First, let’s get some given’s, like the WAN interface:

# echo $(get_wanface)
vlan2

Or this way:

# nvram show 2>&1|grep -Ei wan_ifname=
wan_ifname=vlan2

Stop WAN or LAN

ip link set $(get_wanface) down

To bring things back up:

ip link set $(get_wanface) up

Command for WAN in this case:

udhcpc -i vlan2 -p /var/run/udhcpc.pid -s /tmp/udhcpc -O routes -O msstaticroutes -O staticroutes -x hostname:DD-WRT-HEIMDALL

NOTE: Change the ‘hostname’ to the hostname that’s set in the UI.

Enjoy!