A router upgrade means the old router gets tossed in a drawer or thrown away. But I try to repurpose it. A couple of months ago, I turned my old ASUS RT-AC66U router into an access point. Later, I repositioned my main router, and then coverage stopped being an issue. Obviously, that meant sending the older router back into the drawer.

I decided to continue using my old router on my network until it lasts — after all, it still worked, so I set it up as a dedicated smart home network. Gradually, I realized how it solved two problems at once for my home network.

Dealing with a messy smart home

No plan but only devices

I’ve been slowly building my smart home over the past few months. Like many people, I never really planned it properly and just kept on adding devices. Before I fired up Home Assistant for the first time, my home already had a smart TV, a Fire TV, an Apple TV, a HomePod, Philips Hue bulbs, and a couple of other things.

All those devices live on the same network as my phones, laptops, and desktop. I never bothered checking the network chaos and chatter caused by the constant plugging in of ESP32-based devices and sensor nodes. However, the security implications of cheap smart devices sharing the network with my personal devices had been nagging at me for a while, and I needed a good reason to finally do something about it.

For a couple of months, I ran an IoT VLAN for smart devices, and it worked fine. But I always kept second-guessing the firewall rules I created in OPNsense on Proxmox. Turns out, I had a long, exhausting list of rules. So I tried a different approach with a specific piece of hardware.

An old router gets a dedicated job

Giving it a second life​

Even though the AC66U is a Wi-Fi 5 router that you wouldn’t buy today, it’s still useful. It has a decent build quality and dual-band support. The one crucial reason I still considered it: support from community firmware projects for older Broadcom chip-based routers. I picked FreshTomato since it continues to receive updates even in 2026 and gives capabilities that were absent from most stock firmware. That’s remarkable for such old router hardware.

The best part was that it didn’t cost me anything to carry out this project. I already owned the router and had a couple of Ethernet cables sitting in a box. So if you've got an old router gathering dust, put it to good use. But first, check FreshTomato’s hardware compatibility before flashing it.

Setting up an old router as a smart home network was easy

There was a catch, though

I flashed the latest FreshTomato 2026.2 firmware on the AC66U and connected it to my main router (AX88U) using an Ethernet cable. The physical setup was straightforward: one end of an Ethernet cable plugged into a LAN port on the main router (AX88U), and the other into the WAN port on the AC66U. I switched the WAN on the AC66U to DHCP mode, and it automatically assigned an IP address from the main network. With the internet working through AC66U, the first hurdle was cleared.

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In FreshTomato’s interface, I renamed the 2.4GHz SSID to Smart Home and set a password. Since most IoT devices operate on 2.4 GHz, I turned off the 5GHz band entirely. For the virtual interface (Advanced -> Virtual Wireless), I assigned a dedicated subnet separate from the one on the main router. That’s to isolate the smart devices completely from the main network at the routing level.

One honest catch: connecting the older router to the main router using an Ethernet cable. I hoped to set up and connect my old router to the main router wirelessly, without running a cable. Recent FreshTomato builds removed wireless client mode for the MIPS RT-AC devices. A cable is a more reliable solution. After setting up the network, putting Home Assistant over turned out to be yet another decision.

Moving Home Assistant to a smart network is tricky

Extra step for Proxmox users

Creating a dedicated smart home network means the smart home hub must be on that network as well. If you run Home Assistant on a Pi, then connect its Ethernet port to the LAN port of the older router. But if you run Home Assistant in a VM, as I do, you’ll need to use a second NIC.

Since my mini PC had a second NIC available, I plugged it into the LAN port of the AC66U router. In Proxmox, I created a new Linux bridge (vmbr1) for that NIC and attached it to the Home Assistant VM as a second network adapter. Home Assistant now has one foot on both networks. On the primary network, it manages media players and receives commands from my phone to control Apple TV and HomePod.

Meanwhile, it remains reachable through an IP on a different subnet and connects to the smart home SSID. I set up a DHCP reservation on the older router to ensure Home Assistant's IP never changes. Running Home Assistant on a Raspberry Pi? Just connect the Pi directly to a LAN port on the older router. Since the Pi only has one Ethernet port, move Home Assistant entirely onto the IoT network, and you’re done.

Two problems got solved, one I didn’t expect

Isolation and peace of mind

The first problem is security. The smart devices are now on their own isolated subnet. Even if a cheap smart plug gets compromised, it can’t touch anything on my main network. Home Assistant only reaches smart devices through a separate network interface, whereas IoT devices can’t initiate connections to the main network.

The second problem that rarely gets enough attention is maintenance overhead. Running a home lab is my passion, but maintaining enterprise-grade complexity for a home network isn’t. I tried setting up VLANs using OPNsense on my mini PC before settling on this setup. Though it sounds technically superior, I constantly looked over my shoulder, wondering if I left a hole with a missing firewall rule. Or worse, discovering that a newly added device had quietly broken something I hadn’t accounted for.

That kind of persistent uncertainty is exhausting and defeats the purpose of a home network that just works. The old router sidesteps all that. With two routers, I get two networks with natural isolation and no firewall rules to audit or second guess. The home network is the one I completely understand and can troubleshoot confidently when something stops working late at night.

Sometimes the simplest solution is the right one

Like Occam’s Razor principle, the simple answer is the correct one. An old router and an Ethernet cable are enough for home segmentation. That’s how I should’ve built it from the start. It’s now running reliably using hardware I almost threw away. I don’t have to write any firewall rules or maintain tight VLAN configs. For my home network and home lab, peace of mind is worth more than architectural elegance.

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