哪个 libc 函数保留一个端口号，以便操作系统不允许其他进程使用它？

Question

I am writing a my first low-level networking application (a simple VPN) in rust and need to modify both the IP source address and TCP/UDP source port for each packet. Therefore I need to use raw sockets and don't get the added convenience of the OS reserving port numbers.

How can I tell the OS to reserve a range of ports so that it won't assign them to other applications and create a conflict?

Answer 1

There is no way to tell the OS to "reserve" a port apart from associating it with a socket, ie create a socket and bind to the address and port.

Apart from that VPN are typically implemented by having a virtual network adapter like TUN/TAP with its own IP address and with appropriate routing to define which traffic should be passed through the VPN. No address or port rewriting needs to be done in this case.