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In Windows, I can configure a network adapter like this:

Ip Address: 192.0.0.1
Subnet Mask: 224.0.0.0

but not like this:

Ip Address: 192.0.0.1
Subnet Mask: 192.0.0.0

Why? Why can't the subnetwork be the same as the subnetwork mask?

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marked as duplicate by Jenny D, Chris S Apr 17 '13 at 14:31

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1  
You should not configure your machine to use that 128.0.0.1 IP. That's a public internet address, and a quick lookup indicates it's assigned somewhere in Romania. I don't think it belongs to you. You need to use an IP from one of the reserved private ranges: 10.0.0.0/8, 172.16.0.0/12, or 192.168.0.0/16 –  Joel Coel Apr 17 '13 at 14:23
    
lol .. I'm not using this IP on my network. I'm developing an app that has to validate the network entered by the user, before configuring the windows adapter, and I'm trying to see what IP address windows accepts, so I can inform the user if windows is going to accept that configuration. –  Chris Apr 17 '13 at 14:28
    
@Hauke Laging 128.0.0.1 is a valid IP for a network adapter on windows –  Chris Apr 17 '13 at 14:30
1  
Yeah, realised that as I posted it, hence the deletion, I'm now trying to find out what the OS may dislike about that IP/netmask combination –  USD Matt Apr 17 '13 at 15:05
2  
I suspect it's something to do with the fact that everything past 223.x.x.x is either multicast or reserved. Windows will not allow you to put anything above 223 in the first octet of the IP field. The 224.0.0.0 subnet above covers 192.0.0.0-223.255.255.255, however using a 192.0.0.0 netmask goes into the multicast/reserved area. –  USD Matt Apr 17 '13 at 15:13

1 Answer 1

up vote 0 down vote accepted
128.0.0.0/1 = Block of 128  = 1000 0000.0000 0000.0000 0000.0000 0000

1st Subnet - 0.0.0.1 --> 127.255.255.254
2nd Subnet - 128.0.0.1 --> 255.255.255.254

So, your 1st subnet encompasses the loopback address (127.0.0.1) and your second subnet (the one you're trying to use encompasses the multicast and reserved ranges. My guess is Windows isn't going to allow you to do this because of potential problems. I'm not sure why it's even letting you use a /2. Regardless of the technical aspects... what the heck are you trying to accomplish by using a /1!!

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With /1 you have a huge lot of hosts... :-) –  Hauke Laging Apr 17 '13 at 14:22
    
I'm building an app that validates user network configuration before it tries to apply it. So I'm considering valid whatever windows accepts. –  Chris Apr 17 '13 at 15:02

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