Cisco CCNA Certification How And Why Switches Trunk
Below is a MRR and PLR article in category Computers Technology -> subcategory Computer Certification.
Cisco CCNA Certification: Understanding How and Why Switches Trunk
Summary
To excel as a network administrator and achieve your CCNA certification, it's crucial to grasp not only why Cisco switches use trunking but also how it functions. Dive into these essential insights with this tutorial from Chris Bryant, CCIE12933.
Article Body
As you pursue your CCNA certification, you'll encounter extensive information about switches?"an essential foundation for configuring and troubleshooting Cisco switches both on the exam and in the real world. This is especially true for trunking!Trunking allows two or more switches to communicate and transfer frames to remote hosts. Understanding the primary trunking protocols is vital for exam and real-world success. First, let’s cover the necessary cables.
To connect two Cisco switches, you'll need a crossover cable. These cables contain eight wires, with four crossing over from one pin to another. On many modern Cisco switches, simply connecting them with a crossover cable creates a trunk. For example, 2950 switches automatically trunk when linked with the correct cable. Using the wrong cable will leave you troubleshooting longer than necessary!
Today's Cisco switches utilize two trunking protocols: ISL and IEEE 802.1Q (commonly known as "dot1q"). Here are the key differences:
1. Proprietary vs. Industry Standard: ISL is a Cisco-proprietary protocol, while dot1q is the industry standard. In a multivendor environment, ISL might not be suitable. Moreover, some Cisco switches only support dot1q despite ISL being Cisco’s own protocol.
2. Encapsulation Overhead: ISL encapsulates the entire frame, increasing overhead. Dot1q adds only a header to the frame and sometimes skips even that, resulting in significantly less overhead compared to ISL.
3. Native VLAN Handling: The native VLAN is the default VLAN for switch ports that aren't explicitly assigned another VLAN. On Cisco switches, this is typically VLAN 1, though it can be changed. With dot1q, frames sent across the trunk that lack a header are presumed to belong to the native VLAN. ISL, however, encapsulates all frames regardless of their VLAN, ignoring the concept of a native VLAN entirely.
Switching theory is a fundamental aspect of your CCNA studies and can initially seem daunting. Break down your studies into manageable pieces, and you'll soon earn the prestigious "CCNA" designation!
You can find the original non-AI version of this article here: Cisco CCNA Certification How And Why Switches Trunk.
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