Home Internet access is NAT, and Ping is not connected to other IP on the network segment (confirm online). What isolation technology is used?

How to ensure that the authentication information (AccessToken, etc.) sent by the client is not obtained or forged? Which encryption method would be better?

We know that the PDU of the application layer is a message, and finally becomes the bit stream of the physical layer to propagate, so what is the relationship between the message format of a protocol and the body of this message? What is the role of understanding the message format of a protocol?

Where are the TCP connection-oriented features?

Recently, I was reading the article about TCP connection. I have a doubt. I hope you can help. Where is the connection-oriented feature of TCP? Because the three-way handshake of TCP seems to the router to forward three ordinary packets, the router will not reserve bandwidth resources for this session. Where is the "connection" feature of TCP?

First, let ’s make a statement. The default route and default route (Default Route) of all devices on the earth are “0.0.0.0”. The device here refers to any host, virtual host, router, switch, firewall. Therefore, there is no problem if the default route of the subject is "0.0.0.0".

How to understand that TCP at the transport layer is byte-oriented and UDP is message-oriented? The two are defined by whether they will be segmented (mss)?

TCP transmission information always misses, and then how to deal with the missing information in the next transmission?

Recently, I suddenly remembered that the state of last_ack seemed to be used. The party who actively cut off the connection intentionally did not send the last ack, would it run out of server resources?

Since the IP protocol can also perform connectionless and unreliable transmission of data, why do you need the UDP protocol?