IP4 address changing problem(netIF_SetOption )


I am following this (https://www.keil.com/pack/doc/mw/Network/html/network_create_app.html#Runtime%20Configuration) tutorial about the Network library with CMSIS. I could change the Mac address via " netIF_SetOption (NET_IF_CLASS_ETH | 0, netIF_OptionMAC_Address, buf, NET_ADDR_ETH_LEN);" without any problem but by using the

netIP_aton (ip_addr, NET_ADDR_IP4, buf);
nothing work. I need to know if changing IP address function has any problem. before calling the above lines my ETH works fine with the default IP address which is set in "Net_Config_ETH_0.h"  (for examples: but by using the above lines I could not be successful to change the IP address to or any other values which are not available on my network and I missed the connection ( even the default value
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