Subnet Masking - Can I use any mask I want?

Stellios · 26 Aug 2008 at 16:17

Hi guys, just a quick check. I am in the middle of updating a network design which specifies I can only have a maximum of 40 hosts on the network, which by my maths means I need a subnet of 255.255.255.213 to accomodate for 40 hosts + network address + broadcast address, but as far as im aware you can only use already existing masks and not make up your own. Is it possible to use a 255.255.255.213 subnet mask, or will I have to work with a /29 network that accomodates 62 hosts?

Ive had a look around trying to find an answer and cannot find much really.

Cheers

howler · 26 Aug 2008 at 16:22

You can't just make up a mask, the mask must contain consecutive 1's in its binary form

Chief Wiggum · 26 Aug 2008 at 16:23

afternoon fella

no, you have to use one of the existing ones, the rule of a mask is that it has to be a contiguous group or 1's or 0's (you can't mix and match)

you can have
11111111.00000000.00000000.00000000

but not
11111111.00000000.00000000.11111111
or
11111111.00000000.00000000.00000001

Kev

Stellios · 26 Aug 2008 at 16:26

Excellent, my query confirmed. My assignment just made me want to double check as it said specifically a MAXIMUM of 40 hosts, so I just wanted to make sure you couldnt just make up your subnet mask.

Thank you for the answers, and once again thanks to Chief Wiggum, if I ever bump into you I owe you a free night of drinks

Chief Wiggum · 26 Aug 2008 at 16:32

No problem at all