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This approach does risk creating issues with legitimate services which rely on fragments, but this trade off may be deemed worthwhile when under attack. A better solution is to use rate-limiting, which will not block anything during peacetime, but will drop the majority of packets (both good and bad because rate-limiting has no idea what is what) and the destination under attack will be unaffected. One possible denial of service mitigation approach is to block all non-initial fragments, but this will result in an issue with legitimate traffic, which relies on those fragments. This involves inspecting incoming packets to determine if they breach fragmentation rules. The most common mitigation approaches involve ensuring that malicious data packets are prevented from reaching targeted servers. The approach for preventing IP/ICMP fragmentation DDoS attacks depends on the type and extent of the attack.

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How to Mitigate and Prevent an IP/ICMP Fragmentation DDoS Attack? The result is that data packets overlap and the targeted server becomes completely overwhelmed and ultimately fails. In such a case, fragmented packets are prevented from being reassembled.

TCP fragmentation DDoS attacks – This type of DDoS attack, also known as a Teardrop attack, targets TCP/IP reassembly mechanisms.

Since the packets are fake and can’t be reassembled, the server’s resources are quickly consumed, which ultimately renders it unavailable to legitimate traffic. These packets are designed to look like they are larger than the network’s MTU, but only parts of the packets are actually sent.

UDP and ICMP fragmentation DDoS attacks – In this type of DDoS attack, fake UDP or ICMP packets are transmitted.

The receiver has no clue what is legitimate and what is not, because the initial fragment has been lost. Those non-initial fragments are tricky because they might belong to a legitimate session, but will in most cases be junk traffic. In many cases, the receiver will not see the initial fragment (those often get lost in the avalanche of incoming packets) it just sees lots of packets with no protocol header (non-initial) fragments.

UDP flooding – In this type of DDoS attack, attackers use botnets to send large volumes of fragments from numerous sources.

Such attacks manifest themselves several in different ways: IP/ICMP fragmentation DDoS attacks bombard the destination with fragmented packets, causing it to use memory to reassemble all those fragments and overwhelm a targeted network. What Are the Signs of an IP/ICMP Fragmentation DDoS Attack? This in turn causes the fragments to be placed in temporary storage, taking up memory and in some cases exhausting all available memory resources. ICMP-based fragmentation attacks typically submit fake fragments that cannot be defragmented. The attacker can employ IP fragmentation to target communications systems, as well as security components. These fragments contain no information on protocol, size or ports.

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The remaining fragments are “naked” in the sense that they simply consist of an IP header plus a data payload. This leads to several packets being sent, one which contains all the info about the packet, including the source/destination ports, length, etc.

When a packet is too large, it must be sliced into smaller fragments in order to be transmitted successfully. Such a limit is described as a maximum transmission unit (MTU). This process is necessary to meet size limits that each network can handle. IP fragmentation occurs when IP datagrams are broken apart into small packets, then transmitted across a network, and finally reassembled into the original datagram as part of normal communications. In such an attack, datagram fragmentation mechanisms are used to overwhelm the network. What is an IP/ICMP Fragmentation DDoS Attack?Īn Internet Protocol (IP)/Internet Control Message Protocol (ICMP) fragmentation DDoS attack is a common form of volumetric denial of service (DoS) attack.

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