How do you connect a router as a switch? Don't throw away the extra routers—just plug in the AP and you'll get four more network ports

started because the equipment on my TV cabinet kept piling up: TV, set-top box, N100 mini console, and even a game console—all needed network cables, but there was only one network port on the living room wall. Buying a switch can of course solve the problem, but I happen to have a retired Redmi AC2100 lying in my drawer, so I guess I'll just put it to use. During this process, I found that there are many explanations about "using routers as switches": some say just plug in the LAN port, some say turn off DHCP, and some say switch to AP mode. Who exactly should you listen to? I tried all three routes, and this article clearly explains the differences and pitfalls.

first clarify: plugging in a router only brings three things

you open it up, a regular home router is actually packed router, switch, and AP into one box. The routing section is responsible for dialing and assigning IP addresses (DHCP); The switching part is the small chip behind the LAN ports, responsible for transferring data between the ports; The AP section consists of those two antennas, responsible for transmitting WiFi.

"used as a switch" means only borrowing its switching and AP parts, turning off or bypassing the routing part. Once you understand this, all the subsequent connections become easy to grasp—all the operations you perform are essentially "leaving only one device in the home to assign an IP."

Why can't both units run DHCP? I tested it: both routers are connected and have DHCP enabled, and there are two 'IP senders' in the local area network. When the phone connects to the router's WiFi, it gets gateway A, the TV plugged into B, and the gateway is B. The result is can get internet but can't ping each other, casting and NAS access are all blind. This issue is especially subtle. At first, I thought it was a firewall issue, but after a long search, I found out it's a dual DHCP.

the first way: Plug the network cable into the LAN port, which is the simplest but comes with a premise

the easiest way to connect: plug a cable out of the main router's LAN port and plug it into the old router's LAN port (note: not the WAN port), then turn off the old router's DHCP. This way, the old router is 'downgraded' to just a switch plus an AP, while other devices plug into its remaining LAN port, or even get its WiFi directly from the main router. The whole house has one network segment, and both screen casting and NAS work fine.

key steps are two. Step one: Connect the old router separately (connect the computer network cable directly to its LAN port or its WiFi), log in to the management backend, find DHCP settings, and turn off . In the "Common Settings → LAN Settings" for Xiaomi and Redmi, TP-Link is under "Routing Settings→ DHCP Server," and ASUS has unchecked "Enable DHCP Server on Internal Network (LAN) →DHCP Server" tab. Step two: change its management IP so it doesn't treat the main router the same way. My main router is 192.168.31.1, so I changed AC2100 to 192.168.31.2. From now on, if I want to access its backend, the addresses won't conflict.

after changing these two settings, plug in the cables—don't reverse the order—change settings first, then cascade, and you'll always find it; Connect the cable first and then make changes. If there is an IP conflict or DHCP conflict, you might find that the backend can't log in no matter what, so you have to reset and try again. The first time, I only remembered I hadn't turned off DHCP after plugging in the cable, but the background was intermittent and unresponsive. After fiddling for half an hour, I had to reset and it finally got back to work.

second option: switch directly to AP mode in the background, which is suitable for newer routers

2020 years have either "AP mode" or "wireless access point" options in their firmware settings, allowing you to do it all in one go without manually turning off DHCP; the system automatically handles everything for you.

after switching to AP mode, there's a change to remember: into its backend, it's recommended to assign it IP directly via the main router. In AP mode, it no longer enables DHCP. The IP is assigned to it by the main router. Go to the main router's device list and find this device (usually showing the hostname). That IP is its new backend address. My device switched to AP mode and changed to 192.168.31.108. At first, I foolishly tried accessing 192.168.31.2, but naturally it wouldn't open. Bind it to a static IP or record it in your computer's hosts so you won't lose track next time.

AP mode? According to the manual, most WAN ports and LAN ports are randomly plugged in— the firmware switches to AP mode, and internally the WAN port is also bridged to the switch chip, making all four ports equal. This is more respectable than manually turning off DHCP, though there are exceptions: some models (I once encountered an old Mercury) only recognize the WAN port in AP mode, and the LAN port doesn't work. If it doesn't work, try switching ports instead of stubbornly trying it.

Should you plug in WAN or LAN? A comparison chart explains everything

this is the most confusing part, so I categorize it by 'which path did you choose':

the third line is the 'Not Recommended' solution I mentioned: use the old router as a secondary router, connect the WAN port for wiring, and the device mounted below is in the second segment. It works, and internet access is fine, but LAN services like screen casting, NAS, and printer sharing are blocked by two-level NATs, and port forwarding must be installed on both layers. Unless you want to isolate a dedicated network (for example, for rental housing or dedicated surveillance), don't choose this one.

one more reminder: after LAN cascading, only three LAN ports remain on the old route (one is occupied by the cascaded line). Count the ports carefully. If the port isn't enough, you really need to buy a switch. An eight-port gigabit foolproof switch costs forty or fifty yuan, which is less hassle than relying on a second old router.

WiFi after switching to the switch: conveniently extended the signal

the AP (or LAN cascade) is changed, the machine's WiFi works as usual, which means there's another signal point in the living room. But this is not Mesh, there is no seamless roaming . When the phone moves from the study to the living room, it clutches the weak signal of the main router tightly until it hits rock bottom, then switches again, sometimes even lags for a second or two during the switch.

two improvement methods. First, set the SSID and password on both devices exactly the same (the encryption method is also the same, both WPA2 or a mix of WPA2/WPA3), so at least the phone doesn't need to re-enter the password, so switching is quicker. Second, simply turn off the old router's WiFi and use it purely as a wired switch. The WiFi at home has only one source, which actually feels refreshing—this is my final solution: turn off the AC2100's WiFi and only supply the network cable to the TV cabinet devices, with one main router managing the whole house.

If you want "signal at full bars everywhere you go, seamless switching," then you're heading in the wrong direction. What you should focus on is Mesh networking. I previously wrote about the of Mesh wired backhaul connections, which are different from the AP modification method in this article, so don't confuse them.

the order and closing checks I suggest

ranked by the cost of my pitfalls, here is the least likely to fail in the order of actions

1. old router supplies power independently, connecting directly to the computer to log in to the background;
2. firmware has AP mode, switch directly; if not, manually disable DHCP or change management IP;
3. after the changes, restart once to confirm you can log back into the background;
4. Connect the network cable from the main router (LAN cascade into the LAN port, AP mode into the WAN port);
5. find a device plugged into an old router and check whether the IP it receives is the main router's subnet and whether the gateway is the main router.

final step: Check if the TV cabinet's device can be found in the mobile app by casting, or directly ping the main router's address. If it can connect and cast screens, it means the entire link is correct. Currently, all four devices in my TV cabinet are plugged into AC2100s. After running for several months, the gigabit port measured about 940Mbps, which is no different from a direct main router. This 2019 machine has truly made use of its remaining strength.