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@etodd
Last active October 24, 2024 16:28
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dump route table on macos
// stolen from https://stackoverflow.com/a/11265543
#include <stdio.h>
#include <stdlib.h>
#include <err.h>
#include <sys/param.h>
#include <sys/sysctl.h>
#include <sys/socket.h>
#include <netinet/in.h>
#include <arpa/inet.h>
#include <net/route.h>
/* Darwin doesn't define this for some very odd reason */
#ifndef SA_SIZE
# define SA_SIZE(sa) \
( (!(sa) || ((struct sockaddr *)(sa))->sa_len == 0) ? \
sizeof(long) : \
1 + ( (((struct sockaddr *)(sa))->sa_len - 1) | (sizeof(long) - 1) ) )
#endif
static void
ntreestuff(void)
{
size_t needed;
int mib[6];
char *buf, *next, *lim;
struct rt_msghdr *rtm;
struct sockaddr *sa;
struct sockaddr_in *sockin;
char line[MAXHOSTNAMELEN];
mib[0] = CTL_NET;
mib[1] = PF_ROUTE;
mib[2] = 0;
mib[3] = 0;
mib[4] = NET_RT_DUMP;
mib[5] = 0;
if (sysctl(mib, 6, NULL, &needed, NULL, 0) < 0) {
err(1, "sysctl: net.route.0.0.dump estimate");
}
if ((buf = (char *)malloc(needed)) == NULL) {
errx(2, "malloc(%lu)", (unsigned long)needed);
}
if (sysctl(mib, 6, buf, &needed, NULL, 0) < 0) {
err(1, "sysctl: net.route.0.0.dump");
}
lim = buf + needed;
for (next = buf; next < lim; next += rtm->rtm_msglen) {
rtm = (struct rt_msghdr *)next;
sa = (struct sockaddr *)(rtm + 1);
sa = (struct sockaddr *)(SA_SIZE(sa) + (char *)sa);
sockin = (struct sockaddr_in *)sa;
inet_ntop(AF_INET, &sockin->sin_addr.s_addr, line, sizeof(line) - 1);
printf("defaultrouter=%s\n", line);
}
free(buf);
}
int
main(int argc __unused, char *argv[] __unused)
{
ntreestuff();
return (0);
}
// stolen from https://stackoverflow.com/a/8095530
#include <stdio.h>
#include <netinet/in.h>
#include <stdlib.h>
#include <sys/sysctl.h>
#include "getgateway.h"
#include "route.h"
#include <net/if.h>
#include <string.h>
#define CTL_NET 4 /* network, see socket.h */
#if defined(BSD) || defined(__APPLE__)
#define ROUNDUP(a) \
((a) > 0 ? (1 + (((a) - 1) | (sizeof(long) - 1))) : sizeof(long))
int getdefaultgateway(in_addr_t * addr)
{
int mib[] = {CTL_NET, PF_ROUTE, 0, AF_INET,
NET_RT_FLAGS, RTF_GATEWAY};
size_t l;
char * buf, * p;
struct rt_msghdr * rt;
struct sockaddr * sa;
struct sockaddr * sa_tab[RTAX_MAX];
int i;
int r = -1;
if(sysctl(mib, sizeof(mib)/sizeof(int), 0, &l, 0, 0) < 0) {
return -1;
}
if(l>0) {
buf = malloc(l);
if(sysctl(mib, sizeof(mib)/sizeof(int), buf, &l, 0, 0) < 0) {
return -1;
}
for(p=buf; p<buf+l; p+=rt->rtm_msglen) {
rt = (struct rt_msghdr *)p;
sa = (struct sockaddr *)(rt + 1);
for(i=0; i<RTAX_MAX; i++) {
if(rt->rtm_addrs & (1 << i)) {
sa_tab[i] = sa;
sa = (struct sockaddr *)((char *)sa + ROUNDUP(sa->sa_len));
} else {
sa_tab[i] = NULL;
}
}
if( ((rt->rtm_addrs & (RTA_DST|RTA_GATEWAY)) == (RTA_DST|RTA_GATEWAY))
&& sa_tab[RTAX_DST]->sa_family == AF_INET
&& sa_tab[RTAX_GATEWAY]->sa_family == AF_INET) {
if(((struct sockaddr_in *)sa_tab[RTAX_DST])->sin_addr.s_addr == 0) {
char ifName[128];
if_indextoname(rt->rtm_index,ifName);
if(strcmp("en0",ifName)==0){
*addr = ((struct sockaddr_in *)(sa_tab[RTAX_GATEWAY]))->sin_addr.s_addr;
r = 0;
}
}
}
}
free(buf);
}
return r;
}
#endif
#include <stdio.h>
#include <stdlib.h>
#include <sys/param.h>
#include <sys/sysctl.h>
#include <sys/socket.h>
#include <netinet/in.h>
#include <arpa/inet.h>
#include <net/route.h>
/* Darwin doesn't define this for some very odd reason */
#ifndef SA_SIZE
# define SA_SIZE(sa) \
( (!(sa) || ((struct sockaddr *)(sa))->sa_len == 0) ? \
sizeof(long) : \
1 + ( (((struct sockaddr *)(sa))->sa_len - 1) | (sizeof(long) - 1) ) )
#endif
static int ntreestuff(void)
{
int mib[6];
mib[0] = CTL_NET;
mib[1] = PF_ROUTE;
mib[2] = 0;
mib[3] = 0;
mib[4] = NET_RT_DUMP;
mib[5] = 0;
size_t needed;
if ( sysctl( mib, 6, NULL, &needed, NULL, 0 ) < 0 )
{
return -1;
}
char * buffer;
if ( ( buffer = (char *)( malloc( needed ) ) ) == NULL )
{
return -1;
}
if ( sysctl( mib, 6, buffer, &needed, NULL, 0 ) < 0 )
{
return -1;
}
struct rt_msghdr * rtm;
int count = 0;
for ( char * i = buffer; i < buffer + needed; i += rtm->rtm_msglen )
{
rtm = (struct rt_msghdr *)( i );
if ( rtm->rtm_type != RTM_GET )
continue;
if ( !( rtm->rtm_flags & RTF_UP ) )
continue;
if ( !( rtm->rtm_flags & RTF_GATEWAY ) )
continue;
if ( !( rtm->rtm_addrs & ( 1 << RTAX_DST ) ) )
continue;
if ( !( rtm->rtm_addrs & ( 1 << RTAX_NETMASK ) ) )
continue;
printf( "flags: %x\n", rtm->rtm_flags );
struct sockaddr * sa = (struct sockaddr *)( (char *)( rtm ) + sizeof( struct rt_msghdr ) );
struct sockaddr_in * sockin;
char line[MAXHOSTNAMELEN];
if ( rtm->rtm_addrs & ( 1 << RTAX_DST ) )
{
sockin = (struct sockaddr_in *)( sa + RTAX_DST );
inet_ntop( AF_INET, &sockin->sin_addr.s_addr, line, sizeof( line ) - 1 );
printf( "dest: %s\n", line );
}
if ( rtm->rtm_addrs & ( 1 << RTAX_NETMASK ) )
{
sockin = (struct sockaddr_in *)( sa + RTAX_NETMASK );
inet_ntop( AF_INET, &sockin->sin_addr.s_addr, line, sizeof( line ) - 1 );
printf( "netmask: %s\n", line );
}
if ( rtm->rtm_addrs & ( 1 << RTAX_GATEWAY ) )
{
sockin = (struct sockaddr_in *)( sa + RTAX_GATEWAY );
inet_ntop( AF_INET, &sockin->sin_addr.s_addr, line, sizeof( line ) - 1 );
printf( "gateway: %s\n", line );
}
printf( "iface: %hu\n", rtm->rtm_index );
count++;
}
printf( "count: %d\n", count );
free( buffer );
return 0;
}
int main( int argc, char ** argv )
{
(void) argc;
(void) argv;
ntreestuff();
return 0;
}
@Wangzihaooooo
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There are many such outputs on Mac -> dest:0.0.0.0 and gateway:0.0.0.0
But using "netstat -nr", there is no 0.0.0.0 in the result
How to fix it, pls help me

@keyallis
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@Wangzihaooooo 0.0.0.0 is the default value to my understanding. Mac has many network devices these days and not all of them will have a gateway configured. I think it can be assumed that 0.0.0.0 is not a valid gateway address, and if that value is encountered in the sockaddr struct, then it is essentially unset.

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