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Eventually, additional connection attempts from clients will be denied.

Slowloris: Invented by Robert ‘RSnake’ Hansen, this attack tries to keep multiple connections to the target web server open, and for as long as possible.

Smurf attack, ICMP flood, and ping flood take advantage of this by inundating the server with ICMP requests without waiting for the response.

ICMP Protocol Attacks: Attacks on the ICMP protocol take advantage of the fact that each request requires processing by the server before a response is sent back.

Ping flood is the present-day incarnation of this attack. This has largely been fixed in newer systems. If the packets, when put together, are larger than the allowable 65,536 bytes, legacy servers often crash. TCP/IP fragmentation deals with large packets by breaking them down into smaller IP packets.

Ping of Death: Attacks involve the deliberate sending of IP packets larger than those allowed by the IP protocol.

UDP Flood: A type of attack in which random ports on the target are overwhelmed by IP packets containing UDP datagrams.

HTTP Flood: A type of attack in which HTTP GET or POST requests are used to attack the web server.

This attack exploits weaknesses in the TCP connection sequence, known as a three-way handshake.

SYN Flood: A succession of SYN requests is directed to the target’s system in an attempt to overwhelm it.

UDP Flood, TCP Flood, NTP Amplification and DNS Amplification are some examples.

Volumetric attacks are easy to generate by employing simple amplification techniques, so these are the most common forms of attack. Volumetric Attacks send high volumes of traffic in an effort to saturate a victim’s bandwidth. Syn Flood and Ping of Death are some examples. Such attacks consume all the processing capacity of the victim or other critical resources (a firewall, for example), resulting in service disruption. Protocol Based Attacks focus on exploiting a weakness in Layers 3 or 4 of the protocol stack. These attacks exploit a weakness in the Layer 7 protocol stack by first establishing a connection with the target, then exhausting server resources by monopolizing processes and transactions. If a result is found, this constitutes a match.įor a modifier redirect=domain, the SPF record for domain replaces the current record.The goal of DoS or DDoS attacks is to consume enough server or network resources so that the system becomes unresponsive to legitimate requests:Īpplication Layer Attacks go after web applications, and often use the most sophistication. Perform an A query on the provided domain. If a valid hostname ends in domain, this mechanism matches. The hostnames are then validated: at least one of the A records for a PTR hostname must match the original client IP. The hostname or hostnames for the client IP are looked up using PTR queries.

If the client IP is found among them, this mechanism matches. If the connection is made over IPv6, then an AAAA lookup is performed instead.Īll the A records for all the MX records for domain are tested in order of MX priority. If no prefix-length is given, /128 is assumed (singling out an individual host address).Īll the A records for domain are tested. The argument to the "ip6:" mechanism is an IPv6 network range.

If no prefix-length is given, /32 is assumed (singling out an individual host address). The argument to the "ip4:" mechanism is an IPv4 network range.

If the lookup does not return a match or an error, processing proceeds to the next directive. The specified domain is searched for a match. It usually goes at the end of the SPF record.