EtherChannel

EtherChannel combines multiple physical Ethernet links into one logical link. This provides more bandwidth and redundancy between switches, routers, or servers while allowing STP to treat the bundle as a single link.

By the end of this module, you should be able to:

• Explain link aggregation and EtherChannel.
• List EtherChannel benefits and restrictions.
• Compare PAgP and LACP.
• Configure EtherChannel using LACP.
• Verify and troubleshoot EtherChannel bundles.

Link aggregation groups several physical interfaces so they behave as one logical interface. Traffic can be balanced across member links based on a hashing method, such as source/destination MAC address, IP address, or port information.

EtherChannel does not usually split a single flow evenly across all links. Instead, it chooses a member link for each flow based on the load-balancing algorithm.

EtherChannel provides:

• increased aggregate bandwidth,
• link redundancy if one member link fails,
• simpler STP behavior because the bundle is one logical port,
• load sharing across active links,
• the ability to add capacity without replacing hardware immediately.

Member interfaces must have compatible settings. Common requirements include:

• same speed and duplex,
• same switchport mode,
• same access VLAN or trunk settings,
• same native VLAN if trunking,
• same allowed VLAN list if trunking,
• no incompatible security or QoS settings.

If member links are inconsistent, the EtherChannel may fail or place ports into a suspended state.

PAgP

Port Aggregation Protocol is Cisco-proprietary. Common modes include:

• desirable: actively tries to form an EtherChannel,
• auto: waits for the other side to initiate PAgP.

LACP

Link Aggregation Control Protocol is standards-based. Common modes include:

• active: actively tries to form an EtherChannel,
• passive: waits for the other side to initiate LACP.

Static EtherChannel

Using mode on creates a channel without negotiation. Both sides must be manually configured correctly.

EtherChannel problems often happen when member ports do not match. Check for:

• different trunk allowed VLAN lists,
• different native VLANs,
• one side access and the other side trunk,
• mismatched negotiation protocol or mode,
• speed/duplex mismatch,
• interfaces assigned to different channel groups,
• configuration applied only to physical ports but not the port-channel interface.

EtherChannel bundles multiple Ethernet links into one logical connection. It improves bandwidth and resilience while simplifying STP. Successful configuration depends on consistent member interface settings and compatible negotiation modes.