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Function xn_dhcp_server_daemon

This function starts the background DHCP server task.

int xn_dhcp_server_daemon(dhcps_config * cfg);

Parameters

cfg

Pointer to the structure whose fields determine the server configuration. The individual fields are described below.

return value

On failure, the function returns SOCKET_ERROR and xn_getlasterror and xn_geterror_string return the error value. Error Codes further describes each error. If the function succeeds, it never returns.

This routine implements a DHCP server over UDP and may be called after the interface has been initialized. The routine takes as parameter a pointer to a dhcps_config structure, whose fields are used to configure the server. The dhcps_config structure consists of a simple address pool, a few configuration parameters (DNS server, default gateway, etc.), and a field which allows the server to be extended to give the client additional configuration parameters.

The fields in the dhcps_config structure determine the server configuration. This structure is declared in Dhcpsapi.h as:

struct dhcps_address_binding { 
   BYTE  start_ip[4]; 
   BYTE  end_ip[4]; 
   DWORD lease_time; 
}; 

struct dhcps_option { 
   int    number; 
   int    length; 
   PFVOID value; 
}; 

struct dhcps_params { 
   BYTE                  subnet_mask[4]; 
   BYTE                  default_gateway[4]; 
   BYTE                  dns_servers[2][4]; 
   struct dhcps_option * extra_options; 
   int                   num_extra_options; 
}; 

struct dhcps_client_profile { 
   BYTE                  hw_addr[16]; 
   BYTE                  ip_addr[4]; 
   DWORD                 lease_time; 
   struct dhcps_params * params; 
   BYTE                  status; 
   DWORD                 cur_lease_time; 
}; 

struct dhcps_config { 
   struct dhcps_address_binding address_pool[8]; 
   struct dhcps_params          pub_params; 
   struct dhcps_client_profile  client_profiles; 
   int                          num_client_profiles; 
};

See below for instructions on how each field should be initialized. Fields not mentioned here should be initalized to zero and are for the DHCP server's internal use.

dhcps_config.address_pool

The address_pool is a list of IP address ranges and associated lease times. For example, initializing this field to:

{ {205,161,8,200}, {205,161,8,205}, 10000 }, 
{ {205,161,8,220}, {205,161,8,225}, 20000 }, 
{ {205,161,8,230}, {205,161,8,230}, 30000 }

dhcps_config.pub_params.subnet_mask

This field specifies the subnet mask that the server will configure the clients with. For example, initializing this field to:

{255,255,255,0}

dhcps_config.pub_params.default_gateway

This field specifies the default gateway for the subnet. For example, initializing this field to:

{205,161,8,1}

dhcps_config.pub_params.dns_servers

This field specifies a list of DNS servers used to configure DHCP clients. Initializing this field to:

{ {205,161,8,5}, {205,161,8,1} }

dhcps_config.pub_params.extra_options and num_extra_options

These fields are used to make the server pass additional configuration parameters to the clients. Assuming the following global variable has been declared:

char my_domain_name[]="on-time.com"; 
struct dhcps_option my_extra_options[]= { 
   { DOMAIN_NAME, sizeof(my_domain_name), my_domain_name } 
};

Example (Simple):

struct dhcps_params dhcps_parms = 
{ 
   { 255, 255, 255,   0},    // subnet mask 
   { 192, 168,   1,   1},    // default gateway 
   {{192, 168,   1,   1}},   // 1st DNS server 
   NULL,                     // extra_options 
   0                         // num_extra_options 
}; 

struct dhcps_config dhcps_cfg =  
{ 
   {{{192, 168, 1, 128}, {192, 168, 1, 254}, 3*24*60*60}},  // 3 days 
   &dhcps_parms 
}; 

/*-----------------------------------*/ 
int main(void) 
{ 
   // initialize the stack 
   NetInitialize(); 

   // run the DHCP server 
   if (xn_dhcp_server_daemon(&dhcps_cfg) == SOCKET_ERROR) 
      Error("xn_dhcp_server_daemon failed"); 

   // the server never returns 

   return 0; 
}

Example (with Options):

char  my_dom_name[] = "on-time.com"; 
dword dhcps_mdrs    = 4000;              // max frag size 
dword dhcps_ip_ttl  = 60; 

struct dhcps_option my_extra_options[] = 
{ 
   { DOMAIN_NAME,    sizeof(my_dom_name),  my_dom_name      }, 
   { MDRS,           sizeof(dhcps_mdrs),   &dhcps_mdrs  }, 
   { DEFAULT_IP_TTL, sizeof(dhcps_ip_ttl), &dhcps_ip_ttl}, 
}; 

struct dhcps_params dhcps_parms = 
{ 
   { 255, 255, 255,   0},    // subnet mask 
   { 192, 168,   1,   1},    // default gateway 
   {{192, 168,   1,   1},    // 1st DNS server 
    {192, 168,   1,   2}},   // 2st DNS server 
   &my_extra_options, 
   sizeof(my_extra_options) / sizeof(my_extra_options[0]) 
}; 

struct dhcps_config dhcps_cfg =  
{ 
   {{{192, 168, 1,  64}, {192, 168, 1, 127}, 1*24*60*60},   // 1 day 
    {{192, 168, 1, 128}, {192, 168, 1, 254}, 3*24*60*60}},  // 3 days 
   &dhcps_parms 
}; 

/*-----------------------------------*/ 
int main(void) 
{ 
   // initialize the stack 
   NetInitialize(); 

   // run the DHCP server 
   if (xn_dhcp_server_daemon(&dhcps_cfg) == SOCKET_ERROR) 
      Error("xn_dhcp_server_daemon failed"); 

   // the server never returns 

   return 0; 
}

DHCP Server

DHCP Server Configuration