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#include <errno.h>
#include <netdb.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <unistd.h>
#include <netinet/ip_icmp.h>
#include "icmp.h"
static int fd, mtu_size;
static struct sockaddr_in to;
static void usage(void)
{
fprintf(stderr,
"usage: mtu -i <mtu-size> <host>\n"
" mtu -d <host>\n");
exit(3);
}
static int do_ping(int seq, int size)
{
__u8 buf[1500];
struct iphdr *ip = (struct iphdr *) buf;
struct icmphdr *icp;
struct sockaddr_in from;
int len, retry;
for (retry = 0; retry < 3; retry++) {
icmp_send_ping(fd, (struct sockaddr *) &to, sizeof(to),
seq, size);
if ((len = icmp_read_reply(fd, (struct sockaddr *) &from,
sizeof(from), buf, sizeof(buf))) <= 0)
continue;
if (icmp_parse_reply(buf, len, seq,
(struct sockaddr *) &from,
(struct sockaddr *) &to))
return -1;
icp = (struct icmphdr *) &buf[ip->ihl * 4];
switch (icp->type) {
case ICMP_ECHOREPLY:
return 0;
case ICMP_DEST_UNREACH:
if (icp->code != ICMP_FRAG_NEEDED)
return 0;
return ntohs(icp->un.frag.mtu);
default:
return -1;
}
}
return -1;
}
static void do_discover(void)
{
int seq = 1;
int low_mtu, high_mtu, try_mtu;
/* Check if the host is up */
if (do_ping(seq++, 0) < 0) {
fprintf(stderr, "Host is not up\n");
return;
}
/* Check if there is no PMTU or if PMTU discovery works */
low_mtu = do_ping(seq++, 1500);
if (low_mtu == -1) {
/* Binary search for working MTU */
for (low_mtu = 68/2, high_mtu = 1500/2; low_mtu < high_mtu; ) {
try_mtu = low_mtu + (high_mtu - low_mtu + 1) / 2;
if (do_ping(seq++, try_mtu * 2) == 0)
low_mtu = try_mtu;
else
high_mtu = try_mtu - 1;
}
low_mtu *= 2;
} else if (low_mtu == 0) {
low_mtu = 1500;
}
fprintf(stdout, "%d\n", low_mtu);
}
static void do_inject(void)
{
__u8 buf[1500];
struct sockaddr_in from;
int len, seq = 0;
icmp_send_ping(fd, (struct sockaddr *) &to, sizeof(to),
++seq, mtu_size);
for (;;) {
if ((len = icmp_read_reply(fd, (struct sockaddr *) &from,
sizeof(from),
buf, sizeof(buf))) <= 0)
continue;
if (icmp_parse_reply(buf, len, seq,
(struct sockaddr *) &from,
(struct sockaddr *) &to))
continue;
if (seq != 1)
sleep(1);
icmp_send_ping(fd, (struct sockaddr *) &to, sizeof(to),
++seq, mtu_size);
icmp_send_frag_needed(fd, (struct sockaddr *) &to, sizeof(to),
(struct iphdr *) buf, mtu_size - 2);
}
}
int main(int argc, char **argv)
{
struct hostent *hp;
void (*action)(void) = NULL;
char *target;
int opt;
while ((opt = getopt(argc, argv, "di:")) != -1) {
switch (opt) {
case 'd':
action = do_discover;
break;
case 'i':
action = do_inject;
mtu_size = atoi(optarg);
break;
default:
usage();
}
}
if (action == NULL || optind >= argc)
usage();
target = argv[optind];
fd = icmp_open();
if (fd < 0)
exit(1);
memset((char *) &to, 0, sizeof(to));
to.sin_family = AF_INET;
if (inet_aton(target, &to.sin_addr) != 1) {
hp = gethostbyname(target);
if (!hp) {
fprintf(stderr, "mtu: unknown host %s\n", target);
exit(2);
}
memcpy(&to.sin_addr, hp->h_addr, 4);
}
action();
}
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