Hello everyone,

I have always been told that to calculate the number of hosts on a network you need to do the following:

2^n - 2

n being the number of bits in the host part of the mask.

However, does this still apply to a classless subnet???

For example if you do: 172.16.1.0/22

2^10 -2 = 1022

Shouldn't it be 2^10 -8 = 1016?

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This is a pretty good article that may help clear things up a bit more for you.

http://www.winnetmag.com/Articles/I...ArticleID=16222

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quote:

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Originally posted by l9nux
Hello everyone,

I have always been told that to calculate the number of hosts on a network you need to do the following:

2^n - 2

n being the number of bits in the host part of the mask.

However, does this still apply to a classless subnet???

For example if you do: 172.16.1.0/22

2^10 -2 = 1022

Shouldn't it be 2^10 -8 = 1016?

---

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Best Regards
Alex
alexisgarcia72@hotmail.com
Cuban in Mexico
www.cm2gj.com

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quote:

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Originally posted by Pavlov
This is a pretty good article that may help clear things up a bit more for you.

http://www.winnetmag.com/Articles/I...ArticleID=16222

---

__________________
Best Regards
Alex
alexisgarcia72@hotmail.com
Cuban in Mexico
www.cm2gj.com

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REALLY good article! thanks for posting pavlov.

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quote:

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Originally posted by l9nux

Shouldn't it be 2^10 -8 = 1016?

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2^10 -8 = 1016

I arrived at that because 172.16.4.0/22 only has 1016 usable hosts. The range for the first available network is:

172.16.4.1 - 172.16.7.254

This range only has 1016 hosts and 62 networks right?

Please someone correct me if I'm wrong, but 1022 hosts includes 0 and 255 in the last octet but this is reserved for network id and broadcast isn't it? Or does the calculate above have to include this?

When I produce how many hosts are available to my supieriors they don't want to know about broadcasts etc!

Last edited by l9nux on 09-23-02 at 08:15 PM

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You are correct in the fact that there will be 62 networks, because 2^6 - 2 = 62. The same goes for the number of usable hosts per subnet, which is 2^10 - 2 = 1022. The 1022 does not include the network ID and the brodcast addresss, if you did that then there would be 1024. So what you need to tell your superiors is that there are a maximum of 1022 hosts per subnet, not 1016. Hopefully I cleared it up. If not feel free to say so.

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quote:

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Originally posted by l9nux
This range only has 1016 hosts and 62 networks right?

Please someone correct me if I'm wrong, but 1022 hosts includes 0 and 255 in the last octet but this is reserved for network id and broadcast isn't it? Or does the calculate above have to include this?

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You are wrong...
Just kidding, you are confused about the 0 and the 255, every 0 does not have to be a network, nor does every 255 has to be a broadcast... if you have a class C, 192.168.0.0/24, there are 256 network (in M$, network does not minus 2, only hosts are minus 2... this drives me nuts for some time)... and 254 hosts, and every .0 is a network and every .255 is broadcast. However, if you have 10.0.0.0/16, you also have 256 network, but you have 2^16-2 hosts, the first network would be 10.0.0.0 and the broadcast would be 10.0.255.255, and 2nd network will be 10.1.0.0 and its broadcast would be 10.1.255.255. The 10.0.0.255 is a normal host and not a broadcast. Therefore it is still only 2^bits -2 hosts.

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Isn't there some standard or something that allows you to use the subnet address with all 1s and all 0s for hosts? I thought I remembered hearing something about that. I'm guessing thats the reason why MS doesn't subtract 2 for the available number of networks.

Also its a safe bet to assume that everytime you see all .255s in the host ID of an IP address its referring to a broadcast. However not all broadcast addresses are like that. For example, say you have 192.168.1.0/27. Lets pick, for example, subnet 192.168.1.32 and 192.168.1.64. The host addresses would be 192.168.1.33-192.168.1.62, and the broadcast will be 192.168.1.63. So don't assume just because there is no .255 that it isn't a broadcast. Just a little more information from what Twister was saying.

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