Re: Simultaneous use of link-local + DHCP for IPv4

[Thomas Haller <thaller redhat com>]

Hi,

On Wed, 2022-11-02 at 11:39 +0100, Christian Eggers wrote:
> According to Wikipedia [1], IPv6 hosts are required to always
> configure a
> link-local address, even if a global address is available. As far as
> I
> know, NM allows only one type of address (link-local / DHCP / manual)
> for an
> IPv4 connection (although multiple addresses may be configured in
> manual mode).
>
> Would it be useful (or is it already possible), to allow parallel use
> of
> link-local + dhcp/manual for IPv4?
>
> Background: On our (embedded) product, we currently implement only
> IPv4 (nobody
> asked for IPv6 support yet). The user is responsible for choosing the
> address
> selection method according to his needs in order to communicate with
> our device.
>
> In future versions, we would like to add peer-to-peer communication
> between
> our devices which shall work independently of a proper IP address
> configured
> by the user. So if the device is configured for DHCP (factory
> default),
> discovery and communication between our devices shall work also for
> such cases,
> where no DHCP server is present.
>
> We try to avoid the "Microsoft" approach where link-local is used as
> a fallback
> if no DHCP server is responding. This would increase startup time and
> doesn't
> perform well if the DHCP server is connected later (due to the mobile
> nature of
> our equipment).
>
> regards,
> Christian
>
>
> [1]
> https://en.wikipedia.org/wiki/Zero-configuration_networking#Address_selection


Since 1.40, you can configure `ipv4.link-local` property. Try that.

One problem is that if you use DHCP + link-local, then the "activated"
state will not be reached before we get an DHCP and link-local address.
And the timeout for link-local addresses is rather high.



Thomas