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Re: question about net address

From David Wright <deblis@lionunicorn.co.uk>
Newsgroups linux.debian.user
Subject Re: question about net address
Date 2023-03-22 15:50 +0100
Message-ID <Gc7WN-ejnf-3@gated-at.bofh.it> (permalink)
References <GbTTP-eaO0-1@gated-at.bofh.it>
Organization linux.* mail to news gateway

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On Tue 21 Mar 2023 at 18:27:42 (-0400), Stefan Monnier wrote:
> > me second. 192.168.1.1/24 just makes me confused with 192.168.1.1/32
> > which is a real host address.
> 
> Interesting.
> I can't remember ever seeing 192.168.1.1/32 used.  In my my part of the
> world, it's only meaningful as a degenerate form: all the syntaxes I've
> seen which accept the IP/NN notation also accept just IP to mean IP/32,
> so writing IP/32 is just more verbose and half-confusing (makes you
> wonder why the guy bothered to add /32).

On Tue 21 Mar 2023 at 18:40:00 (-0500), David Wright wrote:
> 
> I assume the reason that host-ip-address/cidr-length is a permitted
> domain-spec for ipv4: is by analogy with host-domain/cidr-length for
> a:. So a:colo.example.com/28 could, if colo.example.com had an A
> record with 93.184.216.34, be written 93.184.216.34/28. If you had
> to write a strict network address, you'd have to figure out that it's
> 93.184.216.32/28. Easy in this case, but error-prone when you're
> obliged to convert, say, a looked-up x.y.z.185/28 to its network
> address of x.y.z.176/28.

Looking back at the OP's context, I think we're making a
false assumption that the /<cidr-length> notation is
specifying a network address. I don't think it is. If we
take the example of a typical /24 network, 192.168.1.0,
the fact that we set an ipv4: mechanism of, say,
192.168.1.176/28 doesn't mean that there's a network or
a subnet with that address/netmask.

Such a network will still have an address of 192.168.1.0,
and broadcast on 192.168.1.255, but the SPF notation
indicates that hosts 192.168.1.176 through 192.168.1.191
are awarded a pass, because only those addresses match
in the first 28 bits. The host 192.168.1.192, on the
same network, with the same network address, will fail
that particular test.

As you can see from my quote above, the eye is less
deceived by the notation a:colo.example.com/28 than
it is by ipv4:93.184.216.34/28 into thinking that
the latter is a network address.

Cheers,
David.

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Thread

question about net address coreyh@free.fr - 2023-03-18 12:30 +0100
  Re: question about net address Markus Schönhaber <debian-user@list-post.mks-mail.de> - 2023-03-18 13:40 +0100
  Re: question about net address Timothy M Butterworth <timothy.m.butterworth@gmail.com> - 2023-03-18 14:30 +0100
  Re: question about net address Kushal Kumaran <kushal@locationd.net> - 2023-03-18 23:20 +0100
    Re: question about net address coreyh@free.fr - 2023-03-19 00:40 +0100
      Re: question about net address David Christensen <dpchrist@holgerdanske.com> - 2023-03-19 11:10 +0100
        Re: question about net address coreyh@free.fr - 2023-03-19 11:30 +0100
          Re: question about net address Joe <joe@jretrading.com> - 2023-03-19 11:40 +0100
          Re: question about net address Jeremy Ardley <jeremy@ardley.org> - 2023-03-19 11:40 +0100
            Re: question about net address coreyh@free.fr - 2023-03-19 11:40 +0100
              Re: question about net address jeremy ardley <jeremy@ardley.org> - 2023-03-19 11:50 +0100
              Re: question about net address <tomas@tuxteam.de> - 2023-03-19 12:10 +0100
              Re: question about net address Greg Wooledge <greg@wooledge.org> - 2023-03-19 13:20 +0100
                Re: question about net address Curt <curty@free.fr> - 2023-03-19 18:20 +0100
                Re: question about net address David Wright <deblis@lionunicorn.co.uk> - 2023-03-19 19:50 +0100
              Re: question about net address Stefan Monnier <monnier@iro.umontreal.ca> - 2023-03-19 16:00 +0100
            Re: question about net address Yassine Chaouche <a.chaouche@algerian-radio.dz> - 2023-03-19 12:10 +0100
              Re: question about net address <tomas@tuxteam.de> - 2023-03-19 12:20 +0100
              Re: question about net address <tomas@tuxteam.de> - 2023-03-19 12:20 +0100
                Re: question about net address Nicolas George <george@nsup.org> - 2023-03-19 12:20 +0100
                Re: question about net address Jeremy Ardley <jeremy@ardley.org> - 2023-03-19 12:40 +0100
                Re: question about net address Nicolas George <george@nsup.org> - 2023-03-19 12:50 +0100
                Re: question about net address Greg Wooledge <greg@wooledge.org> - 2023-03-19 13:30 +0100
                Re: question about net address David Wright <deblis@lionunicorn.co.uk> - 2023-03-19 18:30 +0100
                Re: question about net address David Wright <deblis@lionunicorn.co.uk> - 2023-03-19 19:50 +0100
                Re: question about net address Jeremy Ardley <jeremy@ardley.org> - 2023-03-20 00:40 +0100
                Re: question about net address fh@dnsbed.com - 2023-03-20 01:30 +0100
                Re: question about net address Stefan Monnier <monnier@iro.umontreal.ca> - 2023-03-21 23:30 +0100
                Re: question about net address Jeremy Ardley <jeremy@ardley.org> - 2023-03-22 00:00 +0100
                Re: question about net address David Wright <deblis@lionunicorn.co.uk> - 2023-03-22 00:50 +0100
                Re: question about net address David Wright <deblis@lionunicorn.co.uk> - 2023-03-22 15:50 +0100
                Re: question about net address Jeremy Ardley <jeremy@ardley.org> - 2023-03-19 12:40 +0100
                Re: question about net address Yassine Chaouche <a.chaouche@algerian-radio.dz> - 2023-03-19 13:10 +0100
                Re: question about net address Curt <curty@free.fr> - 2023-03-19 18:10 +0100
              Re: question about net address fh@dnsbed.com - 2023-03-19 12:40 +0100
                Re: question about net address <tomas@tuxteam.de> - 2023-03-19 13:00 +0100
              Re: artifiial intelligence (was: Re: question about net address) Yassine Chaouche <a.chaouche@algerian-radio.dz> - 2023-03-20 10:30 +0100
          Re: question about net address David Christensen <dpchrist@holgerdanske.com> - 2023-03-19 23:20 +0100
  Re: question about net address Yassine Chaouche <a.chaouche@algerian-radio.dz> - 2023-03-19 10:00 +0100
    Re: question about net address Yassine Chaouche <a.chaouche@algerian-radio.dz> - 2023-03-19 10:10 +0100
    Re: question about net address debian-user@howorth.org.uk - 2023-03-19 17:50 +0100

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