How to configure EtherChannel easily? - A Demonstration

Ethernet is a LAN technology based on the Institute of Electrical and Electronics Engineers (IEEE) 802.3 standard. Ethernet is a shared medium between the networking devices and provides the specific bandwidth to the end users. Ethernet also evolves as the users and their need of accessing the resources increases.

The evolutions helps end-users’ effective access to resources, both on- and off- the campus network. However, today's mission-critical applications and services demand networks that provide high availability and reliability. This article will focus on the technology that you can use in your network to provide higher bandwidth and reliability between switches.

Switch Port Aggregation with EtherChannel

We need to expand our network, to accommodate the increasing number of end-users. And the selection of the switch port speed also depends on the factors of, how many users, applications type, etc.

 In the above graphic (Figure-1), 4-PCs, PC1 to PC4, want to access the File Server (File_Server-FS1). There can be more end devices too. But, there is only one link between the switches SW1 and SW2. If that link goes down, the communication between the devices will be no more. For the high availability and reliability, we need more than one link between the devices. Right? 

We added three more links between SW1 and SW2. If any link will go down, another will forward the traffic. It might seem logical to simply add more links between two switches to scale the bandwidth incrementally.

What do you think, now the available bandwidth will be four time?
No, because each link acts independently.

In case of redundant links between the switches, Spanning Tree Protocol is responsible for providing the layer 2, loop-free network. For this, STP will place only one link in the forwarding state and rest of the links will be in the blocking state.

In this case, only one link is forwarding the traffic out of three links. It means that our resources are underutilized.

How can we use all these four links, without occurring the bridging loop?

Cisco offers a technology of "EtherChannel", which providing the method of logically aggregating or bundling the parallel links. Two to eight links of either Fast Ethernet (FE), Gigabit Ethernet (GE), or 10-Gigabit Ethernet (IOGE) can be bundled as one logical link of Fast EtherChannel (FEC), Gigabit EtherChannel (GEC), or 10-Gigabit Etherchannel (IOGEC), respectively. 

As the above graphic presents, the four 1Gbps Physical links, bundled into a single 4Gbps EtherChannel Logical link. Now for STP only one link exists and it will be in forwarding state, i.e. all the links in this bundle will be in forwarding state.

Distribution of the traffic across the links, is dependent upon the what Load-balancing hash algorithm will be in use.

EtherChannel also known as:

• Port Channel
• Channeling
• Link Aggregation (LAG)
• NIC Teaming

Working of EtherChannel or Port Channel

EtherChannel can be configured statically or dynamically. Statically configured EtherChannel will not exchange any negotiation information of the Port Channel. And for dynamically configuration, there are two types of EtherChannel negotiation protocols:

1. Port Aggregation Protocol (PAgP) is a Cisco proprietary solution
2. Link Aggregation Control Protocol (LACP) is IEEE 802.3 AD a standards based

PAgP Modes

PAgP negotiates EtherChannel formation and maintenance:

• On: channel member without negotiation (no protocol)
• Desirable: actively ask if the other side can/will
• Auto: passively wait for other side to ask
• Off: EtherChannel not configured on interface 

LACP Modes

• On: channel member without negotiation (no protocol)
• Active: actively ask if the other side can/will
• Passive: passively wait for other side to ask
• Off: EtherChannel not configured on interface 

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7-Steps for EtherChannel or Port Channel Configuration 

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https://luminisindia.com/it-networking-blog/155-how-to-configure-etherchannel-or-port-channel-easily-a-demonstration