Code:
#include <stdio.h>
#include <stdlib.h>
#include <sys/types.h>
#include <sys/socket.h>
#include <arpa/inet.h>
#include <unistd.h>
#include <string.h>
// la dimensione del datagramma č data da MTU - ( ip header + udp header ) e cioč 1500 - ( 20 + 8 ) = 1472
#define DGRAM_SIZE 2020
int main()
{
int sockfd = socket(PF_INET, SOCK_DGRAM, IPPROTO_UDP);
if ( sockfd == -1 ) { perror("Socket"); exit(0); }
int optval = IP_PMTUDISC_DO;
if (setsockopt(sockfd, IPPROTO_IP, IP_MTU_DISCOVER, &optval, sizeof(optval)) == -1) { perror("MTU Discover"); exit(0); }
void *buf = malloc(DGRAM_SIZE);
memset(buf, 0x1f, DGRAM_SIZE);
struct sockaddr_in svraddr;
svraddr.sin_family = PF_INET;
svraddr.sin_port = htons(69);
svraddr.sin_addr.s_addr = inet_addr("192.168.1.107");
if ( connect(sockfd, (struct sockaddr*)&svraddr, sizeof(svraddr)) == -1 ) { perror("connect"); exit(0); }
int dgram_size, dg_len = sizeof(dgram_size);
/*
if ( getsockopt(sockfd, IPPROTO_IP, IP_MTU, &dgram_size, (socklen_t*)&dg_len) == -1 ) {
perror("getsockopt"); exit(0);
}
printf("Dimensione max fragment ( prima dell'invio ): %d\n", dgram_size);
*/
if (sendto(sockfd, buf, DGRAM_SIZE, 0, (struct sockaddr*)&svraddr, sizeof(svraddr)) == -1 ) {
dgram_size = 0;
if ( getsockopt(sockfd, IPPROTO_IP, IP_MTU, &dgram_size, (socklen_t*)&dg_len) == -1 ) {
perror("getsockopt"); exit(0);
}
perror("Sendto");
printf("Dimensione max fragment ( dopo l'invio dei dati ): %d\n", dgram_size);
} else printf("Successo\n");
return 0;
}