CODEWITHSUNDEEP
clinuxsocketsposix
Jane Watson
Jane Watson

Reputation: 575

C open socket on a specific IP

My website can be accessed using any of 2 different static IPs (IPv4).

Is it possible to open a TCP connection to another server, specifying which of the 2 IPs to use as a return address ?

x.x.x.x (my server) => z.z.z.z (destination server)
y.y.y.y (my server) => z.z.z.z (destination server)

Error-checking, etc. in this example has been omitted for simplicity sakes :

struct addrinfo hints, *result;
hints.ai_flags = 0;
hints.ai_family = AF_INET;
hints.ai_socktype = SOCK_STREAM;
hints.ai_protocol = IPPROTO_TCP;
hints.ai_addrlen = 0;
hints.ai_canonname = NULL;
hints.ai_addr = NULL;
hints.ai_next = NULL;

getaddrinfo(domain, "80", &hints, &result);

socket(result->ai_family, result->ai_socktype, result->ai_protocol);

Upvotes: 2

Views: 7796

Answers (2)

Some programmer dude
Some programmer dude

Reputation: 409136

Like @hochl says, you use the bind system call:

struct sockaddr_in sin = { 0 };
int sock;

/* Create a socket address, with a specific port and (local) ipnumber */
sin.sin_family = AF_INET;
sin.sin_port = htons(80);
inet_aton("1.2.3.4", &sin.sin_addr);

/* Create socket */
sock = socket(AF_INET, SOCK_STREAM, 0);

/* Bind socket to the local address */
bind(sock, (struct sockaddr *) &sin, sizeof(sin));

/* Now connect to remote server... */
/* connect(...) */

It should be noted that use of inet_aton is normally discouraged, in favor of inet_pton.

Upvotes: 6

hochl
hochl

Reputation: 12920

Not sure, but can't you bind your socket to one of your local addresses before you connect? In this case you may choose which of your IPs is used for the connection.

Upvotes: 1

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