Bdtyktl

I have a router (ASUS RT-N12). I use it as an Wi-Fi extender like this:

Internet <--Coaxial Cable--> Modem <--UTP Cable--> Main Router <--Wi-Fi--> ASUS RT-N12 <--Wi-Fi--> Laptop.

Now, I want to test the WAN port of this ASUS RT-N12 to be sure it works well also as an ordinary router.

I have no physical access to the main router or the modem. I want to connect my laptop as a modem simulator to the WAN port of the Asus, like this:

Laptop <--UTP Cable--> WAN port of ASUS RT-N12 <--Wi-Fi--> Mobile Phone.

Is it possible?

Any other method that allows me to test the WAN port is welcomed. (I want to verify this Asus thoroughly to be sure that, sometime in the future, I can use it as a router connected to a modem.)

There's no such thing as a "modem simulator", because your router does not really care whether it's connected to a modem or not. It can be connected to any Ethernet port that provides the bare minimum needed for auto-configuration.

In default settings, the router will act as a DHCPv4 client on the WAN side. (It has other modes, such as static configuration or PPPoE, but generally DHCP will be the default.) It may also attempt SLAAC & DHCPv6-PD for IPv6, but I'll just describe the IPv4 part here.

When the router is a DHCPv4 client, your laptop needs to become a DHCPv4 server. Install some DHCP server software and configure it to serve addresses on the Ethernet port (on a different subnet than what the router normally uses for LAN).

• If it's running Windows, enabling the built-in "Internet Connection Sharing" would do the job (as long as you have a connection to share, that is).


• If your Windows version does not have Internet Connection Sharing, you can still use a third-party DHCP server app such as Tftpd32. While it won't provide Internet access, it will still allow you to access the laptop itself.


• On Linux, there are tutorials for dnsmasq or ISC dhcpd. (In fact, there are complete tutorials for turning a Linux computer into a router, with dnsmasq+iptables.)

You'll end up with something like this (which looks pretty much the same as "stacking" two routers together, for example, or just connecting the router to an ISP):

┌──────────────┐ ← Web server running (e.g. HFS or Caddy)

│    Laptop    │

└── Ethernet ──┘

       ||    ↖ 192.168.56.1/24, DHCP server

       ||

       ||    ↙ 192.168.56.xx/24, DHCP client

┌──── WAN ────┐

│    Router   │

└── LAN/WLAN ─┘

       ~~    ↖ 192.168.1.1/24, DHCP server

       ~~

       ~~    ↙ 192.168.1.xx/24, DHCP client

┌ ─ ─ WiFi─ ─ ┐

¦    Phone    ¦

└ ─ ─ ─ ─ ─ ─ ┘ ← Tries to visit web server (http://192.168.56.1)

Now log in from your phone to the router's settings panel. It should show the WAN side as having successfully obtained an IP address (ignore that it's a "192.168" address).

At this point, if your laptop actually runs some form of "Internet Connection Sharing", then both the router and the phone should even have Internet access.

But if the laptop has no connection to share whatsoever, it needs to run its own services that the phone could attempt to access. It would be simplest to install a small HTTP server (HFS, Fenix, Caddy, or even Apache/XAMPP if you want), then visit the laptop's IP address on the phone.

If the phone can access services hosted on the laptop, then your router works fine.