Introduction

Because every LAN needs some switching technologies and even the exam’s updated name contains the word “switching,” this is a rather weighty topic. Switches are basic devices that connect hosts and other network devices, and every upper-level technology uses the functionality they provide. Therefore, it’s imperative that network technicians know as much as they can about switching.

What Percentage of the CCNA Exam Covers LAN Switching?

If you plan to take the 200-120 composite exam, the percentage of the topic is 21%, according to the official documentation. That means that, if the whole exam consists of 70 questions, you can expect 14-15 questions on this topic.

What Topics Are Covered in This Section of the Exam?

There are 10 main topics under the LAN switching section, many of them subdivided even further. The essential list follows:

  • Describe and verify switching concepts and interpret Ethernet frame format
  • Configure, verify, and troubleshoot VLANs and interswitch connectivity
  • Configure, verify, and troubleshoot STP protocols and related optional features
  • Configure and verify Layer 2 protocols
  • Configure, verify, and troubleshoot (Layer 2/Layer 3) EtherChannel

High-Level Overview of Routing Technologies Topics

This article is just an overview of the above topics, but let’s look further at the most important areas.

Describe and verify switching concepts and interpret Ethernet frame format

The first part of this section is about the basic switching concepts: What the purpose is of a LAN switch, and how it works. You need to know the Ethernet frame format, the fields and their meanings. It’s important to be able to describe how the switch maintains the MAC address table and what kind of frame-delivering methods exist, namely store-and-forward, cut-through and fragment-free switching. You need to understand the cases when (and why) a switch floods a frame.

In addition to the theory, you need to be familiar with the commands to show the MAC address table, delete from it and enter static address-port relations. It’s also good to know how the table looks when a port connects to another switch or hub, or just a single end device.

Subtopics about troubleshooting are everywhere in the study, so you have to be familiar with eliminating issues with switch ports and cabling. Loose or bad cables, disabled ports, lack of the MDIX function, incorrectly-configured speed and duplex settings are the most common causes of errors. You need to know how to recognize and solve these kinds of problems, especially using the built-in “show” commands.

Here, we should mention the topic of describing switch stacking and chassis aggregation, which is only a theoretical part of the exam.

Configure, verify, and troubleshoot VLANs and interswitch connectivity

Virtual LANs are essential parts of a modern network, so we need to know about them both in theory and in practice. Knowing the configuration (creating, renaming, deleting VLANs, assigning ports to a VLAN and displaying the settings) and troubleshooting are absolutely necessary to be successful in the exam. You need to know the access port types related to end devices, namely data and voice, and the special VLAN, the default one.

VLANs usually exists on multiple switches, so you need to know the concept of trunks. What method can be used to distinguish the frames on a trunk (although ISL is mentioned in the study materials, you have to be familiar with the 802.11Q protocol only), how you enable/disable VLANs on a trunk, and how switches can negotiate the port state with the Dynamic Trunk Protocol (DTP). It’s good to know the DTP modes and its security issues. Closely related to these topics is the concept of the native VLAN, what it is and why to use it.

The unified management of VLANs is a lot easier if you use VTP, the VLAN Trunk Protocol. In the CCNA exam, you should know how to configure and troubleshoot Versions 1 and 2.  

Configure, verify, and troubleshoot STP protocols and related optional features

In a modern network, we need high availability, which requires some of the redundancy that can cause problems in switched networks. The solution can be the Spanning Tree Protocol (STP). The CCNA candidate should know why we need this protocol, what kind of problems can it eliminate, and how. It doesn’t hurt if you can solve the spanning tree of any network, consisting of four or five switches, but knowing the steps of the convergence is essential.

You need to know the default STP mode on Cisco switches (PVST+), and the Rapid STP implementation (RPVST+). If it’s necessary, you have to choose the proper root bridge and set it in any VLAN, for primary as well as secondary role. Of course, you need to know the election process of the root bridge; moreover, you need to know what the BID is and how to change it to manipulate the STP process.

Besides the basic theory and configuration of STP, there are some optional features you should be aware of. Namely, you need to know when and how to apply the PortFast feature to eliminate the need for STP convergence on edge ports, and BPDUGuard to make the network more secure by refusing BPDUs on access ports.

Configure and verify Layer 2 protocols

There are cases when you have to identify a neighbor device. What kind of device it is, what is its address, and so on. Cisco has a proprietary solution to this: CDP, or Cisco Discovery Protocol. This is also natively accessible on switches and we consider it as a Layer 2 protocol, so it fits into LAN switching. You should know about interpreting the information CDP provides, and how to enable/disable it for security reasons.

Cisco recognized that it would be useful to know about similar technologies that other network devices from other vendors use. So in the CCNA exam, the LLDP (Link-Layer Discovery Protocol) also appears. You don’t have to learn a lot more because LLDP is really very similar to CDP.

Configure, verify, and troubleshoot (Layer 2/Layer 3) EtherChannel

One more topic related to redundancy and high availability is EtherChannel, which is a Cisco technology for bonding or aggregating individual physical ports into a logical one. You need to know why we need this, under what conditions we can apply it, and how to apply it. All three modes are important: the static and the two dynamic methods with PaGP (Port Aggregation Protocol) and LACP (Link Aggregation Control Protocol). You should know the effect of pairing various modes — for example, when you pair auto-auto or passive-passive modes, EtherChannel won’t form.

On multi-layer switches, we can use the ports as switch ports and routed ports, too. In the latter case, we can form a Layer3 EtherChannel in the same manner as in Layer2, so you shouldn’t learn a totally different concept.

Where should I focus my study time?

Just like any other discipline, LAN switching has its theory, but it’s not really so complicated and heavy. STP could be considered an exception to that rule, but once you understand the STP theory, the configuration is really very simple.

The emphasis should be on practice, and I recommend creating a lot of labs, because practical knowledge comes during this kind of activity. If you can access some real devices, fine, but if you can only use a simulator like Packet Tracer, that’s fine also. All the necessary protocols are there and you can experiment freely even with larger topologies.

If I were to emphasize the most important topics, then I would definitely mention VLANs (and related protocols) and STP. The majority of the questions are dealing with these technologies, so if you know them well, you’ll definitely earn enough points from this segment.

Conclusion

LAN switching is one of the most important topics in the CCNA exam because switches are essential parts of a network. If the physical layer and Layer2 (at which switches operate) are stable and error-free, then we can expect our network to operate properly. In order to do this, you should know the switching theory, as well as configuring and troubleshooting, especially the VLANs and related protocols (DTP, VTP), STP and EtherChannel. If you can lock down those topics, you’re well on your way to an exemplary CCNA exam score.

 

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