net/ddns-scripts/samples/slaac_sample.sh

   1 #!/bin/sh
   2 #
   3 # script to determine and return SLAAC ipv6 address using prefix from a locally configured interface and the MAC address of the device
   4 # (c) 2018 Keve Mueller <keve at keve dot hu>
   5 #
   6 # activated inside /etc/config/ddns by setting
   7 #
   8 # option ip_source      'script'
   9 # option ip_script      '/usr/lib/ddns/slaac_sample.sh br-lan AA:BB:CC:DD:EE:FF'
  10 #
  11 # the script is executed (not parsed) inside get_local_ip() function
  12 # of /usr/lib/ddns/dynamic_dns_functions.sh
  13 #
  14 # useful when this box is the only DDNS client in the network and other clients use SLAAC
  15 # so no need to install ddns client on every "internal" box
  16 #
  17 # NB: this will not catch the actual IPV6 used by the host when it is configured to use temporary addresses
  18
  19 #NB: we need a valid MAC address that is fully expanded with leading zeroes on all positions
  20 format_eui_64() {
  21     local macaddr="$1"
  22     echo ${macaddr:0:1}$(echo ${macaddr:1:1}|tr 0123456789abcdefABCDEF 23016745ab89efcd89efcd)${macaddr:3:2}:${macaddr:6:2}ff:fe${macaddr:9:2}:${macaddr:12:2}${macaddr:15:2}
  23 }
  24
  25 # expand :: in an ipv6 address specification to the appropriate series of 0:
  26 # result will have 8 ipv6 fragments separated by single colon
  27 # NB: input must be a valid IPv6 address, e.g. ::1
  28 # NB: numbers are not prepended with leading zeroes
  29 expand_ipv6_colons() {
  30     local ipv6=$1
  31 # we need :: to be in the middle, so prepend a 0 if the input starts with : and append 0 if it ends with it
  32     if [ "${ipv6:0:1}" = ":" ]; then ipv6=0${ipv6}; fi
  33     if [ "${ipv6: -1:1}" = ":" ]; then ipv6=${ipv6}0; fi
  34 # retain only the real colons
  35     local colons=${ipv6//::|[0123456789abcdefABCDEF]/}
  36 # count them
  37     local num_colons=${#colons}
  38     local filler=":0:0:0:0:0:0:"
  39 # replace the :: with the appropriate substring from filler
  40     local ipv6_x=${ipv6/::/${filler:0:(7-$num_colons)*2-1}}
  41     echo $ipv6_x
  42 }
  43
  44 # obtain the first ipv6 address of the device passed in $1
  45 addr_net=$(ip -6 -o addr show dev $1 scope global up | cut -d" " -f 7 | head -1)
  46 #addr_net=$1
  47 addr=${addr_net%/*}
  48 # TODO: we assume /64 subnet
  49 # get the first 64 bits of the address
  50 prefix=$(expand_ipv6_colons $addr | cut -d: -f -4)
  51 # compute the SLAAC 64 bits from the MAC
  52 suffix=$(format_eui_64 "$2")
  53
  54 echo -n $prefix:$suffix
  55 exit 0
  56
  57 #echo "Should never come here" >&2
  58 #exit 2
  59