Subnetting massacre

Terminal Velocity

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How many subnets do I have with a subnet mask as follows 11111111.11111111.11111111.11000000

2 in the power of 26 - 2 ie 67,108,862
or
2 in the power of 2 - 2 ie 2 subnets?
 


I'm lazy. After converting your binary to 255.255.255.192 decimal, I entered the mask into this subnet converter. The result is 262,144 subnets with 64 hosts per subnet. Two hosts are reserved (network and broadcast) so only 62 hosts are usable.

[EDIT] With a little more digging, I found this short YouTube video that explains much better. Especially watch at the 6:21 mark where it talks about how to determine how many subnets are available. His example uses 16 subnet bits, but your example would be using 18 subnet bits (pulling 2 more from the host side). 2 ^ 18 = 262,144... showing the above calculator result to be accurate. NOTE: This only holds true if your IP address is a "Class A" network address... and you did not provide the IP address, so there is not really a definite answer to your question without it.

Continue watching the same video and next he will use your same netmask, but he applies it on a "Class C" network address. This is totally different! If you use a Class C address... you only get 4 subnets. Big difference! Here is a quick diagram from Oracle that shows the division between the different class networks.

The video goes on to show a Class B network too. It's well worth watching the whole thing, which I should have done sooner! Sorry, I am very rusty with this stuff. :oops:
 
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This is a great video, it didn't appear in my searches, Thank you. He subtract 2 only from the number of hosts not the number of networks, this is new to me
 

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