• Added support for detecting duplicate IPv4 addresses, with a timeout configurable through the ipv4.dad-timeout connection property.


dad-timeout / int32 / -1

Timeout in milliseconds used to check for the presence of duplicate IP addresses on the network. If an address conflict is detected, the activation will fail. A zero value means that no duplicate address detection is performed, -1 means the default value (either configuration ipvx.dad-timeout override or zero). A value greater than zero is a timeout in milliseconds. The property is currently implemented only for IPv4.

-- IPv4 Settings

Quote taken from the manual for NetworkManager, as of version 1.14.4.

I failed to find ipvx.dad-timeout documented anywhere. It is described as an "override", not a default. So it sounds more likely that ipvx.dad-timeout is not set by default. In other words, the default is not to enable IPv4 Duplicate Address Detection. Is that right?


These properties are generally part of the connection profile. However, some of these properties have a special value that indicates the "default" value. For those, the default value may be configured in NetworkManager.conf. Consequently, that's documented in man NetworkManager.conf -- as opposed to man nm-settings.

But note that the default value in NetworkManager.conf only matters if you don't specify an explicit value in the profile itself. The profile's value has precedence.

"-1 means the default value (either configuration ipvx.dad-timeout override or zero)" means that -1 is the default value for this property in the profile. This allows fallback to a configured default value in NetworkManager.conf, and in case that it is still unspecified there, the final value 0 (disabled) is used.

  • Ahh. I see there is not a literal setting ipvx.dad-timeout, but there is a global setting ipv4.dad-timeout corresponding to the connection setting ipv4.dad-timeout. (And the same for ipv6, except the setting is not implemented for ipv6 yet anyway, which is why it is not mentioned in the current version of man NetworkManager.conf). – sourcejedi Feb 6 at 23:14

By default the parameter is set to -1 , you can check it through :

nmcli con show "connexion_name" | grep ipv4.dad-timeout

Use the nmcli con show to get the name of the connexion.

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