Stateful Inspection; Table 11-3 Legal Netbios Commands; Table 11-4 Legal Smtp Commands - ZyXEL Communications ZyWall 10 User Manual

The only legal NetBIOS commands are the following - all others are illegal.
All SMTP commands are illegal except for those displayed in the following tables.
AUTH DATA
QUIT RCPT
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.
4. 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.

11.5 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:
Firewalls

Table 11-3 Legal NetBIOS Commands

MESSAGE:
REQUEST:
POSITIVE:
NEGATIVE:
RETARGET:
KEEPALIVE:

Table 11-4 Legal SMTP Commands

EHLO ETRN
RSET SAML
ZyWALL 10~100 Series Internet Security Gateway
EXPN HELO
SEND SOML
HELP MAIL
TURN VRFY
NOOP
11-7