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SubjectRe: all zeroes/all ones used in host IP's...
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@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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> > Please read the FAQ at http://www.tux.org/lkml/
>
>
>
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--
Michael H. Warfield | (770) 985-6132 | mhw@WittsEnd.com
(The Mad Wizard) | (770) 331-2437 | http://www.wittsend.com/mhw/
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PGP Key: 0xDF1DD471 | possible worlds. A pessimist is sure of it!

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