This is perhaps a symptom of ifplugd
. My speculation is that taking one ethernet down causes the link-up status on the peer ethernet to go away, and the ifplugd
daemon sees this, and de-configures the link. It is unclear why the link would then come back to life, however.
Is one or both of these a laptop? As I understand it, ifplugd
is targeted primarily at laptops, which are prone to ad hoc
connects and disconnects. Does the symptom persist if the connection between the hosts includes a network switch? If not, this would also point to ifplugd
as a cause.