The ESP header is located after the IP header and before the transport mode protocol (UDP or TCP) or before an encapsulated IP header when using tunneling.

ESP报头位于IP报头之后，传输模式(UDP或者TCP)之前，或者当使用隧道时是在封装的IP报头之前。

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Tunneling (RFC 2893) : it allows you to encapsulate one packet head into the other and one protocol will communicate with others through the encapsulation in the other protocol.

隧道技术(RFC 2893)：是指将一种协议报头封装在另一种协议报头中，这样，一种协议就可以通过另一种协议的封装进行通信。

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The implementation of IP-over-IP tunneling (IPIP) and the Generalized Routing Encapsulation (GRE) protocol is based on the creation of a virtual device.

IPIP的实现和通用路由封装协议是基于一个虚拟设备的创建。

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