Re: Automatically assign link local ipv4 address if dhcp fails

On Wed, Mar 15, 2017 at 7:22 PM, Beniamino Galvani <bgalvani redhat com> wrote:
On Wed, Mar 15, 2017 at 04:24:02PM +0100, Viktor S. Wold Eide wrote:

> As written, a different DHCP client could have been an option, but no luck
> so far in this direction.

AFAIK dhcpcd support in NetworkManager hasn't received updates since
long time and I don't know if it is still working well, but you should
be able to turn it on. You said that dhcpcd supported the fallback to
link-local addresses, but I don't see code in NM to do that. Maybe
this logic was done entirely in the client, but I wonder if this works
when dhcpcd is controlled by NM.

I did install and test dhcpcd separately. It seems like dhcpcd works as expected and provides ipv4 link local addresses when no dhcp reply is received, as expected.
dhcpcd --version
dhcpcd 6.10.1
Copyright (c) 2006-2016 Roy Marples

I know that dhcpcd is no longer supported by NetworkManager, but I did test anyway. I changed the dhcp client for NetworkManager by configuring NetworkManager.conf:

The log reports the following, even if dhcpcd is installed and should be available:
DHCP client 'dhcpcd' not available

Are there any simple ways of re-enabling dhcpcd support in NetworkManager, at least just for testing first?


> Alternatively, it might be possible to hook into
> the system, for example via a script in /etc/NetworkManager/dispatcher.d
> that can check for DHCP failure / success. However, I was wondering if I
> had missed something or whether there is some recommended configuration to
> achieve the desired behavior.

As an alternative approach, I tried the NetworkManager hooking support, by scripts in NetworkManager/dispatcher.d/
It does not seem possible to have a script invoked when for example dhcp fails (only pre-up, up, dhcp renew, etc.). In other words, it seems a script is only invoked when configuration is successful or renewed. Did I overlook something?

We have an open bugzilla [1] about supporting multiple IP methods
(DHCP, link-local, static) at the same type for a connection. Probably
that enhancement would solve your case, but at the moment I don't
think anybody is working on it.

Thanks for the info and the reference. Yes, that appears to be a reasonable enhancement to resolve the issue.

It seems this issue with ipv4 link local addresses pops up from time to time. I was hoping for some way to achieve the behavior, which from what I understand is standard on (some) other platforms.

Best regards

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