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My bare knuckles networking understanding led me to believe that if I set an IP address of, for example, with netmask on a machine, it should see all hosts in the subnet (and many others on the whole subnet)

I just tried it, but the machine with didn't see at all addresses.

Two questions:

  1. How to set up such a network simply?
  2. What's the mistake in my understanding?
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possible duplicate of How does IPv4 Subnetting Work? – Tom O'Connor Apr 3 '13 at 10:47
@TomO'Connor I'm not sure this practical question is answered directly in the canonical answer about IPv4 subnets. – Vinko Vrsalovic Apr 3 '13 at 12:38

3 Answers 3

up vote 9 down vote accepted

I just tried it, but the machine with didn't see at all addresses can send packets to, but when tries to respond it thinks the opther host is outside it's network hence will try to send the packets back through a router (or fail).

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How to set up such a network simply?

Just as you did, you got it right in principal, there must just be an issue with the implementation - certainly there's nothing wrong with the idea of doing what you did.

What's the mistake in my understanding?

Nothing, you just need to ensure that this use of a /16 is implemented everywhere appropriate, on every machine in that range, in every router etc.

Use of non-/24 netmasks is extremely common these days and works great, but you do need to ensure they're properly, and thoroughly, implemented.

Otherwise good work ;)

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Obviously, if the other machine is a /24, it can only see machines in that scope. The subnet masks need to match if they are going to be visible to one another.

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