Question about ARP protocol. In this video https://www.youtube.com/watch?v=iBOT_aVjc9k&t=5s (from 0:25). Can someone explain why in 15th and 16th frame there is ARP protocol again, asking for 192.168.1.11 MAC address, if that node already knows the MAC address (from the first and second frame) and it's even in the destination? Is it something with aging or second node just wants to check first nodes MAC address (is it still the same)?