Main_P2P

void build_interface_list() {
signed int v1;
char outbuf[76*32];
int bytes_returned;

v1 = WSASocketA(2, 2, 0, 0, 0, 0);
if ( v1 != -1 ) {
/* SIO_GET_INTERFACE_LIST = 0x4004747f, i/o control code for
     retrieving interface list */
if ( !WSAIoctl(v1, 0x4004747Fu, 0, 0, outbuf, sizeof(outbuf), (DWORD
   *)&bytes_returned, 0, 0) )
     check_interface_IPs(bytes_returned / 76, outbuf);
   closesocket(v1);
}
}

void check_interface_IPs(int num_interfaces, void* interface_list) {
EnterCriticalSection(lpCriticalSection);
for (i=0; i < 32; i++)

intf_active[i] = 0;

for(int i=0; i < num_interfaces; i++) {

iflags = *(_DWORD *)(interface_list + 76*i);
ipaddr = *(_DWORD *)(interface_list + 76*i + 8);
netmask = *(_DWORD *)(interface_list + 76*i + 56);

if (iflags & 1 && !(iflags & 4) ) {
    if (is_legit_IP_address(ipaddr) && (_BYTE)ipaddr != 127 ) {
    for (j=0; j < 32; j++) {
      if ( intf_ips[j] == ipaddr && intf_netmasks[j] == netmask ) {
       intf_active[j] = 1;
           break;
    }
    }
    if (j < 32) continue;

    for (j=0; j < 32; j++) {
    if ( !intf_used[j] ) {
       intf_used[j] = 1;
           intf_ips[j] = ipaddr;
           intf_netmasks[j] = netmask;
           /* checks for 10./8, 172.16-31 and 192.168/16 space */
           intf_pvt_subnet[j] = is_private_subnet(ipaddr);
       intf_active[j] = 1;
        }
    }
}

}

}
LeaveCriticalSection(lpCriticalSection);
}

bool is_legit_IP_address(int a1) {
int v2;
v2 = a1 & 0xFFFFFF;

return !((1 << (a1 & 0x1F)) & dword_9B9604[(unsigned __int8)((_BYTE)a1 >> 5)])
    && a1 & 0xFF000000                   /* *.*.*.0 addresses */
    && (a1 & 0xFF000000) != 0xFF00000000 /* *.*.*.255 addresses */
    && (unsigned short)(a1 & 0xFEFF) != 4806
    && (_WORD)a1 != 65193                /* 169.254.*.* (dhcp failure self-assigned
addresses) */
    && v2 != 192                         /* 192.0.0.0/24 reserved */
    && v2 != 131264                      /* 192.0.2.0/24 earmarked for books etc*/
    /* 192.88.89.0/24 no idea why this is blacklisted. This belongs to Teledyne Brown
   Engineering in Huntsville Alabama */
    && v2 != 5855424
/* 253.255.255 (a possible typo.) They may wanted 0xffffdf which translates to
   223.255.255 the beginning of multicast range instead of 0xfffffd */
    && v2 != 16777213;
}

bool is_private_subnet(unsigned short a1) {
     return a1 == 0xA8C0 ||                        /* 192.168 /16 */
         (_BYTE)a1 == 10 ||                        /* 10.0.0.0/8 */
         (unsigned short)(a1 & 0xF0FF) == 0x10AC; /* 172.16 - 172.31 */
}

SOURCE LISTING 3: Interface management code