Router Access DDNS when WAN is down

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Michael Schemmer

Occasional Visitor
Hi All,

I'm hoping that you can help...
I'd like to be able to access my router admin page using the DDNS entry e.g hostname.asuscomm.com when WAN goes down. I seem to recollect that this used to work, but for the life of me I can't remeber which setting allowed me to do so.
Any ideas?

Thanks
 

ColinTaylor

Part of the Furniture
Strictly speaking that's not possible as by definition the DDNS address is the address of your WAN interface which would not exist if it were down.

However you may have been thinking of creating a hosts file entry for the DDNS name that resolves to the router's internal LAN address (e.g. 192.168.1.1).
 

dosborne

Very Senior Member
I'd like to be able to access my router admin page using the DDNS entry e.g hostname.asuscomm.com when WAN goes down.
I think we all would *like* to be able to do that, but as mentioned above already, if your WAN link is down, you can't really expect to be able to access your system remotely. Kind of like asking how to get your light switch to turn your lights on/off when the main breaker has been thrown.

Hopefully you can clarify if you meant something else :)
 

Crimliar

Occasional Visitor
If you were using PiHole or something with similar capability then rather than using the "hosts" file on one local machine you could add an entry into the PiHole local DNS. Here's a snippet from the one I use:
1635403253749.png


Using this it's possible to replicate your DDNS for local use without causing any conflicts.
 

Dabombber

Senior Member
I think we all would *like* to be able to do that, but as mentioned above already, if your WAN link is down, you can't really expect to be able to access your system remotely. Kind of like asking how to get your light switch to turn your lights on/off when the main breaker has been thrown.

Hopefully you can clarify if you meant something else :)

I believe he means accessing it locally, but using the ddns hostname. It should be possible by adding a dnsmasq.conf.add line to point it to the routers LAN address instead of resolving to the WAN address.

I think using the interface-name option should let it work for both IPv4 and IPv6, but it might need testing to make sure it still works without a WAN connection.
Code:
interface-name=hostname.asuscomm.com,br0
 

Michael Schemmer

Occasional Visitor
@Dabombber Thanks for your response, that's what I'm looking for.
Yeah, I thought that there could be something that resolves the DDNS hostname when a local device is connected to the internal router IP and then when I connect remotely it would use the WAN IP to connect.

Whats the difference between using the following in the dnsmasq.conf.add file:

interface-name=hostname.asuscomm.com,br0

and

address=/hostname.asuscomm.com/InternalRouterIP

Could there be an issue using the second method when reacquiring or reregistering DDNS since it points straight to the local IP? Therefore you'd suggest the interface-name method?
Do you forsee any issues with either?

Thanks
 

Dabombber

Senior Member
Could there be an issue using the second method when reacquiring or reregistering DDNS since it points straight to the local IP? Therefore you'd suggest the interface-name method?
Do you forsee any issues with either?

Either should work, but as I mentioned interface-name will also resolve the IPv6 address.
--interface-name=<name>,<interface>[/4|/6]
Return DNS records associating the name with the address(es) of the given interface. This flag specifies an A or AAAA record for the given name in the same way as an /etc/hosts line, except that the address is not constant, but taken from the given interface. The interface may be followed by "/4" or "/6" to specify that only IPv4 or IPv6 addresses of the interface should be used. If the interface is down, not configured or non-existent, an empty record is returned. The matching PTR record is also created, mapping the interface address to the name. More than one name may be associated with an interface address by repeating the flag; in that case the first instance is used for the reverse address-to-name mapping. Note that a name used in --interface-name may not appear in /etc/hosts.



I suggest simply using a hosts.add file rather than the more complicated syntax used by dnsmasq. Why make things unnecessarily complex.

Dnsmasq is what provides the client's DNS responses, so it seems to me like the appropriate place to set the configuration. Just personal preference really.
 

ColinTaylor

Part of the Furniture
Dnsmasq is what provides the client's DNS responses, so it seems to me like the appropriate place to set the configuration. Just personal preference really.
And dnsmasq reads the local hosts file and adds it into DNS. That's how it resolves the router's own names:
Code:
# cat hosts
127.0.0.1 localhost.localdomain localhost
192.168.1.1 RT-AX86U.home.lan RT-AX86U
192.168.1.1 RT-AX86U.local
192.168.1.1 router.asus.com
192.168.1.1 www.asusnetwork.net
192.168.1.1 www.asusrouter.com
But as you say, personal preference. I guess your method using interface-name has the advantage that you don't have to hard-code the LAN IP address.
 
Last edited:

ColinTaylor

Part of the Furniture
I think using the interface-name option should let it work for both IPv4 and IPv6, but it might need testing to make sure it still works without a WAN connection.
Code:
interface-name=hostname.asuscomm.com,br0
I've just tried this an it seems to work OK when I unplug my WAN connection.
 

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