Hardware Week Part 3: Routing Basics & “Router on a Stick”

If a switch is a neighborhood manager, a Router is the highway system connecting different towns. While a switch looks at MAC addresses, a router looks at IP Addresses to decide where data goes next.

Today, we’re exploring how routers handle traffic and how we can sue a single router to manage dozens of different VLANs

1. The Mission: Inter-VLAN Routing

By design, a VLAN is its own separate world. Without a router, traffic cannot leave its assigned VLAN. To get traffic from VLAN 10 to VLAN 20, you have to send it to a Layer 3 device that understands how to “Route” it.

2. The Traditional Way vs. Router on a Stick (RoAS)

In the old days, if you had four VLANs, you had to run four separate physical cables from your switch to your router. That is a massive waste of ports.

Router on a Stick (RoAS) is the mordern solution:

• You run one single physical cable between the switch and the router
• You configure that port as a Trunk Port (from yesterdays post).
• On the router side, you create Sub-Interfaces (Virtual Ports) for each VLAN ID.

3. How a Router Makes decisions: The Routing Table

When a packet arrives at the router, it doesn’t guess where to send it. It consults its Routing Table.

• Directly Connected: Networks physically plugged into the router.
• Static Routes: Routes a technician (like us) manually typed in.
• Dynamic Routes: Leanred automatically from other routers using protocols like OSPF or BGP
• Default Route (0.0.0.0/0): The “Gateway of Last Resort.” if the router doesn’t know where to send a packet, it sends it here (usually towards your ISP).

4. The Default Gateway: Your Exit Ticket

For a computer at your job to reach the internet, it must have a Default Gateway configured. This is simply the IP address of the router’s interface on that specific VLAN.

Support Tip: If a user can talk to their neighbors in the same room but can’t get to Google, the first thing I check is their Default Gateway. If that IP is wrong, the computer is “trapped” in its own neighborhood.

5. The “Support Associate” Perspective: Layer 3 switches

In many modern businesses like schools, a lot of Layer 3 Switches (multilayer switches) to do this work. They will act like a switch and a router in one box. They can route traffic between VLANs at “wire speed,” which is much faster than sending everything up a “Stick” to a separate router.

What’s Next?

We’ve handled the wired side of the house. Tomorrow, we will be cutting the cord. We’re driving into Wireless Acess Points (WAPs). We’ll talk about frequencies (2.4GHz vs 5GHz), security standards, and why the microwave in the break room might be killing the Wi-Fi.