EtherChannel Configuration

• A company needing increased bandwidth between two switches while avoiding blocked links with STP should use EtherChannel.

EtherChannel Defined

• It's a link aggregation technology grouping multiple physical Ethernet links into a single logical link.
• Network performance improves via increased bandwidth, redundancy, and load balancing across multiple links.
• A port-channel interface is the virtual interface created when configuring.
• STP views the EtherChannel as a single logical link, preventing blocking of individual links within.

EtherChannel Configuration and Requirements

• All member ports require the same speed, duplex, and VLAN configuration.
• Mixing Fast Ethernet and Gigabit Ethernet interfaces is not supported.
• A single EtherChannel can bundle up to 8 interfaces.
• All ports must be in the same VLAN or configured as trunks.

Protocols

• LACP (Link Aggregation Control Protocol) should be used in multi-vendor environments.
• PAgP automatically detects and negotiates aggregation between Cisco switches.
• PAgP modes include: On, Desirable, Auto.
• If one switch is set to PAgP Auto and the other to Auto, an EtherChannel will not form; at least one device must be in Desirable mode.
• Mismatched configurations will prevent PAgP from forming an EtherChannel.
• LACP is the IEEE standard that supports multi-vendor environments.
• LACP modes include: On, Active, Passive.
• If one switch is set to LACP Passive and the other to Passive, an EtherChannel will not form; at least one side must be in Active mode.
• LACP verifies matching speed, duplex, and VLAN settings before forming an EtherChannel.

Configuration Commands

• channel-group [number] mode [mode] is used to configure on Cisco switches.
• Using an interface range command allows configuring multiple interfaces at once, ensuring consistency.
• show etherchannel summary verifies its status after configuring.
• VLAN settings are changed by configuring the VLAN settings on the port-channel interface.

Troubleshooting

• Check that all member ports have the same speed, duplex, VLAN, and mode settings if a newly configured EtherChannel is not working.
• Check the load balancing method used if the EtherChannel is active, but load balancing is not working properly.
• show interfaces etherchannel provides detailed information about the physical interfaces.
• show etherchannel port-channel checks the status if an EtherChannel is operational, but some ports are not active.

Best Practices

• Configure EtherChannel before enabling STP to prevent STP from potentially blocking ports or causing network instability if configured incorrectly.
• Trunk settings should be applied to the port-channel interface to maintain consistency, instead of configuring trunking mode on individual ports.
• The EtherChannel will not form if its allowed VLAN range is different on the two switches.

EtherChannel Benefits

• Provides faster failover compared to STP since STP does not need to reconverge.
• PAgP or LACP enables dynamic negotiation of EtherChannel between switches.
• Remaining links continue operating as part of the logical port-channel if an EtherChannel link fails.