number of vlaid subnets

Answered Question
Mar 2nd, 2009

Hi every body!

Let say we have class C 192.192.192.0 network with subnet mask 255.255.255.192

The total number of subnets are:

192.192.192.0


192.192.192.64


192.192.192.128


192.192.192.192


According to cisco book , the valid subnnets are = total subnets-2


The subnet "192.192.192.0 " and " 192.192.192.192" are not considered valid subnets . My question is why?


Thanks a lot!

Correct Answer by Richard Burts about 7 years 12 months ago

Sarah


To be bit less subtle that Harold, the book you reference is presenting a very old (and out moded) view of the principles of subnetting. In modern practice neither of the subnets is not permitted. (you might however, be careful on certification tests, some of which may still reflect the old practice).


HTH


Rick

Correct Answer by Harold Ritter about 7 years 12 months ago

Sarah,


Here's a paper that explains why usage of the subnet zero and all one's subnet was discouraged by RFC950.


Subnet zero and all one's are now widely used.


http://www.cisco.com/en/US/tech/tk648/tk361/technologies_tech_note09186a0080093f18.shtml


Regards

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Leo Laohoo Mon, 03/02/2009 - 19:24

IP Addresses 192.192.192.0 & 192.192.192.192 are not valid IP ADDRESSES because they are subnet addresses.


I think this is one of those trick questions again.

Correct Answer
Richard Burts Mon, 03/02/2009 - 20:04

Sarah


To be bit less subtle that Harold, the book you reference is presenting a very old (and out moded) view of the principles of subnetting. In modern practice neither of the subnets is not permitted. (you might however, be careful on certification tests, some of which may still reflect the old practice).


HTH


Rick

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