Re: DHCP and static IP configuration hangs when no DHCP

[Francesco Giudici <fgiudici redhat com>]

Hi David,

On 6/11/19 12:24 AM, David Bourgeois wrote:
> Hi,
>
> I can't find the proper configuration to have an always enabled static 
> IP address and an optional DHCP address when connected to a network that 
> has a DHCP server. My use case is a portable device that connects to 
> local embedded devices using a private local LAN so the static IP should 
> always be there. When we need to connect on the internet, I would like 
> to plug a DHCP enabled connection to the switch and receive a second IP 
> automatically from DHCP for this.
>
> I can setup both DHCP and static using this configuration:
> [ipv4]
> address1=10.192.11.10/16 <http://10.192.11.10/16>
> method=auto
>
> The problem is that the whole connection profile will fail if no DHCP 
> server is found, the static IP will never be set. As soon as I plug the 
> DHCP network, both IP will appear. But I would need the static IP to be 
> available from the beginning. I have the same problem if I try the 
> ifupdown configuration through /etc/network/interfaces. I had gentoo in 
> the past and could achieve this using their RC system, DHCP would be 
> assigned to eth0:0 and a static IP to eth0:1. I just can't find a way to 
> do this with Network Manager.
>
> Any idea if that's possible with the profile configuration, or if I need 
> to use 2 configurations or play with some scripts?

I think you can achieve your desired configuration by setting the dhcp 
timeout value to something really big.
As easy as:

$ nmcli connection modify $YOUR_CONNECTION_NAME ipv4.dhcp-timeout infinity

This way, the connection will keep trying getting an ip from time to 
time, and will never be teared down.

Francesco

> Thank you,
> David
>
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