This week I've added the following nifty subnet calculator to the Cisco Tools web page:
The NetQoS Subnet Calculator offers a view of every bit in the IP address to help network engineers understand how IP subnetting works, according to network performance management vendor NetQos, and it also has a feature allowing entry of a real address mask of your own to test if it is on the same or remote network.
"Until one takes some real addresses and experiments with how the mask affects the address bits, it is challenging to understand," said Bill Alderson - NetQoS Technology Consulting Officer. "Most people don’t know or use binary math. It is simple, yet non-intuitive. I developed the Subnet Calculator to make learning more demonstrative and fun."
Alderson continued, "Dotted decimal was originally created to try to make network addresses appear in decimal form that more people could understand, with each eight bits being converted to decimal.
"Below are two addresses broken out from dotted decimal to binary and then redisplayed with dots separating octet boundaries:"
1.1.1.1 is 00000001000000010000000100000001 or 00000001.00000001.00000001.00000001
2.2.2.2 is 00000010000000100000001000000010 or 00000010.00000010.00000010.00000010
Alderson expounded, "Applying a Mask of 11111111.11111111.11111111.00000000 adds to the complexity and introduces binary addition required to understand the result. The result in the cases above would be: nnnnnnnn.ssssssss.ssssssss.hhhhhhhh where:"
n= network
s=subnet
h=host
Alderson added, "In the subnet calculator the binary and the n, s, and h are clearly defined for easy understanding in different scenarios. For example, start by entering your address and mask in the calculator. Then add another target destination address you might want to send a packet to and calculate the result. The calculator will tell you if it is on your segment (switch) or if it must be sent to the router for forwarding beyond your segment."
Alderson concluded, "Once the basics are understood, it will help you understand the more complex. For instance, let’s say you want to know all the dotted decimal addresses that end up falling under a non-octet boundary subnet mask. Just enter the mask and address, hit calculate and a list of networks will be shown."
Screenshot of the NetQoS Subnet Calculator:
View more Cisco Tools.
How useful do you find this subnet calculator?
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Great...well maybe not
Generally I would think that this knowledge would be foundational for anyone that touches a network. So it is great for us lazy folks that understand address schemes and sub-netting, but just don't want to do the math. However, probably very dangerous for someone that doesn't understand the theory and ramifications of addressing, and just starts popping in ip addresses and re-configuring their network.
I Hear Ya
I hear ya, often use my computer's Microsoft Calculator for calculations I know "first graders" could solve.
Sincerely,
Brad Reese
BradReese.Com Cisco Refurbished
Sadly enough, most students
Sadly enough, most students in high school and university don't comprehend how binary numbers work, or how to do simple arithmetic in the binary system.
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