3.4. EtherChannel (LACP)

💡 First Principle: EtherChannel bundles multiple physical links into one logical link, providing increased bandwidth and redundancy. Think of it like lanes on a highway—instead of one lane carrying all traffic, you have multiple lanes that combine into a single road, and if one lane closes, traffic reroutes to the others. If one link fails, traffic continues over the remaining links. Without EtherChannel, Spanning Tree would block those redundant links as loop prevention; EtherChannel lets you use them all.

Consider this scenario: You have two switches connected by two gigabit links for redundancy. Without EtherChannel, STP blocks one link—you get 1 Gbps and one backup. With EtherChannel, both links combine into a 2 Gbps logical link. When one cable fails, you don't even notice—traffic shifts to the remaining link automatically. You get both redundancy AND increased bandwidth.

What happens when EtherChannel goes wrong: You configure EtherChannel on one switch but forget the other. Now you have two active links with no logical bundling—STP sees a loop and blocks one. Worse, if settings mismatch (different VLANs, different trunk modes), the ports may enter a suspended state where neither works. Always configure both sides together.

EtherChannel Benefits

• Increased bandwidth: Combined throughput of all links
• Redundancy: Failure of one link doesn't bring down the channel
• Load balancing: Traffic distributed across links
• Simplified management: One logical interface to configure

Layer 2 vs Layer 3 EtherChannel