linux - Is raw socket on loopback interface possible? -

we trying communicate server listening on linux loopback interface via raw socket , seems server not single packet us. packets send visible in wireshark.

is raw socket on loopback possible @ all? (please, don't ask why need it: it's complicated explain here)

edit: how open it

_i_rawsocket = socket( pf_packet, sock_raw, htons(eth_p_all)))  memset( &ifr, 0, sizeof( ifr ) ); strcpy( ifr.ifr_ifrn.ifrn_name, _interfacename);  ioctl( _i_rawsocket, siocgifindex, &ifr )  memset( &sll, 0, sizeof( sll ) ); sll.sll_family   = af_packet; sll.sll_ifindex  = ifr.ifr_ifindex; sll.sll_protocol = htons( eth_p_all );  bind( _i_rawsocket, (struct sockaddr *) &sll, sizeof( sll )) 

the server lighttpd , it's reachable via normal socket on localhost. netstat --raw prints empty table i'm absolutely sure have 2 functional raw sockets on normal eth devices.

raw sockets behave particularly fizzy bind() , connect(), can't confirm issue lies them. suggest follow more straightforward approach:

sender

#include <sys/socket.h> #include <sys/types.h> #include <netinet/ip.h> #include <arpa/inet.h> #include <string.h> #include <stdio.h> #include <stdlib.h>  #define dest "127.0.0.1"  int main(int argc, char **argv) {   int s;  struct sockaddr_in dst_addr;  char packet[50];   struct iphdr *ip = (struct iphdr *)packet;     if((s = socket(af_inet, sock_raw, ipproto_raw)) < 0) {   perror("error:");   exit(exit_failure);  }   dst_addr.sin_family = af_inet;  dst_addr.sin_port = 0; /* not needed in sock_raw */  inet_pton(af_inet, dest, (struct in_addr *)&dst_addr.sin_addr.s_addr);  memset(dst_addr.sin_zero, 0, sizeof(dst_addr.sin_zero));   memset(packet, 'a', sizeof(packet));   /* payload */   ip->ihl = 5;  ip->version = 4;  ip->tos = 0;  ip->tot_len = htons(40);  ip->frag_off = 0;  /* nf */  ip->ttl = 64;  ip->protocol = ipproto_raw; /* has ipproto_raw */  ip->check = 0;  ip->saddr = dst_addr.sin_addr.s_addr;  ip->daddr = dst_addr.sin_addr.s_addr;   while(42) {   sleep(5);   if (sendto(s, packet, sizeof(packet), 0,     (struct sockaddr *)&dst_addr, (socklen_t)sizeof(dst_addr)) < 0)    perror("uh oh:");  }  return(0); } 

receiver

#include <sys/socket.h> #include <sys/types.h> #include <netinet/ip.h> #include <arpa/inet.h> #include <string.h> #include <stdio.h> #include <stdlib.h>   int main(int argc, char **argv) {  int s;  struct sockaddr_in src_addr;  char packet[50];   if ((s = socket(af_inet, sock_raw, ipproto_raw)) < 0) {   perror("error:");   exit(exit_failure);  }   memset(packet, 0, sizeof(packet));  socklen_t *len = (socklen_t *)sizeof(src_addr);  int fromlen = sizeof(src_addr);   while(42) {   if (recvfrom(s, &packet, sizeof(packet), 0,    (struct sockaddr *)&src_addr, &fromlen) < 0)    perror("uh oh:");    int = sizeof(struct iphdr); /* print payload */   for(; < sizeof(packet); i++) {    printf("%c", packet[i]);   }   printf("\n");  }  return(0); } 

i hope these behave want them to. read man 7 raw gory details of why works , more importantly man 7 packet if want extend it. also, take note ipproto_raw implies ip_hdrincl socket option, why we're constructing ip header ourselves - although ip checksum , total length computed , filled in kernel, still.

edit: in addition, if wanted raw socket send valid data application lighttpd, you'd have match protocol argument socket() provide valid values ip header fields. proper ethernet header not mandatory - important field filled kernel stack.