Patent ID: 7748034

Claim:
A method comprising: maintaining a list of sequence numbers in a state list at a security gateway, wherein a first set of the sequence numbers corresponds to packets having a first time stamp that is associated with a first epoch window, and wherein a second set of the sequence numbers corresponds to packets having a second time stamp associated with a second epoch window; removing the first set of sequence numbers from the state list when the first epoch window expires, wherein the first epoch window expires when a packet having the second time stamp arrives at the security gateway; receiving, at the security gateway, a plurality of packets from a peer security gateway, wherein each packet has an associated sequence number and a time stamp; performing a first tier check on a packet, wherein the packet is valid according to the first tier check if the packet includes a time stamp associated with the second epoch window; performing a second tier check on the packet, wherein the packet is valid according to the second tier check if the packet includes a sequence number that is not listed in the state list; accepting the packet if both the first tier check and the second tier check indicate that the packet is valid; and rejecting the packet if either the first tier check or the second tier check does not indicate that the packet is valid.