Brauche schnelle hilfe in C IPv4 zu IPv6

#include <errno.h>
#include <netdb.h>
#include <string.h>
#include <stdio.h>
#include <unistd.h>
#include <arpa/inet.h>
#include <netinet/in.h>
#include <sys/socket.h>
#include <sys/time.h>
#include <sys/types.h>
#include "hl_common.h"
 
void contact(char* host) {
 
    // ermitteln der adresse
    struct addrinfo tip, *ergebnis;
    memset(&tip, 0, sizeof tip);
    memset(&ergebnis, 0, sizeof *ergebnis);
    tip.ai_family = AF_UNSPEC;    // erlauben von IPv4 oder IPv6
    tip.ai_socktype = SOCK_DGRAM; // Datagram socket
    tip.ai_flags = 0;            // Flags
    tip.ai_protocol = 0;          // Jedes Protokol
    const char *service = "2673";
    if (getaddrinfo(host, service, &tip, &ergebnis) != 0) {    //von vorheriger aufgabe getaddrinfo
        printf("getaddrinfo failed\n");
        return;
    }
 
    // Create socket
    int sock = socket(AF_INET6, SOCK_DGRAM, IPPROTO_UDP);// 6 für IPv6 hinzufügen
    if (sock == -1) {
        perror("socket creation failed");
        return;
    }
 
    // Compose message
    char sendbuf[1+MAXSIZE];
    int msglen = snprintf(sendbuf, sizeof sendbuf, "M%s", get_hostname()) + 1;
 
    // Configure socket timeouts
    struct timeval timeout;
    memset(&timeout, 0, sizeof timeout);
    timeout.tv_sec = 1;
    if (setsockopt(sock, SOL_SOCKET, SO_RCVTIMEO, &timeout, sizeof timeout) == -1) {
        perror("setsockopt(SO_RCVTIMEO) failed");
        close(sock);
        return;
    }
    if (setsockopt(sock, SOL_SOCKET, SO_SNDTIMEO, &timeout, sizeof timeout) == -1) {
        perror("setsockopt(SO_SNDTIMEO) failed");
        close(sock);
        return;
    }
 
    // Send message
    if (sendto(sock, sendbuf, msglen, 0, ergebnis->ai_addr, ergebnis->ai_addrlen) == -1) {
        perror("sendto failed");
        close(sock);
        return;
    }
 
    char recvbuf[4*MAXSIZE];
    struct sockaddr_in6 peer; // 6 für IPv6 hinzufügen
    socklen_t peer_len = sizeof peer;
    size_t msgsize = recvfrom(sock, &recvbuf, sizeof recvbuf, 0, (struct sockaddr*) &peer, &peer_len);
    if (msgsize == -1) {
        if (errno == EWOULDBLOCK) {
            fprintf(stderr, "No response from %s!\n", host);
            close(sock);
            return;
        }
 
        perror("recvfrom failed");
        close(sock);
        return;
    }
 
    recvbuf[msgsize-1] = '\0';
 
 
 
    char peeraddr[INET6_ADDRSTRLEN]; // 6 für IPv6 hinzufügen und
    inet_ntop(AF_INET6, &peer,peeraddr, INET6_ADDRSTRLEN); //inet_ntoa durch inet_ntop
    if (recvbuf[0] != 'R') {
        fprintf(stderr, "Reply from %s(%s) does not follow protocol!\n"
                        "Expected message type 'R', but got %c\n",
                        peeraddr, host, recvbuf[0]);
        close(sock);
        return;
    }
 
    printf("\"%s\" from %s (%s)\n", recvbuf+1, peeraddr, host);
 
    close(sock);
}
 
int main(int argc, char** argv) {
    if (argc == 1) {
        fprintf(stderr, "No remote host given!\n");
        printf("Usage: %s server-ip [server-ip..]\n", argv[0]);
        return 1;
    }
 
    char** host = argv+1;
    while (argc > 1) {
        contact(*host);
        host++;
        argc--;
    }
 
    return 0;
}