Ethernet Switching and Network Infrastructure Fundamentals

Ethernet Switching
Objectives:
● 1.2 - Compare and contrast networking appliances, applications, and functions
● 2.2 - Given a scenario, configure switching technologies and features
● 4.3 - Given a scenario, apply network security features, defense techniques, and
solutions
● Ethernet Fundamentals
○ Introduction to Ethernet
■ Early computer networks lacked standardization, leading to various
competing technologies
■ Ethernet emerged as the dominant protocol for Layer 2 communication in
local area networks (LANs)
○ Evolution of Ethernet
■ Originally, Ethernet used coaxial cables with BNC connectors and vampire
tabs (10Base2 and 10Base5)
■ Transitioned to 10Base-T Ethernet
● Utilizes twisted pair cables (Cat 3)
● 10 Megabits per second (Mbps) speed, significant at the time
(1980s)
● Covers distance of up to 100 meters only
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CompTIA Network+
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○ Deterministic vs. Contention-based Access
■ Deterministic Access
● Organized and orderly access (e.g., Token Ring)
■ Contention-based Access
● Chaotic, but more efficient use of bandwidth (e.g., Ethernet)
○ Carrier Sense Multiple Access with Collision Detection (CSMA/CD)
■ Allows devices to detect collisions and manage network access
■ Carrier Sensing (CS)
● Devices listen for existing transmissions
● Carrier
○ Refers to the signal that carries information or data in
electronics
■ Multiple Access (MA)
● Many devices can access the network simultaneously
■ Collision Detection (CD)
● Devices detect and handle collisions
● Random Back-off Timer
○ Devices involved in collisions pause, then select random
back-off times before retransmitting
○ Allows two devices to attempt to retransmit again when
the timer hits zero
○ Avoids simultaneous retransmissions, reducing collisions
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○ Collision Domain
■ Area where collisions can occur
○ Ethernet Switches
■ Break networks into smaller collision domains, improving efficiency
■ Each switch port is its collision domain, allowing full-duplex
communication
○ Key Takeaways
■ Ethernet is the primary Layer 2 protocol for modern networks
■ Switches are preferred over hubs for efficient network management
● Network Devices
○ Hubs
■ Layer 1 device
■ Known as multi-port repeaters
■ Types:
● Passive – repeats signal without amplification
● Active – boosts signal to overcome cable length limitations
● Smart – active hub with enhanced features like SNMP for remote
configuration
■ Connect collision domains, making them bigger
○ Bridges
■ Layer 2 device
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■ Analyzes source MAC addresses to populate MAC address table
■ Makes forwarding decisions based on destination MAC addresses
■ Breaks up collision domains and adds security and efficiency to networks
○ Switches
■ Layer 2 device
■ Modern alternative to hubs, known as multiport bridge
■ Each port acts as a separate collision domain
■ Learns MAC addresses and makes forwarding decisions based on MAC
tables
■ Efficiently manages traffic, reduces collisions, and improves security
■ Full duplex support allows simultaneous communication without
interference
○ Routers
■ Layer 3 device
■ Operate based on IP addresses
■ Connect dissimilar networks and makes routing decisions
■ Separates broadcast domains, enhances network efficiency
■ Support various interface types for versatile connectivity
○ Layer 3 Switches (Multilayer Switches)
■ Combine functions of switches and routers
■ Operate at Layer 3 like routers, with each port as a broadcast domain
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■ Efficient for internal networks but less effective for large-scale routing
operations
○ Exam Tips
■ Switches – Layer 2 devices focused on MAC addresses unless specified as
multilayer or Layer 3 switches
■ Routers – considered Layer 3 devices focused on IP addresses
■ If the exam question mentions multilayer or Layer 3 switch, treat it like a
router
● Understanding Network Devices: Demonstration
● Virtual Local Area Network (VLAN)
○ Virtual Local Area Network (VLAN)
■ Logical subdivision of a network that segments it into separate broadcast
domains
■ Unlike traditional LANs, VLANs group hosts together regardless of physical
connections
■ Achieved through software rather than hardware and cabling
■ Benefits:
● Flexibility in network configuration
● Efficient resource allocation and management
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CompTIA Network+
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○ Traditional LAN vs. VLAN
■ Before VLANs, separate network segments required additional routers,
cables, and switches
■ VLANs reduce hardware requirements by allowing different logical
networks to share the same physical hardware
○ How VLANs Work
■ Operate at Layer 2 (Data Link Layer) of the OSI model
■ Switches tag each data frame with a VLAN identifier (ID) as it passes
through, defining its VLAN
■ Tags
● Used to determine the path of frames, ensuring they stay within
their VLAN
○ Reasons for Using VLANs
■ Enhanced Security
● Isolate sensitive data, reduce data breach risks
■ Improved Performance
● Reduce broadcast domain size, decrease unnecessary traffic
■ Increased Management
● Easier policy implementation, troubleshooting
■ Cost Efficiency
● Utilize existing infrastructure more effectively, reduce hardware
requirements
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○ VLAN Database
■ Contains VLAN configurations for switches
● Identifier
● Name
● MTU size
■ Cisco Switch
● VLAN.DAT
○ Ensures consistent VLAN configurations and easy
deployment across the network
○ Switch Virtual Interface (SVI)
■ Virtual interface on a switch providing Layer 3 processing for VLANs
■ Allows routing between VLANs without the need for a separate router
■ Enhances network efficiency by minimizing additional routing devices
● VLAN Configuration
○ Virtual Local Area Network (VLAN)
■ Offers flexibility, performance, and security in network design
■ Proper configuration is essential
○ 802.1Q Tagging
■ Refers to IEEE standard that facilitates the management of multiple
VLANs on a single network
■ Essential for VLAN configurations
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■ Inserts VLAN tags into Ethernet frames
● Tags contain VLAN identifiers (VIDs) for switch identification and
forwarding
● Trunking
○ Transmission of traffic from different VLANs across the
same physical network infrastructure while keeping that
traffic from each VLAN separate and secure
○ Native VLAN
■ One VLAN on a trunk port that does not get tagged with VID
■ Default VLAN for untagged frames
■ Used for devices that do not support VLAN tagging
■ Should be consistently configured across interconnected switches to
avoid misrouting
○ Voice VLAN
■ Dedicated VLAN for voice traffic (VoIP)
■ Ensures quality and reliability of voice communications by segregating
voice traffic
■ Enables the application of quality of service (QoS) policies for better voice
call quality
○ Link Aggregation
■ Also known as port channeling/bonding, combines multiple network
connections into a single logical link
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■ Enhances bandwidth capacity and provides redundancy for network
availability
■ Commonly used for trunking lines between switches and for high-speed
connectivity in data centers
○ Speed and Duplex Configurations
■ Settings that determine the rate at which data is transmitted and the
mode of communication between the network devices
■ Speed
● Refers to the rate of data transfer (Mbps or Gbps)
■ Duplex
● Refers to how data is sent
● Half duplex
○ Device can either send or receive data, but cannot do both
at the same time
● Full duplex
○ Allows device to send and receive data simultaneously
■ Misconfigurations can significantly impact network performance and
throughput
○ Configuration Best Practices
■ Auto-negotiation
● commonly used when devices automatically select the highest
performance settings that they have in common
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■ Consider manual configurations for specific requirements
● Understanding VLANs Demonstration
● Spanning Tree Protocol (STP)
○ Spanning Tree Protocol (STP)
■ Additional Ethernet feature for preventing loops in network traffic
■ Known as 802.1d
○ Importance of STP
■ Enables redundant links between switches
■ Prevents broadcast storms and ensures network availability
○ Network Without STP
■ Can lead to switching loops and broadcast storms
● Broadcast Storm
○ Multiple copies of frames being forwarded back and forth
which then consumes the network
○ STP Functionality
■ Uses a root bridge and non-root bridges
● Root bridge
○ Where a switch is elected to act as a reference point for
the entire spanning tree
○ Elects root bridge based on lowest Bridge ID (BID)
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■ Bridge ID (BID)
● Made up of a priority value and a MAC
address, with the lowest value being
considered the root bridge
● Non-root bridge
○ Every other switch on the STP topology
○ STP Port Types
■ Root port
● Every non-root port has a single root port, closest to root bridge in
terms of cost
● If cost is determined based on cable types:
○ The lowest port number on the switch will be chosen
○ Faster cables – lower cost
○ Slower cables – higher cost
■ Designated port
● On every network segment, closest to root bridge in terms of cost
● All ports on root bridge
■ Non-designated port
● Blocks traffic to prevent loops
○ STP Port States
■ Blocking
● Stops forwarding frames
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CompTIA Network+
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■ Listening
● Learns MAC addresses but does not forward frames
■ Learning
● Processes BPDU and determines role in spanning tree
■ Forwarding
● Forwards frames as designated or root port
○ Link Cost
■ Associated with link speed
● Lower speed – Higher cost
● Higher speed – Lower cost
● Network Access Control
○ Network Access Control (NAC)
■ A method for increasing the security of a given network by inspecting
devices as they try to connect to the network to determine if they're
secure enough to be granted access
○ NAC Process
■ Devices present themselves for inspection when connecting to the
network
■ Devices are isolated and inspected based on NAC configurations
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■ Inspection process:
● Port Security
○ Secures physical network ports to prevent unauthorized
access
○ Limits the number of devices that can connect to a
network switch or hub
○ Can be configured to allow specific MAC addresses or a set
of specified MAC addresses
● MAC Filtering
○ Controls access to the network based on devices' unique
MAC addresses
○ Maintains a list of approved MAC addresses
■ Allow listing
● Only approved MAC addresses allowed
■ Block listing
● All devices allowed except those on the list
■ 802.1X Authentication
● Provides an authentication framework for networks
● Ensures only authenticated users can access network services
● Encapsulates the Extensible Authentication Protocol (EAP) within
networks frames to enable more robust authentication
mechanisms
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● Three components
○ Supplicant – user device
○ Authenticator – network device
○ Authentication server – authenticates user device
○ Implementation
■ Can be used in conjunction with port security, MAC filtering, and 802.1X
authentication
■ Persistent agent
● For company-provided computers
■ Non-persistent agents
● For personally owned devices
● Use captive portals
■ Devices that fail inspection are either denied access or placed in a
quarantine zone for further remediation
○ Advanced NAC Features
■ Time-based Access Control
● Limits network access based on specified hours
■ Location-based Access Control
● Verifies the physical location of the device
■ Role-based Access Control
● Grants permissions based on user roles
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CompTIA Network+
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■ Rule-based Access Control
● Grants or denies access based on predefined rules
○ Benefits
■ Strengthen network security by ensuring only authenticated devices can
access the network
■ Provide a scalable solution for modern and diverse network
infrastructures
● Maximum Transmission Unit
○ Maximum Transmission Unit (MTU)
■ Refers to the largest size of a frame that can be set over a network
■ Measured in bytes, dictates data transmission capacity
■ Analogous to maximum load capacity for frames within a network
○ Impact of MTU on Network Performance
■ Properly configured MTU ensures optimal data packet and frame size
● Enhances network performance and efficiency
■ MTU too high – packet loss and retransmission
■ MTU too low – increased overhead and slow network
○ MTU Configuration
■ Wired Ethernet
● Standard MTU size is 1500 bytes for efficiency and compatibility
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CompTIA Network+
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■ Wireless Networks
● Smaller MTU size due to instability and higher error rates
■ VPN and PPPoE Connections
● Require smaller MTU due to encapsulation overhead
● Recommended size – 1400 to 1420 bytes
■ Jumbo Frames
● Frames exceeding standard 1500 bytes
● Typically configured at 9000 bytes
● Beneficial for high bandwidth applications but require careful
configuration
● Challenges and considerations:
○ Not all network equipment supports jumbo frames
○ Fragmentation may occur if encountering smaller MTU
devices
○ Limited support in traditional network troubleshooting
tools
○ Consistent configuration across all network devices
necessary