You are unable to connect to your Synology device via DDNS.

Your Synology device’s settings are as follows in either DSM or SRM:

• DDNS: example.synology.me
• DSM local IP address: 192.168.1.123
• SRM local IP address: 192.168.1.1

• Preliminary checks
• Unable to connect to DDNS from the Internet
• Unable to connect to DDNS from your local network

Preliminary checks

1. Temporarily assign "8.8.8.8" to the Preferred DNS server and "8.8.4.4" to the Alternative DNS server at the following locations:¹
• In DSM: Go to Control Panel > Network > General > Manually configure DNS server.
• In SRM: Go to Network Center > Internet > Connection > Manually configure DNS server.
2. Temporarily disable the IPv6 connection by doing the following:
• In DSM: Go to Control Panel > Network > Network Interface. Select your network interface and click Edit. Under the IPv6 tab, select Off from the IPv6 setup drop-down menu.
• In SRM: Go to Network Center > Internet > Connection > Primary Interface/Secondary Interface (LAN 1) > IPv6 Setup, and select Off from the IPv6 setup dropdown menu.
3. If your Synology device is joined to a domain, make sure that the DNS server of the domain can resolve the domain names required by DDNS and External IP Analyzer. For domains created by Synology Directory Server, you can Enable resolution service and Enable forwarders in the DNS Server package. Refer to this article for more information.
4. Select an NTP server and click Update Now to make sure that the time shown on your Synology device is correct by doing the following:
• In DSM: Go to Control Panel > Regional Options > Time > Time Setting > Synchronize with NTP server and select Update Now.
• In SRM: Go to Control Panel > System > Regional Options > Current Time and select Update Now.
5. If you have configured firewall settings or proxy servers in your network environment, make sure that the domain names required by DDNS and External IP Analyzer are not blocked.

Unable to connect to DDNS from the Internet

1. Make sure that the Status of your DDNS is Normal.
• In DSM: Go to Control Panel > External Access > DDNS to view the Status.
• In SRM: Go to Network Center > Internet > QuickConnect & DDNS > DDNS to view the Status.
2. Confirm that your DDNS hostname can be resolved into your external IP address. Refer to this article for more information.
3. Confirm that your Synology device can be accessed within the same local network. You can test this by entering your Synology device’s IP address in the address bar through a web browser. For example:
• DSM: http://192.168.1.123:5000
• SRM: http://192.168.1.1:8000
4. Make sure that you have set up port forwarding rules to forward ports required by DSM / SRM services on your parent router/modem to the same ports on your Synology device.² Refer to this article for more information.
5. Make sure that the firewall rules on your parent router/modem and Synology device allow forwarded ports to be accessed from the Internet. You can temporarily disable firewall rules to make sure that this works. Refer to these articles (DSM/SRM) to learn more about configuring a firewall on a Synology device.
6. Certain Internet Service Providers (ISPs), such as cellular networks and community networks, do not support port forwarding under certain circumstances. Please confirm this with your ISP. In this is the case, you can try accessing your Synology device via QuickConnect instead of DDNS. Refer to this article for more details.

If the issue persists after trying the methods above, please contact Synology Technical Support for further diagnosis.

Unable to connect to DDNS from your local network

1. Make sure that your Synology device can be accessed within the same local network. You can check this by entering your device’s IP address into the address bar through a web browser. For example:
• DSM: http://192.168.1.123:5000
• SRM: http://192.168.1.1:8000
2. Make sure that your DDNS hostname can be resolved into your external IP address. Refer to this article for more information.
3. Try connecting to the External IP address at the locations listed below. If the connection is successful, go through the Preliminary checks section again. If the connection fails, contact your router’s manufacturer to check if your parent router/modem supports the NAT loopback function.^{3 4}
• In DSM: Go to Control Panel > External Access > DDNS.
• In SRM: Go to Network Center > Internet > QuickConnect & DDNS > DDNS.

If the issue persists after trying the methods above, please contact Synology Technical Support for further diagnosis.