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What is the Deny Fragment Option?



Article ID: KB4731 KB Last Updated: 09 Jun 2010Version: 3.0
What is the Deny Fragment Option?


Note: This article applies to ScreenOS 4.0 and higher.

As packets traverse different networks, it is sometimes necessary to break a packet into smaller pieces (fragments) based upon the network's maximum transmission unit (MTU).

IP fragments may carry an attacker's attempt to exploit the vulnerabilities in the packet reassembly code of specific IP stack implementations. When the target system receives these packets, the results range from not processing the packets correctly to crashing the entire system. When this option is enabled, the NetScreen device blocks all IP packet fragments.

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