Allied-telesis AT-S62 Bedienungsanleitung PDF herunterladen (Seite 213)

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AT-S62 User’s Guide

Section II: Advanced Operations 213

Denial of Service Defense Overview

The AT-S62 management software can help protect your network

against the following types of Denial of Service attacks.

❑ SYN Flood Attack

❑ SMURF Attack

❑ Land Attack

❑ Teardrop Attack

❑ Ping of Death Attack

❑ IP Options Attack

The following subsections briefly describe each type of attack and the

mechanism employed by the AT-S62 management software to protect

your network.

Note

Be sure to read the following descriptions before implementing a

DoS defense on a switch. Some defense mechanisms are CPU

intensive and can impact switch behavior.

SYN Flood

Attack

In this type of attack, an attacker sends a large number of TCP

connection requests (TCP SYN packets) with bogus source addresses to

the victim. The victim responds with acknowledgements (SYN ACK

packets), but since the original source addresses are bogus, the victim

node does not receive any replies. If the attacker sends enough requests

in a short enough period, the victim may freeze operations when the

number of requests exceeds the capacity of its connections queue.

To defend against this form of attack, a switch port monitors the number

of ingress TCP connection requests it receives. If a port receives more

than 60 requests per second, the following occurs.

❑ The switch sends a SNMP trap to the management workstations

❑ The port discards all ingress TCP-SYN packets for one minute.

However, the port continues to allow existing TCP connections to

go through.

This defense mechanism does not involve the switch’s CPU. You can

activate it on as many ports as you want without it impacting switch

performance.

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