EtherChannel Basic Concepts Explained

An EtherChannel is a group of links that work together as a single link. The two most common reasons for using EtherChannels are that they offer higher bandwidth and provide redundancy for critical network resources. This tutorial explains basic concepts and fundamentals of EtherChannel through examples.

EtherChannel example

The following image shows a network. This network has two LAN segments connected via a single 1 Gbps link.

PC1 wants to send an 800 MB file to Server1. At the same time, PC2 wants to send an 800 MB file to Server2. Both use the same link to reach their destinations. The link's bandwidth is 1Gbps, which is less than the total traffic both PCs want to send.

1 Gbps (Link's bandwidth) < 1400 MB (800MB [PC1's traffic] + 600 [PC2's traffic])

In this case, Switch1 queues both PC's traffic. It first sends traffic from one PC. Afterward, it sends the second PC's traffic. In normal circumstances, you will not notice this delay. For example, if you are uploading, downloading, or exchanging text files, this delay does not cause any interruption. But if you are watching movies, live streaming, or engaging in video calls, it could negatively affect your experience.

You have two solutions to this problem. You can replace this link with a higher bandwidth link or use an additional link. The first solution is less feasible. It requires the supporting ports on both switches. For example, if you want to replace it with a 10Gbps link, both switches must have a 10Gbps port. In its absence, you can not use this option.

The second solution is more convenient and flexible. You can create an additional link on any available ports. If more bandwidth is required, you can add more links.

However, this solution has a technical issue. Connecting two switches with multiple links creates a switching loop. A switching loop blocks the network from functioning. Switches use the STP protocol to find and remove switching loops. STP virtually blocks all ports, causing loops. As soon as you add the second link, STP blocks the port associated with it to prevent a loop.

Again, you have two solutions to this problem. You can disable STP or use EtherChannel. Disabling STP can cause loops. A network never works with loops. The second solution allows you to create multiple links without disabling STP. It uses EtherChannels. An EtherChannel combines links into a single link for STP. For example, if you make two links between two switches, both will appear as a single link to STP, but will function as two links for the switches.

EtherChannel V/s Port Channel V/s Channel Group

The terms EtherChannel, Port Channel, and Channel-group are synonymous. They all refer to the same thing. A switch can use any one or all terms to refer to EtherChannel and its functions. For example, Cisco switches use the term Channel-group for the EtherChannel configuration command, the term EtherChannel for the EtherChannel configuration display command, and the term Port Channel to refer to EtherChannel in the output of the EtherChannel configuration display command.

Type of EtherChannel

There are two types of EtherChannels: Static and Dynamic. Static EtherChannel needs manual configuration. Dynamic EtherChannel uses an EtherChannel protocol. The protocol dynamically adds and manages links in the EtherChannel. There are two EtherChannel protocols: LACP and PAgP.

Link Aggregation Control Protocol (LACP)

IEEE developed LACP as part of the 802.3ad standard. It is an open standard protocol. It works with all vendors' switches. It can combine up to 16 links. However, it uses only 8 of them at a given time. It keeps remaining in the waiting. If any active link fails, it adds a waiting link to the pool.

Port Aggregation Protocol (PAgP)

Cisco developed PAgP as a proprietary protocol. It works only on Cisco switches. It can combine up to 8 links. It works similarly to LACP but uses different terms for its modes. Cisco switches support both protocols. You can use anyone you want. However, you cannot PAgP on non-Cisco switches.

EtherChannel Restrictions/Requirements

EtherChannels have some restrictions. You cannot add any port to an EtherChannel. The following configuration must be identical across all ports in an EtherChannel.

• Port Speed
• Port Duplex mode
• Access or trunking state (all ports must be either access or trunks)
• If it is an access port, the configured VLAN on the access port
• If it is a trunk port, the allowed VLANs on the trunk link
• STP timers

If you configure static EtherChannels, switches use CDP (Cisco Discovery Protocol) to verify the above settings. If you configure dynamic EtherChannels, switches use the configured EtherChannel protocol (PAgP or LACP).

EtherChannels allow you to combine up to eight physical interfaces into a single virtual interface. For example, you can combine:-

• Up to eight Fast Ethernet connections, providing up to 800 Mbps
• Up to eight Gigabit Ethernet connections, providing up to 8 Gbps
• Up to eight 10-Gigabit Ethernet connections, providing up to 80 Gbps

You can have a total of six EtherChannels on a switch. Interfaces in an EtherChannel must have identical speeds, duplex settings, and VLAN settings. Interfaces in an EtherChannel appear as a single interface for STP.

Conclusion

EtherChannels allow you to configure multiple physical links to work together as a single logical link. You can use an EtherChannel to increase bandwidth and redundancy for network connections. By understanding the basic concepts of EtherChannel, including its types, protocols, and configurations, you can enhance network performance and reliability by using EtherChannels more effectively.