ZyXEL P-660HW-T1 User Manual download pdf (Page 121)

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P-660H/HW/W-T Series User’ Guide

121 Chapter 10 Firewalls

10.4.2 Types of DoS Attacks

There are four types of DoS attacks:

1 Those that exploit bugs in a TCP/IP implementation.

2 Those that exploit weaknesses in the TCP/IP specification.

3 Brute-force attacks that flood a network with useless data.

4 IP Spoofing.

5 "Ping of Death" and "Teardrop" attacks exploit bugs in the TCP/IP implementations of

various computer and host systems.

• Ping of Death uses a "ping" utility to create an IP packet that exceeds the maximum

65,536 bytes of data allowed by the IP specification. The oversize packet is then sent to

an unsuspecting system. Systems may crash, hang or reboot.

• Teardrop attack exploits weaknesses in the re-assembly of IP packet fragments. As data is

transmitted through a network, IP packets are often broken up into smaller chunks. Each

fragment looks like the original IP packet except that it contains an offset field that says,

for instance, "This fragment is carrying bytes 200 through 400 of the original (non

fragmented) IP packet." The Teardrop program creates a series of IP fragments with

overlapping offset fields. When these fragments are reassembled at the destination, some

systems will crash, hang, or reboot.

6 Weaknesses in the TCP/IP specification leave it open to "SYN Flood" and "LAND"

attacks. These attacks are executed during the handshake that initiates a communication

session between two applications.

Table 33 Common IP Ports

21 FTP 53 DNS

23 Telnet 80 HTTP

25 SMTP 110 POP3

1 2 ... 116 117 118 119 120 121 122 123 124 125 126 ... 464 465

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