Subnet Mask Reference Table

By Joshua Erdman
Digital Foundation, inc.

Subnet Masks in Binary

Here we have provided for you a subnet mask reference table. By looking up the size of a subnet you want, you can find the correct subnet mask.

Subnet size (# of hosts)	Subnet Mask	First host in block
2 hosts	255.255.255.252	1,5,9,13,17,21,25,....
3 - 6	255.255.255.248	1,9,17,25,33,...
7 - 15	255.255.255.240	1,17,33,49,65,...
16 - 31	255.255.255.224	1,33,65,97,129,...
32 - 63	255.255.255.192	1,65,129,193,...
64 - 127	255.255.255.128	1 & 129
128 - 255	255.255.255.0	1
256 - 511	255.255.254.0	1,5,9,13,17,21,25,....
512 - 1023	255.255.252.0	1,9,17,25,33,...

CLUE: Referring to the table above, you can see that for sizes above 256 the 3rd segment of the subnet mask begins to countdown in the exact same pattern as how the 4th segment counted down for subnets of sizes 2 - 255.

References:
Calculating Subnet Masks

TCP/IP Addressing

Handy Tools:
subnet mask calculator
Ring Of Saturn - Binary conversion tool & subnet calculator

Article last reviewed: 06/09/2004

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Created by: Digital Foundation, inc.

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