Zyxel-communications 802.11g Wireless ADSL2+ 4-port VoIP IAD P-2602HWNL Manual de usuario descargar pdf (Pagina 204)

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P-2602HWNLI User’s Guide

204 Chapter 13 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 107 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.

Table 73 ICMP Commands That Trigger Alerts

5 REDIRECT

13 TIMESTAMP_REQUEST

14 TIMESTAMP_REPLY

17 ADDRESS_MASK_REQUEST

18 ADDRESS_MASK_REPLY

Table 74 Legal NetBIOS Commands

MESSAGE:

REQUEST:

POSITIVE:

VE:

RETARGET:

KEEPALIVE:

1 2 ... 199 200 201 202 203 204 205 206 207 208 209 ... 441 442

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