EtherChannel

1. What is EtherChannel ?

EtherChannel is a networking technology that lets you combine multiple physical Ethernet links into a single logical link.

Which function is provided by EtherChannel?

EtherChannel improves network efficiency by aggregating links, providing more bandwidth and redundancy while preventing loops caused by Spanning Tree Protocol (STP).

Without EtherChannel

In traditional Ethernet networks, connecting devices with multiple physical links seems like an easy way to improve bandwidth and reliability.

However, Spanning Tree Protocol (STP) blocks redundant links to prevent loops, leaving some links unused and bandwidth underutilized.

• 🔴 Blocked links → Only one link is active.
• 🔴 Bandwidth wasted → Other links sit idle.

With EtherChannel

With EtherChannel, multiple physical links are bundled together into one logical channel.

STP sees the EtherChannel as a single logical link, so it does not block any of the physical links inside the bundle.

• ✅ All links active → Aggregate bandwidth for better performance.

• ✅ Built-in redundancy → If one link fails, traffic automatically continues over the remaining links without STP recalculation.

This is exactly which function is provided by EtherChannel: improving performance, adding fault tolerance and preventing blocked links caused by STP !

2. EtherChannel Protocols

EtherChannel can be configured in three ways:

1. Static EtherChannel – Manual setup, no negotiation.
2. Port Aggregation Protocol (PAgP) – Cisco-proprietary dynamic bundling.
3. Link Aggregation Control Protocol (LACP) – IEEE standard for multi-vendor environments.

Static EtherChannel (Manual Mode)

In Static (On) Mode, EtherChannel is manually configured with no protocol negotiation.

Both sides must be explicitly set up to bundle the same interfaces.

⚠️ No verification of link consistency!

All bundled interfaces must match in:

• Speed
• Duplex mode
• VLAN settings

If parameters are not consistent, the EtherChannel will not work properly.

🔵 Port Aggregation Protocol (PAgP)

PAgP is a Cisco proprietary protocol that automates the negotiation of EtherChannel formation between two devices.

PAgP Modes:

• Auto → Passively waits for a PAgP negotiation request.
• Desirable → Actively sends PAgP negotiation requests.

⚠️ Important: If both devices are set to Auto, no EtherChannel will be established.

Auto + Desirable → EtherChannel forms.
Auto + Auto → No EtherChannel.

🔴 Link Aggregation Control Protocol (LACP)

LACP (IEEE 802.3ad) allows link aggregation between devices from different vendors.

It works similarly to PAgP but follows an open standard.

LACP Modes:

• Active → Actively initiates LACP negotiation.
• Passive → Waits for incoming LACP packets.

⚠️ Important: If both devices are set to Passive, no EtherChannel will be established.

Active + Passive → EtherChannel forms.
Active + Active → EtherChannel forms.
Passive + Passive → No EtherChannel.

Static vs. PAgP vs. LACP Comparison

Feature	Static (Manual Mode)	PAgP (Cisco Only) 🔵	LACP (IEEE Standard) 🔴
Compatibility	Any devices	Cisco devices only	Multi-vendor environments
Modes available	On	Auto, Desirable	Active, Passive
Standardization	None (Manual configuration)	Cisco proprietary	IEEE 802.3ad
Negotiation mechanism	No negotiation	Dynamic (PAgP packets)	Dynamic (LACP packets)
Link consistency check	No	Yes	Yes
Best use case	Controlled environments	Cisco-only networks	Multi-vendor networks

3. Conclusion

You have now learned which function is provided by EtherChannel: it allows you to bundle multiple ports together to avoid being blocked by Spanning Tree Protocol (STP), improving both bandwidth and redundancy.

There are three ways to configure an EtherChannel:

• Static : Manual configuration without negotiation.
• PAgP : Cisco proprietary dynamic negotiation.
• LACP : IEEE standard dynamic negotiation.

In the next course, we will focus together on how to configure Static EtherChannel step by step ! 😉