4 EtherChannel
Learn how EtherChannel bundles compatible Ethernet links, how negotiation modes form a channel, and how to verify membership and flow-based traffic distribution.
Purpose and behavior
combines multiple physical Ethernet links between the same two devices into one logical interface. The bundle provides redundancy and distributes traffic across its member links. Switches treat the bundle as one logical link for functions such as spanning tree, rather than treating each member as a separate path.
Configure a bundle
For a Layer 2 trunk, member interfaces must have compatible settings on both switches. Examples include matching speed and duplex, trunk mode, native VLAN, and allowed VLANs. Configure the logical consistently with its members; exact requirements can vary by switch platform and software.
This Cisco IOS XE example configures two links with . Apply equivalent settings on both switches, adjusting interface names as needed. The channel-group command assigns physical interfaces to the logical channel. With enabled, compatible ports negotiate membership, and the carries the configured trunk traffic.
Choose compatible negotiation modes
The two ends of a bundle must use compatible negotiation modes. is generally the interoperable choice when the peer supports it. Do not mix and on the same bundle. The static on mode bundles ports without protocol negotiation, so both ends must deliberately be configured to match; a mismatch can cause connectivity problems.
active: Starts negotiation. It can form a bundle with active or passive mode.
passive: Responds to messages but does not initiate negotiation. It can form a bundle with active mode; passive–passive does not form a channel.
desirable: Starts negotiation. It can form a bundle with desirable or auto mode.
auto: Waits for messages. It can form a bundle with desirable mode; auto–auto does not form a channel.
On: Bundles ports without negotiation. Both ends must be configured for
on.
Verify membership and troubleshoot
Useful Cisco IOS XE checks include the following commands:
In show summary, confirm that the exists, the protocol is the intended one, and all expected member ports are bundled. Cisco output commonly marks a Layer 2 with Po and bundled ports with P; consult the platform command reference for exact status codes.
If a member is absent or suspended, compare member and settings at both ends and inspect neighbor information. The summary, detailed, load-balance, and protocol-specific status commands help verify the bundle.
Understand traffic distribution
normally distributes traffic using a of selected packet fields, such as source or destination MAC or IP addresses, depending on the platform and configured algorithm. The assigns a flow to a member link so packets in that flow generally stay in order.
The bundle can increase capacity across multiple flows, but one flow usually does not use every member at once. A can also produce an uneven split when there are few flows or their fields map unevenly. The configured algorithm shown by show load-balance describes the selection method; compare member-interface counters under representative traffic to see how traffic is actually distributed.