[Show Running-Config] - P1 - Configure EtherChannel

This post summarizes how to configure EtherChannel using different methods based on the bundling and link aggregation negotiation protocol. EtherChannel can be configured using the Port Aggregation Protocol (PAgP), developed by Cisco, and the Link Aggregation Control Protocol (LACP), which is an international standard.

Method 1: Using LACP (Link Aggregation Control Protocol)

Step 1: Select Ports and Enter Configuration Mode

Identify the physical ports you wish to bundle and enter configuration mode.

Switch> enable
Switch# configure terminal

Step 2: Create EtherChannel with LACP

Use LACP to negotiate the EtherChannel formation automatically.

Switch(config)# interface range FastEthernet0/1 - 4
Switch(config-if-range)# channel-group 1 mode active
Switch(config-if-range)# exit

In this example, "mode active" initiates LACP negotiation.

Method 2: Using PAgP (Port Aggregation Protocol)

Step 1: Select Ports and Enter Configuration Mode

Similar to the above, identify the ports and enter configuration mode.

Switch> enable
Switch# configure terminal

Step 2: Create EtherChannel with PAgP

PAgP also supports automatic negotiation but is a Cisco-developed protocol.

Switch(config)# interface range FastEthernet0/1 - 4
Switch(config-if-range)# channel-group 1 mode desirable
Switch(config-if-range)# exit

"mode desirable" initiates PAgP negotiation.

Method 3: Configuring EtherChannel Without Negotiation

Step 1: Select Ports and Enter Configuration Mode

Identify the ports you want to bundle.

Switch> enable
Switch# configure terminal

Step 2: Create EtherChannel Without Negotiation

This configures EtherChannel without using automatic negotiation.

Switch(config)# interface range FastEthernet0/1 - 4
Switch(config-if-range)# channel-group 1 mode on
Switch(config-if-range)# exit

Using "mode on" to create EtherChannel without LACP or PAgP.

Final Step for All Methods: Configuring the Port-Channel

After creating the EtherChannel, configure the Port-Channel.

Switch(config)# interface Port-channel 1
Switch(config-if)# description Link to Other Switch
Switch(config-if)# switchport mode trunk

Verify Configuration

Check the EtherChannel status:

Switch# show etherchannel summary

Note that when using EtherChannel, all ports in the group must have the same configuration (speed, duplex, and switchport settings). Configuration mismatches can cause issues with the formation or operation of the EtherChannel.

Some notes:

In EtherChannel, ports can negotiate to form a Link Aggregation using two common protocols: PAgP (Port Aggregation Protocol) and LACP (Link Aggregation Control Protocol). Below is a table describing how ports negotiate in EtherChannel using these protocols:

In the table:

• Active: This port will actively negotiate an EtherChannel link using the LACP protocol.
• Desirable: This port will actively invite negotiation to form an EtherChannel link using the PAgP protocol.
• Passive: This port waits for a negotiation request from a partner; if the partner is in "active" mode, an EtherChannel link can be formed.
• Auto: Similar to "passive" in PAgP, this port waits for an invitation from a partner in "desirable" mode.
• On: This port will automatically join an EtherChannel link without any negotiation protocol; both ends need to be set to "on" for the link to function.

Note that when two ports are in the same mode (e.g., both are "active" or both are "passive"), an EtherChannel link will be formed. However, if both ports are in a non-negotiating mode (e.g., both are in "auto" or "passive" for PAgP), a link will not be established.