Arch Linux

ifplugd.action (part of the ifplugd package) should have ifdown match the network script (that is, it is missing an additional "ifconfig $1 down" call)

On my machine this causes issues when switching from wired to wireless, where the eth0 connection does not go down, and apps like firefox will use eth0 before wlan0 (dunno how it orders them)

My modified ifdown looks like this:
ifdown()
{
varname="\$${1}"
eval new_ifline=$varname
if [ "$new_ifline" = "dhcp" ]; then
/bin/kill `cat /etc/dhcpc/dhcpcd-${1}.pid`
fi
/sbin/ifconfig $1 down
return $?
}