Question on cascading router and IP pass-thru.

Hey @rsherrard, we are here to walk you through the right path.

AT&T doesn't have to do anything to change your NAT type.  You must make changes in the Gateway or your network equipment to make that happen.

We recommend you to check on How to connect your non-AT&T router to the internet.

We also recommend you to check on how to configure IP passthrough.

This configuration is often suitable for you if desiring to connect third party equipment for networking, such as a router, to the AT&T provided gateway. IP Passthrough is also commonly used as an alternative to using a bridged mode.

Let us know if this helps or if you need further assistance.

Bruce, AT&T Community Specialist 

Could you help me understand the differences between IP pass-thru and the cascading router option?

Hey @rsherrard,

Thank you for contacting us on AT&T Community Forums! We can help you understand the difference between IP Passthrough and a cascading router. 

IP Passthrough is a feature that allows a personal router to bypass the ISP’s router and directly obtain the IP address from AT&T. It is similar to the bridge mode where users can use their own router behind the gateway provided by the ISP. Whereas, a router cascade means that 2 or more routers that are connected to each other through an Ethernet cable.

Here are the steps to set up a cascading router with your AT&T router/modem:

1. Connect your secondary router to your computer using an Ethernet cable.
2. Access the router’s local IP settings using a web browser.
3. Disable the router’s DHCP Server and set it to Operation Mode.
4. Change the last digit of the secondary router’s IP address.
5. Use an Ethernet cable to connect the secondary router to the primary router. 

Please find the detailed instruction to setup a cascade router. Follow the steps mentioned below:

1. Ensure that your router's LAN is set up on a different IP subnet than the Gateway
2. Connect the WAN port of your router to a LAN port of the Gateway (probably avoiding port 1)
3. Connect some device with a browser to a LAN port of the Gateway (probably avoiding port 1)
4. use that browser to go to http://192.168.1.254
5. Go to Firewall > IP Passthrough, enter the password from the sticker on the side of the Gateway when prompted
6. Select "Passthrough" for Allocation Mode
7. Set "Fixed" for Passthrough Mode
8. Select your router in the drop down for the MAC address
9. Hit Save
10. Power off your Gateway and Router
11. Power on the Gateway after 30 seconds
12. Power on the Router after 5 minutes
13. Check that the router's WAN address is something other than 192.168.1.x
14. Test everything out
15. Turn off the Wi-Fi on the Gateway (Home Network > Wi-Fi) if desired.

We hope this helps! Let us know if you have any other questions.

Happy to assist!

Jennifer, AT&T Community Specialist.

IP Passthrough allows your Public Dynamic address to be assigned to a router behind your gateway, doesn't NAT traffic going to or from that router, and sends unsolicited traffic from the Internet to that device.

Cascaded Router works with a Public Static Address Block, available from AT&T at an additional monthly cost, and assigns that block to your router to manage and routes all traffic to/from the Internet for the router for that subnet.  Unless you're getting a Public Static Subnet, leave this option off.

What are the cases where I would use cascading router versus IP pass thru, or use them together... with my above use-case?

@JefferMC Thank you for that. Based on this use-case. Would I need to use both IP pass-thru and cascading or one over the other?

I recently had some fiber pulled into our offices, w/ a few static IPs. I'm trying to figure out the optimal config whereby I can use my Edgerouter from Ubiquiti behind the AT&T gateway/router. I find myself confused between the cascade options and IP pass-thru and when I should be using one or the other. Behind my edge router, I'll have a number of machines where I'd like to NAT and PAT inbound traffic to. Basically, traffic comes in over one of those statics assigned to me, and then NAT that traffic back to a server behind my edge router. Ideally, I'd manage all NAT, PAT, and firewall rules on my edgerouter.

If all you want is to have a single Public Static Address to be used for all your traffic, then you still would not use Cascaded Router.  You'd just assign the single static address to the WAN of your router and use the Public Subnet configuration of the Gateway.  The Gateway will then route all the traffic to that IP back and forth between the Internet and your router (without NAT) and your router can do NAT/PAT, etc. for you. 

If you want to have multiple hosts behind your router to have public IP addresses, or something different from your dynamic clients, then you want Cascaded Router.   The NAT can be 1:1 for some hosts, and/or 1:many dynamically for other clients depending on the sophistication of the router and whoever's configuring it.

In my case, I've got ~29 static IPs that are usable. Are you saying I drop those into the Public Subnet Hosts config on the ATT router/gateway side? Once this is done, is it still required to select IP pass-thru? Am I then "binding" those to the outside interface on my Ubiquiti router... and then creating my NAT and PAT rules there to machines on the inside interface?

Thank you again.

IP Passthrough is used to pass the Public Dynamic Address, and unsolicited traffic to it, on to your router.  If you want that passed, then turn on IP Passthrough.  If you turn on IP Passthrough, then the way you set up Cascaded Router changes (because your IP Passthrough router's IP address changes), but otherwise, the two having nothing to do with each other.

@JefferMC I'm still struggling a bit here on config paths/options.

My goal is to take my /27 from ATT, and allow me to "pass" those to my EdgeRouter/Ubiquity device, and then do my config on that router. In terms of config, it's really just being able to use those assigned IPs in that /27, and build my NAT's and PAT's on that device. To achieve this should I be using IP pass-thru, and assigning the WAN interface on my device one of the IPs in the /27 I get from AT&T? Once this is done, is it safe to assume the others in that static IP block could also be used/assigned to servers behind my own router? Would traffic behind my router, which doesn't have a NAT, be sourced thru whatever static IP I assigned my WAN interface on my router?

Maybe I'm over complicating/thinking here?