How to access WAN modem from LAN with different subnet mask?

[eightace]

Apologies in advance if this is more of a general networking question.
Using an AC-68U with latest Merlin firmware.

On my old NT-66U I could access the WAN modem on 192.168.8.1 from my LAN 192.168.1.2 etc

I think however that was because I had them both on the same subnet as I am not that good.
I have now done it correctly I think with the WAN subnet 255.255.255.0 and the LAN subnet 255.255.0.0 however I cannot access the modem. Is there a way in the Merlin firmware of doing this? I have looked things up and VLANs keep cropping up but I think it may be simpler than that.

Thanks

 

[eddiez]

Apologies in advance if this is more of a general networking question.
Using an AC-68U with latest Merlin firmware.

On my old NT-66U I could access the WAN modem on 192.168.8.1 from my LAN 192.168.1.2 etc

I think however that was because I had them both on the same subnet as I am not that good.
I have now done it correctly I think with the WAN subnet 255.255.255.0 and the LAN subnet 255.255.0.0 however I cannot access the modem. Is there a way in the Merlin firmware of doing this? I have looked things up and VLANs keep cropping up but I think it may be simpler than that.

Thanks

I have not done anything to the Asus on default config on 192.168.1.1 and I can still access my modem on 192.168.100.1 ...

 

[coxhaus]

If you add a 255.255.0.0 mask to your LAN of your router for your inside network then you will not be able to access the 192.168.8.1 255.255.255.0 modem outside on the WAN port. You have told your router that IP addresses in the mask 255.255.0.0 are contain inside your network on the LAN side. Change your LAN mask back to 255.255.255.0. Since 192.168.8.1 is not contained in your new LAN mask the router will send all traffic for the 192.168.8.1 network out through the WAN port where the modem will respond.

 

[eightace]

Thanks will see if that works.

 

[jpclarke]

Your modem will need to have a route back to your internal lan, if it doesn't know how to get back to your lan it won't work.

You probably need to add a sub interface to your router on the same subnet as your modem for it to work.

 

[jpclarke]

Look at my approach to access my modem's web interface on this link:

http://www.snbforums.com/threads/draytek-vigor-130-vdsl-wan-stats-via-router.28044/#post-223660

 

[coxhaus]

Your modem will need to have a route back to your internal lan, if it doesn't know how to get back to your lan it won't work.

You probably need to add a sub interface to your router on the same subnet as your modem for it to work.

The modem is directly attached to the router so I don't think you need a static route back to the router. Mine works fine this way.

 

[jpclarke]

It depends how the modem is operating, my Vigor is a bridge and needed the sub interface setup to work.

If your modem is operating in a different setup and the router isn't getting the wan address you may not need to use my method.

 

[coxhaus]

I have an outside IP address on my router. AT&T setup the sub interfaces on my Motorola modem when they installed my connection. Sounds like Vigor modem varies. I never have used a Vigor.

If he uses a 255.255.0.0 mask on the LAN IP address the 192.168.8.1 is going to be contained in the inside LAN IP address so it will not work with that mask which contains 192.168.8.1. The router will not route the IP address out through the WAN port.

 

[jpclarke]

That is correct but if the modem doesn't know how to route back to the client PCs access won't work.

By adding a sub interface onto the Merlin build router wan port with the same subnet details as the management IP and subnet mask of the modem it will allow the router to nat the traffic behind the directly connected subnet and should work.

Has eightace tried anything suggested?

The addition of the sub interface is removed after a reboot.

 

[martinr]

Look at my approach to access my modem's web interface on this link:

http://www.snbforums.com/threads/draytek-vigor-130-vdsl-wan-stats-via-router.28044/#post-223660

And ifconfig eth0:0 192.168.2.2 netmask 255.255.255.0 is the command that creates the sub-interface? I've not come across the term before, but Google's brought up enough to keep me busy.

 

[jpclarke]

Yes that should give your wan port (if it's eth0) an IP address and subnet mask on the same local network as the modem's management IP address.

 

[jpclarke]

Change the ip address and subnet mask to match your setup.