How to find up address of DSL modem behind router

What about log-on to the router and check WAN interface address ?

Plug the WAN interface of your DSL Modem into your internet source of supply.

Plug a computer into a LAN port and ensure you are using DHCP.   That should give you an external IP at your computer.

If that does not work you will need to get a router that you can log into and configure. The WAN interface setup in the router will show you the external IP address. My router does this.

Go...to....

https://www.whatismyip.com


.....answer character minimum length required.  😒

Are you looking for LOCAL IP of your Modem or PUBLIC WAN IP ?

You need to get internet first so that the above website will work for you.

You should know by then from the modem / PC connection what the IP address is

I am looking for the Local IP which was assigned to the modem, not the Public address

Did you try as I suggested in my first post here.   Perhaps reset the DSL modem before you do this. Unplug it, wait 1 minute, plug it back in, wait 10 minutes and connect your PC to the LAN port.

If you have a firewall that is behind the modem...the local inside ip of the modem is the gateway of the firewall.  If you were connected directly to the modem....your gateway would be the inside ip of the modem.

Like I said,,, try log on to router, go to statistic or some info and check WAN interface.
For your router WAN will be local IP of your modem

Plug into the modem directly.....and look at the properties of your LAN connection.  Or run a command line....:  Ipconfig /all

...the gateway is the inside IP of the modem.

You can usually verify that by going to.... Https://whatevertheipaddressis

A WAN is an outside IP address.....the LAN is local inside.

Inside = inward facing...this is the gateway(s) of the next router/firewall/computer/device ...in the chain.

It is however...usually possible to set an outside IP address on an inside interface....thus exposing it to the public and the next hop (gateway) would be your ISP gateway.

For the inside IP of your modem...plug directly into it...and check your interface gateway,....or look at the gateway setting of the device between you and the modem. (Your router)

When connected directly to the modem at ipconfig its only producing a 169. Ip

Who owns the modem - you or the ISP.  I would ask your ISP if you can and have them ensure it is working properly

The modem is owned by me, not the ISP

The modem would appear not to be working. I would still ask your ISP Support. Set your computer up for wired Ethernet, DHCP, plug it into the modem and then call Support and ask why no internet.

If you can, try a completely different computer on the modem (a friend's laptop, for example).

What kind of Router you have ?
Most of Routers has information about LAN (DHCP) and WAN address, like I said before the WAN IP for your Router will be your LAN IP for Modem.

@Tom, how would my objective be accomplished using Google Wifi router?

You must have Google WiFi App

https://support.google.com/wifi/answer/7183148?hl=en

The Google Wifi app does not provide the details I want to see.

Before getting too far out there, let's start over. Does the DSL Modem even include routing capability?  I've had DSL lines from multiple carriers -- the first one indeed used a router, which then had its own internal and external address.  However, the second DSL carrier I used utilized network bridges only.  In other words, the packets from my internal firewall were simply repeated through the DSL modem out to the carrier network, and inbound packets were sent back in the same way.  This made the external address of my firewall the external address of the network, even though the bridge was outside the firewall.

Please post the exact model number of the DSL Modem, or check the specs on-line or in the manuals to determine if an IP address is even assigned.

"How can I find the up address of the DSL modem behind a router?"
Did you mean this question exactly as you asked it? The norm would be for the router to be behind a modem.

Assuming you meant the question exactly how you asked it, there is one fundamental problem: DSL modems use the part plugging into the phone line as the WAN interface, NOT any of the Ethernet ports.

Assuming that you meant the normal scenario, which would be getting the IP address of a DSL modem from behind the router, Tom's very first answer would've been it. However, as Bill posted in his response, a lot of modems simply act as bridges.

It's time to get to fundamentals - assuming the modem is working properly:
- The modem needs to be set for DHCP (that's on the LAN side) in order to get an address that's *not* starting with 169 on the computer.  The problem is knowing if DHCP is enabled or disabled.  One way to likely assure this is to reset the modem back to factory defaults.  
And, if you do that from the manual, you will surely read what the default subnet is.
- If DHCP is disabled and you don't want to reset the modem then you could try guessing at the subnet:

1) Set up the computer with a common subnet like 192.168.0.0/24 or 192.168.0.0 subnet mask 255.255.255.0 and an unlikely computer IP address like 192.168.0.143.
2) Set the subnet to match; in this case 192.168.0.0/24 or 192.168.0.0 subnet 255.255.255.0
3) The gateway entry can be blank for this test.
4) DNS can be blank for this test.
5) PING 192.168.0.1; if you get a response then that's the LAN IP address of the modem.

Then try subnets and modem addresses like:
192.168.1.0/24 and addresses to PING of 192.168.1.1, 192.68.1.50, 192.168.1.254
10.0.0.0/24 and addresses to PING of 10.0.0.1, 10.0.0.50, 10.0.0.254

Even easier when you get to the PING part is to use SoftPerfect NetScanner version 6.1.4 (free) and PING the entire subnet in each case:
i.e. PING 192.168.0.1 to 192.168.0.254.
If you're on the right subnet, the modem should respond
Now you're only guessing at the subnet - and there aren't many common ones.
Don't forget to change the computer address and subnet for each subnet scan.

First of all, the public ip address IS the address assigned to the modem and Ron's answer ( https://www.experts-exchange.com/questions/29129662/How-to-find-up-address-of-DSL-modem-behind-router.html?anchorAnswerId=42756911#a42756911 ) is technically correct.
Second, if the DSL modem was put into bridge mode, the login information is in the router so the modem alone can't login to the DSL.  DSL requires a login name and a password just like dialup.
Third, even if the modem is logging in, many of today's devices record the MAC address of what they are connecting to and won't connect to any other device because the MAC address is different.  I, for example, have to call Spectrum/Time Warner if I replace the cable modem or the router.

@100questions

May be worth advising why you want to know or what problem you are trying to solve, as this may help us advise you.
Taking your question at face value however, I reiterate the suggestion made by previous responders to simply look at the 'WAN' interface on the router you've advised is in place. Assuming internet access is working, the WAN interface will be on the same subnet as the DSL modem's  LAN port. It should also have a next-hop or gateway noted, which IS the DSL modem.

Alternatively, if you have the DSL modem in bridge or 'ransparent' mode. the modem wont actually have an IP and will simply be passing all internet traffic to the routers WAN interface. if this is the case I'd expect the router's WAN interface to be DHCP enabled and have an internet IP address directly assigned to it.

If the router/internet access isn't working however, we many need more background before we can assist.