Re: "Shared to other computers" question

[Ken Taylor <di604admin embarqmail com>]

On 09/29/2017 11:30 AM, Dan Williams wrote:
> On Fri, 2017-09-29 at 09:52 -0400, Ken Taylor wrote:
> > Several months ago I setup a PC to share a VPN connection among the
> > PCs
> > on my LAN. A CentOS 7 box serves as a "gateway" and accesses the VPN
> > using the openvpn client.
> >
> > NIC1 connects to my router using DHCP on the router to obtain an IP
> > address such as 192.168.0.116.
> >
> > NIC2 is set to "Share to other computers". ifconfig shows this device
> > to
> > have the address 10.42.0.1.  By connecting another PC with a hard
> > coded
> > IP address in the 10.42.0.xxx range to a switch and thereby to the
> > dual
> > NIC machine, my second PC can connect to the Internet. MAGIC :-)
> The "Shared" option actually runs its own DHCP server (using dnsmasq),
> so you shouldn't need a second one anywhere.
>
> > I then decided to do a little daisy chaining.  I added a second NIC
> > to
> > the second PC. I configured that interface to "Share to other
> > computers." This connection gained the IP address 10.43.0.1 Cool.
> >
> > I put the first dual NIC PC in "production" between my Internet
> > connection and my LAN. I installed a DHCP server on the box and it
> > serves up 10.42.0.xxx addresses to my LAN PCs.  Works great and has
> > been
> > in use for about 3 - 4 months.
> >
> > Today I needed to setup something to do some firewall experimenting.
> > I
> > plugged a test PC with 2 NICs to my LAN with NIC1. It received an IP
> > address 10.42.0.xxx from my DHCP server. So far, so good.
> >
> > I configured the second NIC as "Shared to other computers" as
> > described
> > above.  This time the second NIC received the address 10.42.0.1
> > which
> > will not work. That is the address of the first dual NIC PC.
> >
> > I have redone this several times. I also tried an Ubuntu 16.04 PC.
> > I
> > still get the 10.42.0.1 address on the second NIC. I am at a loss.
> Any time you pick "Shared" the subnet on that NIC will get the default
> IP subnet of 10.42.x.  Unless you change it.
>
> Which you can do by either adding an IP address to the connection by
> editing its config file, or by running nm-connection-editor, finding
> your "shared" connection, and setting the IP address in the IPv4 tab.
> When you do that, NM will change its DHCP server to use the subnet that
> you specify there, and reserve a few addresses for static servers.
>
> So for example, if I created a new "Shared" connection and assigned it
> the IP address 172.16.55.1/24, the sharing NIC would get 172.16.55.1.
> NM will set up a DHCP server for the 172.16.55.0/24 subnet, and reserve
> about 10 IPs for static services like printers or servers or whatever.
> It will then start a DHCP server to provide IPs and DNS to other
> computers on that NIC's network, starting around 172.16.55.11 or so.
> It will then NAT everything on that NIC/subnet to the IP address of
> your upstream connection, whatever that might be.
>
> Dan
>
> > Was the original 10.43 address a fluke?
> > Perhaps a newer version of network-manager-applet is hosed?
> > Something I need to configure manually in the firewall to cause an
> > new
> > subnet to be assigned to NIC2?  I really have no idea where the
> > 10.42
> > address came from in the first place.
> >
> > The test PC is running CentOS 7.4 with network-manager-applet
> > 1.8.0.3.
> >
> >
> > Any advice appreciated.
> >
> > TIA,
> >
> > Ken
> >
> > _______________________________________________
> > networkmanager-list mailing list
> > networkmanager-list gnome org
> > https://mail.gnome.org/mailman/listinfo/networkmanager-list

Thank you Dan!

Let me digest your comments and do a little more testing.

Ken