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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.
Smurf Attack By pretending to be a Host, the attacker broadcasts request packets for ICMP
response in the LAN. When receiving the request packet, all the Hosts in the LAN
will respond and send the reply packets to the actual Host, which will causes this
Host to be attacked.
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 can not correctly process the URG (Urgent
Pointer) of TCP packets, the attacker sends this type of packets to the TCP
port139 (NetBIOS) of the Host with the Operation System bugs, which will cause
the Host with a blue screen.
Table 11-1 Defendable DoS Attack Types
