14.5
DoS Defend
DoS (Denial of Service) Attack is to occupy the network bandwidth maliciously by the network
attackers or the evil programs sending a lot of service requests to the Host, which incurs an
abnormal service or even breakdown of the network.
With DoS Defend function enabled, the switch can analyze the specific fields of the IP packets
and distinguish the malicious DoS attack packets. Upon detecting the packets, the switch will
discard the illegal packets directly and limit the transmission rate of the legal packets if the
over legal packets may incur a breakdown of the network. The switch can defend several types
of DoS attack listed in the following table.
DoS Attack Type
Description
Land Attack
The attacker sends a specific fake SYN packet to the destination
Host. Since both the source IP address and the destination IP
address of the SYN packet are set to be the IP address of the Host,
the Host will be trapped in an endless circle for building the initial
connection. The performance of the network will be reduced
extremely.
Scan SYNFIN
The attacker sends the packet with its SYN field and the FIN field set
to 1. The SYN field is used to request initial connection whereas the
FIN field is used to request disconnection. Therefore, the packet of
this type is illegal. The switch can defend this type of illegal packet.
Xmascan
The attacker sends the illegal packet with its TCP index, FIN, URG
and PSH field set to 1.
NULL Scan Attack
The attacker sends the illegal packet with its TCP index and all the
control fields set to 0. During the TCP connection and data
transmission, the packets with all the control fields set to 0 are
considered as the illegal packets.
SYN packet with its
source port less than
1024
The attacker sends the illegal packet with its TCP SYN field set to 1
and source port less than 1024.
Blat Attack
The attacker sends the illegal packet with its source port and
destination port on Layer 4 the same and its URG field set to 1.
Similar to the Land Attack, the system performance of the attacked
Host is reduced since the Host circularly attempts to build a
connection with the attacker.
Ping Flooding
The attacker floods the destination system with Ping broadcast
storm packets to forbid the system to respond to the legal
communication.
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