Dual-WAN vs Link Aggregation: The 2x Bonus

As mentioned in the piece about 10Gbps Internet, I’ll explain the differences between Dual-WAN vs Link Aggregation and how to set up each when applicable.

In most homes, both of these features can be unnecessary. They are nice to have but might not be worth the extra cost. And for that reason, you will not find Dual-WAN or Link Aggregation in every Wi-Fi router. But many support one of the two or even both.

For this post, I use an Asus RT-AX89X, which, like most high-end Asus home routers, comes with these features and flexible network ports. The router also has a ton of LAN ports to spare.

If you have any Asus routers, you’ll find what I describe here closely applicable. Otherwise, while the interfaces differ among router brands, the general principles of these features remain.

By the way, Dual-WAN or Link Aggregation is generally stripped down in home routers and not as robust as in enterprise hardware. Still, they are advanced features and, therefore, can be confusing. Keep that in mind.

Dong’s note: I first published this post on Apr 7, 2022, and updated it on May 25, 2023, with additional relevant information.

Asus RT AX89X 10Gbps Internet 4
Dual-WAN: Here’s my Asus RT-AX89X running a 10Gbps Fiber-optic WAN. Note its Gigabit WAN port is available for a second WAN I was about to plug in.

Dual-WAN vs Link Aggregation: (Almost) totally two different things

I’ve gotten many questions where folks mentioned Dual-WAN and Link Aggregation as the same thing. While you can use Link Aggregation in a WAN (Internet) connection, a.k.a WAN Link Aggregation, the two are quite different.

Let’s start with Dual-WAN. That’s when you have two separate Internet connections and want to use both with one router. Using one router for an Internet connection is single-WAN, which is a basic normal setup.

Dual-WAN vs Single-WAN

Generally, in a network, the router handles the WAN connection (or connections in the case of Dual-WAN.) That’s also the case when you use a mesh. Specifically, you can’t make a satellite unit of a Wi-Fi system host an Internet connection, be it the first or second WAN.

The bottom line is that to use Dual-WAN, you need a router that supports this feature.

Using two Single-WAN routers to host two Internet connections won’t give you a Dual-WAN setup. Instead, you get two local networks, and if you link them somehow, such as via VPN, you’ll still use one of the two WAN connections at a time.

Dual-WAN: It’s a matter of (extra) Internet bandwidth vs speed

When working with an Internet connection, a.k.a the wide-area network or WAN, we often talk about speed in megabits per second (Mbps) or Gigabits per second (Gbps).

Data transmission speeds in a nutshell

As you read this page, keep in mind that each character on the screen, including a space between two words, generally requires one byte of data.

Byte — often in megabytes (MB) or gigabytes (GB) — is generally used to convey storage space. For data transmission, we use bits.

One byte equals eight bits.

One million (1,000,000) bits = 1 Megabit (Mb).

Megabits per second (Mbps) — the number of megabits being manipulated in one second — is the common unit for data transmission nowadays. Based on that, the following are common terms:

  • Fast Ethernet: A connection standard that can deliver up to 100Mbps.
  • Gigabit: That’s short for Gigabit Ethernet (GbE) and generally means transmission speeds in Gigabit per second (Gbps). This is currently the most popular wired connection standard. 1Gbps = 1000Mbps.
  • Gig+: A connection that’s faster than 1Gbps but slower than 2Gbps. It often applies to 2×2 Wi-Fi 6/6E or Internet speeds.
  • Multi-Gigabit: That’s multiple Gigabits — a link that’s 2Gbps or faster.
  • Multi-Gig: A new BASE-T wired connection standard that delivers 2.5GbE, 5Gbe, or 10GbE over CAT5e (or a higher grade) network cables, depending on the devices involved, and is also backward compatible with Fast Ethernet and Gigabit.

Multi-Gig explained: Faster-than-Gigabit and beyond

And that’s easy to relate to since we all want to know how fast our connection is. But speed and bandwidth can be two different things. Here’s a scenario:

Suppose you have a 500Mbps broadband connection. On one computer, you run a speed test and get 500Mbps. At the same time, if you do the same test on another computer, it will get 0Mbps. Or, more realistically, you’ll get 250Mbps on the 2nd computer, and the first computer’s test result will also be cut in half.

That’s because 500Mb is also the total bandwidth of your Internet pipe — the max amount of data the connection can deliver at any given time.

So to get two concurrent 500Mbps connections, we’ll have to have a Gigabit (1000Mbps) connection. Or you can get two separate 500Mbps lines — and that’s where Dual-WAN comes into play.

Dual-WAN will not increase your Internet speed, only the bandwidth.

Specifically, with two separate 500Mbps broadband plans, you will never see the rate of 1000Mbps in a single test. Instead, you’ll be able to get the full 500Mbps on two devices simultaneously. And that can be a good thing (vs using a single 1000Mbps line) since no computer in the network can hog all the Internet bandwidth.

But that’s only the case when you load-balance a Dual-WAN setup.

Dual-WAN: Load-balancing vs failover

In a Dual-WAN setup, you must pick between two popular approaches: load balance or failover.

Load-balance Dual-WAN: It’s about increased bandwidth

Load-balancing is when you use two WAN connections simultaneously to improve the bandwidth.

For this reason, it’s most applicable when the two WANs share similar speed grades, such as when you have a Gigabit Cable plan and a Gigabit Fiber-optic line.

When you have two lopsided connections, load-balancing works, too, just not as effectively, there are two scenarios:

  • Equal bandwidth: You divide the bandwidth equally between the two WANs. That’s often referred to as the 1:1 load balance. In this case, the slow WAN will get clogged up quickly, while the fast WAN is hardly used.
  • Proportionate bandwidth: You allocate the network’s Internet usage proportionately between the two WANs according to their speeds. For example, if you load-balance a 900Mbps WAN and a 100Mbps WAN (the former is 9x faster), you can make the first handle 90 percent of the network’s Internet bandwidth and leave the rest 10 percent to the second WAN. That’s a 9:1 load balance.

Depending on the speed gap between the two WANs, a proportionate load-balance setup might make sense. However, if one is significantly faster than the other, the slow one might never play any role in a load-balance configuration — it’s just not ever needed.

Since load-balancing requires extra resources from the router — it has to deal with two WAN connections at all times — in the case of severely lopsided WAN connections, like the one mentioned above, it’s best to use them in the failover configuration.

Failover Dual-WAN: It’s about high availability

In failover Dual-WAN, you pick the faster WAN as the primary and the slower one as the secondary — it’s a backup. The former is in use by default, and the latter will kick in only when the former becomes unavailable.

A failover setup keeps the local network’s Internet connection from being disconnected and is applicable when you can’t afford to go offline. It maximizes availability.

In reality, there’s still a brief outage before the router switches from the primary WAN to the secondary. And that brings us to the next part on adjusting the parameters in a Dual-WAN connection.

Dual-WAN setups (on an Asus router): Understanding the standard settings

RT AX89X Dual WAN Failover Web UIRT AX89X Dual WAN Load Balancing Web UI
Dual-WAN: Failover vs Load-Balance (right). Here are the network maps of the Asus RT-AX89X running Dual-WAN in load-balancing vs failover.

Setting up a Dual-WAN connection is simple. It’s the same as setting up a single WAN connection plus another one. Here are the general steps on a supported router:

  1. Identify the network port used for the Primary WAN and another for the Secondary WAN. For this post, I’d use the 10Gbps Base-T Multi-Gig port for the former and the router’s default Gigabit WAN port for the latter.
  2. Connect the WAN ports to their respective internet sources. In my case, they are the 10Gbps Sonic Fiber-optic ONT and the Comcast Cable modem.
  3. Log in to the router’s web interface, go to the WAN (Internet) section, and set up the Dual-WAN accordingly. In my case, I tried both Failover and Load-Balance (one at a time.)

And that’s it. We’re done with the hardware part. It’s easy enough.

RT AX89X Dual WAN FailoverRT AX89X Dual WAN Load Balancing
Dual-WAN settings on an Asus router: Failover vs Load-Balance (right). Note the “Routing rules” option in the latter, which allows assigning a particular WAN to specific local devices.

With that, let me explain a few basic settings in a Dual-WAN setup via the interface of an Asus router, as shown in the screenshots above. (If you use a different brand, the wording and the settings should be similar.)

  • Basic configurations:
    • Primary WAN: This is the main (faster) Internet connection.
    • Secondary WAN: The secondary (slower) Internet connection.
    • Dual-WAN Mode: Either Load Balance or Failover. You have to pick one. The former is generally the default.
  • Auto Network Detection: This part includes the setting for the router to detect when a WAN connection becomes unavailable and behave accordingly. Specifically, in a Failover setup, it will switch to the secondary WAN, and in a Load-Balance setup, it’ll use the available WAN 100%. This section includes the following parameters:
    • Detect Interval: The frequency at which the router will check WAN connections for their online statuses. It’s best to set this number to 30 seconds or longer. A lower value might cause the router to overwork. This is generally the maximum amount of time the network has no Internet when the primary WAN is down — if the Trigger Condition below is set to 1.
    • Failover-applicable settings:
      • Allow fallback: Allow the router to move back to the primary WAN when it becomes available when the secondary WAN is in use.
      • Failover Trigger Condition: The number of consecutive times the primary WAN appears unavailable before the router switches to the secondary WAN. Multiply this number with the value of the Detect Internal above to know how long the router remains disconnected from the Internet before it switches to the secondary WAN.
      • Fallback Trigger Condition: The number of consecutive times the primary WAN appears available before the router switches back to it. Multiply this number with the value of the Detect Internal above to know how long the router keeps using the secondary WAN before it moves back to the primary WAN.
    • Network Monitoring: The methods used for the router to find out if a WAN connection is online. There are two options:
      • DNS Query: It’s fast and safe. However, there’s a chance that the information is cached and therefore not accurate — you might want to set the Trigger value mentioned above to be higher than 1. You need to pick a domain (Resolve Hostname) and an IP address (Resolved IP Address) that belongs to that domain. You can select any of your choosing. Just make sure you use one that has a high uptime. When this domain is down, your router will think your WAN is unavailable. The value in the screenshots is those of Google’s free DNS service. You can use them.
      • Ping Target: An IP address or domain that the router can send a Ping command. This method is effective when it works. However, some domains might block the ping command, especially when that happens frequently. Keep the Trigger value at 1 in this case.
    • Load-Balance-applicable Settings:
      • Load-Balance Configuration: This is the proportionate bandwidth allotment for the two WANs mentioned above. You can enter from 1 to 9 for each WAN depending on how they are different in terms of speeds.
      • Enable Routing rules: You can set rules to make a specific device within the network access a particular public IP address via a specific WAN connection (primary or secondary). Generally, a router supports about 30 such rules, but there’s no need to use them unless you have special purposes.

Again, in my experience, when you have two lopsided WAN connections, like in my case, it’s best to use the Failover setting.

And I’ve used that with great success. Among other things, I could remove one WAN connection from my personal router and connect it to a test router without causing any issues within my home network.

Asus RT AX89X 10Gbps Internet 3
Dual-WAN: My Asus RT-AX89X with two Internet connections in action.

For most homes, though, Dual-WAN might not be worth the cost or even available. But, in this case, two is better than one.

With that, let’s move on to Link Aggregation.

Link Aggregation: It’s all about local bandwidth

Link Aggregation, also known as bonding or Link Aggregation Group (LAG), is more straightforward than Dual-WAN.

In a nutshell, it’s when you combine two network connections (ports) of the same speed into a single link.

Link Aggregation in business and enterprise applications has a lot of flavors, but for home usage, the most popular, often the only available, is the 802.3ad standard. In consumer-grade applications, this standard applies only to Gigabit ports.

Specifically, you can combine two Gigabit ports into a 2Gbps connection to deliver the combined bandwidth and Failover capacity. If one of the two ports fails, you still get a Gigabit connection from the LAG.

Netgear Orbi RBS860 WAN Link Aggregation
Here’s a router with a 10Gbps WAN port that can be combined with a Gigabit port in a WAN Link Aggregation setup. In this case, you’ll get a 2Gbps connection out of them, which is applicable when your Internet terminal device doesn’t have a Mulit-Gig port but only LAG-ready Gigabit ports.

It’s important to note that while you can use a Multi-Gig port as part of a LAG, it will function in the Gigabit mode among home applications.

So if you combine a 10Gbps Multi-Gig port and a Gigabit port, you’ll still get a 2Gbps connection. This option is applicable when you don’t have Multi-Gig ports on both ends of a link.

Link Aggregation vs separate ports

If a device (such as a server) has more than one LAN port, you can plug them all into a network.

Without Link Aggregation, only one of those ports is used at a given time — the rest is on standby. The bandwidth between the device and your network remains at that of whichever port is being used — often the one plugged in last.

Link Aggregation is required if you want to take advantage of more than one port simultaneously.

Link Aggregation is available on both the WAN and the LAN sides. But in either case, it’s always about the local network — it’s never available in the service line.

A LAG connection is awkward and messy because it requires multiple network cables. And for Link Aggregation to work, you need a supported router (or switch) and supported device — most NAS servers have it. In other words, you need support on both ends of the bonded connection.

WAN Link Aggregation: Relatively rare

On the WAN side, Link Aggregation is when you use two network ports on a terminal device (most likely a Cable modem) to connect to two ports on a router as a 2Gbps connection.

Motorola MB8600 Cable ModemMotorola MB8600 Cable Modem WAN Link Aggregation
WAN Link Aggregation: The Motorola MB8600 is a Cable modem that supports WAN Link Aggregation via its LAN1 and LAN2 ports.

It’s somewhat a “cheat” way for an Internet service provider to deliver 2Gbps broadband to its customer. With Muti-Gig routers and modems commonplace, WAN Link Aggregation is slowly losing relevancy.

Personally, I’ve never used WAN Link Aggregation.

LAN Link Aggregation (on an Asus router): It’s a bonus

On the other hand, I’ve used LAN Link Aggregation for years.

Indeed, most Asus routers have these features. You can combine its first and second LAN ports into an 802.3ad LAG, and virtually all Synology NAS servers with two or more LAN ports also support 802.3ad Link Aggregation (and other LAG flavors.)

RT AX89X Link Aggregation
LAN Link Aggregation: Steps to enable LAG on an Asus router.

If you have both, the setup steps are easy (I used an Asus router and a Synology NAS server as an example, but if you have a pair of any LAG-supported device and switch/router, the steps are similar):

  1. Create the LAG on the router using its web interface, as shown in the screenshot, using LAN1 and LAN2.
  2. Use two network cables to connect the router’s two LAN ports to the server.
  3. On the server’s end, go to the Network section of the Control Panel and create a bond using the two LAN ports using the Balance-TCP mode, which is a different name for 802.3ad LAG.

Mission accomplished.

Synology Link Aggregation
LAN Link Aggregation: Steps to enable LAG on a Synology server. Note the connection speed.

A couple of years ago, before the age of Multi-Gig, a LAG connection used to be the only easy way to achieve a multi-Gigabit connection to increase local bandwidth — a LAG-enabled server can simultaneously deliver full Gigabit connections to two Gigabit clients.

And that has been the case in my experience. Link Aggregation is a pure bonus.

Dual-WAN vs Link Aggregation: The recap

Some routers can simultaneously support two Internet sources, such as Cable and Fiberoptic. That’s a Dual-WAN setup.

In this case, it can have two WAN ports (or turn one of its LAN ports into the secondary WAN) or use a USB port as the second WAN to host a cellular dongle.

A Dual-WAN setup increases your network’s chance to remain online during outages (Failover), or you can simultaneously use the two Internet connections to get more bandwidth (Load-Balance).

Link Aggregation, also known as bonding, is where multiple network ports of a router aggregate into a single connection of combined bandwidth. Typically, you can have two Gigabit ports working in tandem to provide a 2Gbps link.

Many routers from known networking vendors have this feature. You can have Link Aggregation in WAN (Internet) or LAN sides.

The former requires a supported modem. And in the latter, your wired client also needs to support it. Most NAS servers do.

Apart from delivering more bandwidth, a Link Aggregation connection is also capable of failover.

While Dual-WAN and Link Aggregation are both about increased bandwidth, they differ in that the former is about using two distinctive broadband connections simultaneously, while the latter is about combining two identical local connections to form a single fast link.

The takeaway

Again, while neither Dual-WAN nor Link Aggregation is a must-have in most home networks, they are a bonus when you can use them.

Between the two, Dual-WAN requires extra costs and multiple service lines. It’s not always feasible, nor is it necessary.

On the other hand, many routers support LAG, and if you have a network device, such as a server, that also supports it, there’s no reason you shouldn’t get an additional network cable and try it out.

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