How do you implement ESP anti-replay protection in IPSec?

1 What is ESP anti-replay protection?

ESP anti-replay protection is a feature that prevents an attacker from reusing or reordering the ESP packets sent by a legitimate sender. It works by using a sequence number for each packet, which is incremented by one for each new packet. The receiver keeps track of the sequence numbers of the packets it receives and discards any packets that have a lower or duplicate sequence number. This way, the receiver can detect and reject any packets that have been replayed or tampered with.

3 How to check ESP anti-replay protection?

To check if ESP anti-replay protection is working, you can use tools such as tcpdump or wireshark to capture and analyze the ESP packets. You can look at the ESP header format and fields to see the sequence number of each packet. You can also compare the sequence numbers of the packets sent and received by the sender and the receiver. If the sequence numbers are consistent and increasing, then ESP anti-replay protection is working. If the sequence numbers are inconsistent, missing, or repeated, then there might be a replay attack or a configuration error.

5 What are the limitations of ESP anti-replay protection?

ESP anti-replay protection also has some limitations that you should be aware of. It does not prevent an attacker from dropping or delaying the packets, which can still cause disruption or data loss. It also does not prevent an attacker from modifying the packets before encryption or after decryption, which can affect the confidentiality or authenticity of the data. It also depends on the synchronization and accuracy of the sequence numbers between the sender and the receiver, which can be affected by network conditions, clock drift, or restarts. It also has a limited window size, which can cause valid packets to be discarded if they arrive too late or too fast.

7 Here’s what else to consider

This is a space to share examples, stories, or insights that don’t fit into any of the previous sections. What else would you like to add?