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I was setting up ip addresses between two devices and I noticed something odd. I feel like I am missing an important fundamental here:

Context:
Device A: 10.30.0.1/12
Device B: 10.2.0.2/12

if I set up the IP like this, then A and B cannot ping each other

However, if I do
Device A: 10.30.0.1/12
Device B: 10.30.0.2/12
OR
Device A: 10.2.0.1/12
Device B: 10.2.0.2/12

Then A and B can ping each other just fine. My understanding is that with a /12 netmask, the wildcard mask is 0.15.255.255, therefore the 2nd octet can be any value between 0 through 127.

Are there two groups of valid IPs being created here or is it a whitelist?

DSdavidDS
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1 Answers1

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Device A: 10.30.0.1/12

Device B: 10.2.0.2/12

A and B are in different subnetwork.

For A

Network: 10.16.0.0

Host Min: 10.16.0.1

Host Max: 10.31.255.254

For B

Network: 10.0.0.0

Host Min: 10.0.0.1

Host Max: 10.15.255.254

As you can se both are different networks.

I left this reference IP Addressing and Subnetting for New Users, this reference will help you identify the difference between Network Mask and Wildcard

  • A network mask helps you know which portion of the address identifies the network and which portion of the address identifies the node.

  • A wildcard mask is a mask of bits that indicates which parts of an IP address are available for examination.

Alejandro F.
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  • Thanks a lot! Sample Exercise 1 was fantastic in explaining how to determine if an IP is in the same subnet and was exactly what I was looking for. – DSdavidDS Jan 26 '22 at 18:58