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11 - Day 23 - EtherChannel.md

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Day 23 - EtherChannel

Reviewed: No

Introduction:

  • EtherChannel allows grouping multiple physical interfaces into a single logical interface.
  • Benefits include increased bandwidth, redundancy, and simplified management.
  • The CCNA exam requires understanding how to configure and verify both Layer 2 and Layer 3 EtherChannels using the Link Aggregation Control Protocol (LACP).

Key Concepts:

  1. Problem Solved by EtherChannel:
    • Adding multiple links between switches without EtherChannel leads to only one link being active due to Spanning Tree Protocol (STP), which disables other links to prevent Layer 2 loops.
    • EtherChannel solves this by grouping multiple physical interfaces, treating them as a single logical interface, which STP then treats as one interface.
  2. EtherChannel Functionality:
    • EtherChannel is represented in network diagrams by a circle around grouped interfaces.
    • Traffic is load-balanced across the physical interfaces in the EtherChannel using an algorithm based on “flows” between nodes.
    • Load balancing inputs can be the source MAC address, destination MAC address, source IP address, destination IP address, or both source and destination MAC/IP addresses.

EtherChannel Load Balancing:

  • Flow-Based Load Balancing: Traffic in the same flow uses the same physical interface to avoid out-of-order packet delivery.
  • Load Balancing Methods:
    • Source MAC Address
    • Destination MAC Address
    • Source and Destination MAC Addresses
    • Source IP Address
    • Destination IP Address
    • Source and Destination IP Addresses
  • Changing Load-Balancing Method:
    • Use the command PORT-CHANNEL LOAD-BALANCE <method> in global configuration mode.
    • Example: PORT-CHANNEL LOAD-BALANCE src-dst-mac.

EtherChannel Configuration Methods:

  1. PAgP (Port Aggregation Protocol):
    • Cisco proprietary protocol.
    • Modes:
      • Desirable: Actively negotiates the formation of an EtherChannel.
      • Auto: Forms an EtherChannel if the other side is set to desirable.
  2. LACP (Link Aggregation Control Protocol):
    • IEEE 802.3ad standard.
    • Preferred method due to cross-vendor compatibility.
    • Modes:
      • Active: Actively negotiates the formation of an EtherChannel.
      • Passive: Forms an EtherChannel if the other side is set to active.
  3. Static EtherChannel:
    • No negotiation protocol is used.
    • Interfaces are manually configured to form an EtherChannel using the on mode.

Commands for EtherChannel:

  • SHOW Commands:
    • SHOW ETHERCHANNEL LOAD-BALANCE: Displays the current load-balancing method.
    • SHOW ETHERCHANNEL SUMMARY: Displays a summary of all EtherChannels on the switch, including status flags for both port-channel interfaces and physical member interfaces.
    • SHOW ETHERCHANNEL PORT-CHANNEL: Provides more detailed information about the port-channel interfaces.
    • SHOW INTERFACES TRUNK: Verifies the trunk status of the port-channel interface.
    • SHOW RUNNING-CONFIG: Checks configurations applied to both port-channel and physical interfaces.
  • Configuration Commands:
    • INTERFACE RANGE <range>: Configures multiple interfaces at once.
    • CHANNEL-GROUP <number> MODE <mode>: Configures interfaces to be part of an EtherChannel. Mode options include desirable, auto, active, passive, and on.
    • CHANNEL-PROTOCOL <protocol>: Manually sets the EtherChannel protocol (LACP or PAgP) but is generally unnecessary.
    • NO SWITCHPORT: Configures Layer 3 EtherChannel by converting interfaces to routed ports.
    • INTERFACE PORT-CHANNEL <number>: Enters the configuration mode for the virtual port-channel interface to configure additional settings like IP addressing or trunking.

Layer 3 EtherChannel:

  • Configuration:
    • Convert physical interfaces to routed ports using NO SWITCHPORT.
    • Create the EtherChannel with the CHANNEL-GROUP command.
    • Configure the IP address on the port-channel interface.
    • Example commands:
      • INTERFACE RANGE <range>
      • NO SWITCHPORT
      • CHANNEL-GROUP <number> MODE <mode>
      • INTERFACE PORT-CHANNEL <number>
      • IP ADDRESS <address> <subnet>
  • Verification:
    • SHOW ETHERCHANNEL SUMMARY will display the Layer 3 EtherChannel with an R flag, indicating it’s a routed port-channel.

Summary of Key Commands:

  • PORT-CHANNEL LOAD-BALANCE <method>: Configures load-balancing method.
  • SHOW ETHERCHANNEL LOAD-BALANCE: Displays load-balancing method.
  • CHANNEL-GROUP <number> MODE <mode>: Configures EtherChannel on interfaces.
  • SHOW ETHERCHANNEL SUMMARY: Summary of EtherChannel status.
  • SHOW ETHERCHANNEL PORT-CHANNEL: Detailed EtherChannel information.
  • NO SWITCHPORT: Converts interfaces to Layer 3 for Layer 3 EtherChannel.
  • INTERFACE PORT-CHANNEL <number>: Configures the port-channel interface.