EtherChannel Secrets: Boost Your Network Speed Now!

Introduction

It is a method, which combines multiple physical links into a single logical link. The purpose of the etherchannel is to increase link bandwidth and redundancy between switches. We can also call etherchannel link aggregation technology. Through etherchannel, a network administrator can create a more efficient and resilient network infrastructure.

What is Etherchannel?

A company known as Kalpana first invented Etherchannel. This company was then acquired by Cisco in 1994. In 2000, IEEE released the open standard version of Etherchannel, which was 802.3ad.

Multiple ports are combined and act as a single logical link. Normally, we can combine up to 8 physical links. After configuring, all the links act as a single link.

It is cheaper than any other high media link due to the existing switch links. It does not require any extra device for communication.

Why do we need Etherchannel?

If we connect multiple links between switches but do not configure Etherchannel, then one link will act as a forwarding link, but the remaining will be blocked. The remaining links other than the forwarding link will work if the primary link fails.

If we connect two switches via four links, as below;

Now run the “show etherchannel” and “show spanning-tree” protocols;

If we do not configure Etherchannel, then STP blocks all the redundant ports for loop prevention.

Condition for Etherchannel Links (Interfaces)

Before configuring, the following conditions should be fulfilled;

All the links must be of the same speed
Also, it will be of the same duplex
All the links must possess the same VLAN configuration such as native VLAN and allowed VLAN.
The links should be of the same switch port modes e.g. trunk mode or access mode.

Types

There are two types of Etherchannel,

Static Etherchannel
Dynamic Etherchannel

1. Static Etherchannel

We configure static etherchannel manually without the use of any negotiation protocol. It requires an identical configuration on both sides of the switches. It runs quickly because there is no negotiation protocol is needed. However, it leads to misconfiguration if both ends are not set correctly. Moreover, it has only one mode, which is ‘on’ mode, and we configure it manually on each side of the interface.

Configuring Static Etherchannel

We will use the following lab topology for static;

Configure the hostname on each switch.
Assign the domain name as ‘marwat’.
Configure both the switches as VTP mode servers.

Also, configure the above settings for switch2.

Configure the static link aggregation on both the switches as below:

configuring static etherchannel at switch 1 and switch2

‘no shutdown’ of all the interfaces of the switches;

Run the command ‘show etherchannel’, to check the group number, type of Etherchannel whether Layer 2 (L2) or Layer 3 (L3), and the number of interfaces for link aggregation.

Run another command to check which interface is up or down and other information;

‘shutdown’ an interface fast Ethernet 0/4, and then run the command;

shutdown interface and show etherchannel

As Fa 0/4 has been shut down, but also ping from PC1 to PC2;

There is no impact on pinging from PC1 to PC2.

Again ‘no shutdown” the Fa 0/4 of switch1;

1. Dynamic Etherchannel

Dynamic Etherchannel uses a protocol to automatically negotiate link aggregation. Moreover, it ensures compatibility before Etherchannel formation. There are two main types of Dynamic link aggregation, which are;

1. PAgP (Port Aggregation Protocol) – Cisco proprietary

2 LACP (Link Aggregation Control Protocol) – IEEE 802.3ad standard

2.1 PagP

PagP, which stands for port aggregation protocol invented by Cisco early in 1990. It is a Cisco proprietary protocol and works only with the Cisco devices. PagP has two modes, which are Auto and desirable.

Auto: It will convert the interfaces into etherchannel it is requested by the opposite side of the interface. Moreover, it is a passive mode, which only responds to negotiation requests.
Desirable: It will convert the other side of the interface into an Etherchannel. Simply, it initiates Etherchannel formation.

Lab Topology for PagP

We will use the same lab topology for port aggregation protocol (PagP) as we have used it before;

Configure the PagP on switch1 and switch2 as below in the diagram. There are four interfaces, which are Fa 0/1-4. First of all ‘shutdown’ all interfaces and then convert it into trunk links. After that, configure PagP on it. Next, configure PagP on both sides of the switches. One side uses ‘desirable’ mode, while the second side, use ‘auto’ mode.

Check the type of aggregation group whether L2 or l3. Also, check the number of interfaces used in it.

Run another command to check which ‘mode’ we have used on this side for the PagP link;

Desirable modes have been used on switch 1. Run the same command on switch2 for PagP mode;

On this side, we have used ‘Auto’ or ‘Automatic’ mode for PagP.

2.2 LACP

LACP or link aggregation control protocol is an industry-standard protocol, defined in 802.3ad. The function of the LACP is similar to PagP, but it can be configured on every device of the vendor. There are also two modes of LACP, which are;

Active: Active mode sends packets to the other side of the switch interface.

Passive: It waits for LACP packets to be sent by the active mode for Etherchannel formation.

LACP Lab Topology

Use the following lab topology for LACP configuration.

Basic Switch configuration;

LACP configuration, in which on one side it is active mode, while on the other side it is passive;

‘no shutdown’ all interfaces again;

no shutdown all interface on switch1 and switch2

Run another command to check the interface status and switch operational mode;

If we run another command, it will show you how many groups, the type of etherchannel whether L2 or L3 and the number of bundled links.