ZyXEL Communications G-2000 Plus V2, Руководство пользователя

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ZyXEL G-2000 Plus v2 User’s Guide
136 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.
• " Ping of Death " and " Teardrop " attacks exploit bugs in the TCP/IP implementations of
various computer and host systems.
a 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.
b Teardrop attack exploits weaknesses in the reassembly 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.
• 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.