thank you very much

All you need is to do :

1-) Enable LWIP_NETIF_LINK_CALLBACK definition inside lwipopts.h file. By default, the value can be 0. Check it.

2-) Initialize " netif_set_link_callback(netif, ethernetif_update_config); " in void ethernetif_input(struct netif *netif) function.

3-) Read PHY register and do whatever want.

Thanks for yopur response.
But, how could I notify the change of cable connection during the execution of the program, not only when it initiates?

Hi,
it is the initialization process by LwIP that will take time.