A 32 bit wide address number. Typically represented as a 4 8-bit dotted quad (ex. 192.168.0.143). IPv4 addresses start at 0.0.0.0 and end at 255.255.255.255. There are only ~4 billion IPv4 address and they have been exhausted. ## Subnet Mask Subnet masks are a way of 'grouping' ipv4 adresses together, so we can tell if two IP adress's are the same network or not. A 32 bit wide number used as a mask to a IPv4 address to discern whether we are targeting a local network or another. A subnet mask will be some amount of 1's and then all 0s. Subnet's can also be described as `/24` which you can read as $24$ 1's and then all 0's. >[!example] Example: `255.255.255.0`