format_ip6_from_mac(){
  local template=$1
  IFS=':'; set $2; unset IFS
  printf "$template" 0x${3} 0x${4} 0x${5} 0x${6}
}

add_ip6(){
  local interface=$1
  local ip=$2
  local prefixlen=$3
  if has ifconfig; then
    if [[ "$OSTYPE" == "linux-gnu" ]]; then
      ifconfig "$interface" inet6 del "$ip/$prefixlen" || true
      ifconfig "$interface" inet6 add "$ip/$prefixlen"
    else
      ifconfig "$interface" inet6 del "$ip" prefixlen "$prefixlen" || true
      ifconfig "$interface" inet6 add "$ip" prefixlen "$prefixlen"
    fi
  elif has ip; then
    ip addr del "$ip/$prefixlen" dev "$interface" || true
    ip addr add "$ip/$prefixlen" dev "$interface"
  else
    die "no suitable program found to configure the network interface, need iproute2 or ifconfig"
  fi
}

add_ip4() {
  local interface=$1
  local ip=$2
  local netmask=$3
  if has ifconfig; then
    ifconfig "$interface" "$ip" netmask "$netmask"
  elif has ip; then
    local cidr="$(mask2cidr $netmask)"
    ip addr add "$ip/$cidr" dev "$interface"
  else
    die "no suitable program found to set ip address, need iproute2 or ifconfig"
  fi
}