UDP Server works only on local network - c

Question

I'm trying to run an UDP Client-Server message exchange program for a university course, when I try it in a local network even with different PCs works really fine. But the moment I try to run it on different internet connections it seems like the server doesn't receive anything. I am running Ubuntu and allowed the specific port for UDP connection but maybe I'm missing something else
Server side:
int sockfd;
struct sockaddr_in servaddr;
//creating socket file descriptor
if( (sockfd = socket(AF_INET, SOCK_DGRAM, 0)) < 0){
perror("socket creation failed");
exit(EXIT_FAILURE);
}
memset(&servaddr, 0 , sizeof(servaddr));
//filling server information
servaddr.sin_family = AF_INET;
servaddr.sin_addr.s_addr = INADDR_ANY;
servaddr.sin_port = htons(PORT);
//bind the socket with server address
if( bind(sockfd,(const struct sockaddr *) &servaddr ,sizeof(servaddr)) < 0){
perror("bind failed");
exit(EXIT_FAILURE);
}
Client side:
int main(int argc, char ** argv) {
int sockfd;
char username[MAXLENGHT];
struct sockaddr_in servaddr;
//creating socket file descriptor
if( (sockfd = socket(AF_INET,SOCK_DGRAM, 0)) < 0 ){
perror("socket creation failed!");
exit(EXIT_FAILURE);
}
memset(&servaddr,0, sizeof(servaddr));
//filling server info
servaddr.sin_family = AF_INET;
servaddr.sin_port = htons(PORT);
servaddr.sin_addr.s_addr = inet_addr(argv[1]);
I am using as address 192.168.1.179 and the port I am using is 8080

Answer 1

... when I try it in a local network even with different PCs works really fine.
For this reason I doubt that it is a problem in your program.
maybe I'm missing something else
First of all, most internet connections today use a NAT.
This means that one internet access (e.g. at your home) has one IP address in the internet (called the "global address") and multiple computers share that IP address.
The computer's IP address (e.g. 192.168.1.179) is only valid in the local network; in other local networks, there are other computers having that address.
If you send a UDP packet to the IP address of the computer (192.168.1.179), both computers must be in the same local network.
If you send a UDP packet to the "global IP address" of the internet access, the router does not know which computer shall receive the packet because all computers in the local network share the same "global address".
You may configure your router (e.g. WLAN router) in a way that it knows that UDP packets from the internet to port 8080 shall be sent to the computer 192.168.1.179. This is called "port forwarding".
The sending computer must send the UDP packet to the "global IP address" of the internet access, not to the IP address of the computer (192.168.1.179) in this case.
And if it's not your internet access (e.g. it is not your WLAN router), you already have a problem here.
However, because this has nothing to do with programming, it is out of scope on this web site; you might ask further questions on the SuperUser web site, which also belongs to the StackExchange network. Your account (user name and password) is valid on all StackExchange web sites.
Today, many internet connections even use CGNAT.
This means that even multiple customers share one IP address in the internet.
In this case, it depends on your internet provider if it is possible at all to receive UDP packets:
If your internet access shares the IP address with another person that also wants to receive UDP packets on port 8080, there is a problem...