Ether Channel Lab Tips

  • If configuring mode as on then you must configure the other end on within60 seconds! otherwise Spanning Tree will consider this as a loop. Better, shut down the interface and then configure and unshut once both sides are done.
  • show etherchannel load-balance will show the current load balancing algorithm.
  • From global command, port-channel load-balance will allow you to change the algorithm.
  • port-channel and etherchannel commands and sub-commands for link aggregation.
  • All interfaces in the port-channel will inherit the configuration. so just configure logical to save time as physical interfaces will inherit config i.e. configure port-channel 12 instead of fa0/16 etc

Ether-Channel Crib Notes

These are my ‘crib notes’ that I’ve made to serve as a last minute refresher. Please forgive the grammer / spelling as I did not develop these notes with publishing in mind.

Ether Channel                                                                                                                                  

*** Theory ***

  • Etherchannels – Aggregate ports. STP sees it as one link so one link failure will not trigger STP recalculation.  Uses XOR algorithm to determine data send load. You can see the port cost change to verify that the bandwidth has been aggregated
  • Protocols
    • LACP (802.3ad) – Assigns priority value to each port, up to 16 ports can be bundled, but only 8 lowest priority ports will be used at one time. Other are backup
      • Active mode – Will initiate the negotiation
      • Passive Mode – Will wait for partner to initiate
  • PAgP (Cisco) – PagP check the remote port group number (must match), Must be from same device ID e.g. same switch.
    • Dynamic mode – Will initiate the negotiation
    • Auto mode – Will wait for partner to initiate
  • ON – No negotiation
  • Catches: Dynamic Vlans can’t be used in EC. Allowed VLANS must match on both partners.  Following must match for all ports in EC; speed, duplex, native vlan,


*** Commands ***

  • Config-if# channel-group number //Create Etherchannel group
  • Config-if# channel-group 1 mode // What mode PAgP , LACP or ON+
  • Show etherchannel summary