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Re: sharing a network connection from debian to non-debian

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On 1/19/2021 1:40 AM, Dan Hitt wrote:
> On Sun, Jan 17, 2021 at 11:41 PM David Christensen <
> dpchrist@holgerdanske.com> wrote:
>
>> On 2021-01-16 10:28, Dan Hitt wrote:
>>
> I probably never made my situation very clear, but i do now have a
> solution.  I'm posting it here for the benefit of anybody who has a similar
> problem, and finds this thread.
>
> First, the setup is that i have 3 hosts:
> A  --- runs debian 10
> B  --- runs linux mint 16.04
> C  --- old hardware which cannot connect to my internet-modem-router.
>
> Each of the 3 hosts has 2 network interfaces; there are thus 3 LANs (local
> area networks), and each host is on two of them, but not the third.
>
> The internet-modem-router is on the same LAN as A and B, because C cannot
> connect to it directly without destabilizing or sometimes just locking.
>
> I installed linux mint 16.04 on host B about 5 years ago.  Setting up the
> network was easy: all i had to do was select some option in some gui that
> said "shared" or "share network" or something like that.  That just worked,
> and host C could see the internet through host B.  It still does work, by
> the way.
>
> However, i would like to upgrade host B to use debian 10, just like host A.
>
> When i do that, host C will lose (or would have lost) connectivity to the
> internet because host A did not share its internet with host C.
>
> So, before upgrading host B to debian, it was necessary to get the network
> working properly on the LAN connecting A and C.  This, by the way, can be
> tested on C by using the -S argument with ping.  On host C, i can run "ping
> -S X.Y.Z.W google.com".  By setting X.Y.Z.W to the ip of the BC interface,
> it will go through B (mint), and it does that successfully.  But by setting
> X.Y.Z.W to the ip of the AC interface, it would have to go through A
> (debian), and until i fixed it (as described below), this would fail.
>
> So although i agree that in general, it makes sense to upgrade to a clean
> host before trying to get the network running, in this particular case it
> was imperative to first get the network running through a host, A, that was
> already in existence and has a couple of years' usage, before upgrading
> host B (currently mint, but hopefully soon to be debian).
>
> The one advantage of this setup though, is that it was possible to compare
> a working system (B, mint) with a non-working system (A, debian).
>
> I ran across this article by Nico Brailovsky,
> https://monoinfinito.wordpress.com/series/setting-up-a-linux-gatewayrouter-a-guide-for-non-network-admins/
> which explained how to do it.
>
> First, one must adjust /proc/sys/net/ipv4/ip_forwarding.
>
> On host B (mint), the working system, that file had an ascii '1' in it.  On
> host A (debian), the non-working system, that file had a '0' in it.  So i
> changed it on A, to be '1'.
>
> Then, the ip tables have to be updated.
>
> The commands Brailovsky gave need to be modified just slightly, due to
> differences in naming conventions of the interfaces.
>
> They are:
>   sudo iptables --table nat --append POSTROUTING --out-interface enp2s0 -j
> MASQUERADE
> and then
> sudo iptables --append FORWARD --in-interface XXXXXXXXX -j ACCEPT
>

Note that Debian is moving from Iptables to Nftables, the effect of the
above cmds will be lost when rebooting the host.



> Here, enp2s0 is the standard name for the motherboard ethernet port, and
> XXXXXX is to be replaced by the name of the second interface.  In my case,
> it is etherhet-over-usb, so is some long name that would be different for
> every host.
>
> And that's it.  I didn't even have to restart the networking service ---
> although i did restart it after editing /proc/sys/net/ipv4/ip_forwarding,
> just to see if changing that one file would be enough to get things
> working.  (Just for reference, restarting the networking is done by 'sudo
> /etc/init.d/networking restart' . )
>

On Debian you would probably want to use 'systemctl restart networking'
instead of calling the script directly.
Restarting the networking service is not required when you
enable/disable ipforwarding.

Using a frontend to IP/Nftables might be worth considering.

--
John Doe

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Thread

sharing a network connection from debian to non-debian Dan Hitt <dan.hitt@gmail.com> - 2021-01-16 06:10 +0100
  Re: sharing a network connection from debian to non-debian john doe <johndoe65534@mail.com> - 2021-01-16 07:30 +0100
    Re: sharing a network connection from debian to non-debian Doug McGarrett <dmcgarrett@optonline.net> - 2021-01-16 07:50 +0100
  Re: sharing a network connection from debian to non-debian Andrei POPESCU <andreimpopescu@gmail.com> - 2021-01-16 09:00 +0100
    Re: sharing a network connection from debian to non-debian Dan Hitt <dan.hitt@gmail.com> - 2021-01-16 19:30 +0100
      Re: sharing a network connection from debian to non-debian rhkramer@gmail.com - 2021-01-16 20:50 +0100
      Re: sharing a network connection from debian to non-debian Andrei POPESCU <andreimpopescu@gmail.com> - 2021-01-17 08:30 +0100
        Re: sharing a network connection from debian to non-debian john doe <johndoe65534@mail.com> - 2021-01-17 10:30 +0100
        Re: sharing a network connection from debian to non-debian Celejar <celejar@gmail.com> - 2021-01-17 16:00 +0100
      Re: sharing a network connection from debian to non-debian David Christensen <dpchrist@holgerdanske.com> - 2021-01-18 08:50 +0100
        Re: sharing a network connection from debian to non-debian Dan Hitt <dan.hitt@gmail.com> - 2021-01-19 01:50 +0100
          Re: sharing a network connection from debian to non-debian john doe <johndoe65534@mail.com> - 2021-01-19 07:10 +0100
          Re: sharing a network connection from debian to non-debian David Christensen <dpchrist@holgerdanske.com> - 2021-01-19 20:50 +0100
      Re: sharing a network connection from debian to non-debian Andrei POPESCU <andreimpopescu@gmail.com> - 2021-01-24 18:20 +0100
        Re: sharing a network connection from debian to non-debian Dan Hitt <dan.hitt@gmail.com> - 2021-01-24 23:10 +0100
          Re: sharing a network connection from debian to non-debian Dan Hitt <dan.hitt@gmail.com> - 2021-01-25 04:00 +0100
            Re: sharing a network connection from debian to non-debian Andrei POPESCU <andreimpopescu@gmail.com> - 2021-01-25 07:20 +0100
              Re: sharing a network connection from debian to non-debian Andrei POPESCU <andreimpopescu@gmail.com> - 2021-01-25 07:20 +0100
          Re: sharing a network connection from debian to non-debian Andrei POPESCU <andreimpopescu@gmail.com> - 2021-01-25 07:10 +0100
            Re: sharing a network connection from debian to non-debian Joe <joe@jretrading.com> - 2021-01-25 10:40 +0100
              Re: sharing a network connection from debian to non-debian Andrei POPESCU <andreimpopescu@gmail.com> - 2021-01-25 20:10 +0100
            Re: sharing a network connection from debian to non-debian Dan Hitt <dan.hitt@gmail.com> - 2021-01-26 03:50 +0100
  Re: sharing a network connection from debian to non-debian David Christensen <dpchrist@holgerdanske.com> - 2021-01-16 11:10 +0100
    Re: sharing a network connection from debian to non-debian rhkramer@gmail.com - 2021-01-16 15:30 +0100
  Re: sharing a network connection from debian to non-debian Michael Howard <mike@dewberryfields.co.uk> - 2021-01-16 16:00 +0100
  Re: sharing a network connection from debian to non-debian elvis <elvis@dogonfire.com> - 2021-01-19 09:20 +0100

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