Configuring Defense Against TCP SYN Flood Attacks

Context

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.

Procedure

Run system-view
The system view is displayed.
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.
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.