2.4 EtherChannel

Question 1

What is an EtherChannel?

Answer 1

A logical link that aggregates multiple physical links into one.

EtherChannel combines multiple physical links into one logical interface, increasing bandwidth and improving redundancy by distributing traffic across links.

Question 2

What are three advantages of implementing EtherChannels?

Answer 2

1. Adding redundancy to links
2. Balancing load among ports
3. Achieving higher bandwidth

EtherChannels enhance network performance by allowing multiple links to operate as a single logical link, providing redundancy and increased throughput.

Question 3

What command is utilized to configure an interface for EtherChannel?

Answer 3

channel-group 1 mode on

The channel-group command is essential for establishing an EtherChannel configuration on a switch.

Question 4

List three configurations that must match for a switch port to join a Layer 2 EtherChannel.

Answer 4

1. Speed
2. Duplex
3. VLAN settings

For a switch port to participate in a Layer 2 EtherChannel, certain parameters must be identical, including speed and duplex settings, as well as specific VLAN configurations.

Question 5

What additional requirements are required for a port in a Layer 3 EtherChannel?

Answer 5

1. Speed
2. No switchport
3. Duplex

In addition to Layer 2 requirements, Layer 3 EtherChannels necessitate that ports are configured with specific settings, including the ‘no switchport’ command.

Question 6

How do you configure a Layer 3 EtherChannel on a switch?

Answer 6

1. Use the command interface range g0/1 - 2 to select interfaces.
2. Configure each interface with no switchport to enable Layer 3.
3. Add interfaces to the EtherChannel with channel-group mode active or passive for LACP.
4. Verify the configuration with show etherchannel summary to ensure the EtherChannel is correctly formed.

Question 7

Which routing protocols can be used with a Layer 3 EtherChannel?

Answer 7

1. OSPF (Open Shortest Path First)
2. EIGRP (Enhanced Interior Gateway Routing Protocol)
3. BGP (Border Gateway Protocol)

OSPF: A link-state protocol that finds the best paths in large networks.

EIGRP: A Cisco distance-vector protocol with fast convergence and efficient bandwidth use.

BGP: A path-vector protocol for exchanging routing info between autonomous systems.

Question 8

Fill in the blank:

To configure a Layer 2 EtherChannel, use the command ‘channel-group <number> mode _______’.

Answer 8

on

Setting the mode to on forces the interface to aggregate without using any negotiation protocol like PAgP or LACP.

Question 9

Which command shows EtherChannel status on a switch?

Answer 9

show etherchannel

The command is used to display the current status and configuration of EtherChannels on a switch.

Question 10

Which two protocols configure EtherChannel?

Answer 10

• PAGP
• LACP

PAgP (Port Aggregation Protocol): Cisco proprietary protocol for automatic link aggregation.

LACP (Link Aggregation Control Protocol): IEEE standard for dynamic link bundling.

Question 11

What is the primary difference between PAgP and LACP?

Answer 11

LACP supports more links (up to 16), while PAgP supports up to 8.

Both protocols dynamically negotiate link aggregation, but LACP is an open standard, while PAgP is vendor-specific.

Question 12

What are key characteristics of the LACP?

Answer 12

• It is configured using the ‘channel-group’ command.
• It is an open standard.
• It is used for an EtherChannel.

LACP is defined by the IEEE 802.3ad standard and enables dynamic link aggregation. It ensures link compatibility and automatically manages bundled links in an EtherChannel. Unlike PAgP, which is Cisco proprietary, LACP is vendor-neutral.

Question 13

Fill in the blank:

The max number of active ports in an EtherChannel is _______.

Answer 13

8

An EtherChannel can actively use up to 8 ports for LACP, while it can accommodate a total of 16 ports for redundancy. PAgP supports up to 8 ports in total.

Question 14

True or False:

src-dst-port is a load balancing method in EtherChannel.

Answer 14

True

The ‘src-dst-port’ method in EtherChannel uses both source and destination TCP or UDP ports for load balancing decisions.

Question 15

What are the three synonymous terms used for EtherChannel?

Answer 15

1. EtherChannel
2. PortChannel
3. Channel-group

These terms are often used interchangeably to refer to the logical aggregation of multiple physical links into a single interface for increased bandwidth and redundancy. PortChannel and Channel-group are commonly seen in Cisco configurations.

Question 16

True or False:

The ‘on’ keyword in EtherChannel configuration uses PAgP or LACP.

Answer 16

False

When configuring EtherChannel with the channel-group command, using the ‘on’ mode means that EtherChannel is forced to be active without using any negotiation protocol such as PAgP or LACP.

Question 17

What must be true for PAgP to work between two switches?

Answer 17

At least one side must use the desirable mode.

In PAgP (Port Aggregation Protocol), for the EtherChannel to form, at least one of the switches must be set to desirable mode, where it actively attempts to initiate the aggregation. If both switches are set to auto mode, neither will actively negotiate, and the channel will not form.

Question 18

What command is used to configure LACP on a switch?

Answer 18

channel-group <number> mode active or passive.

LACP (Link Aggregation Control Protocol) can be configured with the channel-group command in active mode (initiates aggregation) or passive mode (responds to requests).

Question 19

What does ‘P’ mean in the show etherchannel summary output?

Answer 19

The port is bundled (working) in the channel.

The ‘P’ status code indicates that the port is successfully bundled into the EtherChannel and is actively participating in traffic forwarding.

Question 20

What does the output ‘Protocol: -‘ indicate in the show etherchannel command?

Answer 20

The channel does not use LACP or PAgP.

It means the EtherChannel was manually configured without a negotiation protocol like LACP or PAgP. In this case, the EtherChannel is operating in static mode, where links are aggregated without dynamic protocol management.

Question 21

What is the default STP cost for a 1 Gbps EtherChannel?

Answer 21

4

The STP cost of 4 is the default value for a 1 Gbps link in an EtherChannel, as compared to the default cost of 19 for a single 1 Gbps link in standard STP.

Question 22

What happens when there is a native VLAN mismatch in an EtherChannel?

Answer 22

The port is suspended and removed from the EtherChannel.

For example, if SW1’s G1/0/21 port has a native VLAN mismatch, it will be suspended and removed from the EtherChannel, impacting network connectivity.

Question 23

What is the purpose of EtherChannel load distribution?

Answer 23

To select the physical port for forwarding frames.

EtherChannel load distribution selects the physical link for each frame based on header fields (e.g., MAC or IP addresses) and the configured method (e.g., src-dst-mac, src-dst-ip), ensuring balanced traffic across the links.

Question 24

List the common EtherChannel load distribution methods.

Answer 24

• src-mac
• dst-mac
• src-dst-mac
• src-ip
• dst-ip
• src-dst-ip
• src-port
• dst-port
• src-dst-port

Different switches may support different methods based on their model and software version.

Question 25

What is the **primary goal** of load distribution algorithms in EtherChannel?

Answer 25

* Avoid message reordering * Use forwarding ASICs efficiently * Utilize all active links * Balance traffic across links ## Footnote These goals ensure efficient and effective traffic management in the network.

Question 26

# True or False: The load distribution algorithm attempts to send the **exact same number of bits** over each link over time.

Answer 26

False ## Footnote The algorithm focuses on *balancing traffic* but does not aim for equal distribution of bits.

Question 27

What should be **checked first** when troubleshooting an EtherChannel?

Answer 27

Matching settings ## Footnote Ensure speed, duplex, and VLAN settings are **identical** across all participating ports. Mismatches can cause *EtherChannel failure*.

Question 28

How do you **troubleshoot** EtherChannel protocol negotiation issues?

Answer 28

Use **show etherchannel summary**. ## Footnote Ensure *both ends* of the EtherChannel use the same protocol (LACP/PAgP) and mode (active/passive or desirable).