Podcast Beta
Questions and Answers
What is a LAN?
A LAN is a single broadcast domain, including all devices that will receive a broadcast frame.
How many broadcast domains can you identify in this network?
What is a VLAN?
VLANs are configured on switches on a per-interface basis to logically separate end hosts at layer 2.
What is an access port?
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What are trunk ports used for?
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What are the two main trunking protocols?
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What is the length of the VLAN tag in Ethernet frames?
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What is the purpose of the Drop Eligible Indicator (DEI)?
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What is the VLAN range for normal VLANs?
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What is the default native VLAN on all trunk ports?
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Study Notes
LAN Overview
- A LAN (Local Area Network) is a single broadcast domain comprising all devices that receive broadcast frames.
- A broadcast domain refers to the group of devices responding to a broadcast frame with a specified destination MAC address (FFFF.FFFF.FFFF).
VLAN Introduction
- VLAN (Virtual Local Area Network) logically segments end hosts at Layer 2 of the OSI model, improving network management and performance.
- Reduces unnecessary broadcast traffic, enhancing overall network performance.
- Provides security by limiting access and allowing tailored security policies through routers and firewalls.
VLAN Configuration Basics
- VLANs are set up on switches per interface, with VLAN 1 and VLANs 1002-1005 existing by default and non-deletable.
- Access ports belong to a single VLAN, usually connecting to end devices, while trunk ports can support multiple VLANs.
Trunk Port Functionality
- In small networks, individual interfaces can connect switches and routers for each VLAN, but this becomes impractical as VLAN numbers increase.
- Trunk ports consolidate traffic from multiple VLANs over a single interface, optimizing interface usage.
- Frames sent over trunk links are tagged for identification by receiving switches, distinguishing between access ports (untagged) and trunk ports (tagged).
VLAN Tagging Protocols
- Two primary trunking protocols exist:
- ISL (Inter-Switch Link): An older, Cisco proprietary protocol.
- IEEE 802.1Q: The industry standard protocol commonly referred to as dot1q.
802.1Q Tag Structure
- The 802.1Q VLAN tag is 4 bytes (32 bits) in length, comprising two fields:
- Tag Protocol Identifier (TPID): 16 bits indicating the frame is 802.1Q tagged with a fixed value of 0x8100.
- Tag Control Information (TCI): 16 bits broken into three sub-fields.
TCI Sub-fields
- PCP (Priority Code Point): 3 bits used for Class of Service (CoS) to prioritize important traffic.
- DEI (Drop Eligible Indicator): 1 bit indicating frames that may be dropped during congestion.
- VID (VLAN ID): 12 bits identifying the VLAN, with a range of 1-4094 (0 and 4095 are reserved).
VLAN Ranges
- VLANs are categorized into:
- Normal VLANs: 1-1005.
- Extended VLANs: 1006-4094.
Native VLAN Concept
- The native VLAN is set to VLAN 1 by default on all trunk ports but can be changed manually.
- Untagged frames received on trunk ports are assumed to belong to the native VLAN, making configuration consistency crucial.
Trunk Configuration Summary
- Proper configuration of trunk ports is essential for seamless VLAN communication and network efficiency.
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Description
Explore the fundamentals of VLANs and LANs with this quiz. Learn about broadcast domains, their impact on network performance, and how many broadcast domains can be identified in a given network. Test your understanding of these critical networking concepts.
