add_route4() {
  local interface="$1"
  local subnet="$2"
  local gateway="$3"
  local netmask="$4"
  local cidr="$(mask2cidr $netmask)"

  if has ip; then
    ip route del "$subnet/$cidr" via "$gateway" dev "$interface" || true
    ip route add "$subnet/$cidr" via "$gateway" dev "$interface"
  elif has route; then
    route -n del -net "$subnet/$prefixlen" "$gateway" || true
    route -n add -net "$subnet/$prefixlen" "$gateway"
  else
    die "no suitable program found to set routes, need iproute2 or ifconfig"
  fi
}

add_route6() {
  local interface="$1"
  local subnet="$2"
  local gateway="$3"
  local prefixlen="$4"

  if has ip; then
    ip route del "$subnet/$prefixlen" via "$gateway" dev "$interface" || true
    ip route add "$subnet/$prefixlen" via "$gateway" dev "$interface"
  if has route; then
    if [[ "$gateway" == fe80* ]]; then
      gateway="$gateway%$interface"
    fi
    route -n add -inet6 "$network" "$gateway" -prefixlen "$prefixlen" || true
    route -n add -inet6 "$network" "$gateway" -prefixlen "$prefixlen"
  else
    die "no suitable program found to set routes, need iproute2 or ifconfig"
  fi
}

set_route_policy(){
  # TODO: other operating systems
  if [[ "$OSTYPE" != "linux-gnu" ]]; then
    return
  fi
  if !has ip; then
    warn "Could not set source "
  fi
}