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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.
SYN/SYN-ACK
Flooding
The attacker uses a fake IP address to send TCP request packets to
the Server. Upon receiving the request packets, the Server
responds with SYN-
ACK packets. Since the IP address is fake, no
response will be returned. The Server will keep on sending SYN-ACK
packets. If the attacker sends overflowing fake request packets, the
network resource will be occupied maliciously and the requests of
the legal clients will be denied.
winNuke Attack Since the Operation System with bugs cannot correctly process the
URG (Urgent Pointer) of TCP packets, the attacker sends this type of
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