ZyXEL Communications P-661H Series, Руководство пользователя, Страница: 151 / 383

P-661H/HW Series User’s Guide
Chapter 8 Firewalls 151
8.4.2.3 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 ZyXEL Device blocks all IP Spoofing attempts.
8.5 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 ZyXEL Device uses stateful packet inspection to protect the private LAN
from hackers and vandals on the Internet. By default, the ZyXEL Device’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.
Figure 82 Stateful Inspection