
Страница 372: ...P 662H HW D Series User s Guide 372 Appendix C Wall mounting Instructions ...
Страница 408: ...P 662H HW D Series User s Guide 408 Appendix F Wireless LANs ...
Страница 420: ...P 662H HW D Series User s Guide 420 Appendix H Command Interpreter ...
Страница 436: ...P 662H HW D Series User s Guide 436 Appendix L NetBIOS Filter Commands ...
Страница 462: ...P 662H HW D Series User s Guide 462 Appendix M Internal SPTGEN ...
Страница 484: ...P 662H HW D Series User s Guide 484 Appendix P Triangle Route ...