IT-341 Module-15 Chapter-6: EtherChannel

What is EtherChannel?

A technology that bundles multiple physical links into a single logical link for redundancy and increased bandwidth.

What are benefits of EtherChannel?

Redundancy, fault tolerance, increased bandwidth, and load balancing.

What is the maximum number of physical interfaces in a Cisco EtherChannel?

Up to 16 interfaces: 8 active and 8 standby links.

What happens if one link in an EtherChannel fails?

Traffic continues over the remaining links without disruption.

Does EtherChannel require STP recalculation when a single link fails?

No, STP treats the bundle as one logical link.

What is load balancing in EtherChannel?

Distributing traffic across links using a hashing algorithm based on MAC addresses, IP addresses, or TCP/UDP port numbers.

What protocols are used to negotiate EtherChannel?

PAgP and LACP.

What does PAgP stand for?

Port Aggregation Protocol.

What does LACP stand for?

Link Aggregation Control Protocol.

Which EtherChannel protocol is Cisco proprietary?

PAgP.

Which EtherChannel protocol is IEEE standard?

LACP (802.3ad).

What are the two PAgP modes?

Auto (passive) and Desirable (active).

What are the two LACP modes?

Passive (waits for initiation) and Active (initiates negotiation).

What does PAgP "auto" mode do?

Passively waits to form an EtherChannel.

What does PAgP "desirable" mode do?

Actively attempts to form an EtherChannel.

What does LACP "passive" mode do?

Passively waits to form an EtherChannel.

What does LACP "active" mode do?

Actively tries to form an EtherChannel.

Which combinations form a PAgP EtherChannel?

Auto + Desirable or Desirable + Desirable.

Which combinations form a LACP EtherChannel?

Passive + Active or Active + Active.

What is the command to create an EtherChannel group?

channel-group [group-number] mode [mode]

What is the command to view EtherChannel summary?

show etherchannel summary

What is the command to check port channel interfaces?

show interfaces port-channel

What is a port channel?

The logical interface representing the EtherChannel.

How do you configure EtherChannel on a switch?

Select interfaces, set identical settings, assign to same channel group.

What must match on all interfaces in EtherChannel?

Speed, duplex, trunk/access mode, allowed VLANs.

What happens if EtherChannel member interfaces differ?

The channel will not form or may be placed in err-disabled state.

Can you mix different interface types in an EtherChannel?

No, interfaces must be of the same type and speed.

What command removes a port from an EtherChannel?

no channel-group [group-number]

Can you apply EtherChannel configuration to a port-channel interface?

Yes, apply STP, IP, or other settings to the logical interface.

What happens to STP with EtherChannel?

STP sees only the port-channel, simplifying topology calculations.

How does EtherChannel improve STP convergence?

STP treats the bundle as a single link, avoiding recalculation on failure.

What happens if ports are in different VLANs?

EtherChannel will not form; config must be consistent.

What should you configure before assigning interfaces to a channel group?

Ensure consistent settings (speed, duplex, switchport mode, VLANs).

How does EtherChannel reduce CPU overhead?

It limits STP and routing recalculations during link changes.

How many EtherChannels can a switch support?

Varies by platform; often up to 6 or more.

Can EtherChannel be used for both Layer 2 and Layer 3?

Yes, depending on interface configuration.

How do you configure a Layer 3 EtherChannel?

Configure member interfaces with 'no switchport', assign them to a channel group, and then assign an IP address to the resulting port-channel interface.

What is required to use EtherChannel between switches?

Supported protocols (PAgP or LACP) or manual mode.

What is the on mode in EtherChannel?

Forces EtherChannel without negotiation.

When should "on" mode be used cautiously?

When both sides are manually configured; otherwise loops may occur.

How can misconfigured EtherChannels be detected?

Use show etherchannel summary and show interfaces.

What symbol in show etherchannel summary indicates a Layer 2 port-channel?

S.

What symbol in show etherchannel summary indicates a Layer 3 port-channel?

R.

Can PAgP and LACP be used together in an EtherChannel?

No, both ends must use the same protocol: either PAgP or LACP.

How does EtherChannel interact with Spanning Tree Protocol (STP)?

STP treats the entire EtherChannel as a single link, which prevents loops and allows for faster convergence.

What are common causes for EtherChannel not forming?

Mismatched configurations such as speed, duplex, VLANs, or incompatible EtherChannel modes.

Which command displays the summary of EtherChannel status?

show etherchannel summary

How do you remove an interface from an EtherChannel group?

Use the 'no channel-group [number]' command on the specific interface.