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what does the TCP/IP submask perform

Posted on 2000-05-11
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Last Modified: 2013-11-29
I'm building a small ofice network without a server, as they have a proxy server to access Internet we are using TCP/IP so I got interested on the use of the submask.

Can I section the network by changing the submask number?
Would I lose the printer atached to an external server?
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Question by:xema
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by:deltree
ID: 2802668
The subnet mask limits the number of IP addresses available on a collision domain.
English version: It limits how many systems you can have 'in one building'. In one building is kinda iffy, since you can have more than one subnet in the building.
At work, we have a class B subnet that is mostly in 5 buildings in 3 states. In my building, we subnetted to class C for the most part. The only real difference is that I have to go through a router to get to someone 2 floors above me. It gets kinda complicated at that site.
If you use 10.10.10.0 network with 255.255.255.192 subnet mask, the usable addresses are 10.10.10.1 to 10.10.10.62 (classful routing)
Same network with 255.255.255.0 subnet mask can use 10.10.10.1 to 10.10.10.254 (classful routing again)
Many other subnet masks, with various results. Download a subnet calculator to see what they do, saves doing all the math in your head.
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by:deltree
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Don't know about the printer, but if it's on the same subnet, nothing should change. You would have to route to it, if it's on another subnet.
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by:xema
ID: 2802689
So if I understood it right, if you change the sub net mask you'll need a router to conect both subnets.


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by:Ramspede
ID: 2802736
The answer is Yes - you can subnet.
I don't have enough information about the printer on the external server, but maybe this will answer what you really wanted to ask.

Since you generally want all devices to communicate, you want lots of addresses that are on the same subnet.  Subnetting actually reduces the number of stations you can have on a subnet, but you can have more subnets overall.  You must provide a router to transfer data from one subnet to another.

So for your case, subnetting gains you no benefits, unless you have so much traffic that you wish to segment your network for performance, which I doubt.

Because you have a proxy server, you will likely be using addresses that are shielded from the internet - Internal Addresses.  

There are certain address ranges that have been devoted to this purpose - for example the Class A address range of 10.0.0.0 (and a mask of 255.0.0.0) which provides for a single subnet with 16777214 hosts.  Using that info, your only subnet is 10.0.0.0, and the stations would have addresses like 10.0.0.1, 10.0.0.2, 10.0.0.3, and so on.

As an example, the same internal class A address can also be split into 254 subnets, each supporting 65534 hosts, which may more practical.  

In that case, you would use a mask of 255.255.0.0 and your subnets would be like 10.1.0.0, 10.2.0.0, 10.3.0.0 and so on.  

Your stations on subnet 10.1.0.0 would use adresses like 10.2.0.1, 10.1.0.2, 10.1.0.3, and so on.

The next subnet, 10.2.0.0, would use addresses like 10.2.0.1, 10.2.0.2, 10.2.0.3, and so on.  Of course you would need a router between the 10.1.00 subnet and the 10.2.0.0 subnet.

Notice I said subnet, not segment.  Although a single cable segment (a piece of wire) can support multiple subnets, it's the wrong way to go, and you still need a router between the subnets.

Hope this helps!
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greebo earned 100 total points
ID: 2803990
It may be a pain, but the only way to understand network masking properly is to convert all octets to binary.

An IP address is made up of 4 sets of 8 bit numbers, so an IP address of 192.168.10.1 translates to binary as 11000000.10101000.00001010.00000001
If we apply a subnet mask of 255.255.255.0, this translates to binary as 11111111.11111111.11111111.00000000 and is a 24 bit subnet mask.
This means that the first 24 bits of the IP address (indicated by 1's in the subnet mask) are known as the network address, and the last 8 bits (indicated by 0's in the subnet mask) are the host address.
This would mean that you could have 254 clients on that subnet, from 192.168.10.1 to 192.168.10.254 (you cannot use 0 and 255 as 0 is the network address and 255 is the broadcast address).
If you have less client machines to run on a particular subnet then you may choose to use a different subnet like a 28 bit one 11111111.11111111.11111111.11110000 which is 255.255.255.240 which will leave you 14 host addresses 192.168.10.241 to 192.168.10.254 (you cannot use 240 or 255).
And I'm sure you can see now that if you had a large number of clients on one subnet you may choose to use a smaller network mask like a 16 bit one 11111111.11111111.00000000.00000000 which is 255.255.0.0 this will give you 65534 host addresses 192.168.0.1 to 192.168.255.254

The advantage of subnetting is that it reduces traffic on the local subnet and can speed things up. In the example of having 65534 clients on the same subnet, the number of collisions and dropped packets will be very high, while a small network will run faster with less collisions.

The disadvantage is that you will need to route between subnets, requiring a router which can get complicated.

The choice is yours.

If you are currently using a 24 bit subnet mask you may want to subdivide that into, say, 4 subnets for different departments each having a 26 bit subnet mask 11111111.11111111.11111111.11000000 or 255.255.255.192 giving you 4 address ranges :
192.168.10.1   to 192.168.10.62
192.168.10.65  to 192.168.10.126
192.168.10.129 to 192.168.10.190
192.168.10.193 to 192.168.10.254

If you have trouble calculating decimal to binary and back then the calculator you get with windows has a scientific view which will convert for you (only work on 1 octet at a time though).

As far as the printer goes, it is still possible to use a printer on a different subnet as long as your routers are set up correctly.

I hope this has made things clearer
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by:deltree
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It all boils down to how many systems you plan on having on the network in the next, say 5 years. Hard to plan ahead that far, but you can guess how much it may grow - no need for perfection.
Safest way is to use subnet 255.255.255.0
so you have 254 usable addresses.
If the print server is in the same subnet (and should be), you don't need a router. My assumption is this is for a small office/home/student network.
A smaller subnet won't make it run faster, it just limits the number of systems you can put on that subnet.
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by:oldgreyguy
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