Ever wondered why only one link stays active when connecting two switches with multiple cables? That’s STP (Spanning Tree Protocol) doing its job — blocking redundant paths to prevent loops.
But what if we want to utilize all links for speed and redundancy?
👉 That’s where EtherChannel and channel-groups come into play!
🔹 What is a Channel-Group?
A channel-group is a logical bundling of multiple physical ports into one virtual link using EtherChannel. Instead of blocking ports, STP treats all bundled ports as a single logical connection, allowing all links to stay active.
🔑 Key Benefits:
🚀 Increased bandwidth
🔄 Redundancy
⚡ Faster convergence
✅ Prevents STP from blocking ports
🔧 EtherChannel Basics
Max Ports: 8 per group
Protocols:
PAgP (Cisco proprietary)
LACP (IEEE standard)
🔍 PAgP Configuration Steps
before group-channel one port is block by stp
and
after group-channel all the port ups so its assume switch these are the one port
✅ On Switch 1:
Switch(config)# interface range fa0/1 - 2
Switch(config-if-range)# channel-group 1 mode auto
✅ On Switch 2:
Switch(config)# interface range fa0/1 - 2
Switch(config-if-range)# channel-group 1 mode desirable
📝 auto + desirable creates a successful EtherChannel using PAgP.
🧪 Verification Commands
🔹 Channel-group overview:
Switch# show etherchannel
🔹 Summary of port status:
Switch# show etherchannel summary
You’ll see something like:
Group Port-channel Protocol Ports
1 Po1(SU) PAgP Fa0/1(P) Fa0/2(P)
🔹 Detailed info:
Switch# show interfaces etherchannel
📘 Summary
Before EtherChannel:
➡ STP blocks one of the redundant ports to avoid loops.
After EtherChannel:
✅ All ports bundled together, treated as one logical link, so no port is blocked by STP!
This is one of the smartest ways to scale bandwidth and boost performance between switches.