--- a/debian/scripts/dhcp6c-script	2016-09-04 17:12:35.405042056 -0700
+++ b/debian/scripts/dhcp6c-script	2016-09-05 03:00:05.737812217 -0700
@@ -6,20 +6,47 @@
 
 [ -f /etc/default/wide-dhcpv6-client ] && . /etc/default/wide-dhcpv6-client
 
+# Guess interface to use as link local scope if not provided in
+# $ifname environment variable.
+if [ -z "$ifname" ]; then
+    for IFACE in $INTERFACES; do
+	ifname="$IFACE"
+	break;
+    done
+fi
+
+# exact line match. grep would interpret domain periods as special
+# chars.  The naive loop avoids relying on other non-coreutils
+# commands (sed, awk, etc.).
+has_line () {
+    local line
+    while read line; do
+	if [ "$line" = "$1" ]; then
+	    return 0
+	fi
+    done
+    return 1
+}
+
 if [ -n "$new_domain_name" -o -n "$new_domain_name_servers" ]; then
     old_resolv_conf=/etc/resolv.conf
     new_resolv_conf=/etc/resolv.conf.dhcp6c-new
     rm -f $new_resolv_conf
     if [ -n "$new_domain_name" ]; then
-        echo search $new_domain_name >> $new_resolv_conf
+	has_line "search $new_domain_name" < $old_resolv_conf || {
+	    echo "search $new_domain_name" >> $new_resolv_conf
+	}
     fi
     if [ -n "$new_domain_name_servers" ]; then
         for nameserver in $new_domain_name_servers; do
+	    if [ -n "$ifname" -a "${nameserver##fe80::}" != "$nameserver" ]; then
+		nameserver="$nameserver%$ifname"
+	    fi
+
             # No need to add an already existing nameserver
-            res=$(grep "nameserver $nameserver" $old_resolv_conf)
-            if [ -z "$res" ]; then
-                echo nameserver $nameserver >> $new_resolv_conf
-            fi
+	    has_line "nameserver $nameserver" < $old_resolv_conf || {
+                echo "nameserver $nameserver" >> $new_resolv_conf
+	    }
         done
     fi