Work notes: SendTo failed errno 22

Work notes : sendto Failure errno 22

Today there is a udpclient send out udp The scenario of data to the remote server , Because they were tested on the same virtual machine before , Both the server and the client are 127.0.0.1 No problem .
The solution to online related problems is sendto Of sizeof problem , Or is it bzero The problem of .

	int sock_fd ;
    struct sockaddr_in send_addr, cli_addr;
	bzero( &send_addr, sizeof(send_addr) );

	if ((sock_fd = socket(AF_INET, SOCK_DGRAM, IPPROTO_IP)) == -1)
    {
    
        perror("create socket failed!\r\n");
        exit(1);
    }

    cli_addr.sin_family = AF_INET;
	cli_addr.sin_port = htons(9693);
	cli_addr.sin_addr.s_addr = inet_addr("127.0.0.1");
	if (bind(sock_fd, (struct sockaddr* )&cli_addr, sizeof(cli_addr)) < 0)
	{
    
		perror("bind");
		exit(EXIT_FAILURE);
	}

    // Initialize the pre connected server address 
    send_addr.sin_family = AF_INET;
    send_addr.sin_port = htons(9000);
    send_addr.sin_addr.s_addr = inet_addr(" Extranet ip");
    int addr_length = sizeof(send_addr);

if( sendto(sock_fd, buff, cs_pkg.GetCachedSize(), 0, (struct sockaddr *)&send_addr, sizeof(send_addr)) < 0 )

After testing

c s All in the intranet All are 127.0.0.1,sendto It can send .
s After the external network or non local address ,c If it is 127.0.0.1 Unable to send normally .
Solution to c Set up a 0 / 0.0.0.0 / Or a specific network card address
127…0.0.1 and 0.0.0.0 difference
It's a complete understanding of 127.0.0.1 and 0.0.0.0 What's the difference between addresses ？

Only a maximum of... Can be maintained on a host 65535 individual TCP Is it connected ？
Subject to many restrictions ,fd, Memory ,cpu, Port number, etc . The protocol in the quintuple of the protocol , Fixed .src and dest Of ip and port Can change , More than 65535.

You may also receive NAT The limitation of ,NAT Concept ：

• IP The purpose of the message IP The address is private IP Address , How the network layer handles ？
• NAT A brief introduction to the principle of LAN mapping public network
• Communication between intranet and extranet （ Port mapping principle ）

Because they are all transferred from the intranet NAT Do address conversion into public network . single IP do NAT The maximum number of connections supported . agreement × source address × Source port × Destination address × Destination port = 2 * 1 * 2^16 * 2^32 * 2^16 = 3.68934881e+019 A connection ( Ideal state ) Worst case scenario , All users access the same IP The same port of the same protocol , be ： agreement × source address × Source port × Destination address × Destination port = 1 * 1 * 2^16 * 1 * 1 = 65536 A connection （ The worst ）.

Extended problem , Multiple processes can listen to the same port , Will it cause repeated reads , What is the shock effect
Can a port number be bound by two processes at the same time ？ Corresponding nginx Multiple processes are bound to the same port number , Yes, but the condition is fork Bind a port number before , Make the child and parent processes bound to the same port number , Multiple processes reuse socketNginx

EPOLLEXCLUSIVEepoll How to solve the shock group effect
Different processes must listen to the same fd What should I do
SO_REUSEADDR SO_REUSEPROTsocket Port multiplexing SO_REUSEPORT And SO_REUSEADDR