[NTLUG:Discuss] IP super/sub-netting maddness

[joseph beasley]

Yes it is, but 255.255.255.200 is not.  128,192,224,240,248,252 are
valid. 

--- Wayne Walker <wwalker at bybent.com> wrote:

> On Wed, Sep 20, 2006 at 11:04:15AM -0700, joseph beasley wrote:
> > Don't mean to be pushy....   but here goes...
> > 
> > Odd and invalid.  Here are a few links.
> > 
> > http://www.freesoft.org/CIE/Course/Subnet/6.htm
> says 255.255.255.128 is valid
> 
> >
>
http://www.pku.edu.cn/academic/research/computer-center/tc/html/TC0306.html
> says 255.255.255.128 is never valid.
> says you can't have 25 bit or 32 bit networks.  You can.  32
> bit networks are often used by ip aliases (in BSD I believe) and by
> VPN
> and Point to Point connections.  I have two racks at ISPs where I'm
> allocated a 25 bit subnet.
> 
> Poor choice for verification of anything.
> 
> Neither of them is correct across the board.  Kenneth is right.  Odd,
> recommended for Non-use, yes.  Invalid, NO.  Usable in most OS's IP
> stacks, NO.  Most IP stacks will consider such a subnet mask as
> invalid,
> but that is because that is almost never how a network is defined.
> 
> > http://www.exabyte.net/lambert/subnet/subnet_masking_summary.htm
> "Are any subnet masking limitations due to Microsoft's O/S's?  No,
> it's
> inherent in the architecture of DNS."
> 
> subnet masks and DNS have NOTHING in common.  again a site that
> someone
> threw together to be helpful, but he doesn't know what he's talking
> about.
> 
> >
>
http://freespace.virgin.net/glynn.etherington/subnet_masks_and_ip_for_beginners.htm
> "Beginning IP for New Users"
> 
> true.  far from defining the limits of what can and can't be used in
> a
> netmask.
> 
> NOW, if you can find something supporting either side of the
> discussion
> HERE then it's meaningful:
> 
> http://www.ietf.org/rfc/rfc0791.txt
> 
> http://tools.ietf.org/html/rfc950 shows a mask of 255.255.255.88
> 
> Wayne
> 
> > --- Kenneth Loafman <kenneth at loafman.com> wrote:
> > 
> > > Just a nit, but it is odd, not invalid...
> > > 
> > > 255.255.255.200 == FFFFFFC8 or 1..11001000
> > > 
> > > which means you have 5 bits to play with, just not an adjacent 5
> > > bits,
> > > thus there are 32 possible IPs in the subnet, C8-CF, D8-DF,
> E8-EF,
> > > and
> > > F8-FF.  This fits the def of a submask, but would not be
> compatible
> > > with
> > > CIDR notation except as 4 distinct small subnets of 8 each.
> > > 
> > > I've seen this used for device subnets where redundant devices
> are
> > > subnetted.  Not spiffy, but valid.
> > > 
> > > ...Ken
> 
> Wayne Walker
> 
> www.unwiredbuyer.com - when you just can't be by the computer
> 
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> 
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> 


Joe Beasley
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