Types Of Dos Attacks; Figure 58 Three-Way Handshake; Table 36 Common Ip Ports - ZyXEL Communications PRESTIGE 660H Series User Manual

Prestige 660H/HW Series User's Guide

Table 36 Common IP Ports

12.4.2 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.

Figure 58 Three-Way Handshake

133
21 FTP
23 Telnet
25 SMTP
53 DNS
80 HTTP
110 POP3
Chapter 12 Firewalls