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I know that for addresses like e.g. with subnet mask, address is the network id and is the broadcast address and that valid hosts are from to

I understand why can't be used as a host address since everything sent on this is a broadcast, but I can't understand what is used for?

Is it just a reserved name of the network or is it used for something? Every thing I have read says you can't use it as a host address but not why? Is it just a convention?

Can someone please explain what it is used for and why it can't be a valid host address?

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duplicate of serverfault.com/questions/135267/… –  schöppi Oct 22 '10 at 10:38
See the answer with 10 upvotes there. Used for routing. –  Daniel Beck Oct 22 '10 at 10:40

1 Answer 1

up vote 2 down vote accepted

The network-address is for routing. Look at the binary representations for the ip address and the subnet mask. In the process of determining the route they are binary combined with AND. 1&0=0, 1&1=1, 0&0=0. The network part of the address remains unaffected, but the host part becomes all-zero. If you could use the .0 address for a host too, how would you different it from the net?

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I'm sorry, but that's the answer to another question. Not using subnet zero means if you subnet further to you shouldn't use addresses like and –  omnibrain Oct 24 '10 at 20:51

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