cdist/cdist/conf/type/__network_interface/files/symmetric-routing

#!/bin/sh
#

set -e

error() {
   echo "[ERROR] $@" >&2
}
die() {
   error "$@"
   exit 1
}
info() {
   echo "[INFO] $@" >&2
}
debug() {
   if [ "$DEBUG" ]; then
      echo "[DEBUG] $@" >&2
   fi
}

usage() {
   cat << EOS 1>&2
Usage: ${0##*/} [OPTIONS] ACTION INTERFACE IP_ADDRESS SUBNET_MASK_OR_PREFIX [GATEWAY]
(see -h for more information)
EOS
}

help() {
   usage 2>&1 | head -n -1 1>&2

   cat << EOS 1>&2

Setup policy based routing for the given interface
to ensure symmetric routing.

ACTION must be either 'up' or 'down' to add respectively remove the
routing table entries.

Options:
    -h    show this help message
    -d    run in debug mode
    -x    run with 'set -x' set
    -n    no action, just show what would be done without doing it

Examples:
   ${0##*/} up eth1 192.168.42.23 255.255.255.0 192.168.0.1
   ${0##*/} down eth1 192.168.42.23 255.255.255.0 192.168.0.1
   # gateway is optional
   ${0##*/} up eth1 192.168.42.23 255.255.255.0
   ${0##*/} down eth1 192.168.42.23 255.255.255.0
   # same but using prefix instead of subnet mask
   ${0##*/} up eth1 192.168.42.23 24 192.168.0.1
   ${0##*/} down eth1 192.168.42.23 24 192.168.0.1

EOS
}

die_usage() {
   error "$@"
   usage
   exit 1
}


### Utility functions

# Convert ip to int.
ip2int() {
   _ip="$1"
   { IFS=. read _a _b _c _d; } << _done
$_ip
_done
   echo $(((((((_a << 8) | _b) << 8) | _c) << 8) | _d))
   unset _ip _a _b _c _d
}

# Convert int to ip.
int2ip() {
   _ui32=$1; shift
   _ip=
   for _n in 1 2 3 4; do
      _ip=$((_ui32 & 0xff))${_ip:+.}$_ip
      _ui32=$((_ui32 >> 8))
   done
   echo $_ip
   unset _ui32 _ip _n
}

# Convert the given prefix into a subnet mask.
mask_from_prefix() {
   _prefix="$1"
   _mask=$((0xffffffff << (32 - $_prefix)))
   int2ip $_mask
   unset _prefix _mask
}

# Calculate network number from the given ip and prefix.
network_from_ip_and_prefix() {
   _ip="$1"
   _prefix="$2"
   _addr=$(ip2int $_ip)
   _mask=$((0xffffffff << (32 - $_prefix)))
   int2ip $((_addr & _mask))
   unset _ip _prefix _addr _mask
}

# Calculate number of bits in the given subnet mask.
prefix_from_mask() {
   # Assumes there's no "255." after a non-255 byte in the mask
   _mask="$1"
   _x=${_mask##*255.}
   set -- 0^^^128^192^224^240^248^252^254^ $(( (${#1} - ${#_x})*2 )) ${_x%%.*}
   _x=${1%%$3*}
   echo $(( $2 + (${#_x}/4) ))
   unset _mask _x
}

rt_tables=/etc/iproute2/rt_tables
#rt_tables=/tmp/rt_tables
# Get and if required create a routing table for the given table name.
table_id_from_name() {
   _interface="$1"
   _table_id=$(awk -vname=$_interface '{ if ($2 == name) print $1 }' "$rt_tables")
   if [ -z "$_table_id" ]; then
      # find unused table id and create a new table for this interface
      _used_ids=$(awk '$1 !~ /^(#| |255|254|253|0)/ { print $1 }' "$rt_tables")
      for _tid in $(seq 1 252); do
         if echo "$_used_ids" | grep -q "$_tid"; then
            continue
         else
            _table_id="$_tid"
            [ $NOACTION ] || printf '%s %s\n' "$_table_id" "$_interface" >> "$rt_tables"
            break
         fi
      done
   fi
   echo "$_table_id"
   unset _interface _table_id _used_ids _tid
}


### Parse command line arguments

NOACTION=
DEBUG=
SETX=
while getopts "ndxh" options
do
   #echo "$flag" $OPTIND $OPTARG
   case $options in
      n) NOACTION=1;;
      d) DEBUG=1;;
      x) SETX=1;;
      ?|h) help
         exit 0
      ;;
      *) usage
         exit 1
      ;;
   esac
done
# Strip arguments allready handled by getopts
shift $((OPTIND-1))

[ "$SETX" ] && set -x

# Validate arguments
[ "$#" -ge 4 ] || die_usage "Expected at least 4 arguments, got: $#"

action="$1" # up | down
interface="$2"
ip_address="$3"
subnet_mask_or_prefix="$4"
gateway="$5"

debug "action: $action"
debug "interface: $interface"
debug "ip_address: $ip_address"
debug "subnet_mask_or_prefix: $subnet_mask_or_prefix"
debug "gateway: $gateway"


case "$subnet_mask_or_prefix" in
   *.*)
      # has a dot, must be a subnet mask
      subnet_mask="$subnet_mask_or_prefix"
      prefix=$(prefix_from_mask "$subnet_mask")
      network="$(network_from_ip_and_prefix "$ip_address" "$prefix")"
   ;;
   *)
      # no dot, must be prefix
      prefix="$subnet_mask_or_prefix"
      subnet_mask="$(mask_from_prefix "$prefix")"
      network="$(network_from_ip_and_prefix "$ip_address" "$prefix")"
   ;;
esac

table_name="$interface"
table_id="$(table_id_from_name "$table_name")"

debug "subnet_mask: $subnet_mask"
debug "prefix: $prefix"
debug "network: $network"
debug "table_name: $table_name"
debug "table_id: $table_id"

(
case "$action" in
   up)
      # setup routing table for interface
      printf 'ip route add "%s/%s" dev "%s" proto static src "%s" table "%s"\n' \
         "$network" "$prefix" "$interface" "$ip_address" "$table_name"
      if [ -n "$gateway" ]; then
         printf 'ip route add default via "%s" table "%s"\n' "$gateway" "$table_name"
      fi
      printf 'ip rule add from "%s" table "%s"\n' "$ip_address" "$table_name"
   ;;
   down)
      printf 'ip rule del from "%s" table "%s"\n' "$ip_address" "$table_name"
      if [ -n "$gateway" ]; then
         printf 'ip route del default via "%s" table "%s"\n' "$gateway" "$table_name"
      fi
      printf 'ip route del "%s/%s" dev "%s" proto static src "%s" table "%s"\n' \
         "$network" "$prefix" "$interface" "$ip_address" "$table_name"
   ;;
   *)
      echo "Unknown action: $action" >&2
      exit 1
   ;;
esac
# tell the kernel that it needs to re-parse the policy database
printf 'ip route flush cache\n'
) | (
   if [ "$NOACTION" ]; then
      cat
   else
      /bin/sh -s
   fi
)