FreeBSD Networking

To start a interface (this will start whatever is configured in rc.conf, like a DHCP client):

service netif start em0

To bring down a interface (this will remove routes, etc.):

service netif stop em0

(service netif simply calls /etc/rc.d/netif)

To simply bring an interface up or down without any changes to the routing table, ifconfig em0 start or ifconfig em0 stop suffices.