openwrt-xburst/target/default/target_skeleton/etc/init.d/S50dnsmasq

#!/bin/sh
. /etc/functions.sh

# interface to use for DHCP
iface=lan

ifname=$(nvram get ${iface}_ifname)
ipaddr=$(nvram get ${iface}_ipaddr)
netmask=$(nvram get ${iface}_netmask)

# check for existing DHCP server
udhcpc -n -q -R -s /dev/zero -i $ifname >&- || {

  ipaddr=$(ip2int $ipaddr)
  netmask=$(ip2int ${netmask:-255.255.255.0})
  network=$((ipaddr&netmask))
  
  start=$(nvram get dhcp_start)
  start=$((network+${start:-100}))
  end=$(nvram get dhcp_num)
  end=$((start+${end:-150}))
  
  args="-K -F $(int2ip $start),$(int2ip $end),$(int2ip $netmask),12h"
}
dnsmasq ${args}