int xn_autoip(int          iface_no, 
              const BYTE * low_ip_addr, 
              const BYTE * high_ip_addr, 
              const BYTE * ip_mask, 
              BYTE       * Result);

Parameters

iface_no

Interface number (returned by xn_interface_open or xn_interface_open_config.

low_ip_addr

Pointer to lowest allowed IP address in network byte order. If NULL is specified, default value 169.254.1.0 is used.

high_ip_addr

Pointer to highest allowed IP address in network byte order. If NULL is specified, default value 169.254.254.255 is used.

ip_mask

Pointer to network mask of the local LAN segment. If NULL is specified, default value 255.255.0.0 is used.

Result

Pointer to a 4 byte buffer to receive the IP address obtained. The parameter is optional and may be set to NULL if not needed.

return value

Returns 0 if successful, otherwise SOCKET_ERROR. If an error occurred, call xn_getlasterror and xn_geterror_string to return the error value. Section Error Codes further describes each error.

This function attempts to find a unique IP address in the range given by *low_ip_addr and *high_ip_addr. No DHCP, BOOTP, or other server is required on the LAN for this function to work. The function repeatedly chooses a random IP address and then checks via ARP if it is in use already. If so, a new address is tried until either a free address is found (and applied by calling xn_set_ip) or CFG_MAX_AUTOIP (default: 50) IP addresses have been tried without success (in this case, the function fails).

When successful, the function sends out a gratuitous arp using xn_arp_send and the address will be checked every CFG_PROBE_INTERVAL (default: 8) seconds to make sure that no other host on the network is using the local address. If another host claims the local address at a later time and is unwilling to release it, the local host will restart its algorithm to find and apply a unique IP address. This should only happen in misconfigured networks, for example, if the same IP address range has been assigned to DHCP and Auto-IP, or hosts use hardwired IP addresses out of a DHCP or Auto-IP address range. Setting CFG_PROBE_INTERVAL to zero before xn_autoip is called disables periodic ARP probing.

Care must be taken to allocate enough addresses to Auto-IP. If, for example, 20 hosts shall use Auto-IP to assign themselves unique IP addresses, and only 20 addresses are available, the last connecting hosts may need a lot of time to find a free address. Moreover, it could happen that a host needs more than CFG_MAX_AUTOIP attempts to find a free address, causing xn_autoip() to fail.

If xn_autoip is used to check a single IP address (*low_ip_addr and *high_ip_addr are equal), CFG_MAX_AUTOIP should be set to 1.

Unlike DHCP, the Auto-IP protocol is not able to determine the net mask, default gateway, or DNS server address.

Example:

static BYTE TargetIP[]       = {  0,   0,   0,   0};   // will be filled at run-time 
static BYTE NetMask[]        = {255, 255, 255,   0}; 
static BYTE MinIP[]          = {192, 168,   1, 192}; 
static BYTE MaxIP[]          = {192, 168,   1, 254}; 
static BYTE DefaultGateway[] = {192, 168,   1,   1};   // set to zero if no gateway 
static BYTE DNSServer[]      = {192, 168,   1,   1};   // ditto 
... 

Result = xn_rtip_init();           // Initialize the RTIP stack 
if (Result == SOCKET_ERROR) 
   Error("xn_rtip_init failed"); 

Result = BIND_DRIVER(MINOR_0);     // bind driver we want (see netcfg.h)  
if (Result == SOCKET_ERROR)  
   Error("driver initialization failed");  

// Open the interface 
interface = xn_interface_open(DEVICE_ID, MINOR_0); 
if (interface == SOCKET_ERROR) 
   Error("xn_interface_open failed"); 

Result = xn_autoip(interface, MinIP, MaxIP, NetMask, TargetIP); 
if (Result == SOCKET_ERROR) 
   Error("xn_autoip failed"); 

printf("Auto-assigned IP address %i.%i.%i.%i\n", 
   TargetIP[0], TargetIP[1], TargetIP[2], TargetIP[3]); 

// define default gateway and DNS server 
xn_rt_add(RT_DEFAULT, ip_ffaddr, DefaultGateway, 1, interface, RT_INF); 
xn_set_server_list((DWORD*)DNSServer, 1);

Left Extended RTIP-32 API

Function xn_scriptlogin

Down Function xn_ioacc_init