ZyWALL 5/35/70 Series User’s Guide

All SMTP commands are illegal except for those displayed in the following tables.

Table 66 Legal SMTP Commands

AUTH

DATA

EHLO

ETRN

EXPN

HELO

HELP

MAIL

NOOP

 

 

 

 

 

 

 

 

 

QUIT

RCPT

RSET

SAML

SEND

SOML

TURN

VRFY

 

 

 

 

 

 

 

 

 

 

10.4.2.3 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.

10.5 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.

Chapter 10 Firewalls

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