EtherChannels

Static Configuration

Sections:

Overview:

  • Static Aggregation is an option to manually configure an EtherChannel without the negotiation process from the LACP or PAgP standards
  • Unlike the keepalives messages in LACP & PAgP, Static EtherChannels consist of no keepalive protocol features
  • Static Aggregation also provides no automatic failure detection or recovery
  • With Static Aggregation, it only uses one mode of configuration to successfully form an EtherChannel and consist of the following:

Static Modes of Operation

  • On
    • Setting On mode on one side of the logical link will need to be set to On mode on the other side of the link
    • No negotiation process takes place in the formation of the EtherChannel 

Cisco switch example of the supported available EtherChannel modes 

Lab Topology

Scenario: In this lab exercise, interfaces Gi0/2 and Gi0/3 from the HQ-AccessSW1 switch will be defined in a Static EtherChannel towards the HQ-DistroSW2 switch on ports F0/1 and F0/3.

Static Configuration

Note: Configuring physical ports in an EtherChannel can be accomplished when all ports are in an Up/Up or Down/Down state

  • It is generally recommended to shutdown the physical ports before defining an EtherChannel for the following reasons:
    • Avoids interface/port flapping
    • Ensures a smooth negotiation process
    • Prevents real-time traffic loss if Up/Up ports are actively being defined in an EtherChannel
    • Prevents configuration mismatch or conflicts 

LACP/PAgP/Static bundles all use a channel group number to define an EtherChannel.

Note:

  • On a switch, all local port members in an EtherChannel need to be configured with the same group number
  • Channel group numbers can be different across switches
    • Example: Switch (A) using channel group 1 & Switch (B) using channel group 2 to form a EtherChannel relationship
  • It is best practice to use the same channel group number between switches in an EtherChannel relationship for simplicity

After defining the EtherChannel on the neighbor switch (HQ-DistroSW2) now it is time to bring up the EtherChannel port (po1) on both switches.

Note: 

  • Configuration changes done on the EtherChannel interface will apply to all physical ports in the EtherChannel bundle
  • In this example, bringing up the EtherChannel interface will also bring up the physical ports Gi0/2 and Gi0/3 

Troubleshooting Show Commands

Scenario1: When EtherChannel is Working

Show etherchannel summary

  • Most common show command to verify if the configured EtherChannel is operating correctly 
  • Referring to the Flag key, physical ports showing a key 'P' states that the ports are bundled 
  • Other key statistics is the protocol the channel is operating on including the port channel number 

Show etherchannel 1 port-channel

  • Specifying the port channel number in the command, this command displays more detailed statistics of the EtherChannel interface including the physical ports in the bundle and the overall EtherChannel uptime  

Show etherchannel 1 detail

  • This command shows a more detailed view of each port in the EtherChannel bundle including the port state if any issues are present with the bundling of the physical port

Scenario2: When EtherChannel is not Working

Notes:

  • When a port(s) are having issues bundling into the EtherChannel, it is essential to refer back to the matching parameter pre-requisites list to ensure ports are sharing the same settings to successfully bundle into the channel
  • In this lab exercise, I've purposely changed the interface speed of the Gi0/3 interface to 10Mbps causing the port to go into a suspended state in the Static EtherChannel

Notes:

  • Issuing a more detailed command like 'show etherchannel 1 detail' can help spot any error messages associated with an unbundled port 
  • In this example, this command gives insights into the probable cause of a speed mismatch on port Gi0/3 causing it to go into a suspended state