Bridge mode is a special router mode that disables the router functionality so you can use your ISP's combination router-modem unit solely as a modem paired with your own router.
There’s a feature hidden away in many routers that perform a crucial function when using your own Wi-Fi router with your internet service provider’s hardware. Here’s what you need to know about bridge mode.
What Is Bridge Mode?
In the settings for your Wi-Fi router, you may find an option for enabling “Bridge Mode,” “Passthrough Mode,” or “IP Passthrough.” Although there are small technical differences between true bridge mode and IP passthrough, which we will address in a moment, they function the same for most people. We’ll refer to all of them as “bridge mode” for brevity unless specifically discussing passthrough mode.
Bridge mode is a network setting on your router that instructs your router to stop functioning as a router—a device that analyzes, handles, and directs network traffic—and to start functioning as a simple pass-through device like a network switch.
Effectively, whatever comes in one side goes right out the other, just like real-world traffic over a physical bridge passes from one side of a river to the other.
You’ll find bridge mode and the concept of bridging in other network contexts, too. For example, many mesh Wi-Fi systems have Ethernet ports on the individual mesh nodes. You can use those Ethernet ports to create a wireless bridge so that your laser printer in your home office thinks it is plugged directly into the router. Today, however, we’re focused on the bridge mode in your router and why you might want to use it.
Why Would I Want to Use Bridge Mode?
Not everyone needs bridge mode for their home network, but if you’re in the camp that does, it’s a must-have feature that saves you from a lot of headaches.
The most common reason people use bridge mode is to pair upgraded network hardware with their ISP-supplied modem-router combo unit. Historically many internet service providers (ISPs) supplied you with a modem, and you were on your own when it came to setting up a router and Wi-Fi access.
Now, it’s more common for ISPS to supply an all-in-one unit that is both an internet modem, a router, and a Wi-Fi access point rolled together. So common, in fact, that many people don’t realize that the modem and router functions are separate.
Why does this matter? If you want to upgrade your home network, you can’t just buy the new equipment and slap it on top of the existing equipment your ISP gave you. Doing so will cause numerous problems.
For example, let’s say you have an ATT-supplied fiber modem that is also your router and Wi-Fi access point, like the popular BGW320 Wi-Fi Gateway—but it could be any number of combination units out there.
You go shopping for a new traditional Wi-Fi router or maybe even decide to go for a mesh router platform to increase coverage around your home. You get home, plug the new router into the old one, set everything up, and immediately there are problems.
First, all your internet traffic is passing through two routers, both in routing mode, creating a situation known as a “double NAT.” The acronym NAT stands for Network Address Translation, which refers to the function of your router that takes traffic coming into your public-facing wide area network (WAN) IP address and translates it across the router barrier to all the internal local area network (LAN) addresses within your home.
It’s a great feature and one we should all be thankful for, but if you double it up, then software and services like online gaming servers, VPN connections, and even SSL connections to websites can fail because the connection is being filtered through two address translations.
If you recently bought a new Wi-Fi router, plugged it into the old router your ISP gave you (without changing any settings), you should be surprised if your kids pop in to yell about how their games won’t connect and your spouse is upset their work laptop no longer connects to the corporate intranet via VPN.
Second, on top of a double NAT situation screwing up your internet traffic, if you activate a new Wi-Fi router while the old ISP-supplied one is configured in the default state, you’re blasting twice the Wi-Fi transmissions into the same space creating a lot of radio noise in the processes. And if you reused the same Wi-Fi credentials, you’ll have even more problems as now two different routers will be broadcasting the same SSID.
Putting your old router into bridge mode so that it functions solely as a modem and hands off all the other network functions (like routing and Wi-Fi access) to your new hardware is the proper way to do it. And like most proper ways to do things with computers and networking, it’s also the most frustration-free way to do it.
How Do I Put My Router Into Bridge Mode?
The sub-menu for enabling bridge mode on your router varies from model to model and between ISPs, based on what they call it. The process is pretty straightforward, however.
First, log into your router. While you can do so over a Wi-Fi connection, we strongly recommend using a laptop or desktop computer with an Ethernet connection plugged directly into one of the LAN ports on the back of the router as it’s the most stable way to connect to the router (and the connection will stay active even when the Wi-Fi status of the router changes). Some ISP-supplied routers require you to input an additional security access code whenever you make major changes to the settings. This access code is printed on a label somewhere on the physical body of the router.
Next, look for any options in the network configuration settings called “Bridge Mode,” “Bridging,” “IP Passthrough,” or similar. When you find the bridge mode settings, you will need to input the new router’s MAC address as the destination address. This tells your old router which new piece of network hardware is the endpoint for the bridged network traffic.
Many routers will auto-detect the MAC address of the attached devices and auto-populate the address slot with a drop-down menu. So you can save yourself the headache of typing in the MAC address by hand if you plug the new router into the old one while performing this step.
While most routers will automatically turn off the Wi-Fi radios when you turn on bridge mode, not all routers will, so you should take a moment to check the Wi-Fi status and turn it off. Further, if your ISP-supplied hardware doesn’t have true bridge mode but instead has IP passthrough mode, the Wi-Fi will not automatically turn off when you enable IP passthrough mode.
Once you have updated the bridge mode settings and ensured the Wi-Fi on the older router is turned off (making way for your new WI-Fi access point), then you’re all set!
Frequently Asked Questions About Bridge Mode
Bridge mode is a straightforward networking situation, but that doesn’t mean there aren’t some frequently asked questions worth diving into.
Is Bridge Mode Safe?
Bridge mode is as safe as the hardware you put behind the bridge. If you have a current generation router combo unit from your ISP with good hardware and active security updates, and you flip that combo unit to bridge mode and put a 10-year-old Wi-Fi router behind it, then your home network is immediately less safe.
But if you’re putting in a new Wi-Fi router with current support and security updates, you shouldn’t have any problems. Bridge mode isn’t inherently more or less secure. It’s as secure as the endpoint hardware.
Can Bridge Mode Cause Network Problems?
If your router supports true bridge mode, you should experience zero network problems from using it. In true bridge mode, the network traffic from the bridge-mode router is passed immediately to the new router without any changes.
If your ISP-supplied router/modem only supports IP Passthrough mode, you still shouldn’t have any problems. While IP Passthrough mode isn’t technically a true network bridge, most people won’t have issues with it.
When Should I Use Bridge Mode?
You should use bridge mode any time you wish to retain the modem function of a combination router/modem unit while adding your own router into the mix.
There are use cases beyond pairing an ISP-supplied router to a new third-party router, but the average person isn’t stacking multiple pieces of network hardware on top of each other for fringe use cases.
When Should I Not Use Bridge Mode?
You should not use bridge mode unless you have a specific reason to keep a piece of hardware active. In the case of bridging an ISP-supplied router in the mix to retain the modem function, you need to keep that piece of hardware active (unless your ISP will swap it for a standalone modem or you intend to purchase a compatible one).
But if you’re upgrading your Wi-Fi router by replacing an old Linksys Wi-Fi router with a newer model, there is no reason to put the old model in bridge mode and connect the new one to the old one. You should simply retire the older hardware after taking note of the settings, and then factory resetting it.
Can I Use The Ethernet Ports on My Old Router?
Typically you cannot continue to use the Ethernet ports on your old router once you have put it in bridge mode and should transfer all Ethernet cables from the old router to ports on the new router, adding an Ethernet switch into the mix if you need extra ports.
It’s even more important to avoid using the Ethernet ports if your router only supports IP Passthrough mode as the ports on the old device are likely reserved and still part of the background routing functions of the original router. Plugging anything into them will lead to unexpected results as the devices won’t appear on your home network as you would expect them to—although in rare cases like an ISP-supplied DVR, your ISP may instruct you to do so for proper functionality.
Are Bridge Mode and IP Passthrough the Same?
Bridge mode is a low-level network connection where traffic is passed directly to the new network hardware at the other end.
Several ISPs, most notably ATT, have a pseudo-bridge mode called “IP Passthrough.” Although it functions nearly identically to bridge mode, it is technically not a bridge mode.
IP Passthrough is a form of demilitarized zone (DMZ), wherein rather than bridging the connection, the ISP router simply puts your new router in a wide-open area with no firewall restrictions or NAT applied.
When your ISP-supplied router is put into IP Passthrough mode, it approximates a bridge mode but retains some routing functionality. This is almost always done because the ISP in question offers additional services beyond simple internet access, such as VoIP telephone service, internet-based TV services, and so on.
If the ISP’s router were switched over completely to a true bridge mode, then functionality built into that router that supports those additional services would fail. Thus, they retain partial control of the router to avoid that.
With sufficiently advanced home network hardware—like the Ubiquiti Dream Machine Pro router or a repurposed computer running pfSense—and a lot of technical knowledge, you can circumvent passthrough mode and create a true bridge mode even if your ISP doesn’t support it. It’s very technical, however, and if you want a sense of what it will require, you can review this tutorial on bypassing an ATT fiber modem to directly link a Dream Machine Pro to the internet.
It’s certainly not a beginner project. Unless you have a pressing need to do so, it’s best just to use IP Passthrough mode as is to avoid the hassle.