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I have overlapping also, but, my config is different. Vlan 1 is 192.168.0.36/255.255.0.0 and Vlan 2 is 192.168.11.15/255.255.0.0.

Since the third octet is different, how is overlapping possible?

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    Apr 1, 2018 at 21:18

2 Answers 2

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Your subnet mask is 255.255.0.0 (also written as /16). That means the first 16 bits of the IP address define the network, and the last 16 bits are the host address. With that mask, there are 65534 possible hosts.

In your case, the first 16 bits are the same. That means both IPs are in the same subnet. That's why your switch is complaining.

Remember that there is nothing special about octets. IP addresses are just 32-bit binary numbers. We write them using dotted decimal just to make it easier to read.

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Octets have nothing to do with it. The dotted-decimal notation is simply to make it easier for humans to read IPv4 addresses, which are really 32-bit numbers. A mask tells you which part of the address is the network, and which part is the host. The excellent answer to this question will explain how to subnet.

For your particular case:

192.168.0.36 is 11000000101010000000000000100100

192.168.11.15 is 11000000101010000000101100001110

The mask 255.255.0.0 is a 16- bit mask 11111111111111110000000000000000

If you mask both those addresses, you get the same network:

11000000101010000000000000100100
11111111111111110000000000000000
================================   AND
11000000101010000000000000000000

11000000101010000000101100001110
11111111111111110000000000000000
================================   AND
11000000101010000000000000000000

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