Zyxel-communications P-660H-D Series Uživatelský manuál stáhnout pdf (Strana 104)

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101

P-660R/H-D Series User’s Guide

103 Chapter 10 Firewalls

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 40 Smurf Attack

10.4.2.1 ICMP Vulnerability

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

trigger an alert:

10.4.2.2 Illegal Commands (NetBIOS and SMTP)

The only legal NetBIOS commands are the following - all others are illegal.

Table 29 ICMP Commands That Trigger Alerts

5 REDIRECT

13 TIMESTAMP_REQUEST

14 TIMESTAMP_REPLY

17 ADDRESS_MASK_REQUEST

18 ADDRESS_MASK_REPLY

Table 30 Legal NetBIOS Commands

MESSAGE:

REQUEST:

POSITIVE:

VE:

RETARGET:

KEEPALIVE:

1 2 ... 99 100 101 102 103 104 105 106 107 108 109 ... 420 421

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