IPsec Replay

This tutorial explains how IPsec performs protection against replay attacks. The general idea of a replay attack has been explained by us in an earlier movie; this movie focuses on IPsec. It shows how IPsec uses sequence numbers and a window mechanism to detect such attacks. It also touches the difference between the IPsec window mechanism and that of TCP.

[yingwu]

Thanks for sharing this video, it's very useful. But I have a question here: in your example of out of sequence packets, suppose packet 5 was intercepted by the attacker and was retransmitted to the destination before the real packet arrived at the destination. Maybe the receiver will receive the replayed packet 5 and it will pass the authentication first and mark the window that 5 is received. After that, if the real packet 5 arrives at the receiver, it will discard the packet. Will this happen?