Synology router configuration files for adding dynv6.com DDNS provider.

ddns_provider.conf

# add following lines to /etc.defaults/ddns_provider.conf
[dynv6.com]
        modulepath=/usr/syno/bin/ddns/dynv6.php
        queryurl=http://dynv6.com

dynv6.php

#!/usr/bin/php -d open_basedir=/usr/syno/bin/ddns
<?php

$script = (string)$argv[0];
$ret = 'badagent';

if($argc !== 5)
{
  echo $ret;
  syslog(LOG_CRIT, $script.':'.__LINE__.' '.$ret);
  exit();
}

$token = (string)$argv[1];
$hostname = (string)$argv[3];
$ip = (string)$argv[4];

// check the hostname contains '.'
if(strpos($hostname, '.') === false)
{
  echo $ret;
  syslog(LOG_CRIT, $script.':'.__LINE__.' '.$ret);
  exit();
}

// only for IPv4 format
if(!filter_var($ip, FILTER_VALIDATE_IP, FILTER_FLAG_IPV4))
{
  echo $ret;
  syslog(LOG_CRIT, $script.':'.__LINE__.' '.$ret);
  exit();
}

$url = 'https://dynv6.com/api/update?hostname='.$hostname.'&ipv4='.$ip.'&token='.$token;
// syslog(LOG_CRIT, $script.':'.__LINE__.' REQUEST '.$url);

$req = curl_init();
curl_setopt($req, CURLOPT_URL, $url);
curl_setopt($req, CURLOPT_RETURNTRANSFER, TRUE);
$res = curl_exec($req);
curl_close($req);
// syslog(LOG_CRIT, $script.':'.__LINE__.' RESPONSE '.$res);
switch(trim($res))
{
  case 'addresses updated':
    $ret = 'good';
    break;
  case "addresses unchanged":
    $ret = 'nochg';
    break;
  case 'hostname not found':
    $ret = 'nohost';
    break;
  default:
    $ret = trim($res);
}
echo $ret;
syslog(LOG_CRIT, $script.':'.__LINE__.' '.$ret);

Yes, seems to be an IPv6 specific assignment topic. As I'm still on IPv4, can't be of any assistance here, sorry.

No worries, your suggestions already helped me a lot, thank you for that!