[systemd-devel] [networkd] Mixing DHCP & static IPs on 1 interface

[D.S. Ljungmark]

On 22/02/17 15:57, Reindl Harald wrote:
> 
> please keep repsonses on the list
> 
> Am 22.02.2017 um 15:42 schrieb Ian Pilcher:
>> On 02/21/2017 08:28 PM, Reindl Harald wrote:
>>> since this should be all on the LAN side something is *very* unusual on
>>> your setup - the firewall i setup at office is just a virtual machine
>>> with a single NIC and is able to do NAT and filtering as well as
>>> traffic-shaping (limit all workstations together to 80% of the WAN line)
>>> with a single IP address - so i don't see any reason why your firewall
>>> can't forward packages to your router independent of the WAN state on
>>> the other side of the router
>>
>> It's not a matter for forwarding packets to a *router*.  I'm trying to
>> get packets to go to the cable modem, which listens on that 192.168.X.X
>> address - regardless of the actual public subnet
> 
> but i don't understand why it has a different IP address depending on
> the state of the WAN side - normally you talk to your modem over the LAN
> 
> "If I lose connectivity, however, my firewall doesn't have a default
> route" - solve that
> 
> https://www.cyberciti.biz/faq/linux-creating-or-adding-new-network-alias-to-a-network-card-nic/
> 

It's not that uncommon.

The device is using a DHCP relay/proxy towards the LAN side, and allows
both states at once. You configure a hard-coded subnet for diagnostics
pages, and DHCP gets routed through to the other side.

This means that his devices (linux machine) appear to themselves to be
on the open side of the network, (WAN) and not being NAT-ed at all.

So, it's para-bridging the interfaces and that's a perfectly valid thing
to do.

//D.S