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Configuration Guide - Security

S1720, S2700, S5700, and S6720 V200R011C10

This document describes the configurations of Security, including ACL, local attack defense, MFF, attack defense, traffic suppression and storm control, ARP security, Port security, DHCP snooping, ND snooping, PPPoE+, IPSG, SAVI, URPF, keychain, MPAC, separating the management plane from the service plane, security risks, PKI.
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Configuring Defense Against TCP SYN Flood Attacks

Configuring Defense Against TCP SYN Flood Attacks


An attacker sends a SYN packet to a target host to initiate a TCP connection but does not respond to the SYN+ACK sent from the target host. If the target host does not receive an ACK packet from the attacker, it keeps waiting for the ACK packet. Therefore, a half-open connection is formed. If the attacker keeps sending SYN packets, the target host sets up a large number of half-open connections, thus wasting resources.

To prevent TCP SYN flood attacks, enable defense against TCP SYN flood attacks and set the rate limit for TCP SYN flood attack packets.


  1. Run system-view

    The system view is displayed.

  2. Run anti-attack tcp-syn enable

    Defense against TCP SYN flood attacks is enabled.

    By default, defense against TCP SYN flood attacks is enabled.

    You can also run the anti-attack enable command in the system view to enable attack defense against all attack packets including malformed packets.

  3. Run anti-attack tcp-syn car cir cir

    The rate limit at which TCP SYN packets are received is set.

    By default, the rate limit at which TCP SYN packets are received is 155000000 bit/s.

Updated: 2019-09-23

Document ID: EDOC1000178177

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