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Groups > linux.debian.user > #258622

Re: netmask question

From Dan Ritter <dsr@randomstring.org>
Newsgroups linux.debian.user
Subject Re: netmask question
Date 2023-05-23 02:30 +0200
Message-ID <Gyo4x-aLWm-11@gated-at.bofh.it> (permalink)
References (1 earlier) <Gy5Oh-aAZD-1@gated-at.bofh.it> <Gy8j7-aCxQ-1@gated-at.bofh.it> <Gygql-aHpq-1@gated-at.bofh.it> <Gyj4R-aJ3P-7@gated-at.bofh.it> <GynrP-aLuC-9@gated-at.bofh.it>
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Tom Reed wrote: 
> 
> >
> > That's right, but then they go 0 .. 2^8 - 1. 2^8 is still 256, Tim does
> > have a point there :-)
> >
> 
> For a given ipv4, if I know net addr and broadcast addr, how will I
> calculate the netmask?


You can't.

You can assume that the broadcast address is the last usable
address in the subnet, but it's not unique.

The router sets the addressable area. Without knowledge of that,
you can't tell the difference between 10.3.255.243 being in a
/16, a /24, a /26...

In most networks, the router will tell you the information on
request via DHCP. In most IPv6 networks, the router will either
have DHCP or SLAAC (router solicitation/router advertisement_ available.

But most is not all.

-dsr-

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Thread

netmask question coreyh@free.fr - 2023-05-22 04:50 +0200
  Re: netmask question Timothy M Butterworth <timothy.m.butterworth@gmail.com> - 2023-05-22 05:00 +0200
    Re: netmask question Tim Woodall <debianuser@woodall.me.uk> - 2023-05-22 09:50 +0200
      Re: netmask question <tomas@tuxteam.de> - 2023-05-22 10:10 +0200
      Re: netmask question coreyh@free.fr - 2023-05-22 11:00 +0200
        Re: netmask question Tim Woodall <debianuser@woodall.me.uk> - 2023-05-22 11:10 +0200
          Re: netmask question coreyh@free.fr - 2023-05-22 12:20 +0200
            Re: netmask question Timothy M Butterworth <timothy.m.butterworth@gmail.com> - 2023-05-22 12:30 +0200
            Re: netmask question Dan Ritter <dsr@randomstring.org> - 2023-05-22 13:10 +0200
      Re: netmask question Timothy M Butterworth <timothy.m.butterworth@gmail.com> - 2023-05-22 12:20 +0200
        Re: netmask question Tim Woodall <debianuser@woodall.me.uk> - 2023-05-22 12:30 +0200
        Re: netmask question <tomas@tuxteam.de> - 2023-05-22 13:10 +0200
  Re: netmask question Charles Curley <charlescurley@charlescurley.com> - 2023-05-22 05:10 +0200
  Re: netmask question <tomas@tuxteam.de> - 2023-05-22 07:00 +0200
    Re: netmask question Tim Woodall <debianuser@woodall.me.uk> - 2023-05-22 09:40 +0200
      Re: netmask question <tomas@tuxteam.de> - 2023-05-22 10:00 +0200
      Re: netmask question Timothy M Butterworth <timothy.m.butterworth@gmail.com> - 2023-05-22 12:20 +0200
      Re: netmask question gene heskett <gheskett@shentel.net> - 2023-05-22 18:20 +0200
        Re: netmask question <tomas@tuxteam.de> - 2023-05-22 21:10 +0200
          Re: netmask question gene heskett <gheskett@shentel.net> - 2023-05-23 01:50 +0200
            Re: netmask question Dan Purgert <dan@djph.net> - 2023-05-23 03:20 +0200
              Re: netmask question debian-user@howorth.org.uk - 2023-05-23 12:50 +0200
                Re: netmask question Dan Purgert <dan@djph.net> - 2023-05-23 14:20 +0200
            Re: netmask question tomas@tuxteam.de - 2023-05-23 07:00 +0200
          Re: netmask question "Tom Reed" <tom@dkinbox.com> - 2023-05-23 01:50 +0200
            Re: netmask question Greg Wooledge <greg@wooledge.org> - 2023-05-23 02:10 +0200
              Re: netmask question <tomas@tuxteam.de> - 2023-05-23 06:40 +0200
            Re: netmask question Dan Ritter <dsr@randomstring.org> - 2023-05-23 02:30 +0200
              Re: netmask question "Tom Reed" <tom@dkinbox.com> - 2023-05-23 02:30 +0200
                Re: netmask question Dan Ritter <dsr@randomstring.org> - 2023-05-23 02:50 +0200
                Re: netmask question <tomas@tuxteam.de> - 2023-05-23 06:50 +0200
                Re: netmask question Andy Smith <andy@strugglers.net> - 2023-05-27 03:10 +0200
                Re: netmask question Greg Wooledge <greg@wooledge.org> - 2023-05-27 03:10 +0200
                Re: netmask question Andy Smith <andy@strugglers.net> - 2023-05-27 03:20 +0200
                Re: netmask question Greg Wooledge <greg@wooledge.org> - 2023-05-23 02:50 +0200
                Re: netmask question "Tom Reed" <tom@dkinbox.com> - 2023-05-23 03:00 +0200
                Re: netmask question Dan Ritter <dsr@randomstring.org> - 2023-05-23 03:20 +0200
                Re: netmask question Tim Woodall <debianuser@woodall.me.uk> - 2023-05-23 08:30 +0200
                Re: netmask question Timothy M Butterworth <timothy.m.butterworth@gmail.com> - 2023-05-23 02:50 +0200

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