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

[Wayne Walker]

On Wed, Sep 20, 2006 at 12:01:31PM -0700, joseph beasley wrote:
> Yes it is, but 255.255.255.200 is not.  128,192,224,240,248,252 are
> valid. 
apparently you didn't read the message.

"http://tools.ietf.org/html/rfc950 shows a mask of 255.255.255.88"

RFC 950, 951, 791, etc ARE the standard, not books, web pages and
tutorials written by others.

netmasks do NOT have to be contiguous high bits to be valid.

much of the equipment on the net can't handle non-contiguous netmasks,
but they ARE valid.

Wayne

> --- 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
> > 
> > wwalker at bybent.com                    Do you use Linux?!
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> > 
> > 
> > _______________________________________________
> > http://www.ntlug.org/mailman/listinfo/discuss
> > 
> 
> 
> Joe Beasley
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-- 

Wayne Walker

www.unwiredbuyer.com - when you just can't be by the computer

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