Objectives
| # | Objective |
|---|
| 1 | Configure a LACP EtherChannel (Port-channel 1) using active/active mode between SW1 and SW2 on Gi0/1 and Gi0/2 |
| 2 | Verify the LACP bundle — show etherchannel summary, show etherchannel detail, show interfaces Port-channel1 |
| 3 | Configure a PAgP EtherChannel (Port-channel 2) using desirable/desirable on Gi0/3 and Gi0/4 |
| 4 | Compare LACP and PAgP — modes, compatibility, and when to use each |
| 5 | Configure load-balancing method and verify traffic distribution |
| 6 | Open the EC Load-Balance Simulator — step through LACP negotiation, hash-based load balancing, and link failure resilience |
| 7 | Knowledge check — EtherChannel protocols, modes and load balancing |
Key Concepts
| Concept | What it means |
|---|
| EtherChannel | Bundles 2–8 physical links into a single logical link. The network sees one fast pipe; spanning tree sees one link (not multiple, avoiding blocking). Also known as Link Aggregation Group (LAG). |
| LACP (802.3ad) | IEEE open standard. Modes: active (initiates negotiation) and passive (responds but doesn't initiate). One end must be active. Inter-vendor compatible. |
| PAgP | Cisco proprietary. Modes: desirable (initiates) and auto (responds). One end must be desirable. Works only between Cisco devices. |
| Mode: on | Forces the channel without negotiation — no LACP or PAgP frames sent. Both ends must be "on". Faster but no detection of mis-configuration. |
| Port-channel | The logical interface representing the EtherChannel bundle. Configure VLANs, trunking and STP on the Port-channel, not on individual member ports. |
| Load balancing | How traffic is distributed across member links. Uses a hash of source/destination MAC or IP. Configured with port-channel load-balance. All traffic for one flow stays on one link. |
| Link failure | If one member link fails, remaining links continue carrying traffic immediately — no STP reconvergence, no outage. The Port-channel stays up as long as at least one member is active. |
Topology — Two Switches, Two EtherChannels
| Channel | Protocol | Physical Links | Mode |
|---|
| Port-channel1 | LACP | Gi0/1, Gi0/2 | active / active |
| Port-channel2 | PAgP | Gi0/3, Gi0/4 | desirable / desirable |
Key Commands
| Command | Purpose |
|---|
| interface range Gi0/1-2 | Select multiple interfaces at once |
| channel-group 1 mode active | Add ports to Po1 using LACP active |
| channel-group 1 mode passive | Add ports to Po1 using LACP passive |
| channel-group 2 mode desirable | Add ports to Po2 using PAgP desirable |
| channel-group 2 mode auto | Add ports to Po2 using PAgP auto |
| channel-group 1 mode on | Force channel (no negotiation) |
| show etherchannel summary | Quick overview of all EtherChannels — protocol, flags, members |
| show etherchannel detail | Full detail including partner info and LACP PDU counts |
| show interfaces Port-channel1 | Statistics for the logical port-channel interface |
| port-channel load-balance src-dst-mac | Set load balance method (global config) |
| show etherchannel load-balance | Show current load balance method |
After configuring both EtherChannels and verifying them, click 🔗 EC Simulator to step through LACP negotiation, hash-based load balancing, and what happens when one physical link fails.
All member ports in a channel-group must have identical configuration: same speed, duplex, VLAN, and trunk settings. A mismatch will prevent the port from joining the bundle and show a suspended (s) flag in show etherchannel summary.