Mastering VLANs: The Essential Command for Cisco Subinterfaces

Which command is correct for assigning a subinterface to VLAN 8 using 802.1Q?

• A. Router(config-if)#encapsulation 802.1Q vlan 8
• B. Router(config)#encapsulation dot1q 8
• C. Router(config-if)#encapsulation dot1q 8
• D. Router(config-if)#encapsulation trunk 8

Answer: (C)

The command for assigning a subinterface to VLAN 8 using 802.1Q is accurately represented in the chosen option because it adheres to the proper syntax and commands required for configuring a subinterface in a router. In this context, the command precedes with the interface configuration mode (config-if) and accurately uses "encapsulation dot1q 8," which is the correct format to specify that the subinterface will use VLAN tagging according to the 802.1Q standard. This command indicates that the subinterface will encapsulate traffic for VLAN 8, allowing the router to properly route traffic tagged for that VLAN. Successful execution of this command is essential for VLAN trunking, where multiple VLANs can share a single physical interface. The other options present variations or incorrect syntax. For instance, using “vlan 8” is not a valid syntax for the encapsulation command and therefore would not work in the context of configuring VLAN tagging. Similarly, the term “trunk” does not fit the encapsulation context required for VLAN assignment within a subinterface. This reinforces the understanding that precise command syntax plays a crucial role in the successful configuration of network devices.

Understanding the configuration of VLANs (Virtual Local Area Networks) is a cornerstone for anyone looking to master networking, especially as a Cisco Certified Network Associate (CCNA). Ever thought about what it takes to ensure that your router is routing traffic correctly among these VLANs? Well, grab your Cisco command line and let's break down the essential command for assigning a subinterface to VLAN 8 using the 802.1Q protocol.

So, here’s the big question: which command do you think is correct?

• A. Router(config-if)#encapsulation 802.1Q vlan 8

• B. Router(config)#encapsulation dot1q 8

• C. Router(config-if)#encapsulation dot1q 8

• D. Router(config-if)#encapsulation trunk 8

The correct answer is C: Router(config-if)#encapsulation dot1q 8. Why is that the go-to command? Well, let’s break it down step by step.

First off, this particular command puts you in the interface configuration mode—essentially giving you control over the subinterface settings. You see, when we add dot1q 8, we’re telling the router to encapsulate traffic specifically for VLAN 8 under the 802.1Q standard. This is crucial because it allows your router to successfully differentiate between traffic coming from different VLANs while using a single physical interface.

Imagine yourself at a busy post office. Each letter represents traffic from a different VLAN, and the postal worker (that’s your router, by the way) needs to know exactly where to send each letter without getting mixed up. If the worker doesn't have an effective way to categorize these letters, chaos ensues! That’s precisely why encapsulation is a must.

Now, let's reflect on why the others don’t make the cut. Option A introduces vlan 8 but doesn't follow the correct command syntax. Why’s that important? Well, in networking, precision is key—one misplaced character can lead to a big headache. Similarly, D's use of trunk is more about a connection type rather than the encapsulation process required for VLAN assignment. Remember, using the correct command not only highlights your technical understanding but also ensures your device works seamlessly.

Wrapping your head around command syntax is vital because missteps here can lead to devices that don’t communicate effectively or, worse, to complete network outages. Just think about it: are you willing to chance a misconfigured VLAN that could disrupt an entire department’s work day?

But don’t fret! Mastering this command sets you on the right path, ensuring you’ve got the skills needed to handle VLAN trunking effectively. This means more than just routing traffic; you’re enabling your network to manage multiple VLANs over a single interface. Talk about efficiency!

In a nutshell, getting comfortable with your router commands is like learning to ride a bike—it might be tricky at first, but once you get the hang of it, you’ll be pedaling smoothly along in no time! So, as you prepare for your CCNA, keep practicing this command and remember the principles behind VLAN tagging. Every small detail adds up, and soon enough, those concepts will become second nature. Happy routing!