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Can't access NAS via DDNS - external IP not working

18
2
NAS
DS918+,DS716+ii
Until recently, I've been happily able to access my NAS via DDSN using a custom subdomain on a domain name I own, which points to the external IP given to me in the Synology DDNS settings E.g. nas.domain.co.uk. However, recently this is has stopped connecting through any means - browser, apps, webdav; the lot.

I can still access the NAS locally on my network and Quickconnect is fine as well. The DDNS settings in the Control Panel all show normal; however, I've tried using the external IP from Synology via my browser and that doesn't work, so I'm assuming the problem is somewhere between that address and my network.

I use Google Wifi and have checked the port forwarding rules, and none has changed. I'm in the UK and have an ISP router (Virgin Media) but it's set to modem mode and just passes signal through to the Google router.

Can anyone suggest where the best place to investigate would be?
 
I’m a bit confused. Synology DDNS only works with a set of domains that they own, and you choose a subdomain of one of them. There is t an option to use your own private domain.

So are you using the DDNS feature in DSM to update your domain at a different DDNS service provider? I used to use Namecheap for my domain and then DNSoMatic (OpenDNS) to update it when I was with Virginmedia, like you with their hub router in modem/bridge mode.

I would check that the WAN IP is resolving to a name that suggests it’s a customer home user, I forget the naming they used. Just put that IP address in nslookup or dig commands on the Mac/PC terminal/powershell to see the resolution. I’m hoping they haven’t silently switched to using CGNAT and having non-routable WAN IP when they’ve always had Internet routable WAN IP. If your WAN IP is in the RFC 1918 ranges it won’t be directly Internet accessible.
 
using a custom subdomain on a domain name I own
Then this isn't a DDNS issue, but perhaps an issue with your domain register, or your CNAME record for your subdomain.
 
I’m a bit confused. Synology DDNS only works with a set of domains that they own, and you choose a subdomain of one of them. There is t an option to use your own private domain.

So are you using the DDNS feature in DSM to update your domain at a different DDNS service provider? I used to use Namecheap for my domain and then DNSoMatic (OpenDNS) to update it when I was with Virginmedia, like you with their hub router in modem/bridge mode.

I would check that the WAN IP is resolving to a name that suggests it’s a customer home user, I forget the naming they used. Just put that IP address in nslookup or dig commands on the Mac/PC terminal/powershell to see the resolution. I’m hoping they haven’t silently switched to using CGNAT and having non-routable WAN IP when they’ve always had Internet routable WAN IP. If your WAN IP is in the RFC 1918 ranges it won’t be directly Internet accessible.
The way I've done it is by pointing the sub-domain to the external IP address that's presented in the NAS' Control Panel under External Access/DDNS. That's always worked until now. I did an nslookup on the subdomain address and it returned the external IP so that's working fine. I don't think it's anything to do with the domain's DNS settings, as trying to access the NAS directly via the external IP given in the Control Panel doesn't work either, which makes me think it's something in the local network settings. I might factory reboot my Google WiFi to see if that fixes it.
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Then this isn't a DDNS issue, but perhaps an issue with your domain register, or your CNAME record for your subdomain.
I don't think it's anything to do with the domain's DNS settings, as trying to access the NAS directly via the external IP given in the Control Panel doesn't work either, which makes me think it's something in the local network settings
 
You didn’t say where the client is when this fails: external on the Internet; local on the LAN?

If it’s the LAN then it could be that local loopback isn’t working in the router. For this to work there also needs to be corresponding port forwarding and firewall rules that enable Internet access to the local destination device.

Local loopback recognises local device connections that are directed to WAN IP (because an external DNS resolution has been used). The router realises this and sends this back to the destination device.
 
You didn’t say where the client is when this fails: external on the Internet; local on the LAN?
Sorry, it's happening on the LAN and externally. This is the error I get when trying through my Edge browser:
1720427846416.webp
 
Have you checked that you do have an Internet routable WAN IP from Virgin Media? You might be able to tell your DDNS service provider an IP even if it's not accessible. Maybe.

Have you reconfirmed that the VM Hub router is in modem/bridge mode still? Just to be sure. Even though you have said the Google router's external IP is what is being registered.

Has anything changed in your setup/equipment? We had someone with a network problem where they were adamant that nothing had changed, until on the 2nd or 3rd page of the thread they wondered whether it might be their new router.

If you can run a service on your router, such as VPN server, you might be able to test that this is accessible from the Internet. That would demonstrate the Internet to router connectivity. Then it would be check VM hub setup (reboot it might help). Then the Google router configuration to reconfirm firewall and port forwarding (reboot it too).


You said QuickConnect works, externally?, then I would test disabling use of QC Relay service and see if it still works. The relay service is the fallback that is used when direct access cannot work.
 

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