The protocol is conceptually a shim-layerbetween the application layer and the transport layer, and as such does not provide network-layer gateway services, such as forwarding of ICMP messages.
The protocol is conceptually a shim-layerbetween the application layer and the transport layer, and as such does not provide network-layer gateway services, such as forwarding of ICMP messages.
这个协议可以理解为应用层和传输层中间的一层同时不提供网络层网关服务，如不传递icmp消息。