EtherChannel Configuration

EtherChannel is a port link aggregation technology. It allows grouping of several physical Ethernet links to create one logical Ethernet link for the purpose of providing fault-tolerance and high-speed links between switches, routers and servers. Without EtherChannel, only one link will be available while the rest of the links will be disabled by STP, to prevent loop. An EtherChannel can be created from between two to eight Ports.
EtherChannel Negotiation
An EtherChannel can be established using one of three mechanisms:
PAgP – Cisco’s proprietary negotiation protocol. There are different modes.
  • Desirable: In this mode, the negotiation will be initiated by sending the special frames to form EtherChannel with the other end.
  • Auto: In this mode, negotiation is not initiated. It only responds to the special frames received for negotiation form the other end. So, if both ends are in Auto mode, EtherChannel would not be formed.
LACP This is Standards-based (IEEE 802.3ad) negotiation protocol. Link Aggregation Control Protocol, is used to dynamically build an EtherChannel. There are different modes.
  • Active: The active end of the group sends out a LACP frame and initiates the negotiation to form the EtherChannel. Both ends could be active and the result would be the same.
  • Passive: Passive Mode does not initiate the negotiation. It just responds to LACP packets initiated by other end. So if both ends were passive, the EtherChannel would not be formed.
Static Persistence (“On”) – No negotiation protocol is used
 For this configuration, I am using GNS3 with IOSv-L2

Perform these Task for configuring EtherChannel.

  • Configure LACP between SW1 and SW2. SW1 should actively try to initiate an Etherchannel and SW2 should only respond to requests.
  • Configure PAGP between SW1 and SW3. SW1 should actively try to initiate an Etherchannel and SW3 should only respond to requests.
  • Configure an Etherchannel between SW2 and SW3 without any negotiation protocols.
  • Configure the Etherchannel between SW1 and SW2 to use destination MAC address load-balancing.
Topology
Configurations of LACP Between Switch 1 and Switch 2
SW1(config)#interface range gi0/0-1
SW1(config-if-range)#channel-group 1 mode active 

SW2(config)#interface range gi0/0-1
SW2(config-if-range)#channel-group 1 mode passive

Verify using show EtherChannel summary command

Configurations of PAgP Between Switch 1 and Switch 3
SW1(config)#interface range gi0/2-3
SW1(config-if-range)#channel-group 1 mode desirable
Verify using show EtherChannel summary command

SW3(config)#interface range gi0/2-3
SW3(config-if-range)#channel-group 1 mode auto
Verify using show EtherChannel summary command

Configurations of Static (On) EtherChannel Between Switch 2 and Switch 3
SW2(config)#interface range gi0/2-3
SW2(config-if-range)#channel-group 1 mode on
Verify using show EtherChannel summary command. 

SW3(config)#interface range gi0/2-3
SW3(config-if-range)#channel-group 1 mode on
Verify using show EtherChannel summary command

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