3Com 3C16111 - SuperStack 3 Firewall Web Site Filter, Руководство пользователя

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13
T
YPES OF
A
TTACK AND
F
IREWALL
D
EFENCES
This chapter describes the some of attacks that hackers may use to
infiltrate and attack your network. It also details the way in which the
Firewall will counter the attacks. The following sections are covered in this
chapter:
■
Denial of Service Attacks
■
Intrusion Attacks
■
Trojan Horse Attacks
Denial of Service
Attacks
Denial of Service (DoS) attacks are malicious attacks designed to cause
harm. The consequences of an attack range from the loss of few seconds
of time on a web server or network to the crash of a server. In the worst
case the attacker can learn enough about your company infrastructure
and exploit its vulnerabilities to crash any server at will.
Denial of Service attacks work by exploiting weaknesses in TCP/IP,
exploiting weaknesses in your servers or by generating large amounts of
traffic (brute force attacks). Commonly attempted attacks and the
reaction of the SuperStack
® 3 Firewall are listed below.
Ping of Death A ping of death attack attempts to crash your system by sending a
fragmented packet which, when reconstructed is larger than the
maximum allowable size. Other known variants of the
ping of death
include teardrop , bonk and nestea.
Firewall Response: Packet is dropped. Attack is stopped.
Smurf Attack A smurf attack involves two systems. The attacker sends a packet
containing a ICMP echo request (ping) to the network address of one
system. This system is known as the amplifier.
DUA1611-0AAA02.book Page 175 Thursday, August 2, 2001 4:01 PM