How is the conversion of domain names to IP addresses performed within the system?

The conversion of domain names to IP addresses within the system is performed using the DNS (Domain Name System) service. When an application or system requests access to a domain name, the following process occurs:

1. The local DNS cache is checked to see if there is already a stored IP address for this domain.
2. If not in the cache, a request is sent to the DNS server (usually the provider's or a public DNS).
3. The DNS server responds with the corresponding IP address.
4. The system stores this address in the cache to speed up subsequent requests.

In operating systems, this process is usually implemented through system calls, such as getaddrinfo in Unix-like systems.

Example call in C:

struct addrinfo hints, *res;
memset(&hints, 0, sizeof(hints));
hints.ai_family = AF_INET; // IPv4
int err = getaddrinfo("example.com", NULL, &hints, &res);
if (err == 0) {
    struct sockaddr_in *addr = (struct sockaddr_in *)res->ai_addr;
    printf("IP: %s\n", inet_ntoa(addr->sin_addr));
    freeaddrinfo(res);
}

Thus, DNS acts as an intermediary between human-readable domain names and the numerical IP addresses needed for network communication.