Questions about the our old topic---Subnet mask

confusion about the usable IP address within a subnet

[Tony_Zhou]

Hi mcavic,

the original text you said long long ago is below[What confused me is at the quotes.Please see my comments]:

With an IP of 70.49.98.16, and a mask of 255.255.255.0, it's indicated that all addresses 70.49.98.x are inside your network, and thus any traffic to those addresses will not be sent to the router, but will remain on your LAN.

That's easy. But here's a better example:

Let's say your ISP has assigned you 16 IP addresses. Your workstation is set to an address of 192.168.1.9, with a mask of 255.255.255.240. Just from that, you can calculate the rest of the addresses that belong to you: 192.168.1.8 through 192.168.1.23.

I can not figure out why the 16 IP addresses is what you said from 192.168.1.8 through 192.168.1.23. My reason is from the given IP address[192.168.1.9] and its mask[255.255.255.240], we can get the Network ID[192.168.1.0]. It means the Host address part only occupied 4 bits. Include the all 1s and 0s Host addresses, it can just sum up to 16 IP address. Above is my idea.Can you explain it more clearly?

So, any IPs outside that range are remote, and will be passed to the router. Without the mask, 192.168.1.50 for example would be thought to be local... your workstation would try sending it only on the local LAN, and would get no response.

I agree with you about these words.

Thanks in advance.
Yours sincerely,
Tony

[Leosghost]

?

[Tony_Zhou]

I just can not understand these below words: Suppose your workstation is set to an address of 192.168.1.9, with a mask of 255.255.255.240. Just from that, you can calculate the rest of the addresses that belong to you: 192.168.1.8 through 192.168.1.23.
// My comment goes here：Ｉ think the range should ought to be 192.168.1.0 through 192.168.1.15. But there is a contradiction with my answer, for the all zeros or ones host part is not considered as valid IP address for common usage.

[lawman]

Subject matter: [webmasterworld.com...]

[lammert]

Hi Tony, first of all Welcome to WebmasterWorld!

A netmask masks bits in a network address. The netmask 255.255.255.240 equals to 11111111.11111111.11111111.11110000 in binary representation and practically clears out the last four bits of the network address. The subnet which is represented by 192.168.1.9 netmask 255.255.255.240 in mcavic's example is therefore going from 192.168.1.0 through 192.168.1.15. If you want to represent 192.168.1.8 through 192.168.1.23, you have to split the subnet in two separate blocks i.e:

192.168.1.8 netmask 255.255.255.248 and
192.168.1.16 netmask 255.255.255.248