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Network IP/Nodes Question

Given the class A IP network address 10.x.x., how many sub-networks of how many nodes can be created by applying a sub-net mask of 255.255.0.0?
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ashp87
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ashp87
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Scott1201Commented:
Subnets: 256, if you allow the use of 10.0.X.X and 10.255.X.X

Hosts: 65,534.  256 * 256 is 65,536 minus the host and broadcast addresses.
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ashp87Author Commented:
Could you explain how you get the number of subnets more?? and also how to get the host and broadcast addresses
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pjcooleCommented:
When applying a mask of 255.255.0.0 to a Class A address You are usign 8 bits for the network portion, 8 bits for the subnet and 16 bits for the host portion.

You will be able to have:

256 Subnets
65534 hosts on each subnet.
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Scott1201Commented:
Sure - the choice of subnet mask determines the number of subnets.  In this case, by choosing a subnet mask of 255.255.0.0, you're "borrowing" eight bits for subnets.  So 10.1.X.X will be on a different subnet than 10.2.X.X, and so forth.  Counting up from 10.0.X.X through 10.255.X.X gives 256 subnets.  (It might make more sense if you write out the binary math a bit.)  

The broadcast address for each subnet will be a combination of the network ID followed by all 1's - so, for the 10.1.X.X subnet with a 255.255.0.0 mask, the broadcast address will be 10.1.255.255.  The network address is the network ID followed by all zeroes, or 10.1.0.0.  Neither of these addresses can be used for a host, that's why I subtracted 2 from the (256 * 256) count.  

Here's a fairly long guide from Cisco that might help: http://www.cisco.com/en/US/tech/tk365/technologies_tech_note09186a00800a67f5.shtml
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