Good day, I connected two computers together with an Ethernet straight-through cable. I did not configure any ip address, and after a while they both got APIPA addresses. Now they can ping each other and share files. I am a bit confused because firstly, it's a straight-through cable, so there should be no communication and secondly, when I type in "ipconfig /all" in cmd on both computers, there is no subnet mask. How is communication even possible? I am so confused.
Nowodays, many ethernet interfaces are 'auto MDI/MDIX'.
They detect the type of device connected and if needed reverse internally Transmit and Receive.
This allow connection of 2 devices of the same layer with straight-through cable.
APIPA is specifically made to provide IP addresses and allow IP communication in a network where there's no DHCP server.
There's a subnet mask associated with APIPA-assigned IP addresses, it is 255.255.0.0 (I.E. /16). On a windows 7 machine this subnet mask is shown by "ipconfig /all".
Maybe windows 8 or 10 hide it because it's implicit with APIPA, but I cannot check it right now.