Re: why does network manager start activating disconnected ethernet ports?

[Dan Williams <dcbw redhat com>]

On Wed, 2018-11-07 at 16:23 -0500, David P. Reed wrote:
> I have a Fedora 28 server in my lab that has multiple network
> adapters, but only one of them is cabled to a switch. All the
> software is updated to NetworkManager-1.10.12-1.fc28.

Did you install the Fedora 28 "Server" spin, or something like
Workstation?  Some of the config options are different for different
variants.  That includes installing the "00-server.conf" file into
/etc/NetworkManager/conf.d for Server installs in some cases.

One thing that does is set "ignore-carrier=*" which, as you may guess,
makes NM ignore the carrier detection of the NIC on all interfaces.
Mostly for servers with static IPs where connectivity shouldn't change
even if you unplug or trip over the cable.

Try 'rpm -e NetworkManager-config-server' and then restarting NM or
rebooting and see if that fixes it.

Dan

> However, when I run journalctl -e I typically see pages and pages and
> pages of DHCPDISCOVER requests on the non-connected ports, constantly
> retrying. The logs fill very, very fast.
>  
> I did something yesterday that managed to cause the retrying to stop,
> leaving the unused ports all in the disconnected state (nmcli device
> status said disconnected for each one). I thought, hmm... well that
> problem is now fixed. `journalctl -e` showed everything quiet.
>  
> Today, I thought I'd check. When I did `journalctl -e` there were no
> DHCPDISCOVERs issued, and when I did `nmcli device status` the ports
> were all still "disconnected".
>  
> But then I did `nmcli con show`. It said the ports were in a
> disconnected state.
>  
> However at this point I happened to repeat the `journalctl -e`
> command, and my goodness - the stream of DHCPDISCOVER requests timing
> out were a sight to amaze, and the network manager kept transitioning
> the state of the ports that had no cables correspondingly, trying to
> get an IP address.
>  
> This may be my misunderstanding, but the interface knows whether the
> port is connected to some other port with a cable or if it is not. It
> seems logical also that merely asking for the connection status
> shouldn't "turn on" a lot of useless DHCP discovery on disconnected
> ports.
>  
> So am I confused or is this a bug?
>  
> Tell me what you need to find it if so.
>  
> I'd also like to know how to stop the behavior. I know I could change
> the ports to not be "auto", but I'd really like to be able to just
> plug a cable in and start using the port to talk to some other system
> or switch.
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