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Re: netmask question

From Tim Woodall <debianuser@woodall.me.uk>
Newsgroups linux.debian.user
Subject Re: netmask question
Date 2023-05-23 08:30 +0200
Message-ID <GytGV-aPAf-1@gated-at.bofh.it> (permalink)
References (5 earlier) <GynrP-aLuC-9@gated-at.bofh.it> <Gyo4x-aLWm-11@gated-at.bofh.it> <Gyo4x-aLWm-13@gated-at.bofh.it> <GyonT-aM2U-5@gated-at.bofh.it> <Gyoxz-aM5T-1@gated-at.bofh.it>
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On Tue, 23 May 2023, Tom Reed wrote:

>
>
>> On Tue, May 23, 2023 at 08:24:10AM +0800, Tom Reed wrote:
>>> Sorry for my newbie question too.
>>>
>>> If I know the network addr:  192.168.1.0
>>> And know the broadcast addr: 192.168.1.255
>>> Then I should have the possibility to cal the netmask addr:
>>> 255.255.255.0
>>>
>>> Isn't it?
>>
>> Not necessarily.  PROBABLY yes, but you can't be certain.
>>
>> The netmask in this example could be either /23 or /24.
>>
>> Why are you asking these questions?  What's your ACTUAL issue?
>>
>
> IIRC, last year my ISP gives me 8 IPv4, they said the first is network
> addr, the last is broadcast addr, then I have to calculate the netmask by
> myself.
>
> regards.
>

It's almost certain that you could actually use all 8 addresses assuming
that the reason for having them is to allow routing to/from the
internet and you were connecting via ppp.

I had a static /30 but could use all four addresses for hosting. Once it
reached my ISP (via a /32 ppp address :-) ) it was part of a larger
block.

What I did was pretend I had a /28 - which meant if any of those
'hijacked' addresses around mine tried to connect they'd get no response. If you
don't want to risk that then you can NAT the addresses into the middle
of a rfc1918 range.

That won't work if one of the addresses is the isp's router.

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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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