all zeroes/all ones used in host IP's...

[Michael H. Warfield]

On Fri, Jan 28, 2000 at 03:42:16PM -0700, Michael Loftis wrote:
> 255 is forbidden because it's the broadcast address.  As to 0 being 
> forbidden, uhm..  I think that's only as the last octet in a host 
> sequence.  Why?  My nameserver is at 209.161.0.2 and 209.161.0.3 

	No....  255 is illegal only for a /24.  255.255 is illegal for
a /16.  0.255 is perfectly legal for a /20 or bigger.  0.127 is illegal
for a /25.

> Whatever 1123 says .0 seems to have been accepted in a network mask 
> sense, but I would doubt that as a last octet of a host it would not 
> work.

	It will work just fine if the network mask is bigger than a /24.
130.205.1.0 is perfectly fine if it's a /16 but illegal if it's masked down
to a /24.

	Stop thinking in octets.  This stuff is binary.

> IE 
> 209.161.0.0/32 (Host) is illegal
> 209.161.0.1/32 (Host) is legal
> 209.161.0.0/24 (Network) is legal

> --
> Michael Loftis
> ICQ: 15648280  AIM: DyJailBait
> Funny quip of the moment just happens to be....
> Linux is like a tent:
> no gates, no windows, and an Apache inside!
> 
> 
> -----Original Message-----
> From: "Mike A. Harris" <mharris en meteng.on.ca>
> Date:   Fri, 28 Jan 2000 12:44:51 -0500 (EST)
> Subject: all zeroes/all ones used in host IP's...
> 
> > On another mailing list I'm on there is a small discussion about
> > using "0's" in IP addresses.  Nobody could categorically say
> > wether or not they are allowed or not including myself, so I
> > hunted down RFC 1123, and found the relevant section.
> > 
> > Here it is:
> > 
> >             IP addresses are not permitted to have the value 0 or -1
> > for
> >             any of the <Host-number>, <Network-number>, or <Subnet-
> >             number> fields (except in the special cases listed
> > above).
> >             This implies that each of these fields will be at least
> > two
> >             bits long.
> > 
> > Now I interpreted that as meaning that none of the octets in an
> > IP address could be 0 or "-1" in either the network/subnet or
> > host portions of a valid host IP.  The definition of "-1" is "all
> > ones" in the host or network/subnet portion.
> > 
> > I interpret the above as meaning that it is not legal to have a
> > network like this:
> > 
> > 192.168.0.0/24   or 23.0.0.0/24
> > 
> > with hosts 192.168.0.1 through 192.168.0.254 or with hosts
> > 23.0.0.1 through 23.0.0.254.
> > 
> > The first zero makes it illegal no?  Could someone in the know
> > please clarify this as it has been bugging me for some time and
> > nobody else seems to be able to say with 100% certainty what the
> > proper rule is.  Also, would a network like:
> > 
> > 142.255.255.0/24 be illegal?
> > 
> > Someone has suggested that my interpretation is wrong, and if
> > that is indeed so, I'd like to know the proper interpretation and
> > share it with everyone.
> > 
> > I looked through some of the kernel source and couldn't find any
> > special handling of such addresses.
> > 
> > Thanks very much in advance.
> > Take care!
> > TTYL
> > 
> > --
> > Mike A. Harris                                     Linux advocate    
> > Computer Consultant                                  GNU advocate  
> > Capslock Consulting                          Open Source advocate
> > 
> > Join the FreeMWare project - the goal to produce a FREE program in
> > which you can run Windows 95/98/NT, and other operating systems.
> > 
> >                     http://www.freemware.org
> > 
> > 
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> 
> 
> 
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-- 
 Michael H. Warfield    |  (770) 985-6132   |  mhw en WittsEnd.com
  (The Mad Wizard)      |  (770) 331-2437   |  http://www.wittsend.com/mhw/
  NIC whois:  MHW9      |  An optimist believes we live in the best of all
 PGP Key: 0xDF1DD471    |  possible worlds.  A pessimist is sure of it!


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