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Filtering Smaller Packets

By default, firewall filtering is not supported for packets that are less than 5 bytes in length. To filter packets less than 5 bytes in length, include an additional term to match the packet size.

For example, consider the following filter term:

term 1 {
from {
fragment-offset-except 0;
}
then {
reject;
}
}

To consider packets of 1 through 4 bytes in length, include an additional term that matches the packet size:

term 2 {
from {
packet-length [ 21 - 24 ];
}
then {
reject;
}
}

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