In a case where an em interface is configured via rc.conf, where the network cable is plugged in, but there is no link on the cable, netif will hang the system as it attempts configuration. I believe permanently, but only observed for up to 15 minutes.
This does not happen when there is no cable connected, nor under normal circumstances of having an rc.conf configuration entry and having a live network cable.
ifconfig itself does not cause this problem, as I could plug the dead cable in and assign addresses/bring up the interface to my hearts content.
I believe the problem is in /etc/rc.d/netif, as repeating the above experiment and calling netif start em$dev-num causes it to hang. This is more curable than on boot, as netif will then respond to shell commands to background the process and responds to kill. On initial boot, there is no such luxury.
I also have not observed this case with other interface drivers.
While this scenario is a corner case, it can cause issues in situations where you are provisioning new services, or preparing a server for new services.
Over to maintainers.
Is it still a problem for 10.4-RELEASE or 11.2-RELEASE?