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Manage DHCP leases with IpReleaseAddress, IpRenewAddress

  • Makale

The IpReleaseAddress and IpRenewAddress functions are used to release and renew the current Dynamic Host Configuration Protocol (DHCP) lease. The IpReleaseAddress function releases an IPv4 address previously obtained through DHCP. The IpRenewAddress function renews a lease on an IPv4 address previously obtained through DHCP. It is common to use these two functions together, first releasing the lease with a call to IpReleaseAddress, and then renewing the lease with a call to the IpRenewAddress function.

When a DHCP client has previously obtained a DHCP lease and IpReleaseAddress is not called before the IpRenewAddress function, the DHCP client request is sent to the DHCP server that issued the initial DHCP lease. This DHCP server may not available or the DHCP request may fail. When a host has previously obtained a DHCP lease and IpReleaseAddress is called before the IpRenewAddress function, the DHCP client first releases the IP address obtained and sends a DHCP client request for a response from any available DHCP server.

Note

The IpReleaseAddress and IpRenewAddress functions require that DHCP be enabled to perform correctly.

 

The IpReleaseAddress function takes a pointer to an IP_ADAPTER_INDEX_MAP structure as its only parameter. To obtain this parameter, first call GetInterfaceInfo. For help with the GetInterfaceInfo function, see Managing Interfaces Using GetInterfaceInfo.

To use IpReleaseAddress

  1. Obtain a pointer to an IP_ADAPTER_INDEX_MAP structure using the GetInterfaceInfo function. (For help with the GetInterfaceInfo function, see Managing Interfaces Using GetInterfaceInfo). Create a DWORD object dwRetVal (used for error checking). It is assumed that the variable returned by GetInterfaceInfo is called pInfo.

    DWORD dwRetVal;

  2. If DHCP is enabled, call the IpReleaseAddress function, passing the IP_ADAPTER_INDEX_MAP variable Adapter as its parameter. Check for general errors and return its value to the DWORD variable dwRetVal (for more extensive error checking).

    Note

    The GetAdaptersInfo function returns a parameter that can be used to check whether DHCP is enabled before calling these functions. For help with GetAdaptersInfo, see Managing Network Adapters Using GetAdaptersInfo.

     

    if ((dwRetVal = IpReleaseAddress(&pInfo->Adapter[0])) == NO_ERROR) {
    printf("Ip Release succeeded.\n");
}

Note

It is common to use these two functions together, calling the IpReleaseAddress function and then calling the IpRenewAddress function, passing the same structure as the parameter to both functions. The following procedure assumes that the functions are not used together; however, if the functions are used together, skip step 1.

 

To use IpRenewAddress

  1. Obtain a pointer to an IP_ADAPTER_INDEX_MAP structure using the GetInterfaceInfo function. (For help with the GetInterfaceInfo function, see Managing Interfaces Using GetInterfaceInfo). Declare a DWORD object dwRetVal (used for error checking) if this variable has not been declared. It is assumed that the variable returned by GetInterfaceInfo is called pInfo.

    DWORD dwRetVal;

  2. Call the IpRenewAddress function, passing the IP_ADAPTER_INDEX_MAP variable Adapter as its parameter. Check for general errors and return its value to the DWORD variable dwRetVal (for more extensive error checking).

    if ((dwRetVal = IpRenewAddress(&pInfo->Adapter[0])) == NO_ERROR) {
    printf("Ip Renew succeeded.\n");
}

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