EtherChannel Basic Concepts Explained

An EtherChannel is a group of links that work together as a single link. Administrators use EtherChannels for various reasons. The two most common reasons for using EtherChannels are they offer higher bandwidth and provide redundancy for critical network resources. Let us understand both reasons through examples. The following image shows a network. This network has two LAN segments. Both segments have connectivity through a single 1 GBPS link.

single link

PC1 generates 800MB of traffic for Server1. PC2 generates 600MB of traffic for Server2. Both use the same link to reach their destinations. The link's bandwidth is 1GBPS. It is less than the total traffic sent by both PCs.

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 one PC's traffic. Afterward, it sends the second PC's traffic. In normal circumstances, users will not notice this delay. For example, if they are uploading, downloading, or exchanging text files, this delay does not cause any interruption. But if they are watching movies, live streaming, or communicating via a video call, it could negatively affect their experiences.

Administrators have two solutions to this problem. They can replace the 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 the administrator wants to replace it with a 10GBPS link, both switches must have a 10GBPS port. In the absence of it, the administrator can't use this option.

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

second link

However, this solution has a technical issue. Connecting two switches with more than one link 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 the administrator creates the second link, STP blocks the port related to the second link to prevent the loop.

link blocked

Again, the administrator has two solutions to this problem. He can disable STP or use EtherChannel. Disabling STP can cause loops. A network never works with loops. The second solution allows the administrator to create multiple links without disabling STP. It uses EtherChannels. An EtherChannel combines links into a single for STP. For example, if the administrator creates two links between two switches, both will be visible as a single link to STP but will work as two links for switches.

lan segment

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.

etherchannel terminilogy

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 an 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 can't PAgP on non-Cisco switches.

EtherChannel Restrictions/Requirements

EtherChannels have some restrictions. You can't add any port to an EtherChannel. All ports in an EtherChannel must have the following configuration same.

  • Port Speed
  • Port Duplex mode
  • Access or trunking state (all 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).

Conclusion

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 use identically speed, duplexing, and VLAN settings. Interfaces in an EtherChannel appear as a single interface for STP.

ComputerNetworkingNotes CCNA Study Guide EtherChannel Basic Concepts Explained