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02 - Day 9 - Switch Interfaces.md

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Day 9 - Switch Interfaces

Reviewed: No

Key Concepts

Interface Speed and Duplex

  • Speed: Data rate in bits per second (e.g., 10, 100, 1000 Mbps).
  • Duplex: Whether a device can send and receive data simultaneously.
    • Full Duplex: Send and receive at the same time.
    • Half Duplex: Cannot send and receive at the same time.

Speed and Duplex Autonegotiation

  • Devices negotiate speed and duplex settings automatically.
  • Interface Status: Using show ip interface brief to check Layer 1 and 2 status.

Interface Counters and Errors

  • Cisco devices keep counters for traffic and errors.
  • show interfaces command provides detailed statistics.

Network Topology

  • Single LAN: 192.168.1.0/24 with 1 router (R1), 2 switches (SW1, SW2), and 4 PCs.
  • Focus on SW1 and its interfaces (F0/1 to F0/4).

CLI Commands

Initial Configuration

  1. Enter privileged exec mode: enable
  2. Check interface status: show ip interface brief
    • Connected interfaces: up/up
    • Unconnected interfaces: down/down
    • Router interfaces: administratively down by default
    • Switch interfaces: enabled by default

Configuring Interfaces

  • Speed: speed {10 | 100 | auto}
  • Duplex: duplex {auto | full | half}
  • Description: description <text>

Example Configuration

  • Configure interface F0/1:

    interface f0/1
speed 100
duplex full
description ## Connected to R1 ##

  • Check configuration: show interfaces status

Handling Unused Interfaces

  • Disable unused interfaces for security:

    interface range f0/5 - 12
description ## Unused ## 
shutdown

Interface Errors

  • Common Error Counters:
    • Runts: Frames smaller than 64 bytes.
    • Giants: Frames larger than 1518 bytes.
    • CRC Errors: Frames with cyclic redundancy check failures.
    • Frame Errors: Frames with incorrect format.

Detailed Topics

Half Duplex and Full Duplex

  • Half Duplex: Cannot send and receive simultaneously.
    • Collision domains, handled by CSMA/CD (Carrier Sense Multiple Access with Collision Detection).
  • Full Duplex: Can send and receive simultaneously.
    • Used in modern networks with switches, reducing collisions.

Autonegotiation

  • Interfaces negotiate best speed and duplex settings.
  • If autonegotiation fails, switches default to the lowest speed and half duplex.

Error Analysis

  • Use show interfaces to view detailed error statistics.

Quiz

  1. Question 1: What results from a duplex mismatch between two interfaces?
    • Answer: B, collisions will occur.
  2. Question 2: What is used on half-duplex interfaces to detect and avoid collisions?
    • Answer: A, CSMA/CD.
  3. Question 3: Which command shows various counters of errors detected on an interface?
    • Answer: A, show interfaces.
  4. Question 4: Which are examples of errors that might occur on a network interface?
    • Answer: D, runts, giants, CRC.
  5. Question 5: What speed and duplex settings will SW1 use if SW2 has autonegotiation disabled and is set to 100 Mbps full duplex?
    • Answer: B, speed 100 Mbps, duplex half.