What is a netmask and how do I use one?
Note: for this answer “address” refers to just the last number in an IP address (e.g. 236.192.43.79 is just 79). Think of the addresses that have been given to you as binary numbers. 161 would be represented as: 10100001 ( 128 + 32 + 1 = 161 ) And 175 would be represented as: 10101111 ( 128 + 32 + 8 + 4 + 2 + 1 = 175 ) Your netmask, 240, would be represented as: 11110000 ( 128 + 64 + 32 + 16 = 240 ) A netmask is like a face mask, with holes in it. The 1’s are the holes, and the 0’s are the rest of the mask. So if you see the addresses as faces, and the netmask as the mask, you can actually only see the first 4 bits – 1010. Kind of like this: “Face” (Address) 10100001 “Mask” (Netmask) 11110000 “You” (Router) 1010—- The router “looks” through the netmask at each bit of data on the network, and if it’s going to a destination that doesn’t start with 1010, then it knows it has to route that bit of data somewhere else. That’s how routers work. So your ISP has said that all of the machines
