EtherChannel is a port link aggregation technology used on Cisco switches that combines multiple physical Ethernet links into one logical link for fault tolerance and increased bandwidth. It operates with member ports requiring the same physical settings and supports load balancing across the ports, with the ability to maintain the logical link even if individual links fail. There are multiple configuration options for EtherChannel, including PAgP, LACP, and static modes.

1. Ether channel Concept
EtherChannel is a port link aggregation technology or
port-channel architecture used primarily on Cisco
switches. It allows grouping of several physical Ethernet
links to create one logical Ethernet link for the purpose of
providing fault-tolerance and high-speed links between
switches, routers and servers[1]. All member ports within
the bundle must have the same physical settings such as
port type, speed and duplex. Traffic is load-shared across
the ports. It is important to note that traffic is not
loadbalanced, as load distribution is not always equals
across all member ports.

2. Example of Ether Channel
 EtherChannel is the technology which is used to combine several physical links
between switches or routers into one logical connection and treat them as a
single link. Let’s take an example to see the benefits of this technology:
Suppose your company has two switches connecting with each other via a
FastEthernet link (100Mbps):
 Your company is growing and you need to transfer more than 100 Mbps
between these switches. If you only connect other links between the
two switches it will not work because Spanning-tree protocol (STP)
will block redundant links to prevent a loop:
 To extend the capacity of the link you have two ways:
+ Buy two 1000Mbps (1Gbps) interfaces
+ Use EtherChannel technology to bundle them into a bigger link The first
solution is expensive with the new hardware installed on the two switches. By
using EtherChannel you only need some more unused ports on your switches:
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3. Example of ether channel
 EtherChannel bundles the physical links into one logical link with the combined
bandwidth and it is awesome! STP sees this link as a single link so STP will not
block any links! EtherChannel also does load balancing among the links in the
channel automatically. If a link within the EtherChannel bundle fails, traffic
previously carried over the failed link is carried over the remaining links within
the EtherChannel. If one of the links in the channel fails but at least one of the
links is up, the logical link (EtherChannel link) remains up. EtherChannel also
works well for router connections:
 When an EtherChannel is created, a logical interface will be created on the
switches or routers representing for that EtherChannel. You can configure this
logical interface in the way you want. For example, assign access/trunk mode on
switches or assign IP address for the logical interface on routers..
 Note: A maximum of 8 Fast Ethernet or 8 Gigabit Ethernet ports can be grouped
together when forming an EtherChannel. There are three mechanisms you can
choose to configure EtherChannel:
+ Port Aggregation Protocol (PAgP)
+ Link Aggregation Control Protocol (LACP)
+ Static (“On”)

4. Basic Interview Questionnaires for Ether Channel
Question: What is Ether Channel loadbalancing ?
Answer: If a link within the EtherChannel bundle fails, traffic previously carried
over the failed link is carried over the remaining links within the EtherChannel. If
one of the links in the channel fails but at least one of the links is up, the logical
link (EtherChannel link) remains up. EtherChannel also works well for router
connections.
Question: What is the port channel?
Answer: A port channel is an aggregation of multiple physical interfaces that
creates a logical interface. You can bundle up to eight individual active links into
a port channel to provide increased bandwidth and redundancy. Port channeling
also load balances traffic across these physical interfaces.
What are the advantages of using EtherChannel technology?
Benefits of using EtherChannel. Increased Bandwidth: Use EtherChannel and
combine two or four links into one logical link. It will double or quadruple your
bandwidth. For example, four 100Mb Fast Ethernet connections bonded into one
could provide you up to 800Mb/second, full duplex.

5. Basic Interview Questionnaires for Ether Channel
Question: What is a channel group?
Answer: While "desirable" is a DTP negotiation mode, it is also a ether channel mode.
There are two protocols for ether channel negotiation. PAgP is the Cisco proprietary
protocol that employs desirable and auto, and LACP is the open standard that uses
active and passive.
How many ports we can do port channel?
Answer: The EtherChannel can provide full-duplex bandwidth up to 800 Mbps (Fast
EtherChannel) or 2 Gbps (Gigabit EtherChannel) between your switch and another
switch or host. The number of EtherChannels has the limit of six with eight portsper
EtherChannel.
Question: What is a virtual port channel?
Answer: A virtual PortChannel (vPC) allows links that are physically connected to two
different Cisco Nexus™ 5000 Series devices to appear as a single PortChannel to a third
device. The third device can be a Cisco Nexus 2000 Series Fabric Extender or a switch,
server, or any other networking device.
Question: What is a LACP Port?
Answer: LACP is part of the IEEE specification 802.3ad that allows you to bundle
several physical ports to form a single logical channel. When you change the number
of active bundled ports on a port channel, traffic patterns will reflect the rebalanced
state of the port channel.

6. Basic Interview Questionnaires for Ether Channel
Question: What is the PAGP?
Answer: Port Aggregation Protocol (PAgP) is a Cisco Systems proprietary
networking protocol, which is used for the automated, logical aggregation of
Ethernet switch ports, known as an ether channel. ... PAgP can be configured on
a Cisco switch to operate in three different modes.
Thank you