User Guide
720
Configuring DoS Defend
DoS Defend Configuration
NULL Scan
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
control fields set to 0 are considered illegal.
SYN sPort less
1024
The attacker sends the illegal packet with its TCP SYN field set to 1 and source
port smaller than 1024.
Blat Attack
The attacker sends the illegal packet with the same source port and destination
port on Layer 4 and with its URG field set to 1. Similar to the Land Attack, the
system performance of the attacked host is reduced because the Host circularly
attempts to build a connection with the attacker.
Ping Flooding
The attacker floods the destination system with Ping packets, creating a
broadcast storm that makes it impossible for the system to respond to 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
Because the Operation System with bugs cannot 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.
Ping of Death
Ping of Death attack means that the attacker sends abnormal ping packets larger
than 65535 bytes to cause system crash on the target computer.
Smurf Attack
Smurf attack is a distributed denial-of-service attack in which large numbers of
Internet Control Message Protocol (ICMP) packets with the intended victim’s
spoofed source IP are broadcast to a computer network using an IP broadcast
address. Most devices on a network will, by default, respond to this by sending
a reply to the source IP address. If the number of machines on the network that
receive and respond to these packets is very large, the victim’s computer will be
flooded with traffic.
3) Click
Apply
.
2.2 Using the CLI
Follow these steps to configure DoS Defend:
Step 1
configure
Enter global configuration mode.
Step 2
ip dos-prevent
Globally enable the DoS defend feature.
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