By configuring EtherChannel, we bundle multiple physical connections between two or more Cisco switches into one logical link. This allows for increased bandwidth, improved fault tolerance, and load balancing across the aggregated links. EtherChannel also provides a more efficient use of available network resources and simplifies the management of network connections between switches.
In a conventional network where STP blocks one link to avoid switching loops, EtherChannel forces STP to see both paths or bundled as one logical link while avoiding switching loops.
Cisco IOS Release 15.0SY supports a maximum of 128 EtherChannels.
You can create an EtherChannel with up to eight LAN ports on any switching module.
All LAN ports in each EtherChannel must be the same speed and must all be configured as either Layer 2 or Layer 3 LAN ports.
You can configure EtherChannels manually or you can use the Port Aggregation Control Protocol (PAgP) or the Link Aggregation Control Protocol (LACP) to create EtherChannels.
The EtherChannel protocols allow ports with similar characteristics to form an EtherChannel through dynamic negotiation with connected network devices. PAgP is a Cisco-proprietary protocol while LACP is standard or multi-vendor as defined in IEEE 802.3ad.
Ports configured to use PAgP cannot form EtherChannels with ports configured to use LACP also ports configured to use LACP cannot form EtherChannels with PAgP.
SW1 and SW2 are connected by two crossover cables, one cable connecting port fa0/1 on both switches and the other connecting fa0/2 on both switches.
How to Configure EtherChannel on the Cisco Switch
To enable EtherChannel on an interface, you must configure all ports within the bundle the same as well as their operation status. This means that both ends of an EtherChannel require a similar configuration.
The example below demonstrates the configuration and verification of EtherChannel. You can use the latest version of Packet Tracer version 6.0.1.0011 for practice.
EtherChannel configuration command:
Switch(config)# interface range fa0/1 – 8 {You can use the range or single interface}
Switch(config-if)# channel-group [1 – 6] mode [auto | desirable | on | active | passive]
The EtherChannel Configuration Modes.
Auto: This mode activates PAgP. This is Cisco proprietary implementation (for networks with only Cisco Switches), it places a LAN port into a passive negotiating state, in which the port responds to PAgP packets it receives but does not initiate PAgP negotiation. (Default).
e.g configuration:
SW1(config)#interface range f0/1-2
SW1(config-if-range)#channel-group 1 mode auto
SW1(config-if-range)#end
SW1#
Desirable: This mode also activates PAgP. This is Cisco proprietary implementation and the most recommended mode, it places a LAN port into an active negotiating state, in which the port initiates negotiations with other LAN ports by sending PAgP packets.
e.g configuration:
SW1(config)#interface range f0/1-2
SW1(config-if-range)#channel-group 1 mode desirable
SW1(config-if-range)#end
SW1#
Active activate LACP. This is the industry standard implementation (network with different vendor switches), This mode places a port into a passive negotiating state, in which the port responds to LACP packets it receives but does not initiate LACP negotiation. (Default).
e.g configuration:
SW1(config)#interface range f0/1-2
SW1(config-if-range)#channel-group 1 mode active
SW1(config-if-range)#end
SW1#
Passive activate LACP.This is the industry standard implementation (network with different vendor switches). This mode places a port into an active negotiating state, in which the port initiates negotiations with other ports by sending LACP packets.
e.g configuration:
SW1(config)#interface range f0/1-2
SW1(config-if-range)#channel-group 1 mode passive
SW1(config-if-range)#end
SW1#
Mode forces the interface to channel traffic without PAgP or LACP. You can only use the on mode if only a LAN port group in the on mode is connected to another LAN port group in the on mode.
e.g configuration :
SW1(config)#interface range f0/1-2
SW1(config-if-range)#channel-group 1 mode on
SW1(config-if-range)#end
SW1#
How to Verify EtherChannel on Cisco Switch
After your configuration, use the show spanning-tree command to view the spanning-tree for VLAN 1; you will see only a port-channel, the spanning-tree cost and you will also notice that the port-channel is now being considered as spanning-tree type shared.
You can add more physical ports, Spanning tree will see the logical port-channel as a single port.
Switch0# show spanning-tree
VLAN0001
Spanning tree enabled protocol rstp
Root ID Priority 32769
Address 0bC0.75DA.09cB
Cost 9
Port 27(Port-channel 1)
Hello Time 2 sec Max Age 20 sec Forward Delay 15 sec
Bridge ID Priority 32769 (priority 32768 sys-id-ext 1)
Address 00D0.e011.2C03
Hello Time 2 sec Max Age 20 sec Forward Delay 15 sec
Aging Time 20
Interface Role Sts Cost Prio.Nbr Type
—————- —- — ——— ——– ——————————–
Po1 Root FWD 9 128.27 Shr
Summary
An EtherChannel is a virtual interface that combines several physical interfaces.
Spanning tree treats an EtherChannel as a single interface, so it does not disable duplicate physical connections.
There are three ways to configure an EtherChannel:
- PAgP: A protocol exclusive to Cisco.
- LACP: An industry standard established by IEEE.
- Manual: Combining multiple physical interfaces without a protocol.
EtherChannels offer various load-balancing choices. Be sure to choose a load-balancing method that aligns with your traffic patterns.
Understanding Simple Network Management Protocol-SNMP
Spanning Tree Protocol (STP) VLAN Trunking Protocol (VTP) IPv6 EIGRPv6
RIPv6 OSPFv3 DHCPv6
