ZyXEL Communications ADSL VoIP IAD with 802.11g Wireless 2602HW Series - Manual (Page 160)

Prestige 2602HW Series User’s Guide
160 Chapter 13 Firewalls
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 63 Smurf Attack
13.4.2.1 ICMP Vulnerability
ICMP is an error-reporting protocol that works in concert with IP. The following ICMP types
trigger an alert:
13.4.2.2 Illegal Commands (NetBIOS and SMTP)
The only legal NetBIOS commands are the following - all others are illegal.
All SMTP commands are illegal except for those displayed in the following tables.
Table 44 ICMP Commands That Trigger Alerts
5 REDIRECT
13 TIMESTAMP_REQUEST
14 TIMESTAMP_REPLY
17 ADDRESS_MASK_REQUEST
18 ADDRESS_MASK_REPLY
Table 45 Legal NetBIOS Commands
MESSAGE:
REQUEST:
POSITIVE:
VE:
RETARGET:
KEEPALIVE: