ZyWALL 2 Series User’s Guide

2-b In a LAND Attack, hackers flood SYN packets into the network with a spoofed source IP address of the targeted system. This makes it appear as if the host computer sent the packets to itself, making the system unavailable while the target system tries to respond to itself.

3.A brute-forceattack, such as a "Smurf" attack, targets a feature in the IP specification known as directed or subnet broadcasting, to quickly flood the target network with useless data. A Smurf hacker floods a router with Internet Control Message Protocol (ICMP) echo request packets (pings). Since the destination IP address of each packet is the broadcast address of the network, the router will broadcast the ICMP echo request packet to all hosts on the network. If there are numerous hosts, this will create a large amount of ICMP echo request and response traffic. If a hacker chooses to spoof the source IP address of the ICMP echo request packet, the resulting ICMP traffic will not only clog up the "intermediary" network, but will also congest the network of the spoofed source IP address, known as the "victim" network. This flood of broadcast traffic consumes all available bandwidth, making communications impossible.

Figure 10-4 Smurf Attack

ICMP Vulnerability

ICMP is an error-reporting protocol that works in concert with IP. The following ICMP types trigger an alert:

Table 10-2 ICMP Commands That Trigger Alerts

5

REDIRECT

 

 

13

TIMESTAMP_REQUEST

 

 

14

TIMESTAMP_REPLY

 

 

17

ADDRESS_MASK_REQUEST

 

 

18

ADDRESS_MASK_REPLY

 

 

10-6

Firewalls