ZyWALL 5 User’s Guide
Chapter 9 Firewalls
157
All SMTP commands are illegal except for those displayed in the following tables.
9.4.2.3 Traceroute
Traceroute is a utility used to determine the path a packet takes between two endpoints.
Sometimes when a packet filter firewall is configured incorrectly an attacker can traceroute
the firewall gaining knowledge of the network topology inside the firewall.
Often, many DoS attacks also employ a technique known as "
IP Spoofing
" as part of their
attack. IP Spoofing may be used to break into systems, to hide the hacker's identity, or to
magnify the effect of the DoS attack. IP Spoofing is a technique used to gain unauthorized
access to computers by tricking a router or firewall into thinking that the communications are
coming from within the trusted network. To engage in IP spoofing, a hacker must modify the
packet headers so that it appears that the packets originate from a trusted host and should be
allowed through the router or firewall. The ZyWALL blocks all IP Spoofing attempts.
9.5 Stateful Inspection
With stateful inspection, fields of the packets are compared to packets that are already known
to be trusted. For example, if you access some outside service, the proxy server remembers
things about your original request, like the port number and source and destination addresses.
This remembering is called
saving the state.
When the outside system responds to your
request, the firewall compares the received packets with the saved state to determine if they
are allowed in. The ZyWALL uses stateful packet inspection to protect the private LAN from
hackers and vandals on the Internet. By default, the ZyWALL’s stateful inspection allows all
communications to the Internet that originate from the LAN, and blocks all traffic to the LAN
that originates from the Internet. In summary, stateful inspection:
• Allows all sessions originating from the LAN (local network) to the WAN (Internet).
• Denies all sessions originating from the WAN to the LAN.
Table 47
Legal SMTP Commands
AUTH
DATA
EHLO
ETRN
EXPN
HELO
HELP
NOOP
QUIT
RCPT
RSET
SAML
SEND
SOML
TURN
VRFY
Содержание ZyXEL ZyWALL 5
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Страница 174: ...ZyWALL 5 User s Guide 172 Chapter 10 Firewall Screens Figure 68 Creating Editing A Firewall Rule ...
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Страница 261: ...ZyWALL 5 User s Guide Chapter 15 Certificates 259 Figure 122 My Certificate Details ...
Страница 280: ...ZyWALL 5 User s Guide 278 Chapter 16 Authentication Server Figure 133 Local User Database ...
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Страница 366: ...ZyWALL 5 User s Guide 364 Chapter 23 Logs Screens Figure 188 Log Settings ...
Страница 389: ...ZyWALL 5 User s Guide Chapter 24 Maintenance 387 Figure 210 Restart Screen ...
Страница 390: ...ZyWALL 5 User s Guide 388 Chapter 24 Maintenance ...
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Страница 564: ...ZyWALL 5 User s Guide 562 Appendix C IP Subnetting ...
Страница 570: ...ZyWALL 5 User s Guide 568 Appendix E PPTP ...
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