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#include <errno.h>
#include <netdb.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <unistd.h>
#include <linux/if.h>
#include <linux/sockios.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 -I <host>\n"
" mtu -d <host>\n"
" mtu -D <host>\n"
"\n"
" -i <mtu-size> Inject <mtu-size> as PMTU to <host>\n"
" -I Inject local PMTU as PMTU to <host>\n"
" -d Discover PMTU to <host>\n"
" -D Discover PMTU to <host> and assign it to interface MTU\n"
"\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 int discover_mtu(void)
{
int seq = 1, low_mtu, high_mtu, try_mtu, r;
/* Check if the host is up */
if (do_ping(seq++, 0) < 0)
return -1;
/* Discover PMTU */
low_mtu = 68/2;
high_mtu = 1500/2;
try_mtu = 1500/2;
while (1) {
r = do_ping(seq++, try_mtu * 2);
if (r > 0 && r < try_mtu * 2) {
/* pmtu */
high_mtu = r/2;
try_mtu = high_mtu;
continue;
}
if (r == 0)
low_mtu = try_mtu;
else
high_mtu = try_mtu - 1;
if (low_mtu >= high_mtu)
return 2 * low_mtu;
try_mtu = low_mtu + (high_mtu - low_mtu + 1) / 2;
}
}
static void do_discover(void)
{
int mtu;
mtu = discover_mtu();
if (mtu > 0)
fprintf(stdout, "%d\n", mtu);
else
fprintf(stderr, "Host is not up\n");
}
static int set_mtu(const char *dev, int mtu)
{
struct ifreq ifr;
int fd;
fd = socket(PF_INET, SOCK_DGRAM, 0);
if (fd < 0)
return -1;
memset(&ifr, 0, sizeof(ifr));
strncpy(ifr.ifr_name, dev, IFNAMSIZ);
ifr.ifr_mtu = mtu;
if (ioctl(fd, SIOCSIFMTU, &ifr) < 0) {
perror("SIOCSIFMTU");
close(fd);
return -1;
}
close(fd);
return 0;
}
static void do_discover_and_write(void)
{
int mtu;
char iface[IFNAMSIZ];
mtu = discover_mtu();
if (mtu < 0) {
fprintf(stderr, "Failed to determine MTU\n");
return;
}
if (!netlink_route_get(&to, NULL, iface)) {
fprintf(stderr, "Failed to determine route interface\n");
return;
}
printf("Writing %d to %s\n", mtu, iface);
set_mtu(iface, mtu);
}
static void do_inject(void)
{
__u8 buf[1500];
struct sockaddr_in from;
int len, i, seq = 0;
icmp_send_ping(fd, (struct sockaddr *) &to, sizeof(to),
++seq, mtu_size);
for (i = 0; i < 5; i++) {
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);
}
}
static void do_inject_pmtu(void)
{
u_int16_t mtu;
if (!netlink_route_get(&to, &mtu, NULL)) {
fprintf(stderr, "Failed to determine Path MTU\n");
return;
}
if (mtu == 1500)
return;
mtu_size = mtu;
do_inject();
}
int main(int argc, char **argv)
{
struct hostent *hp;
void (*action)(void) = NULL;
char *target;
int opt;
while ((opt = getopt(argc, argv, "DdIi:")) != -1) {
switch (opt) {
case 'D':
action = do_discover_and_write;
break;
case 'd':
action = do_discover;
break;
case 'i':
action = do_inject;
mtu_size = atoi(optarg);
break;
case 'I':
action = do_inject_pmtu;
break;
default:
usage();
}
}
if (action == NULL || optind >= argc)
usage();
target = argv[optind];
fd = icmp_open(1.0);
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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