What is a Router?

Quick Answer: A router is a device that directs data traffic between different networks, ensuring data reaches its destination efficiently.

So, you’ve heard the word router thrown around, maybe when your internet goes out, and you’re frantically unplugging and plugging it back in. But what exactly is a router, and why does it matter? 

Think of it as the ultimate traffic director for your internet, making sure your cat videos, work emails, and late-night gaming sessions all get where they need to go. But there’s more to routers than just lights and buttons—let’s break it down in a way that won’t make your head spin.

What is a Router?

A router is a device that helps send information (such as videos and messages) to the right place so that your devices can connect and talk to each other. In layman's terms, routers are often misunderstood and mislabeled. However, a router does what it says: It routes. In this case, this refers to routing packets and/or frames that send network traffic through your network. Routers can be a bit more complex than that, though, so let’s explore all that routers do.

What Do Routers Do?

Routers connect discrete network segments. They allow traffic to bridge divides that they most typically wouldn’t be able to. They do this through things called routing tables and, more generally, routes. These routes tell you where traffic should be sent and if it’s supposed to go to another subnet. 

A good example is if you had the network starting with 192.168.1.1. If you want to access something on the internet, you want to go to a public IP from a private IP. There isn’t a direct way for you to do this, so your router at home knows that any traffic bound for an address that isn’t the home subnet should be passed to another public IP like 98.168.55.123. 

In the simplest of cases, it’s just interested in the next hop, and in a simple setting or gateway, that can just be one address. It does a similar thing between internal subnets or VLANs, making simple connections and applying rules that X traffic for Y range gets sent to Z next hop. With VLANs, it’s mostly the same, except the tagged number can change.

Routers generally use one of two strategies to accomplish this: static routes or dynamic routes. 

Static Routes

Static routes are the simplest to conceptualize. They don’t change. They’re simply the mapping of an address or range to another address or range. Anything to or from those two will always go that particular way. 

Static routes are very efficient for configuring small volumes or keeping things straight. However, they rapidly become untenable to manage at larger volumes or with more connections. They cannot be changed if needed; if the hop they are meant for dies, that’s it. No more route and all traffic bound for that direction dies like it would if you unplugged it. 

Dynamic Routes

The other method that can be employed is dynamic routes. These are what they sound like; they’re “next hop instructions” that change depending on specific criteria. Depending on the criteria that the protocol in question uses, the next hop may change at one or more points.

An easy example is OSPF, or “Open Shortest Path First,” which does what it says on the tin: It computes the shortest path between point A and B, and then sends traffic down it. It’s largely not aware of other criteria, but is capable of adapting when a certain route doesn’t work well. 

Another common example would be BGP, or Border Gateway Protocol. BGP relies on actively exchanging information between routers to build maps of what’s available through things called advertisements. 

These advertisements allow information not only about what is possible but also about the detection of when something changes. These aren’t permanent and have to re-transmit the information periodically, which is how it knows when a route needs to change. 

What is the Difference Between a Router and a Switch?

The primary difference between a router and a switch is the segment and OSI layer on which they act on. Switches work primarily on Layer 2, and routers on Layer 3. (Don't understand those terms? Learn more with CBT Nuggets Network+ Training).

This means that routers primarily deal with sending traffic between segments, while switches send traffic along the same logical segment. Layer 2 means that if it’s on the same subnet (or section of IPs) it stays there; they’re connected by MAC addresses, not by IP.

A router is the inverse; it operates on Layer 3. This means that it’s responsible for routing traffic between subnets, VLANs, or other divides. A router can do the job of a switch, but not the inverse. Firewalls are a sort of multi-layer device in this context, not routing or switching, but rather only letting some things through and stopping others.

Routers are also often confused with the wireless AP, especially in a home setting, where we are used to seeing combination devices. In most homes, they actually ARE routers. They transition the network between your inside (home) subnet, and the outside or WAN. 

That said, don’t confuse things—the device you’re familiar with at home consists of logically discrete devices combined in one chassis or casing. The logical part providing your Wi-Fi is not the same as the one sending your traffic to the internet or the reverse. (APs and controllers are admirably covered here: CBT Nuggets Wireless Administration).

Common Router Functions

Much like the wireless AP/router combo discussed above, modern-day routers commonly have diverse and inclusive feature sets. It’s important to remember what the primary goal of a router is, but you may find in an enterprise network that routers will handle the job of several devices. 

A good example is Juniper’s SRX device. It’s actually a pretty able combination of a router and firewall, giving robust features for both. It generally doesn’t have the full features of a dedicated firewall in terms of setting more advanced rules, deep packet inspection, etc. However, it does a mid-level job well enough to be worth it while still maintaining all of the responsibilities of a router. 

Your router will often handle switching functions, but they aren’t interchangeable. Like with a firewall, routers typically have fewer ports, whereas dedicated switches typically have more ports.. They may be able to handle simple static routes, but have many, many more ports to serve devices than a router does. 

Be cautious when choosing your enterprise equipment. There’s no replacement for choosing the right tool for the proper role; it will save both headaches and money. 

Final Thoughts

Understanding the differences between network devices is essential. In the modern day, you have some leeway in what it is that you choose and can often combine your devices, but when troubleshooting, it’s best to think of them as discrete devices. 

Learn them as separate devices and think of them that way, and you’ll be stuck much less often in troubleshooting.

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