Nortel BSR222, Configuration, Page: 163 / 451

Chapter 10 Firewalls 163
Nortel Business Secure Router 222 Configuration — Basics
All SMTP commands are illegal except for those displayed in Table 37 .
• 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 and gain 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 can 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 is
allowed through the router or firewall. The Business Secure Router blocks all
IP Spoofing attempts.
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 an 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
Business Secure Router uses stateful packet inspection to protect the private LAN
from hackers and vandals on the Internet. By default, the Business Secure
Router’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.
Table 37 Legal SMTP commands
AUTH DATA EHLO ETRN EXPN HELO HELP MAIL NOOP
QUIT RCPT RSET SAML SEND SOML TURN VRFY