Network subnetmask

Hey!

I'm currently self-learning Cisco, but the book is pretty fuzzy about "subnetmasks".
See, if I am to for example create a subnetmask that allows me 14 networks for a Class-C network, do I write a subnetmask like 255.255.255.0, or am I allowed to write it like 255.255.240.240 (also is this a subnetmask that allows me 14 networks?).

Many thanks!

No -> 255.255.240.240

Subnet mask for 14 subnets -> 255.255.240.000
This "mask" is used to find the subnet address of an IP within range.

ok, I think I might have figured it out.

255.255.255.240 /28 is a Class-C network with 14 functional networks, is that correct?

Thanks!

>>3
14 functional IPs.

I mean, does the subnet mask 255.255.255.240 /28 provide me with 14 usable sub-networks? If not, how does it look?

>>5
How large do you want your subnetworks? That subnet mask masks 14 functional IPs. You can only have 14 IPs in this subnet(work). You may further divide them with a larger subnet mask to create more networks, but I'm not sure of what you want. For example, with a subnet mask of 255.255.255.248 you can mask two networks within whatever range you wanted.

BTW, the notation is either decimal-dot IP and subnet mask (e.g. IP 192.168.1.0 subnet mask 255.255.255.0), or the real IP plus number of bits that represent the network address (like 192.168.1.0/24).

Gawd damn it...

http://www.subnetmask.info/

Just figure it out with this.

http://www.bitzenbytes.com/Content-Arcanum-18-1-20.html#defsubm
Look at the table for Subnets of Class C Addresses.

Class C address use the first 3 bits as the indicator. The following 21 bits are used as for network ID. The last octet is used as for host ID. So when you do subnetting for class C you will be fiddling with the last octet. 240 or 11110000 gives you 4 bits for subnetworks and 4 bits for hosts. So you do get 14 functional ips for each of the 14 subnetworks.

Someone correct me if I'm wrong.

>>9
 no you are right

IPv6 OR GTFO