Thank you Howard!
I have to ask then would the command "ip subnet-zero" be useless then?
or are there some environments where this command is usefull and others
where this command isn't. It would now seem as though this command would
only be nedded in a classfull environment?
As this message is sent I am reading the RFC's mentioned below and I may end
up answering my own question. Thanks again.
>>>Brian
>From: "Howard C. Berkowitz" <[EMAIL PROTECTED]>
>Reply-To: "Howard C. Berkowitz" <[EMAIL PROTECTED]>
>To: [EMAIL PROTECTED]
>Subject: Re: ip subnetting
>Date: Wed, 20 Dec 2000 09:08:10 -0500
>
> >Group,
> > In determining valid subnetworks it used to be true all were valid
>accept
> >the all 1's subnet and the all 0's subnet. In an environment where all
> >devices are compatible, I understand, that by using the configuration
> >command "ip subnet-zero" it enables the use of the all 0's subnet.
>
>The first thing to remember is that modern routers don't have a
>concept of network or subnet. Classful notation and subnetting is
>more a crutch for people than anything else. Routers understand
>prefixes, which are no more or less than contiguous numbers of bits
>starting on the left.
>
>The following all are perfectly legitimate /20's:
>
> 10.0.0.0/20
> 172.16.240.0/20
> 192.255.240.0/20
>
>The confusion around all ones and all zeroes subnet comes from a lack
>of prefix length information, and situations in which the router
>either had to infer the prefix from the high order "class" bits, or
>from local configuration information. Now, modern routing protocols
>transmit explicit lengths.
>
> >The
> >question I ask then, wouldn't that leave the all 1's subnet still an
>invalid
> >subnet even when using the previous mentioned command? or is there
>something
> >else that allows the all 1's subnetwork? I have been asked this question,
> >and I don't feel I am correct. The new formula noted in the CCNA book
>notes
> >the new equation for determining the amount of valid subnetworks is 2^#
>of
> >subnet bits, and I figured it would be 2^#of subnet bits - 1 (for the all
> >1's subnet). I don't pose this question without first a bit of research
>and
> >everything I have read indicates the "ip subnet-zero" command only
>enables
> >the use of the all 0's subnetwork. I however cannot find anything
>indicating
> >the use of the all 1's subnet is permitted. Any help is appreciated.
> >
> > >>>Brian
>
>My study question to you would be:
>
> why shouldn't all 0's and all 1's work?
>
>You may want to consult RFC 1812, and possibly 1879.
>
>
>--------------------
>
>No CCIE's were harmed or otherwise violated in the preparation of this
>message.
>
>_________________________________
>FAQ, list archives, and subscription info:
>http://www.groupstudy.com/list/cisco.html
>Report misconduct and Nondisclosure violations to [EMAIL PROTECTED]
_________________________________________________________________
Get your FREE download of MSN Explorer at http://explorer.msn.com
_________________________________
FAQ, list archives, and subscription info: http://www.groupstudy.com/list/cisco.html
Report misconduct and Nondisclosure violations to [EMAIL PROTECTED]
