From 3cce724dbec4fdffe5f738bc5b0ed63cec6516c1 Mon Sep 17 00:00:00 2001
From: Keve Mueller <keve@keve.hu>
Date: Sat, 8 Dec 2018 17:33:50 +0100
Subject: [PATCH] ddns-scripts: Working example to use local_script to derive a
 SLAAC IPv6 address

Signed-off-by: Keve Mueller <keve@keve.hu>
---
 net/ddns-scripts/samples/slaac_sample.sh | 59 ++++++++++++++++++++++++
 1 file changed, 59 insertions(+)
 create mode 100755 net/ddns-scripts/samples/slaac_sample.sh

diff --git a/net/ddns-scripts/samples/slaac_sample.sh b/net/ddns-scripts/samples/slaac_sample.sh
new file mode 100755
index 0000000000..ea8f24d879
--- /dev/null
+++ b/net/ddns-scripts/samples/slaac_sample.sh
@@ -0,0 +1,59 @@
+#!/bin/sh
+#
+# script to determine and return SLAAC ipv6 address using prefix from a locally configured interface and the MAC address of the device
+# (c) 2018 Keve Mueller <keve at keve dot hu>
+#
+# activated inside /etc/config/ddns by setting
+#
+# option ip_source      'script'
+# option ip_script      '/usr/lib/ddns/slaac_sample.sh br-lan AA:BB:CC:DD:EE:FF'
+#
+# the script is executed (not parsed) inside get_local_ip() function
+# of /usr/lib/ddns/dynamic_dns_functions.sh
+#
+# useful when this box is the only DDNS client in the network and other clients use SLAAC
+# so no need to install ddns client on every "internal" box
+#
+# NB: this will not catch the actual IPV6 used by the host when it is configured to use temporary addresses
+
+#NB: we need a valid MAC address that is fully expanded with leading zeroes on all positions
+format_eui_64() {
+    local macaddr="$1"
+    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}
+}
+
+# expand :: in an ipv6 address specification to the appropriate series of 0:
+# result will have 8 ipv6 fragments separated by single colon
+# NB: input must be a valid IPv6 address, e.g. ::1
+# NB: numbers are not prepended with leading zeroes
+expand_ipv6_colons() {
+    local ipv6=$1
+# we need :: to be in the middle, so prepend a 0 if the input starts with : and append 0 if it ends with it
+    if [ "${ipv6:0:1}" = ":" ]; then ipv6=0${ipv6}; fi
+    if [ "${ipv6: -1:1}" = ":" ]; then ipv6=${ipv6}0; fi
+# retain only the real colons
+    local colons=${ipv6//::|[0123456789abcdefABCDEF]/}
+# count them
+    local num_colons=${#colons}
+    local filler=":0:0:0:0:0:0:"
+# replace the :: with the appropriate substring from filler
+    local ipv6_x=${ipv6/::/${filler:0:(7-$num_colons)*2-1}}
+    echo $ipv6_x
+}
+
+# obtain the first ipv6 address of the device passed in $1
+addr_net=$(ip -6 -o addr show dev $1 scope global up | cut -d" " -f 7 | head -1)
+#addr_net=$1
+addr=${addr_net%/*}
+# TODO: we assume /64 subnet
+# get the first 64 bits of the address
+prefix=$(expand_ipv6_colons $addr | cut -d: -f -4)
+# compute the SLAAC 64 bits from the MAC
+suffix=$(format_eui_64 "$2")
+
+echo -n $prefix:$suffix
+exit 0
+
+#echo "Should never come here" >&2
+#exit 2
+
-- 
2.30.2