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determines whether the total length of the offset is larger than 65515. If so, the packets
are discarded.
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Repeated fragmented packet attack refers to sending the repeated packet fragments
multiple times, including resending the same packet fragments; the offset is the same
but the packet fragments are different. As a result, the system fails to reassemble packet
fragments and the CPU usage is overhigh. To defend repeated fragmented packet
attacks, the AR1200-S restricts the rate of sending packet fragments on the interface
board and thus ensure that the CPU is not attacked and the Committed Access Rate
(CAR) can be configured.
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Defense against Flood attacks
Flood attacks include TCP SYN flood attacks, UDP flood attacks (including fraggle attacks
and UDP diagnosis port attacks), and TCMP flood attacks. The AR1200-S defends against
TCP SYN flood attacks and ICMP flood attacks by restricting rate to prevent the CPU
resources from being exhausted. To defend against UDP flood attacks, the AR1200-S
discards those UDP packets with port numbers 7, 13, and 19.
NOTE
Attack defense configurations take effect for only the main control board.
Application Layer Association Supported by the AR1200-S
The AR1200-S supports application layer association. The application layer association module
controls some protocols and functions.
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When a protocol is disabled, the AR1200-S directly discards packets of this protocol to
prevent attacks.
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When a protocol is enabled, the AR1200-S limits the rate of protocol packets sent to the
CPU to protect the CPU.
The application layer association module supports SNMP, HW-TACACS, NTP, SSH, DHCP,
802.1x, and PIM protocols and supports HTTP server, Telnet server, STelnet server, FTP server,
SFTP server, BFD, UDP helper, and VRRP services.
NOTE
You can configure application layer association for different protocols and services.
14.2 Configuring Abnormal Packet Attack Defense
Malformed packet attacks are classified into flood attacks without IP payload, IGMP null packet
attacks, LAND attacks, Smurf attacks, and TCP flag-bit invalid attacks.
14.2.1 Establishing the Configuration Task
This section describes the applicable environment, required tasks, and data for configuring
defense against malformed packets.
Applicable Environment
Different types of attacks on a network cause network devices overused, and even failed, thus
affecting network services.
Huawei AR1200-S Series Enterprise Routers
Configuration Guide - Security
14 Configuration of Attack Defense and Application Layer
Association
Issue 02 (2012-03-30)
Huawei Proprietary and Confidential
Copyright © Huawei Technologies Co., Ltd.
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