How to decrypt ESP IPSEC packet using wireshark

rmeddane — Thu, 28 Dec 2023 09:13:27 GMT

Sometimes you want to see how the tunnel mode encapsulation occurs, especially when using GRE over IPsec and VTI IPsec and you would like to decrypt the ESP or IPSEC packet to see how packet is encaspulated on both scenarios (GRE over IPsec and VTI IPsec, especially for studying or may be for troubleshooting.

Below how to do it:

Configue the ESP encryption with null in the IPsec Crypto Profile.

Run the packet capture on PaloAlto to capture the PCAP File.

Open wireshark. right-click on the ESP packet, in this scenario the ESP SA from the source 10.1.15.120 to the destination 10.1.15.121. Under the Protocol Preferences, check the the option "Attempt to Detect/Decode NULL Encrypted ESP Payload" as shown below.

Finally you can see the ESP Packet payload in clear text:

ESP Packet with VTI IPsec

ESP Packet with GRE Over IPsec

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How to decrypt ESP IPSEC packet using wireshark