I need help with a WAN structure

[Dale Sparrow]

I have a particular requirement which I feel should be straightforward but seems to require some black magic.

I have two routers. Router A is in the house and is connected to the internet and router B is in my room which I plug a WAN cable from A into for internet. I disable DHCP on B and tell it to bridge the internet connection through ethernet. If I dont disable DHCP it causes havoc with other devices in the house. Unfortunately this means my devices get assigned IPs that are on A's subnet since it is now the DHCP server. The kicker is I am developing IoT applications that require me to take Router B with me to a location without internet and all the devices I had in my room should still connect to each other over it.

I want Router B to supply internet and local IP's to all devices connected to it, but leave devices connected to Router A alone. Why can't I have two subnets configured like this? Or am I just missing a setting?

Any help would greatly be appreciated.

Kind Regards

Dale

 

[ColinTaylor]

Don't bridge the internet connection on Router B and leave DHCP enabled.

 

[Dale Sparrow]

Don't bridge the internet connection on Router B and leave DHCP enabled.

Hi Colin. Thanks for the reply, how will I get internet on B's network in this case?

 

[ColinTaylor]

You just have one router behind another router. That's a fairly common configuration.

I'm assuming when you say "tell it to bridge the internet connection" you're talking about changing it from "router mode" to "access point mode".

So unless there's something unusual about your routers it should be straight forward. What are the make and model numbers of your routers?

 

[CaptainSTX]

You might be better off to double NAT B behind A. Then when you take router B somewhere else it will be fully functional.

 

[Dale Sparrow]

You just have one router behind another router. That's a fairly common configuration.

I'm assuming when you say "tell it to bridge the internet connection" you're talking about changing it from "router mode" to "access point mode".

So unless there's something unusual about your routers it should be straight forward. What are the make and model numbers of your routers?

It is a DLink DSL 2750U. Hooking B'a WAN port into one of A's LAN ports doesn't give it internet. But if that's what should be happening I'll look at the settings more closely.

 

[Dale Sparrow]

You might be better off to double NAT B behind A. Then when you take router B somewhere else it will be fully functional.

Thank you CaptainSTX, I'l look into this and report back

 

[ColinTaylor]

Are both routers DSL-2750U's ?

They are ancient ADSL modem/routers. Were they supplied by an ISP (if so which one), because ISP's tend to restrict the configuration options? (Apparently the Indian versions are restricted)

As far as I can tell they don't have a "WAN" socket only DSL and LAN. Hopefully you're not trying to jam an Ethernet cable into the DSL socket.

It looks like you need to configure the "WAN Service" to be "IP over Ethernet" instead of "Bridging". Then reassign one of the LAN Ethernet ports to be the WAN port (e.g. remove ppp0 and add eth0 - you'll have to experiment to find out which LAN socket eth0 is mapped to).

 

[Dale Sparrow]

Are both routers DSL-2750U's ?

They are ancient ADSL modem/routers. Were they supplied by an ISP (if so which one), because ISP's tend to restrict the configuration options? (Apparently the Indian versions are restricted)

As far as I can tell they don't have a "WAN" socket only DSL and LAN. Hopefully you're not trying to jam an Ethernet cable into the DSL socket.

It looks like you need to configure the "WAN Service" to be "IP over Ethernet" instead of "Bridging". Then reassign one of the LAN Ethernet ports to be the WAN port (e.g. remove ppp0 and add eth0 - you'll have to experiment to find out which LAN socket eth0 is mapped to).

No I'm not trying to jam an Ethernet cable into a wan socket, it is specifically labeled WAN. I'm an engineer, just not a network specialist. Router A is a very new 2018 model, router B is ancient because the place I'm putting it isn't particularly safe, so for prototyping I decided to use an old one, however maybe buying a new one is worth it at this point.

It was in fact supplied by Etisalat from the UAE and I saw they made it impossible to remove some of their PPP0 and PPoE settings. I considered the IP over Ethernet option but that would require me to put in my ISP's supplied settings like we did for router A? If that's the only way then I'll try that. Thanks for the advice

 

[ColinTaylor]

Thanks for the update. The only pictures I can find for the DSL-2750U (including one from Etisalat) don't show any ports labelled WAN hence my comment. Although I've seen a slightly different model that does.

For the generic models the idea is to remove the ppp/ATM interface and replace it with a simple IP/Ethernet interface. This wouldn't require any ISP login details. I can't find any screen shots on the internet that show the specific steps for doing this. From what I've read the Indian models don't allow this and requires to router to be flashed with a firmware from a different region that doesn't have the restriction.

 

[ColinTaylor]

There's some not very comprehensible notes in the manual which may be relevant:

To access the ETH WAN Interface Configuration window, click the ETH Interface button in the Layer2 Interface directory.
This window is used to configure the ETH interface. You can add and delete ETH interface on this window.
If you are setting up the ETH interface for the first time, click the Add button.

ETH Interface
The ETH PVC Configuration window allows you to set up ETH WAN configuration. This screen allows you to configure a ETH port. Select a ETH port. Select Connection Mode.
Click the Apply / Save button to Save.