Configuring a WAN port on Comtrend AR-5381u router for use with cable modem

Question

First time posting to a forum, this is all very new to me, I hope I do okay. I normally find solutions to my own problems by searching, but I may have met my match. I know very little about networking and have struggled through a lot of information trying to find an answer.

I have recently subscribed to an ISP, and being on a tight budget I opted out of the wifi connection fee and $5 monthly wifi fee. I had a couple old DSL gateways laying around and I figured it would be easy enough to use one of them as an access point. The modem I received from my ISP (Ubee DDM3521) does not have a router. I believe it does not act as a DHCP server either, because I am being served a public IP address that belongs to my ISP. I was not given a PPP username or password, if they even exist for this account. How do I connect this modem to my router?

I have a choice between a Westell A90-750018, and a Comtrend AR-5381u to use as an access point, both of them are ADSL2+ gateways. The Westell has an uplink port, but it has very few configuration options. I have seen guides online showing useful menu options that should be on my model but aren't. The Comtrend is highly configurable, and I have had some success so far.

Links to the user manual:
Part1: https://fccid.io/L9VAR-5381U/Users-Manual/5-Users-manual-1-2010249
Part2: https://fccid.io/L9VAR-5381U/Users-Manual/5-Users-manual-2-R2-2010250

What I have done:
Added an ethernet WAN interface on ethernet port 1 (manual part 1 page 37)
Added a WAN connection using the ethernet interface (page 38)
(Page 46 shows an auto-detection option, unfortunately I don't see that option in my hardware config.)

Now referring to Appendix E, manual part 2, starting on page 160. Here are the configuration options that I'm getting lost in. I have systematically tried a bunch of different combinations but to no avail.

What I have for current settings:
The ethernet interface connection mode is set to default mode.
For the WAN connection I have PPP redirect disabled.
I added the ethernet port 1 interface as the WAN interface.
I have the WAN service type set to IPoE. Jump to page 171, I have WAN IP set to static. Automatic didn't seem to work so I tried using the IP address, subnet mask, and gateway that I receive from the ISP when I plug my modem directly into my computer's ethernet port.
I have NAT enabled. I set the ethernet interface as the only default gateway interface.
I used static DNS IP addresses also taken from my computer when plugged into the modem.

With this configuration, I get a green "Internet" light on my router, and I can ping my modem through the router from my computer, but I cannot ping a website or my ISP server's address.

I greatly appreciate any help or guidance with this matter!

Answer 1

Well it seems I got it working myself! Posting the setup for anybody else who might need it.

First, set up an ethernet port on the router to accept WAN connection from cable modem:
1. Go to Advanced Setup
2. Go to Layer2 Interface
3. Go to ETH Interface
4. Remove any existing interfaces
5. Select Add, choose the ethernet port you want to connect your modem to, for Connection Mode make sure it is set to Default, and then save

Next, configure the WAN service:
1. Go to WAN Service (still under Advanced Setup)
2. Make sure PPP Redirect is Disabled
3. Select Add
4. Select the interface you just set up
5. Select IP over Ethernet and click next
6. Select Obtain IP Address Automatically and click next
7. Make sure NAT is enabled and click next
8. Set your newly configured interface as the default gateway interface and click next
9. Set the same interface as the selected DNS server interface and click next

All done! Now you can power cycle the cable modem and you should be all set. Be careful of power cycling, I learned that from this experience. I had been cycling the router without cycling the modem, but for this particular router model I can leave the router powered on while making configuration adjustments but needed to cycle the modem before the settings would take. It probably has something to do with how my ISP distributes the IP and DNS addresses. Feel free to correct me if I'm wrong and add any more important information I may have left out, like I said I am still pretty new to the technical details of computer networking.