Ipdecap can decapsulate traffic encapsulated within GRE, IPIP, 6in4, ESP (ipsec) protocols, and can also remove IEEE 802.1Q (virtual lan) header.
It reads packets from an pcap file, removes the encapsulation protocol, and writes them to another pcap file.
Extract encapsulated tcp flow to analyze them with conventional tcp tools (tcptrace, tcpflow, …)
Reduce pcap files size by removing encapsulation protocol
Ipdecap was first written to analyze a strange tcp behavior encapsulated by ESP, without intervention on vpn endpoints.