Stateful Inspection; Table 9-4 Legal Smtp Commands - Nortel Contivity 221 User Manual

9-8 Firewalls

Table 9-4 Legal SMTP Commands

AUTH DATA EHLO
QUIT RCPT RSET
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 Contivity 221 blocks all IP Spoofing attempts.

Stateful Inspection

9.5
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
Contivity 221 uses stateful packet inspection to protect the private LAN from hackers and vandals
on the Internet. By default, the Contivity 221'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.
317517-A Rev 00
ETRN EXPN HELO
SAML SEND SOML
HELP MAIL NOOP
TURN VRFY