Patent ID: 7873731

Claim:
A method of blocking attacks on a protected computer network, comprising: receiving, by processing circuitry, a plurality of packets from a network, each said packet having a packet time to live (TTL) value and belonging to a corresponding packet flow; storing, by the processing circuitry, the smallest packet TTL value received from each said corresponding packet flow; and prior to transmitting each said packet, setting, by the processing circuitry, said packet TTL value to said smallest packet TTL value received for said corresponding packet flow; wherein storing the smallest packet TTL value received from each said corresponding packet flow includes, for each said packet: if that packet is the first packet received from said corresponding packet flow, then storing the packet TTL value of that packet as said smallest packet TTL value received from said corresponding packet flow; if that packet is not the first packet received from said corresponding packet flow and the packet TTL value of that packet is less than the stored smallest packet TTL value received from said corresponding packet flow, then storing the packet TTL value of that packet as said smallest packet TTL value received from said corresponding packet flow; and if that packet is not the first packet received from said corresponding packet flow and the packet TTL value of that packet is greater than the stored smallest packet TTL value received from said corresponding packet flow, then refraining from storing the packet TTL value of that packet as said smallest packet TTL value received from said corresponding packet flow.