Lecture 12: EtherChannel

Question 1

What is the main idea behind EtherChannel?

Answer 1

EtherChannel is a link aggregation technology that combines multiple physical Ethernet links into one logical link to increase bandwidth and provide redundancy.

Question 2

Why can’t we just connect multiple links between switches?

Answer 2

STP blocks redundant links to prevent loops. EtherChannel allows the use of multiple links without being blocked by STP, as it treats them as a single logical link.

Question 3

What are the main advantages of EtherChannel?

Answer 3

It increases bandwidth, enables load balancing, adds fault tolerance, and improves redundancy between network devices.

Question 4

How does EtherChannel handle multiple physical links?

Answer 4

It groups them into a single virtual interface called a port channel, which behaves as one logical link for configuration and traffic.

Question 5

Which Ethernet interfaces can be used with EtherChannel?

Answer 5

Fast Ethernet or Gigabit Ethernet interfaces can be grouped if they match in speed, duplex, and configuration.

Question 6

What is a port channel in EtherChannel?

Answer 6

A port channel is the virtual interface created when physical interfaces are bundled using EtherChannel.

Question 7

What protocols are used to manage EtherChannel formation?

Answer 7

• PAgP (Port Aggregation Protocol) – Cisco proprietary
• LACP (Link Aggregation Control Protocol) – industry standard (IEEE)

Question 8

What modes does PAgP support and how do they behave?

Answer 8

• on: forces channel without negotiation
• auto: waits for the other side to initiate
• desirable: actively tries to form EtherChannel

Question 9

What are the LACP operational modes?

Answer 9

• active: actively tries to form a channel
• passive: waits for the other side to be active
• Two passive ports won’t form a channel

Question 10

Which mode combinations will fail to create EtherChannel?

Answer 10

• auto + auto → no channel
• passive + passive → no channel
• on + auto or on + passive → unreliable, not recommended

Question 11

What are the basic configuration steps for EtherChannel?

Answer 11

1. Select physical interfaces: interface range g0/1-2
2. Set mode: channel-group 1 mode desirable (or active)
3. Exit and configure port channel: interface port-channel 1
4. Set trunking or VLAN: switchport mode trunk

Question 12

What must match on bundled interfaces?

Answer 12

Speed and duplex must be the same, and interfaces must be in the same VLAN or trunk configuration.

Question 13

What commands are used to check if EtherChannel is working?

Answer 13

• show etherchannel summary – shows status of port channel
• show running-config – shows config details
• show interface f0/1 – verifies individual port status